heres the scoop , was getting ready to send my engine off to the machine shop when i spotted on one the local craigslist , all the goodies , fresh machine work , forged pistons , etc . etc . went to look at it and got it for a fraction of what he was asking i could'nt even to begin to pay for machine work on my block for what i picked the whole motor up for ! heres the basics , 1968 ford 302 .60 over ( a little nervous on the over bore but thats another subject ) 1965 289 heads which have been all re done 3 angle valve job umbrella seals screw in studs ported etc . , my old time engine builder has kind of contradicted himself , at first he said that compression would'nt be a problem and now he is wanting me to get a set of heads with a bigger combustion chamber ! i would like to use these heads since they already have the work done , they were just barely shaved to clean them up and the block has not been decked . i found a pair of edelbrock aluminum heads i can pick up new for around $ 900 . would like to use what i have and spend the money else where . i live in iowa and ethynal is available all over and most stations have 91 , i drive the s#@t outa my stuff as far as milage and do quite a bit of traveling , planning to make it outa state with it and dont wana have to worry about finding gas . what do you think askin for trouble or ok . thanks for the input brock !
10:1 should be no problem with mid-grade or better. Just don't through a bunch of timing at it. If you haven't got your fuel system, I would suggest setting it up to run on E85. The octane level is 105-107 and it makes any motor super response on the hit of the throttle. The issues will be regional availability...not in all areas, and mpg. sounds like you got a good deal unless it is a bogus build.
should have mentioned i already picked up a holley 670 street avenger new in the box off craigslist too on the cheap and was planning on running that !
i'd say 10.5:1 is borderline. your detonation threshold is increased with aluminum heads and with some fairly conservative timing you should be safe on 91 octane. if you run a cam with a little bit longer duration on the intake you'll bleed off some cylinder pressure. set your carb to run a little fat to help cool and control combustion.
Im going thru the same thing as you but I have Aluminum Brodix heads so I can get away with more compression. Heres the link for my chevelle 496 engine . Someone on this subject gave me a couple links to go to you will see the the have alot of info. You can get away with compression but they are talking about the quench area. Im learning on this one too check it out. Building a 10 second or faster on 93 octane.. Do it ... just do it. http://www.chevelles.com/forums/showthread.php?t=256366
i run 11.3:1 in a 347 stroker with afr heads on 93 and never have a problem but i haven't put the n2o too it yet
With a mild street cam I'd rather see 9.5 for myself. 10.5 might be OK with a real big cam. Can you cut some of the dome off the piston to drop the compression?
10 to 1 works ok here at 4,000 ft elevation with aluminum heads on pump gas. 11 to 1 works ok here with a big cam alum heads on pump gas IMO 9 to 1 is workable, add one point for alum heads and 1 more point for a big cam.... We have not had any issues using this formula here... Elevation may change things a little though...
I built a '95 chevy lt1 383 stroker for my buddy recently(see avatar)....We have 11.8:1 static timing and running on premium fuel! Engine and cylinder head design will dictate the limits. This engine has alluminum heads= big plus...EFI=plus....reverse flow cooling=big plus. 10.5 can be borderline but will need premium fuel which can be cosly if driven alot.(just a thought). Is your compression ratio based on the sellers spec? Or has it been speced out? Make sure you use one of the many free compression ratio calculators to verify. ...you may be moreor less???? The piston below/at/above deck is critical as well as what head gasket is used. You may be able to manipulate your CR a little by different thickness gaskets.
I'm running a 302 with Edelbrock aluminum heads at 11:1 with no problem on California 91 octane. Secret? Fair amount of valve overlap to bleed off compression at lower rpm. Good lumpy idle too
Run With It. Last 'hot' motor I had was a 350 block with 327 Closed Chamber heads and 11:1 pop-up pistons. Cam was 480L-288D and it ran JUST fine. Only problem I had was finding decent competition...lol
run some pretty low gears like 3.70-4.11 and a cam w/ lots of overlap, 106-108 lobe sep? with a 2500 or so converter or a stick and no problem. nothing over 32-34 deg timing i would think. thickest head gasket you can find. 10.5 is up there unless a light car with all these other things in line...
Running 10-1 forged in my 66 FL with andrews #6 cam. pistons were set up at 3k min clearance. That tight of a fit required heat cycling the pistons at break in. Run it 15 minutes let it cool, repeat for first 100 miles. First 300 keep it under 50 mph etc. The high lift with long duration has good town manners, wicks up nice when up on cam. As posted by others, the cam is the key here. my 2-cents.
http://www.jalopyjournal.com/forum/showthread.php?t=143904&highlight=static+compression I read this a while back, its and older tech, the first part is missing so I had to read it twice to get the full idea. INCREDIBLE KNOWLEDGE IN HERE. I also messaged the author, great man. Hope it helps
Run it. The older blocks like that are thicker wall. Not ideal @ +.060" but not the end of the world either. I would prefer the AFR's but then they are a better head all the way around (not knockin' Ford engineering, AFR only really has to make the heads do one thing, haul ass, I'm very happy w/ my 165s).
