I'm close to the testing stage for my 283. I have a friend who is rebuilding a 500 cfm carb for the engine, which is what I was under the impression was the maximum amount of airflow the thing could take. Is this true? If not, I have a 650 cfm carb that I was considering using just for testing purposes, to see if it the motor will even fire up....or if it's a brick. Thoughts?
Is your 283 stock head, stock cam, stock exhaust? If it is 500 i'd say is the max... you can squeak in the 650 with some work on the above mentioned parts. -Chris
I've successfully run 600 cfm vacuum secondary Holleys on my old 283. No bog and good Throttle response. That 500 is Probably better suited for it though. Is the 650 a double pumper? Should be ok to fire it up with.
depends on how you drive it, if 8000 rpm blasts with a big cam are in the plan then it differs from a driver. 500 cfm should be nice and responsive for cruising.
My 283 is bored .080 over with an Engle EP-20H RV cam, good small chamber power pac heads and a GM aluminum intake. I am running a WCFB, which is less than 400 cfm. I have also run a 500 cfm Elelbrock AFB. If your 500 is set up correctly it will run great. I personally like the WCFB, but after tuning both, I can't tell any difference in performance or mileage.
You don't NEED more than a 500 chm carb on a normal street driven 283. In fact you probably don't even need a 500 cfm carb period. That said though, what the engine actually needs and what you can use and will actually work are two different things. If the carb has vacuum or air-flow actuated secondaries, you can use a substantially bigger carb and still have it "work" simply because the secondaries will only open as much, and flow as much air, as the engine can use. A good example of this a Rochester Q-Jet . Wide open they can flow somewhere between 750 to 800 chm, yet GM used them successfully on on al kinds of relatively small engines - 305 Chevy V8's and even on little 230 and 250 Pontiac OHC sixes and Chevy 4.3 V6 marine engines. I think they even put Q-Jets on some 3.8 and 4.2 liter Buick V6s too. The tiny primaries on a Q-jet were small enough to give good drivability and mileage at low and moderate speeds on these little engines, but when you 'got on them', the air valves on the theoretically "way too big"secondaries would only open as much as, and flow the amount of air, that the engine actually required. From personal experience too, years ago, I ran a 735 cfm Holley carb from a 428 Ford CJ on the 283 in my 'daily-driver and weekend racer' '64 Chevelle, just because that was the carb I happened to have. I had to play with the jets, power valves and secondary diaphragm springs to get it dialed-in to work well on my 283, but once done it worked really well. At the dragstrip, circa 1973-74, my slightly built - ie - Crane solid lifter cam, headers, 1.94 valve 327 heads and 'theoretically way too big' 735 cfm Holley carbed 283 in a 3400 llb., 3.08 geared '64 4-speed Chevelle, ran consistent, but traction-limited 14.0 - 14.2 ETs at 97-98 mph. One time, when it hooked up, it went a best of 101 mph! Not bad for a home-brew, low-buck combination literally thrown together with parts I had lying around, that according to all the so-called "experts', shouldn't have worked! The engine certainly didn't need a carb capable of flowing 735 cfm and it probably would have made just as much power, with maybe slightly better drivability and mileage with a much smaller carb, but with a bit of tweaking, the big carb did work and as I said, I already had it and it didn't owe me anything. If you've got a good 500 cfm carb now, I'd keep it and use it. If you 've got a good. somewhat bigger carb - at least as long as it's got vacuum or or air-flow actuated secondaries, I'd use that too. Either way, I wouldn't spend money for a new carb, *just* because it was either bigger or smaller and therefor 'theoretically better' than what you've got. Good luck and have fun. Mart3406 =============================
During high school back in the late sixties, my brother-in-law had a '64 Chevelle, 283, two speed aluminum Powerglide. It came with a 2 bbl. He changed to a stock cast iron manifold and Quadrajet. Tweaked the distributor advance. Made some mods to the bands in the Powerglide. He carefully beat the sheet metal over the back wheels outward some with a rubber mallet and installed Fenton magnesium wheels with G70 tires. That was it, just basically stock. That car ran like a bat from hell. It was street raced alot and won alot. He finally got so many tickets, he started racing at the track in Kennydale and won races there. Point is a stock 283 can run a 750 cfm Qjet just fine. Tony
Between 500 and 600 unless Its a race motor Then the 650 will be fine ,Id personally go for the 600 holley and tweak it to what you need .Alot of people don't know this ,the rear spring for vacumn secondaries doesn't open till 5500 rpm stock .Got to change that .And if you are running to rich ,Change the power valve down to a 9.5 or 10.5 ........ Before and After power valve change do a vacumn reading to dial in . On a stock motor the needle will keep rising . 20 to 21 is ideal .
