Hi Guys, just about finished my 32 coupe project and are seeking info on jet and power valve sizing when running 4 x 2 97 carbs on a 276 flathead, I know you are all going to say I need to get it running sync my carbs take it for a run and read my plugs first, but if some hamer has allready been there and done that it will save me buying a lot off different size jets and power valve that will not be used. Engine specs 59A flathead running 4" stroke crank with 0.125 overbore 276 cubes, Isky 400 cam, Harmon & Collins mag, Edelbrock 4 x 2 manifold and 4 x brand new Stromberg 97 carbs. With jets sizes running from 33 to 50 and power valves 60 to 71, new carbs are fitted with 45 jets and 65 power valves. Thanks in advance for and info given.
I'm no expert but a 4x2 flattie could be over carburetted. A single 97 flows 150cfm so that's 600cfm at WOT (Wide open throttle). A progressive linkage would allow you to run only the centre 2 carbs until throttle is 65% open. With this setup, it only idles on the centre 2 carbs. The most common and/or biggest problem is over carbing an engine. Essentially an engine is a big pump, if you have to much going in you won't get it out as the engine will be running too rich. Most engines don't run 100% volumetric efficiency (VE) and run around the 80% mark. Most of us don't run the engine to 5,000 rpm with the most common range from idle to 3,500 rpm with the occasional squirt every now and again. Using this VE calculator, your engine turning 5k RPM only requires 399cfm. http://www.4secondsflat.com/Carb_CFM_Calculator.html I'm sure there are more folks out there with more knowledge than me
Ill be watching this thread i cant offer any help but i will be building my four carbed 8ba soon. Theres a guy cheaterspete on here i saw a clip of his car running a 4x2 on youtube maybe he could help you out i dont know him but his car is sick...
I have read a few posts on running 4 x 2 set up on a flathead some people say it can't be done over carbed others say it can, I am going to give it a go, but at having to buy 4 sets of jets and power valves at a time with shipping to Australia I am looking a $100 each time I change out, could end up very costly to get it right, if at all. I know there are hot rodders out there who have been down this road before I am seeking there advise on where a good starting point might be as far as jets and power valves sizing for my size and spec engine, like I said I am going to see if I can make it work and if I do I will post the out come.
I'd check into putting on a set of adjustable jets. I think you can get them from vintage speed, and speedway motors. They start with a larger jet, then you can dial them down with a needle that is like your idle/mix screws. I put a set on a pair of 97's I was running, saved a lot of time and parts guessing.
I am running 4 x 2's on and 8ba but have fuel injectors under the intake so we are looking at different setups here. What I found on mine and I think would be true in your build is off idle like at a stop sign and etc. With eight throttle blades opening at once, it is letting a lot of air in at very low rpm. I have my accelerator set up so it moves the throttle linkage very little as it is pressed until it is pushed far enough down to kick in the regular travel of the linkage. It makes it more enjoyable for stop and go travel. On the highway the slow movement part of the accelerator gets me up to around 55 to 60 mph after that the accelerator linkage moves pretty fast. A lot of rambling here and might have been more confusing than anything. Vergil Forgot to say your engine looks great.... like it bunches...
You CANNOT run progressive linkage on a flathead 4X2 manifold. There are only small balance passages between the 4 carbs, each of which is feeding 2 intake ports, one on each side of the engine. Try to run progressive and you're gonna starve some cylinders for fuel and bring on all sorts of problems. If you've already got the mainifold and carbs and are determined to run them, then good luck, and try to work out linkage as mentioned above to minimize throttle plate movement at just off idle. (This is where you'll wish you had refained some of the stuff in that geometry class in school! Stromberg 81s, which came on V8-60hp would be a better bet if you can find them. Not at all sure about the adjustable jets, sounds good, but can you get them all the same? Dave
ADjustable jets are silly in my opinion. There is no way to know that each venturi is jetted the same. CAn't really help on your 4 x 2 set up.
There is no way in the world that I would start a new engine on anything other than a single carb. Get the engine broken in and then go fooling around with your carb setup. Yoyu'll be happy you did it this way.
Read this thread, it's the most informative: http://www.jalopyjournal.com/forum/showthread.php?t=164109
The last three 4x2 flathead setups I've done responded very well with .042 main jets in all four, with #67 pv's in the two middle carbs and #69 pv's in the end two carbs. Keep in mind that most 4x2 manifolds are not true open plenum or IR types. The interconnecting runners act as balance tubes. Not a good idea to use progressive linkage with these manifolds. Getting the idle just right requires some dancing, but once done they run well.
^^^^^The Man Myth and Legend Uncle MAX has spoken^^^^^^ This man got my 4x2 to fire my engine for the initial break in and idle to the tune of angels singing. He's simply the best out there.
Back in 57 I ran 4-2's on my 53 Ford vert, It had a Harmon & Collins 3/4 cam , Offy heads and 60 over pistons. Ran real good with 4:11 rear but i ran a gas bill of 17 bucks every week. Guy who owned gas station said i was his best customer and how to you burn so much gas ? Also had straight linkage to carbs.
I notice in your post that you say you have brand new 97 carbs. I hope you didn't buy the ones speedway sells.
Carbs are new genuine Strombergs,thanks uncle max I will try your suggested jet and power valve combination.
Hi guys for all who have been reading this post, I can now report that I have the 32 up and running, at first I started the engine with the factory fitted 45 jets and 65 PV and to my surprise started ok. But I took uncle Max's advise and fitted 42 jets to all 4 carbs 67 PV to centre carbs and 69 PV to end 2 carbs, engine started ok, I set the timing at 5 deg advance, sync all 4 carbs air flow pulling 18 on all 4 carbs with my carb sync gauge, engine running ok no splutter when the butterflys were opened, but was running a little rough at idle and puffing a bit too much black smoke out the exhaust, I checked the idle mixture screws which were all set about 2 1/2 turns out from factory, I screwed all the idle mixture scews in fully and backed them out 1/2 a turn, engine started ok but kept wanting to stall, I turned the idle mixture screws out 1/2 a turn more. Now the engine starts and idles like a dream no more puffing black smoke, and when you dive it and put you foot into it there is no hesitation pulls like a train, I am very happy with it so if any of you are thinking of running a 4 x 2 set up I highly recomend it, many thanks again to uncle Max for the advise, now I just have to work out why I am getting front wheel shakes up under speed and braking better do so research on the Hamb. Regards Cully
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