Small Block 327 Flooding Help
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Small Block 327 Flooding Help My uncle built my dad's motor a long time ago. All I know is that is how many cubic inches it has and that it is mated to a muncie m22 rock crusher four speed. For some reason, the car loads up every time we drive it and it'll shut off. No matter what we do. We have changed from dual four-barrels to a single carb back to smaller duals back to a smaller single. I don't understand what's going on. Any suggestions? Since my uncle built it and has since passed away no one has any idea what is in the motor. All we know is that it makes 550 rwhp and similar torque.
Staging Lane
Joined: Sep 2012
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From: Virginia Beach, VA
Concur with Pancherj's suggestion to check out the fuel pressure to the carb(s). Anything over 5-7 psi is too much and won't allow the fuel inlet to close resulting in excess fuel usually through the booster venturis.
Another item to look at is the idle rpm. Running a 331ci in B Production racing back in the early 70's, my idle was set between 1000-1200 rpm for 415 HP at the flywheel. Of course intake manifold design as well as header design is much better these days; however, I would still expect your idle to be in the above range to keep the engine running.
Finally, a 327 making that much HP isn't going to have much intake vacuum compared to a street engine. Is it possible that all the carbs you tried out (including the original dual 4-bbls) are basically street carbs and haven't had their power valve changed out for lower intake vacuum? (Essentially, the power valves are engaged all the time enriching the mixture from idle upwards dumping excessive fuel all the time.)
Hope this info helps. Good luck with your uncle's engine.
Another item to look at is the idle rpm. Running a 331ci in B Production racing back in the early 70's, my idle was set between 1000-1200 rpm for 415 HP at the flywheel. Of course intake manifold design as well as header design is much better these days; however, I would still expect your idle to be in the above range to keep the engine running.
Finally, a 327 making that much HP isn't going to have much intake vacuum compared to a street engine. Is it possible that all the carbs you tried out (including the original dual 4-bbls) are basically street carbs and haven't had their power valve changed out for lower intake vacuum? (Essentially, the power valves are engaged all the time enriching the mixture from idle upwards dumping excessive fuel all the time.)
Hope this info helps. Good luck with your uncle's engine.
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Well I don't know anything about what is in the car as far as branding or sizes for anything. How would I check the fuel pressure? Sounds messy. It definitely idles lower than 1200. It doesn't have a tach but I'd say probably closer to the 6-700 rpm range. But I'm totally guessing. I do know it's lower than 1200 though. It runs and idles, but when you drive it not wot, especially in town with red lights, it'll die within 10 minutes. And we don't live in a huge city so traffic isn't the problem. Basically, if we stay in the gas (like at the interstate) it won't do it. But if we slow down for more than a few minutes that's it. And how would I check a power valve?
Staging Lane
Joined: Sep 2012
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From: Virginia Beach, VA
Use a fuel pressure gauge to measure pressure at the carb's inlet to see what you've got. If the pressure is too high, there are aftermarket fuel pressure regulators you can install to get it to the desired range. BTW, if the fuel pump mechanical or electric? It's possible that your uncle installed a high pressure/high flow unit to feed the engine's high HP.)
As for checking the power valve, it depends upon the type of carb you're using. Holley's are the easiest to check as the opening vacuum is stamped on the side of the power valve. Carter/Edelbrock power valves use different tension springs to determine when the power valve opens. First though, you need to determine your idle and cruising vacuum with a gauge to know where you stand. Then select a power valve or spring that will open at a lower setting than either of the two values. Basically a test & tune type of operation.
Your idle rpm is way too low for a high performance 327 making the 550 HP. It sounds more like a street engine tune. (My old stock 327/365 '64 Vette idled around 700 rpm.)
Have you check the spark plugs to see what condition they're in? If you're running too much fuel, one or more could be fouled. It's worth a check.
As for checking the power valve, it depends upon the type of carb you're using. Holley's are the easiest to check as the opening vacuum is stamped on the side of the power valve. Carter/Edelbrock power valves use different tension springs to determine when the power valve opens. First though, you need to determine your idle and cruising vacuum with a gauge to know where you stand. Then select a power valve or spring that will open at a lower setting than either of the two values. Basically a test & tune type of operation.
Your idle rpm is way too low for a high performance 327 making the 550 HP. It sounds more like a street engine tune. (My old stock 327/365 '64 Vette idled around 700 rpm.)
Have you check the spark plugs to see what condition they're in? If you're running too much fuel, one or more could be fouled. It's worth a check.