All of the above is good advise, if you are not running the original intake manafold. If you are putting an adapter on it and stuffing a 500 cfm 2bbl, it will probably work, but not as well. Good Luck.
According to Dons law 566 cfm. For the street go nearest low for the strip go nearest higher I e 550 street, 600 race
--------------------------- I humbly disagree on your suggestions for setting up a bigger carb to work on a 283. First, on a Holley carb, if it's too lean or too rich, you need to play with jets, not power valves. The power valve only adds extra fuel during the off-idle transition and does not control overall mixture richness or leanness. That's what the jets do. Secondly, you can't give an across the board recommendation to use a 9.5 or 10.5 or whatever number power valve. Holley power valves are rated in the inches of vacuum that they stay closed at and the number of the power valve required is dependent and the actual amount of vacuum the engine produces at idle. When you open the throttle from an idle, the vacuum drops and the purpose of the power valves is to add extra fuel to smooth the off-idle transition - but it has to have a high enough vacuum number that it stays closed at an idle. To select the proper power valve, you need a vacuum gauge and you measure the actual vacuum at idle Then, select a power valve with a number slightly lower than your lowest idle vacuum reading. For example, in setting up the 735 Holley I had on my 283, the Crane cam I was running only produced about 7 or 8 inches of vacuum at idle. To get a power valve that stayed closed and didn't dribble fuel into the engine when the throttles were closed, I needed to use 5 or 5.5 PV. If I had used a 9.5 or 10.5 PV like you suggested, it would have remained open all the time and pissed fuel into the engine even at an idle! Also about secondary diaphragm springs. Just because one particular spring on a particular engine might not open the secondaries until as you say 5000 rpm, that doesn't *necessarily* mean that that's the wrong spring. Some engines might not need the secondaries to come in until 5000 rpm. That's the whole key to a vacuum secondary carb - to not over-carburete an engine by using a spring that only allows the amount of air flow the engine requires at a given speed and load. The only real way to determine what spring to use is trial and error - and best done at a dragstrip where you can make back to back runs and compare actual ETs to determine which secondary spring the engine needs. You can't properly do this 'seat of the pants' by feel or by sound. Just because a certain spring might bring the secondaries in earlier and the sound of the back barrels kicking at a lower speed might sound neat or tough, doesn't mean that the engine might run not quicker and better with a stiffer spring.and the secondaries coming in latter.Trial and error, with ET clocks to verify what the engine actually needs is the only way. if you want to get it dead on. Mart3406 ============================
Bigger carbs will always make more power - less restriction. However, you will need engine setup to utilize them. So dual 1450 cfm dominators are fine for Pro stock even though formula says smaller CFM is OK. But unless you are at full throttle you wouldn't like them for normal driving. It's all about throttle response and economy. In a mild 283 the cylinder heads are the biggest restriction so smaller carb is good choice. But 650 cfm is a little better if engine likes it. Try 'em both. Either one can be tuned to work fine. FYI The power valves do what they say - add more fuel when engine is under acceleration. Has nothing to do with idle or off idle unless you have put the pedal to the floor. Normally under mild acceleration they will remain closed. The power valves in a Holley allow additional fuel to enter the main fuel wells bypassing the main jets to give more fuel to engine when accelerating hard. If you look carefully you can see the power valve restrictions in the metering body in the indentation where the valve is installed. Vacuum keeps valve closed until it drops and allows fuel to enter from fuel bowl directly thru restrictions into main fuel wells. They will affect economy because the point at which they open is determined by vacuum so if they open easily - fine for racing - but kills economy. Holley Instuctions - To properly size a power valve, take a vaccum reading at idle and if it is above 12" for a standard transmission a 6.5" will be safe to use. For automatic transmissions take a vaccume reading in gear at idle and if the vaccum is below 12" divide that in half for proper size. Example 9" of vaccume in gear at idle will require a 4.5" power valve. Incidentally All the fuel in a Holley passes through the main jets except when power valve opens. This includes idle. The size of the main jet or power valve has no effect at idle. Fuel at idle is drawn thru main jet and then thru idle feed restriction and into idle slots in baseplate. The power valve has no effect at idle because it only adds fuel to the main wells feeding the boosters above venturi.
