New 383 setup/tuning question
Thread Starter
Heel & Toe
Joined: Feb 2007
Posts: 19
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New 383 setup/tuning question
With a hyd roller cam dur. of 246 at .050 and 558 lift does anyone think a vac can is necessary? Trick flow alum heads, air gap int Holley street avenger 760cfm. Anyone heard of drilling holes in the butterflys for this setup. Trying to get it to run good. Also what total time do you suggest for these strokers? I have it at 38 total now. The setup is a Trick flow 500 hp kit, heads, cam, roller rockers etc. from Summit. Need help here....
Safety Car
Joined: Oct 2004
Posts: 3,926
Likes: 739
From: Youngstown Ohio
How is it running now?.....combo sounds good, but before adding vac cans or drilling butterflys, if you don't have problems, they don't need fixed. Are the headlights working OK?......8-10 in. of vacuum, though low, will still allow functioning in most cases.......tune the carb (adjust butterfly slot openning) before thinking about drilling....you shouldn't have to drill it.......my 383 is at 38 total timing also; this is not unusual for performance engines.
Melting Slicks
Joined: Apr 1999
Posts: 2,010
Likes: 3
From: Moon Twp. PA USA
I believe the TF heads are considered 'Fast Burn' so you should be able to reduce timing from 38*.
Lars said that 32-34* is ok with Fast Burn heads. I am running 36* @ 2700 RPM on my 383 and I will try 32* as soon as I get the intake oil leaks squared away.
Lars said that 32-34* is ok with Fast Burn heads. I am running 36* @ 2700 RPM on my 383 and I will try 32* as soon as I get the intake oil leaks squared away.
Thread Starter
Heel & Toe
Joined: Feb 2007
Posts: 19
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It starts well, but throttle response is marginal and the motor sounds really ragged. Vacuum readings bouncing around a bit but about 10 is the best vac it will pull at a1000 RPM idle.. Everything is new, chev hei with a decent internal coil for spark, stock chev fuel pump though. Bad idea there? Those are the two areas I know need improvement, but I just installed a 700r4 when we did the engine so I had a big hole in my wallet. Torque converter is another area im concerned about. 2300 stall good enough for a 700r4 with the setup Ive got- and 3.08 gears? Opionions welcome.
Last edited by stingraysteve; Jun 18, 2007 at 12:46 AM.
Instructor
Joined: Mar 2007
Posts: 223
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From: Henryville Indiana
Sounds like your tuning issue is in the primary side of the carb.
1)Make sure you have a 5.5 power valve in the primary.
2)Try going to a different size squirter...if it stumbles and hesitates,go bigger ,I've had good luck with #34 or #37.
Whats the stock jets???
I have had some that I tuned that I have to change the jets on both ends.Try 72 jets in the primary and see what happens.
1)Make sure you have a 5.5 power valve in the primary.
2)Try going to a different size squirter...if it stumbles and hesitates,go bigger ,I've had good luck with #34 or #37.
Whats the stock jets???
I have had some that I tuned that I have to change the jets on both ends.Try 72 jets in the primary and see what happens.
Instructor
Joined: Feb 2006
Posts: 118
Likes: 25
From: Killearn Scotland
I had a 383ci motor, with a TH700 and 3.08 rear. I put a TKO-600 in it last winter 
While I had the TH700, I tried running a B&M Holeshot 3000 and hated it!
It was built into a 10" housing, which made the available clutch surface too small to lock-up fully once the fluid was warm. It was like a slipping clutch, except with the added problem of cooking the trans fluid.
I dropped the original converter back in, which is a 12" housing and it locked up solid and kept the fluid temp down.
Driving was a bit awkward as the motor tended to bog down, so I usually manual shifted.
If your 2600rpm stall is in a 12" case, this would probably be ideal. Corvettes are relatively light, and the torque from a good 383 should move the car well on the street.
While I had the TH700, I tried running a B&M Holeshot 3000 and hated it!
It was built into a 10" housing, which made the available clutch surface too small to lock-up fully once the fluid was warm. It was like a slipping clutch, except with the added problem of cooking the trans fluid.
I dropped the original converter back in, which is a 12" housing and it locked up solid and kept the fluid temp down.
Driving was a bit awkward as the motor tended to bog down, so I usually manual shifted.
If your 2600rpm stall is in a 12" case, this would probably be ideal. Corvettes are relatively light, and the torque from a good 383 should move the car well on the street.
Melting Slicks
Joined: Aug 2004
Posts: 2,165
Likes: 950
From: Keizer Oregon
I know you probably already have, but triple check that your plug wires are completey locked on to the plugs and the cap. During my recent 383 fire up, my engine was acting the same. Come to find out the number 2 cylinder was missing. If you have an infared temp gun measure your header temps real quick while running, a "cold" header tube is a dead givaway for a miss.
Also follow the timing procedure outlined by LARS, if you haven't already. Then adjust your idle screws to get the max idle vacuum.
Good Luck
Also follow the timing procedure outlined by LARS, if you haven't already. Then adjust your idle screws to get the max idle vacuum.
Good Luck
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
If your Street Avenger is stock out of the box, you're running too lean. Bump primary jetting up 4 sizes and then bump secondary jetting up so it's 8 sizes bigger than primary.
You don't need to drill holes. Set your secondary idle speed screw correctly so you can reduce primary idle down to .020" transition slot exposure.
You're running too much timing. If those are fast burn heads, you need to be down around 28 to 32. If they're not fast burn, you should be at 36 max. But make the curve come in quick, and make the curve short enough to allow about 18 degrees initial timing while limiting the total to the above noted specs.
You don't need to drill holes. Set your secondary idle speed screw correctly so you can reduce primary idle down to .020" transition slot exposure.