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So while snooping around in the car looking at some stuff to try and see where the block came from and other weird stuff like that, I found dyno sheets from 2009. We took it to a performance shop near my house and dad had always told us i put down 550hp. Looking at the dyno sheets, it's considerably lower. They read 368hp and 363tq. I forget the rpm that was achieved, but it was very high for what I'm used to seeing with my truck. Now, with this I know we found and corrected another problem that give the car considerably more power, but we never had it dynoed again so I have no idea where the car would be now. Probably closer to the low to mid 400's. Does this change anything?
a 327 cubic inch making 550 rwhp (rear wheel you said) seems like kind of a stretch.
how do you know?
what are you running for fuel?
when it does idle, is it smooth and consistent or is it choppy and erratic?
what ever the size of the engine, i think it's safe to assume that it was a performance built motor having a large duration cam which means the engine will have little and poor vacuum signal at lower rpms no load... which is the condition you describe when the engine cuts out. carbs rely on vacuum signal, generated by piston moving downward and intake valve open. the camshaft spec's (duration, overlap, and open/closing points) have an affect on that vacuum signal seen by carb mounted on the intake manifold. and if it's a single plane intake, then vacuum signal is worse compared to dual plane intake. i'm guessing it also has a single plane intake but that's what it takes to flow more air at higher rpm in order to make more horsepower.
that said you need to measure fuel pressure at the carb inlet to know like previously said.
and you need to use a vacuum gauge hooked up to the intake manifold, that will help you diagnose what's going on. and doing a compression check on the motor may also help to figure out what you got, really you need to know the camshaft specs but a cylinder compression check will at least rule out a bad cylinder and is more or less free and easy to do.
and what does it have for an ignition system?
how do you know?
what are you running for fuel?
when it does idle, is it smooth and consistent or is it choppy and erratic?
what ever the size of the engine, i think it's safe to assume that it was a performance built motor having a large duration cam which means the engine will have little and poor vacuum signal at lower rpms no load... which is the condition you describe when the engine cuts out. carbs rely on vacuum signal, generated by piston moving downward and intake valve open. the camshaft spec's (duration, overlap, and open/closing points) have an affect on that vacuum signal seen by carb mounted on the intake manifold. and if it's a single plane intake, then vacuum signal is worse compared to dual plane intake. i'm guessing it also has a single plane intake but that's what it takes to flow more air at higher rpm in order to make more horsepower.
that said you need to measure fuel pressure at the carb inlet to know like previously said.
and you need to use a vacuum gauge hooked up to the intake manifold, that will help you diagnose what's going on. and doing a compression check on the motor may also help to figure out what you got, really you need to know the camshaft specs but a cylinder compression check will at least rule out a bad cylinder and is more or less free and easy to do.
and what does it have for an ignition system?
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going back and reading what you just posted, it would have to spin high rpm being less than 350 cubic inch to make over 400 hp at the crank, which then it likely has a solid lifters not hydraulic lifters. and that would mean you would have to adjust rocker arms to set valve lash, which can have a dramatic affect on idle and low rpm low load conditions if not set right.
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It does have a very large cam. It's very choppy, but not erratic sounding. It's just a great sounding lope. For fuel we usually run 93 octane. We tried 110 and it didn't change it loading up. I think I'm just going to try to find a good performance shop near here and take it there. Neither of us have the knowledge to know how to fix it. I'll show them this thread when we take it. The motor was built by my uncle completely by parts ordered from summit racing. I have no clue as to the specs of the cam. He had it in his 69 z28 camaro with a 6speed. We got the motor and it is now in my dads 66 chevy 2 with a four speed. It was essentially taken apart whenever we got it and someone put it back together wrong and the motor ran like crap. We took it to a speed shop in Birmingham alabama and they basically rebuilt the motor and told us it was earlier running on about 20% power. The we dynoed it and got the 368hp from that. Later, we found something else wrong with it and it made another huge difference. Thanks for all of your help guys. I'll be sure to put up some number and what was wrong whenever I can find a better performance shop around here.
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flooding I hope this will be of some value, I am not a expert, this is only what I remember doing to my 68 Camaro that had a 302 engine. The engine had a lot of compression and camshaft. The engine idle was cleaned up by 2.5 power valves . .125 holes in the throttle plate . Restricting the fuel in the metering plate. This was on a 750 carb. At the time I ran a set of autolight plugs set a .045 . The engine vacuum was not very good . The engine has a iskey 600 roller camshaft.