I'm not sure how to start, but guys if you DO NOT HAVE A CLUE then please do not offer up advise. There are always replies in the threads about carbs cfm tuning etc that come from guys who do not know wtf they are talking about and if someone reads it and thinks it is right then they are not just as far out to lunch as the person who replied knot knowing wtf they were talking about. There are way too many factors to decide what is right or wrong in carb sizes for a certain cfm. Guys who read something then think they are an expert are not much help either. I'm sure the ones that have replied to this thread that really have no idea, know who they are. There are others who seem to sound like they know, but still do not have the right answers either. MART3406 called out carcrazyjohn and rightfully so. carcrazyjohn was out to lunch with his reply. What he suggests is going to do nothing but cause more problems and lead a guy way off course. But, part of what MART3406 posted in the reply to carcrazyjonh was not correct either...close but still incorrect. "The power valve only adds extra fuel during the off-idle transition and does not control overall mixture richness or leanness." This is the part that is not 100 correct. Yes the power valve cicuit does enrich/add fuel during the off-idle transition, but that is not only when it does this. As long as fuel is being pulled in through the main metering circuit and the vacuum level is below that of the rating on the power valve(meaning the power valve is open) then the power valve circuit will be enrichening the fuel mixture as it flows into the main wells that the main jets feed and lead to the boosters. So, anytime the power valve is open, and fuel is being pulled through the booster then the power valve circuit is enrichening the mixture. MART3406's advise about tuning the vacuum secondaries is good advise. You will not always "feel" of "hear" the secondaries opening/working. So the best way to adjust.tune them is to actually do it under a timed setting or on a chassis dyno to at least be able to measure actual results. If you ahev a really good tune on your vacuum secondaries, you should not be able to feel them dump in...if you do they are opening to quickly at that point. It should be a smooth steady increase in power. You check it by timing the car for ditance traveled(drag strip would be best) or on a dyno and watch the graphing of the tq/hp output. jamesgr81, this reply is just not right. "Bigger carbs will always make more power - less restriction." You cannot be serious? If you have too big of a venturi it will slow down the signal to the booster and the air speed through both the venturi and booster. If too big then it will be sluggish and nonresponsive and would actually cause a drop in tq/hp output. It's statements like this that are just rediculous. Yes a bigger carb can make more power...if the engine needs/can use it. As for your restriction comment...what restriction? If you have a big carb that has a lot of sating flash inside it from when it was cast there will be restrictions in that carb as much as or more than a slightly smaller carb that does not have any casting flash in it. Same goes with booster desing...you put an annular discharge booster in big carb and there is a lot more "restriction" in that then one with a downleg or straight booster would have. Again, a statement that is very very misleading. This part of your reply is also out too lunch, "In a mild 283 the cylinder heads are the biggest restriction so smaller carb is better choice." How do you know that the cylinder heads on someone mild 283 are going to be the biggest restriction? YOU DON'T. If a mild 283 has a powerpak head or some from a 327-350 there is a huge possability that the intake manifold itself would be the biggest restriction on the engine. Now, lets take the second part of that sentence about needing a smaller carb if the cylinder heads are the biggest restriction, meaning the cylinder heads are small in intake runner cc's/cfm flow. If you have a smaller cc intake runner, let just give some numbers for sake of comparison, a set of 160cc intake runners versus 180cc intake runners. If the engine is mild with mostly a camshaft upgrade then it would be highly possible that you would have to have a SMALLER carb on the engine with the 180cc runeers than the one with the 160cc runners. The reason why is VELOCITY. The bigger the size of intake runner on a given cubic inch engine the less velocity you are going to have, as long as all other engine aspects remain the same. The speed the air