You're running too much timing. If those are fast burn heads, you need to be down around 28 to 32. If they're not fast burn, you should be at 36 max. But make the curve come in quick, and make the curve short enough to allow about 18 degrees initial timing while limiting the total to the above noted specs.
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Thread Starter
Heel & Toe
Joined: Feb 2007
Posts: 19
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The rpm where it sounds the worst is about 2-3 thousand at which point it has such a bad vibration it makes me think we have the wrong flex plate or harmonic ballancer, which I have checked and am re-checking. It is hard for me to distinguish if it is a more serious problem, or just a tuning issue. I sure appreciate what you folks have posted to try to help me, your knowledge is first hand and really helps. The heads are trick flow cnc Kenny Duttweiler 23 degree and not sure if that is a fast burn or not. Thanks. We had a 6.5 power valve in it at first, but changed it to a 3.5. I will change the timing to 36 and see what happens. I have the advance coming in fast now. I had a carb backfire while starting yesterday so maybe it is lean.
Last edited by stingraysteve; Jun 18, 2007 at 01:45 PM.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
It starts well, but throttle response is marginal and the motor sounds really ragged. Vacuum readings bouncing around a bit but about 10 is the best vac it will pull at a1000 RPM idle.. Everything is new, chev hei with a decent internal coil for spark, stock chev fuel pump though. Bad idea there? Those are the two areas I know need improvement, but I just installed a 700r4 when we did the engine so I had a big hole in my wallet. Torque converter is another area im concerned about. 2300 stall good enough for a 700r4 with the setup Ive got- and 3.08 gears? Opionions welcome.
IMO - 246 is to much duration on a little 383
I use a stock type mech pump on my 383 & 434
You really need something like a 3.90 rear end to make a 700R4 work right.
As for stall speed 3500 is what big duration roller motor need. That what I used for many years in my 700 equiped Vette with 4.11 gearing
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Your cam can be made to run. you mentioned bad vibration. Is your motor internally or externally balanced?
I would reinstall your 6.5 PV Rich motors run nice they just are rich. Any tuned motor should run fine from idle to red line in park. That will tell you that the idle and primary side is working fine.
Thread Starter
Heel & Toe
Joined: Feb 2007
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Oh yeah, thats 112degree lobe center, that helps make up for the long duration doesnt it? I also have 76 cc combustion chambers and flattop K.B. hypereutectic pistons. Compression should be ok?
Last edited by stingraysteve; Jun 19, 2007 at 07:24 PM.
Thread Starter
Heel & Toe
Joined: Feb 2007
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I bought this motor from a guy in olympia, I am contacting him to find out if somehow he put the ext bal flywheel and harmonic on an internally bal motor by accident. Last time I buy something someone else assembled...
Burning Brakes
Joined: May 2007
Posts: 945
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From: Ventura California
The rpm where it sounds the worst is about 2-3 thousand at which point it has such a bad vibration it makes me think we have the wrong flex plate or harmonic ballancer, which I have checked and am re-checking. It is hard for me to distinguish if it is a more serious problem, or just a tuning issue. I sure appreciate what you folks have posted to try to help me, your knowledge is first hand and really helps. The heads are trick flow cnc Kenny Duttweiler 23 degree and not sure if that is a fast burn or not. Thanks. We had a 6.5 power valve in it at first, but changed it to a 3.5. I will change the timing to 36 and see what happens. I have the advance coming in fast now. I had a carb backfire while starting yesterday so maybe it is lean.
Team Owner
Joined: Apr 1999
Posts: 21,953
Likes: 1,445
From: Reno Nevada
2024 C3 of the Year Finalist- Modified
You also can not put any old 400 flexplate and balancer on a motor. They are balanced as a set.
Last edited by gkull; Jun 20, 2007 at 08:10 AM.
Thread Starter
Heel & Toe
Joined: Feb 2007
Posts: 19
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Yes, its part of the rotating mass, so I assume the flexplate and balancer was given to the engine builder for balancing. Perhaps my problem lies elsewhere. I plan to change the jets in the carb, back off the timing to 36 and see if that helps. These are not fast burn heads, they are made only by chevrolet.
Melting Slicks
Joined: Jun 2002
Posts: 2,844
Likes: 99
From: Orrtanna Pa.
I run a solid Isky cam with 254@.050 in my 406. The idle problem I had was trying to go lower than 1200 rpms the engine would stall. I did drill my throttle plates,(which didn't help) and rejetted the primaries to 74's,PV to a 4.5 and now can idle at 1000 rpms with 7.5 inches vacuum.
I found large cams need a huge initial timing setting,mine's at 18,but still keep the total mechanical advance to 36 degrees . I baught an MDS ProBillet HEI for that reason,plus the old distributer had 250,000 miles on it and was pretty well shot.
This has absolutely nothing to do with vibration. If you're vibrating that bad,check your firing order,and if that looks good,get a hold of the engine builder and ask him to confirm the balance job.
I also ran a 700r4 with a 2200 stall before I blew that one,and even with the solid Isky,had no problem driving it.I do have 3.70 gears which worked out well with the OD. I think you'll find 3.08's with OD will lug the engine unless you drive 80 mph all the time.
I found large cams need a huge initial timing setting,mine's at 18,but still keep the total mechanical advance to 36 degrees . I baught an MDS ProBillet HEI for that reason,plus the old distributer had 250,000 miles on it and was pretty well shot.
This has absolutely nothing to do with vibration. If you're vibrating that bad,check your firing order,and if that looks good,get a hold of the engine builder and ask him to confirm the balance job.
I also ran a 700r4 with a 2200 stall before I blew that one,and even with the solid Isky,had no problem driving it.I do have 3.70 gears which worked out well with the OD. I think you'll find 3.08's with OD will lug the engine unless you drive 80 mph all the time.