Hey folks,

New member to the website but have been reading info from here for 2+ years; this is a great source of corvette intelligence. Right now I’m trying to figure out a problem with a new 383 stroker I had built for a little more power than the stock 200hp in my 72 vette. First, some specs on the engine (or at least what I know). It has a forged crank, forged pistons, and 6 inch I beam rods. The heads are World Products S/R Torquer Heads assembled with 2.02 valves, 76cc chambers (approximately 9.75 compression ratio). IT has hydraulic flat tappet cam and lifters 230@.050 109LSA .480 lift. Sorry, that’s all I know about the engine.

When I initially got the car back from the rebuild, I kept using oil like crazy so I took it back to them (a quart every 45 min of driving time). It turns out the rings they installed were for a racing setup and the engine needed to run at a higher RPM (6,000 RPM) for the rings to seat. With a 3.37 rear end, I could never get it to the RPM needed for that to happen (or was brave enough to try). So I took it back to them a second time to have the rings replaced. While there, I also had the intake manifold replaced install a new Edelbrock performer intake and a Holley 650 CFM carb. They also refreshed the transmission and installed a 2800 stall torque converter. When they worked on it, they called me and said they were having problems getting the engine to perform with the new carb. It was cutting out at higher RPMs. It turned out to be a problem with the spark; the carb was pumping in so much fuel it was actually extinguishing the spark (Again what I was told). So they put on a MSD coil and replaced the points with a Petronix electronic ignition (I know – not a true electronic ignition – another great post on this forum). I gotta tell you, on the way home from the shop, it ran like a raped ape. But now I’m having problems with it missing out again; when driving it normally, it runs fine but when I put the hammer down it acts like its running on 6 cylinders. I’ve replaced the plugs and wires, checked the timing (14 degrees initial) 34 degrees at 3500 RPM. Right now I have the vacuum advance disconnected & plugged. The engine builder said I wouldn’t need it. I’m still going to replace the distributor cap and rotor but after that don’t know where to turn next.

I’d love some thoughts if you have any…

Thanks in advance

 

There are a bunch of red flags here IMHO - some of the information they're relaying is frankly wacko. I have thoughts on the build overall...but let's focus on the tuning of what you've got.

Fuel extinguishing the spark? That's wacko. I would definitely check in with a good local shop to check the F/A ratio before doing much else. The fact they couldn't get a Holley carb to work is frankly a really disturbing sign...and if the problem was too much gas (stupid) then why change out the ignition?

Depending on your skillset, I would tend towards a) bringing the carb back to out-of-the-box jetting and power valve - which still won't be right, but I'm betting it'll be closer b) reconnecting the vacuum advance and c) check for vacuum leaks.

Ultimately, you're headed for a dyno tune to figure out what's happening and to get the engine tuned right.

Sounds like another racing shop trying to build street engines and failing miserably. Sorry, not what you wanted to hear

 

I would try reconnecting the vacuum advance and recheck the timing, especially with a power timing light if you have one. If it seems like it's running fine until you go WOT, it could be fuel delivery, but I would check the manifold vacuum first. You could have a vacuum leak. This could be a silly question - are the carb bolts tightened down?

 

Thanks guys for the quick reply.

You know I probably should have done some additional research before letting them build the engine. From the posts I read though they had a good track record. The only positive thing I have right now is I didn't let them screw with the numbers matching engine and quite honestly, I was considering it at the time. Thanks to all those that recommended otherwise on this site.

Billa,
I haven't done anything with the jetting for the carb so unless they did something, it should still have the factory jetting. I noticed I did have a typo regarding the carb I have; it's actually a holley 750 (P/N 80508S). The only thing I've done to the carb is 1) change the air fuel mixture based on some posts here, and 2) replace the vacuum secondary spring because the secondaries weren't opening up. Now I'm thinking about changing it back to the factory spring.

BlackC3,
Thanks for the recommendations! And don't worry about offending me -- I'm open to all suggestions. I did check the bolts and theyr'e tight. I've tried multiple scenarios with the vacuum line on and off and it doesn't make a difference (as far as the missing goes). I've tried several different timing configurations as well. It seems to run the best at 14 degrees initial / 34 degrees at 3500RPM. I hooked up a vacuum gauge and it showed a (fairly) steady 13-14Hg. From what I saw on youtube, that could be normal if I have a beefed up engine.

Agree that a dyno is probably going to give me the true answer but I wanted to rule out all basics first.

Thanks for the feedback.