travel through the smalle intake runner will be at a higher rate(velocity) than the same amount of air traveling through a bigger runner. By haveing a higher velocity, then the carb will see a much stronger signal and will cause the boosters to start pulling in before the engine with less signal. So not always will maller heads mean smaller carb and same goes with bigger heads, not allways does bigger heads mean bigger carb. Now I'm not sure what holley instructions you have for properly sizing a power vale, but I've never heard of taking you reading and cutting it in half? Why would you want to delay the opening/enrichment of the fuel mixture that long after the air suplly has been increased? YOU WOULDN'T. You should not only check the idle vacuum, but you should also check the vacuum as you are driving the car taking note of the vacuum at part throttle(cruising) speeds as well as when you are accelerating under normal driving conditions and also hard acceleration. You should always select a power valve that opens about 2 in(Hg) below the lowest steady cruising speed vacuum reading. THIS IS BEST FOR ECONOMY/DRIVING under most every day driving conditions. It will also be ok for some limited performance driving. Now if you have a performance motor or a race engine you would want to select a power valve that is about 2 in(HG) below what the engine has AT IDLE IN GEAR. This is for cars that see more race/hard driving than just your average everyday driving. There are also two stage power valves, that you can get and tune for better economy/performance, but once again it is all about what you really need and how much time and experience you have with tuning. There really is a lot more to tuning carbs than just what is posted here. It is very complex and not any one engine will be the exact same as another. So to get back to my main reason for replying to this thread was to point out to those who reply and really do not have a clue and or do not really have real experience with what does and does not work. If you read something in a magazing or on the internet DO NOT TAKE THE TO BE 100% EXACT OR CORRECT. They never tell you everything, and most of the time what they leave out is very very important. Just because you read it, also does not make you experienced. If you are not exactly sure about what you are saying when you reply, then say soo...do not just post something as fact when it is really out too lunch. For what it is worth, there is a lot more to selecting pwer valves/tuning carbs then what I included in my reply.... You can make it as easy or difficult as you want. There are just way too many factors that will effect tuning/selection of not only power valves but cfm, vacuum/manual secondaries etc. Now for the OP's original questions: I'm close to the testing stage for my 283. I have a friend who is rebuilding a 500 cfm carb for the engine, which is what I was under the impression was the maximum amount of airflow the thing could take. Is this true? NO this is not true. There are way too many variables to say what is the maximum amount of cfm for any given engine size. PERIOD. If not, I have a 650 cfm carb that I was considering using just for testing purposes, to see if it the motor will even fire up....or if it's a brick. Thoughts? You can easily fire your 283 with the 350 carb. It will at least start and run as long as the carb is in running condition. My suggestion would be go ahead and fire it up with the 650. Once your buddy gets the 500 done then put it on and tune it in. If the 650 is in good running condition, once you get the 500 all sorted out and are happy with the drivability/performance, put the 650 on and also take the time to tune/sort it out. Now do a comparison between the two. Drive the car around and if you have a place to "make a few passes" do so, now put the 500 back on and do the exact same thing, drive it around some and also "make a few passes". Now you have an idea of what seems to work best for YOUR particular engine. This may seem like a bunch of dicking around, but what is experience in tuning and setups really worth? To me EXPERIENCE FIRST HAND IS PRICELESS. If you decide to do this, please start a thread with your experience. Good luck.
Just as a general rule I always use a carb with cfm on the high side and down jet it. doesn't matter if it goes on a minibike ,boat ,airplane(UL), or car. I used a junk yard holly off a 350 cubic AMC. 2 barrel on my 283 had to order small jets. every speed shop I find only stocks big and bigger jets. That air pump has to have air to work. The 500 is plenty.