You should have no problem with that compression or the bore. There are several keys to keeping it from over heating. A good radiator. A good aftermarket water pump. The stock ones do not flow at all and self destruct at 6700 rpms. A Electronic ignition/dizzy. AND make sure the heads have a good porting. Port the exhuast and let it breath. Trash the umbrella seals and go with nylon. They do require a tiny bit if machine work but worth it in the long run. I could run 89 with my 10.5.1 small block, granted I could not beat on it BUT It would run with out pinging. That being said it also loved the hell out of 110 octane.
thanks for the input guys , heres a little more info , the compresion ratio is what i'm going on from the seller , i will try to assemble the short block this weekend and check my piston heigth , 289 heads were ported , good news is i did'nt have a cam yet so i can pick one out with a little more duration , will try to go with the thicker head gaskets , it's going into my rpu in my avatar i have never weighed it but it cant be much over 2000 lbs , good walker radiator , sno white shorty water pump , not sure if i have room to run a mechanical fan yet thinking i may have to go electric !
it does have forged trw pistons with the valve reliefs , i read another post on here about turning them down to the relief but i'm not real wild about that idea !
If your running TRW pistons you can have the pistons dished to lower your compression.Very little material is removed (the eyebrow area) and it doesnt effect the integrity of the piston. But enough is removed to lower your compression after going .060 over. Another option is getting a thicker head gasket, but than your affecting detonation.This company has different head gasket thicknesses but they are pricey. http://www.scegasketsonline.com/products/procopphd.html I ran into the same problem and did the research, my solution, dishing the pistons to lower my compression enought to run on 91 octane.
Verify which pistons you actually have. You should be able to figure out what the nominal volume is for the piston from various TRW/Speed-Pro sources. Another thing is that its almost unheard of for a Ford factory cylinder head to actually cc at its advertized size. They typically run 2-4cc larger (or more). Add in the fact that there is a valve job (or two) on them and you'll gain more volume as the valves sink into the head a bit. ....got new valves that have heads that are tuliped/dished and you'll gain a little more volume too. Even unmolested 289 heads listed at 58ccs are typically 60-63cc's plus. Couple that with the fact that the block hasn't been decked and I think you may be hard pressed to have 10:1 once you run all the numbers. The only way to know is to CC the heads, the piston tops and do the math. DON'T run a thicker head gasket, especially if the motor hasn't been zero-decked. You'll loose what little bit of quench you've got left. I'm a firm believer in zero decking the motor then using the head gasket to set quench distance. You'll gain compression but because of the addition of more effective quench area you should be more detonation resistant compared to a motor with marginal quench. ....anyway, if you do some of the math and WAG it a bit here's what I come up with when using the following parameters. 4.060"bore, 3.00" stroke, .038" headgasket thickness, 0.010" deck height (down in the hole 0.010"), 58cc chamber volume and 5cc for the valve reliefs in the pistons. This calculates out to a rough 9.6:1 and I'm being conservative. The pistons are probably at least that far down the holes, the chambers are probably a couple cc's bigger than 58cc's and the 5cc piston volume is typical for a flat top with reliefs only and absolutely no dish...there's a good chance that the compression is a tad lower than that. In short, double check the machine work, verify all clearances, have the rotating assembly balanced, verify valvetrain geometry, carefully assemble the motor and run it. -Bigchief.
Ok- I feel like I get to chime in here since I've learned so much lately 'round here. The compression ratio you're talking about is the "theoretical" compression ratio. Aside from the normal factors that determine that number: combustion chamber volume, piston volume and deck clearance, and head gasket (bore diameter and thickness)-- there is cam timing that influences cylinder pressure. The "real" or dynamic compression ratio is really what matters, because it can change pretty dramatically depending on the cam you are using. In general: Bigger duration cams will lower cylinder pressure. A tighter LSA (106-108) will increase cylinder pressure (and throttle response), while a wider LSA (112-114) will do the opposite (while giving a wider power band). Your cam card will tell you when (in degrees) the intake valve closes in relation to BDC on compression stroke. This is the crucial number. A 10.5:1 is deinitely within range if you have a decent sized cam with some duration. The best thing to do is to determine- for sure- your theoretical compression ratio and then load your cam specs into a cam utility software IMO. i know that for iron heads, 8.5:1 static is supposed to be good for 91 octane.
This is just a super thread on effective compression ratios and how to apply to real world, how to best choose comp ratio and cam.this is great!!!!!!!!!!!!!!!!!!
Yup, Fridge has nailed it............. Basically your compression stroke only begins after the inlet valve closes on the compression stroke. If the inlet valve shut right at bottom dead center, you would have the full three inches of piston motion, and 10:1 compression ratio. If the inlet valve closed 90 degrees after bottom dead center, then only HALF the piston motion will compress the mixture, and the real compression would be more like 5:1 So your inlet cam duration will definitely effect your true final real compression ratio, and also the cranking pressure you read on a compression gauge when you do a compression test. Cranking pressure is probably the best indication of if what combination you finally end up with is going to be workable or not.
I use 93 octane in my fox car whenever I can. It's a 352W (bores check at 4.001 X 3.500 stroke) roller motor with a .586-288 cam and Trick-Flow T/W heads. The compression ratio is roughly around 9.77:1 That thing is a beast!! Est. horse power, somewhere in the 460 range.
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