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I recently rebuilt an '80 Corvette 350 engine with a 383 stroker conversion, Brawler 650 carb, comp thumpr cam 279/297 479/465 with aluminum heads. it has been to three different mechanics and it absolutely will NOT run right. It will sit and idle but if you give it any throttle, it almost quits. Stalls and sputters. Putting it in gear is guaranteed to kill the engine. I currently do not have a stall converter in it but plan on putting one in. My question is, could a stall converter cause these issues, even at idle? Or do I need to start delving into trying to degree the cam?
Does sound like a horrible cam. Still. Even with that awful cam you would think you could get it better than that.
Who recurved your Distributor? What aluminium heads? Compression ratio? Intake runner size? Head chamber size?
Who picked this combination of parts?
Much, much more information on exactly what you have is nessesary.
And if Lars says loose that horrible cam. I would listen.
From: At my Bar drinking and wrenching in Lafayette Colorado
The problem with that cam and it's very tight LSA is “reversion,” and tuning isn’t going to cure it. Those cams are designed with the sole purpose to sound "bad-***" at idle with everything else being sacrificed. They are absolutely HORRIBLE from right off idle till about 1800-2000rpm’s and really don’t clean up well till a little higher than that, especially if the compression ratio wasn’t raised to at least 10 to 1 or higher. They require a LOT of timing at idle to make idle possible at all, with a very short custom centrifugal curve. If a lot of custom tuning mods, along with a very high compression ratio, is not used, you will have the symptoms you describe, and no amount of carb tweaking, cam degreeing or torque converter changes are going to fix it.
I appreciate the info. When I was doing the rebuild, the techs at Summit racing told me what I needed. So do you have recommendations for a drivable cam? My uncle bought this car new and I would love to drive the wheels off of it but it’s just not possible right now.
Comp designs too many of their cams with pinched lobe separation angle. Maybe that's good for top end HP, but it sure doesn't make for good street manners. The factory goes the other way on LSA. That should tell you something.
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
2016 C3 of Year Finalist
no...go through a reputable dealer like Summit or Jegs or Speedway and order a good cam.
I would call Comp Cams directly and tell them what you have, what you want it to do and they will help guide you....Dont buy your engine parts from Ebay
I appreciate the info. When I was doing the rebuild, the techs at Summit racing told me what I needed. So do you have recommendations for a drivable cam? My uncle bought this car new and I would love to drive the wheels off of it but it’s just not possible right now.
That comment leads me to make a recommendation. I have read many places and also experienced that you should stay under 230 degrees duration at .050" if you want a nice streetable but high performance cam. With your admitted limited engine knowledge I would recommend you do the same. It will idle decent, with a little lope, and pull great down low, and also pull hard to 5800. Very similar to an L46 350-350. One of GMs greatest all-around small blocks ever made. With a 383s TQ and aluminum heads it will really make some power. GMs 430HP ZZ383 has a similar cam, and its only 222/230 dur. Last one of those I tuned would smoke the tires as long as you stayed in it, from half throttle on. Owner has trouble keeping tires on it. LOL! Fun engine!
Your thumper cam has 227/241 dur at .050" It doesn't look too bad until you realize it has an extremely tight 107 LC. Widen that out to 112 or so with a new cam, and pull the exh dur down 10 to 230 and it will run great! The lobe center change will make a HUGE difference. The ZZ383 has 112LC too. 222 intake would make more TQ down low, 227 intake would move it slightly upstairs.
Last edited by leigh1322; Oct 4, 2022 at 10:28 PM.
The 107 LSA would be acceptable for a 383 if the CR were high enough and the advertised duration was not so large. What you have there is about 74* of overlap on that cam. What you likely want is something around 60* to 65* of overlap.
your advertised duration is a large issue, creates lots of overlap on that cam. Look for something in the 275 to 280 advertised duration with a 230ish @.050 duration on the intake.
we don’t know your CR, or what heads your running or your exhaust system, or converter stall rpm, transmission or rear gear ratio, so hard to make a good reccomendation.
These are the heads. 2.5 inch stainless exhaust with x pipe. No stall yet. Factory differential. I don't have an exact number on compression but it is at least 9:1
Last edited by Yellow1980Vette; Oct 5, 2022 at 07:03 PM.
running rough