------------------------------- ------------------------------------------- Excellent, well written post! Thanks for cutting through the B.S and clearing up a lot of myths, mis-information and 'old wives' tales. About my comment on power valves. I didn't really make my point clearly enough and I shouldn't have used the word "only" in my statement. You're right about the power valve flowing fuel, not "only" when the vacuum drops as the throttles open, coming off an idle, - but *anytime* the manifold vacuum drops below the number stamped on the valve. I should have stated that, but didn't. On a healthy engine with a decently sized carb, at wide open throttle, the manifold vacuum will be zero and of course the power valve will be open and flowing fuel. What I was trying to say but didn't state it clearly, was that the main purpose of a power valve is not to set the overall mixture (that's what the jets do and obviously, an open power valve is an open power valve regardless - and when open, a #4 PV for example, will flow the same amount of fuel as #10 PV) - but rather to control when this additional flow initially starts flowing. I was trying to counter the completely erroneous statement 'carcrazyjohn' made, that if the carb was too rich, you simply needed to use a 9.5 or 10.5 PV to correct the mixture - rather than using the correct power PV based on actual manifold vacuum at idle and changing the jets up or down to correct and set the overall mixture..Thanks for clarifying, correcting and adding to what I was trying to say! Mart3406 =============================
So while we are killing all the carb myths let us put an end once and for all to I take a larger carb and "jet it down" garbage. The CFM of a carb does not relate to jetting. CFM is air flow. You cannot jet a carb down to a lower CFM. Jetting down just destroys the carbs characteristics by leaning out the mixture usually to the point it doesnt run right. It does not make a bigger carb more suitable to a smaller engine. Jetting is arrived at first as a percentage of venturi size (I saw in a enginnering manual once approximately 1/240 for a starting point.) Carb jetting is aimed at 14.7 to 1 air fuel ratio (AFR) ideal mixture) Each carb is a bit different so jetting is corrected to that point. Some manifolds are not as efficient as others so in the interest of not having one cylinder running lean we often have to find a decent average or sweat spot where all are reasonably happy. A bigger carb requires a bigger jet to give the SAME mixture as a smaller carb does with a smaller jet. You CAN NOT jet a carb down to get CFM. I just spent half a day searching for a set of Jets for an early Pontiac because some idiot had "jetted it down" previously. In fact of all the carb problems I have had to cure on hot rods this concept is the number one bad thing I come accross. If i knew who ever started this idea I would find him and punch him right in the mouth. If you took the jets out of a carb and threw them in the garbage or sealed them shut with glue it DOES NOT CHANGE THE CFM. Period! Don
A 3800 lb.+ car with a stock small cube motor AND a two speed transmission that won a lot of street races and was forced off the street by the local constabulary and became a racetrack legend. I smell an urban legend or a stock eliminator with many hidden tricks and 5.57 gears!
ross, if this is the 283 that you posted about the other day I would go with the 500cfm carb. pretty sure this is a tired, stock 283 that he just had to pull the heads off to unstick and clean the rust out of the cylinder.....
While I do have a fair amount of hands on carb experience I'll admit I'm no carb expert by any stretchy of the imagination. I probably know just enough to be dangerous LOL so I should probably just keep my mouth shut but to '333 Half Evil' and 'Dolmetsch' I have to say one thing and then I'll button my lip....... THANK YOU !!!
On one of the best running 283's I ever had,I used a #9625 AFB (625 CFM)..When I got the engine ,it had just been rebuilt & according to the PO ,it had "... a mild RV cam"...I found a damn near new 9625,put it on and that engine ran beautifully..crisp response ,no bogging,etc...really decent on mileage also Just my dumbass $0.02 worth of input
I'm not sure who needs to get a clue ...but it ain't me. Go buy a copy of Holley Carburetors by Mike Ulrich and see how they actually work. Nothing I said was wrong or not factual. The power valve does nothing at idle or when fuel is being drawn mainly through the transition slots even if it is open. The power valve adds fuel to the main metering system. And only when vacuum has signalled it to open. Well you guys are obviously rookies in the drag racing field. The carburetor is always a restriction in the intake system. Thats how it works. At WOT less restriction means more airflow. That's why even though the formula gives a certain carburetor size much bigger carbs are used for more airflow. And that's why dominator carbs were developed. If you actually read what I said I also mentioned this would not be practical for everyday driving. The cylinder heads, intake manifold and carburetor will make the horsepower. The power pack heads or whatever plus camshaft selection will help determine maximum power. Those old 1.72 valve heads are a big restriction. If he wanted max HP those heads and manifold would have to go. Look at the HP levels reached by Drag Comp engines revving up to 9500 rpm at 287 cu in. They aren't using power pack heads. But for street driving they will be best unless he wanted max HP. Intake airflow velocity has everything to do with everyday drivability. It's the rpm range at which you're operating that will determine the parameters. The sizing of power valves I posted came from the Holley Website - so go argue with them. You do not want the power valves to be open under under mild acceleration to keep fuel economy from dropping.
Thanks for answering my main question....most of the rest of the discussions were all greek to me...for the time being at least. My knowledge is nowhere near that point at the moment. BTW, the 500 is a 4 barrel Carter. The engine came with a 4 bbl manifold, and was running a 600cfm carb before this....allegedly. I have no idea how well it ran at that point. Indeed....that's the one. Hopefully it's not *that* tired of an engine. I'm not looking for a pristine screamer like a lot of you guys have....most of you have engines that are as slick as a baby's bottom. I just want a decent, reliable engine that I can have a little fun driving. You thought it was tired looking, revkev?
It was seized and full of crud and rust. I wouldn't exactly call that a fresh motor..... at best it will have a solid bottom end and probably burn oil with low-ish compression. did you ever pull the other head to check that side out too??
I know it's far from fresh....I don't have that kind of experience or cash at the moment. I'm really new at this, so I don't know what the demarcation line of "tired" lies. The other head had no problems at all, no corrosion or pitting. It was just that one cylinder. I think, in the end, it was because of a bad head gasket. Somehow the same crud that was inside the coolant cavities made it into the cylinder. There was a vague trail going from one of the holes above the cylinder down to the cylinder itself. I also believe the engine sat with that side facing down for some time before i got it. Hopefully that was all....I didn't find any cracks. ??? Is that synonymous with "half-assed"?
RIGHT ON DON. This is something I also run across all the time...and every time it makes me laugh. You are 100% correct that jetting has absolutely nothing to do with cfm rating at all. But this is not to say that if you have a carb that "thoeretically" is too big or too small that you do not have to change jetting. Thanks for the chuckle this morning!!!
Just busting your stones man, it will probably run fine, just not a "fresh" motor with one compromised cylinder and some miles on it. Rattle Can Rebuild refers to degreasing and painting a motor to make it look newly rebuilt. There, you learned something.
Ah, gotcha. I have a salt spreader mounted on my shoulders at the moment...I need all the luck I can get. Yeah, the motor is far from fresh...and was pretty neglected when I got it. I was fine with it not being "fresh"....I just don't want it to be "brick". And don't worry about that pretty paint job....after taking the heads off, it ain't pretty any more!
I call it like I see it. Not trying to piss you off, but all of your original post was not right. I do not care what book you read to make you the expert. I've got several books from over the years that I read to get another perspective on any given part of the carburation equation. There is a lot to them, they are actually very simple in desing but can be very complex in use. Tuning can be very tedious and time consuming, it all depends on the engine that the carb/carbs are bolted onto. There are soo many variables that it is almost impossible to just say "this will work". No two engines will be the same. I've been at the carb game for 25 years. I started to do carb work to learn and gain performance when I was drag racing and racing stock cars at local dirt tracks. I'm not sure what you are meaning when you say that the intake manifold is always the "restriction" or by saying that the "carb is always a restriction"... What does "restriction" have to do with the power valves and or tuning a carb? Any time the airflow is interrupted, that could be considered a "restristion"....but it doesn't really matter. It is not like the average tuner is going to address the "restriction" as it is part of the build that he has to work with. He will just tune accordingly. "Well you guys are obviously rookies in the drag racing field. The carburetor is always a restriction in the intake system. Thats how it works. At WOT less restriction means more airflow. That's why even though the formula gives a certain carburetor size much bigger carbs are used for more airflow. And that's why dominator carbs were developed. If you actually read what I said I also mentioned this would not be practical for everyday driving." What does drag racing have to do with a carb being a restriction? What does the carb being a restriction in the intake system have to do with how it works? At WOT less restriction means more airflow, so does that mean that at part throttle less restricion means less air flow, no difference, or more air flow? Now if you want ot get into carb setups for DRAG RACING or most any form of racing for that matter you can throw the previous concerns/input for the power valve right out the window. This thread was started with a question about having two carbs, 500cfm and 650cfm and a 283 to run them on. It had absolutely nothing to do with drag racing or racing of any form. If you do want to get into the drag racing aspect of carburation and tuning I'm all ears. I'm sure you being the expert in drag race engine building/tuning that you are have a lot to say about it. Just the simple fact you brought it up in your reply about power valves and tuning for drivability/economy prooves to me just how much of an expert you really are. I'm sorry if this seems harsh, but what I called you out on in your replies was spot on. Some of what you posted was right, but not all of it and I addressed that. Same goes for the reply I quoted again here. Most of what you posted is misleading or confusing to say the least. To proove this point I'll quote another of your off base misleading comments; "The cylinder heads, intake manifold and carburetor will make the horsepower. The power pack heads or whatever plus camshaft selection will help determine maximum power. Those old 1.72 valve heads are a big restriction. If he wanted max HP those heads and manifold would have to go. Look at the HP levels reached by Drag Comp engines revving up to 9500 rpm at 287 cu in. They aren't using power pack heads. But for street driving they will be best unless he wanted max HP." I do not care what heads, intake, and carb you want to use, but if you do not have the right amount of compression, have to right camshaft, there is no way in hell the heads, intake, and carb will make power. You did add a comment about the powerpak heads or whatever and camshaft will help determine maximum power, but that is not all. It is misleading or at the very least confusing mumbo jumbo. Then to top it off you are talking about old 1.72 valve heads, which I agree are small or what you say "a big restriction" then compare them to what a "drag comp" engine is running....WHY? WTF does this have to do with anything from this post to this point? Where at anytime was anyone talking about MAX HP? Same goes for saying that 1.72 heads will be best for street driving unless he wants max hp? WTF again? Why are the 1.72 the best for street driving? I'd think that one could easily have a set of 1.94 heads and those might be better. All I'm trying to say is think about what you are posting and if it really makes sence or better yet if it even has anything to do with the subject at hand. Now to the fact about the power valves and not having them open under mild acceleration for economy. Go back and read what I posted about choosing the corerect power valve for economy or everyday driving. If you do not know how much vacuum you have while driving the car under mild acceleration, how the hell can you know if the power valve is open or closed? If you take your idea of checking vacuum at idle in gear, and lets say it is 12in(Hg) then you say cut it in half you would then have a 6. power valve. Now, if you drive the car, ANYTIME you accelerate and the vacuum drops below 6in(Hg) IT WILL BE OPEN. Take this same vehicle and drive it with a vacuum gauge and see just what vacuum you have while driving steady, driving under mild acceleration, and also hard acceleration and see just what vacuum you have. There are some that might not drop below six under any acceleration, but they will be few. By driving the vehicle and takingan actual reading under all driving conditions you can now select a power valve that will be best suited for everyday driving and maximum economy. Plain and simple. Now here is a question, from what you read and all you expetise on power valve selection, what happens when the engine idles in gear with more than 12" of vacuum? You stated that you take a vacuum reading at idle in gear and if it is below 12" divide it in half". The general rule of thumb for dividing your vacuum reading at idle in half to select a power valve is fine for manual transmission equipped vehicles, but If you were to take and drive your manual trans vehicle and check thevacuum while driving you can then establish an actual vacuum to setlect the power valve by. Under no circumstances if the carb is jetted correctly should you have to select a power valve any more than 2in(Hg) LESS than the vacuum reading. This will be the best for all around, everyday driving and economy. One last thing for DRAG RACING applications what or how would you select the correct power valve?
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