I am in the process of building a 383 for my 89 Corvette. The car has a ZF 6 speed and 3.33:1 gears. The planned usage is mostly street driving. It's not a daily driver but I want to be able to use it that way if I want. The car will see some dragstrip, autocross, and NASA HPDE usage. My target is 375 RWHP (more would be OK too ) with the ability to pass 49 state emissions using a smog-specific tune.

The general build specs are as follows:

AFR 195 Eliminator 65 cc heads (should arrive mid to late March)
Full roller rockers, 1.6 ratio with 7/16" studs
Hydraulic Roller cam -- estimating 22x I/230 E range at .050 with 0.570ish lift
TPIS Miniram; 52 mm TB
MAF and '165 ECU -- custom tune is a given
1 3/4 headers; full 3" dual exhuast with cats and X-pipe
Forged rotating assembly and pistons, 6" rods
6500 RPM redline

I will be verifying all the part specs (chamber cc's, clearances, correct pushrod length, cam timing, etc.) during the build. The devil's in the details ....

I would like to use flat top pistons in this combo to maximize quench. Using a standard -5cc valve relief and a piston to head clearance of 0.044 (.039 gasket, piston to deck at 0.005), I am coming up with an SCR of 10.8 and a DCR of 8.65 using a 224/230 duration 112 LSA cam combo based on Comp Cams' XFI lobe profiles. The next smallest dish volume I've been able to find in a stocked forged piston is -14 cc, which puts me at 9.7 static/7.7 dynamic.

I am looking for advice, suggestions, etc. regarding the following:

1) What DCR should I aim for? I've always heard that 8.2 to 8.4 is about the practical limit for a street engine on pump gas. I want to keep the quench height as tight as I can for better combustion and less octane sensitivity. I looked at opening up the quench height to .050 but I would still be at 10.7 SCR/8.5 DCR with flat tops. I'm afraid that if I go with the dished pistons the DCR will be less than ideal and I will have trouble meeting my power goals and emissions tuning will be more difficult.

2) I would appreciate cam recommendations. My state recently suspended emissions testing but I will most likely have to move in the next year or two for job reasons. I don't want to end up putting in a cam now and then having to change it if I move to a state with required inspections. I probably will have a custom grind done for this combo but I would like to get a feel for how much duration I can use and still have a shot at meeting emissions. I have no problem with making tuning changes and using fuel additives to get the car to pass. I know the cam range I listed above is leaving a lot of power on the table.

Thanks in advance for the help.

 

I think you've got a very good shot at passing emissions with that cam and a sharp tune. Lower compression is a bit easier to pass the sniffer test, too. There's a reason the factory didn't start raising compression to reasonable levels until they started using fuel injection (at least in the 9s). And then they didn't really start cranking it up over 10 until they started getting some real good heads with efficient chambers, more advanced EFI and spark timing capabilities and such.

The factory would really like to use high static compression ratios because it really helps boost fuel ecomomy (and power too, obviously), but it also hurts emissions, so they have to do a balancing act. As the years went by and they got better EFI systems and more efficient heads they could run the compression higher and higher to get the benefits while still hitting increasingly strict emissions standards.

On an older gen1 small block I'd go with the lower compression unless you're going to take extra steps to prevent the detonation like preping the combustion chambers and piston faces with a cam that small.

If in doubt, go with lower compression than you think you need to. Compression that's a little low but able to take an optimum amount of spark advance without detonation will make more power than a a motor with compression that's a little too high requiring the spark advance be pulled back from optimum to stay out of detonation.

BTW- I calculate your compression at 9.80:1 with the -14cc pistons and the specs you provided (the .039" head gasket will be 9cc volume if it's the common Fel Pro gasket for a 350/383). I am sure there are other piston choices available to you- a 12cc D-dish piston (to preserve the quench area) for a 383 is something almost all the usual piston manufacturers offer, which would put you dead-on 10:1.

 

Couple of thoughts. One is that it looks like you are on your way to a very powerfull car. Like you said the devil is in the details. You have to check everything. Be sure to cc your pistons.

1. I would use 3/8" pushrods and the best you can afford. I used the ones by Terry Manton.
2. Catalytic converters. Magnaflow has a series out using Metallic Substrate. They are high flowing and have very little restiction. I have a set on my car.
3. I would use the Comp Cams Pro Magnum 1.6 roller rockers. The XFI cam was designed to use them.
4. I think the 230XFI cam will work great on your car. What ever cam you wind up with make sure it has the high lift to take avantage of those heads.
5. Use at least a 58mm throttle body. I'm serious considering going to a monoblade on my car.
6. You want the quench as close to .035" as posible. I would suggest the GM .028" head gasket part number 10105117. We use it with out problems. I'm running 10.75 compression, 8.5DCR and .035" quench. You will be able to deck your block to get the quench you need. Also your head may not actually be 65cc. Be sure to measure. You should be able to find pistons that will work.
7. Make sure the headers and gaskets do not cover any of the exhaust ports. I have seen this way to many times.
8. Do not use Total Seal Rings. Seen way to many problems with them. Use standard 1/16,1/16,3/16 rings.
9. I would use a straight through muffler design such as Magnaflow or Dynomax. Please stay away from Flowmaster for performance.
10. Do research on oil control. Such as screens and larger oil pans. There is horsepower in oil.
11. Cadillac racing has a new hydraulic roller lifter out. I would use it.
12. Seeing that you will be getting a forged crank get one with the aero wing. You don't want to take the chance of leaving any hp on the table.
All that comes to mind for now.

 

Gents:

Thanks for the input! This is really good information.

Damon -- You're right about the 9.8 SCR with the dish pistons. I forgot to change the deck height from 0.010 to 0.005 when I calculated it. I would love to run a cam in the 230/236 range if I can make it work emissions-wise but I think that will be too much overlap. I will prep the chambers and piston tops in any case. Another thing I'm seriously thinking about doing is converting my ECM to an OBDII LSX style and using a late Gen 1 Vortec distributor and crank/cam position sensor. That would give me a LOT more flexibility in trying to tune this combination and would likely allow me to run the higher CR and larger cam.

89TransAmGTA -- Thanks for the really thorough list. I was planning on doing most of the stuff you listed. In fact, I was planning on high quality pushrods and the Comp Cams Magnum rollers. Every part that has an effect on compression ratio will be cc'ed before it goes into the motor and all the gasket matches will be verified. I'm planning on a high quality standard ring set since this will mainly be a street motor.

Regarding the .035 quench -- isn't that a bit tight with a 383 above 6000 rpm due to the higher piston acceleration rates? Also, what are your thoughts on Hypereutectic pistons in this combination?

BTW -- I HATE Flowmasters .....

 

That's the quench I'm running and many others on this board. I have been winding my motor to 6200rpm. It is still making good power so I intend to wind it a little higher. You can back it off a couple of thousanths if you wish. But remember the tighter the better within reason.

FWIW I'm running the factory cast iron crank aerowinged. Factory PM rods and Speed-Pro Forged pistons. I also have a 4 bolt Vortec block.

Regarding the XFI 230 degree cam. We have a car here locally with one that passes California emmissions. That is on a 350/355 motor. Your 383 will tame it some more.

One more thing. I'm running the XFI268(218@.050) cam and just put down 401rwhp and 390rwtq with a highly moded TPI setup, an automatic with a Yank SS3600 torque converter. More power to be had. Just follow the rules above. Those 3-5hp here and there add up.

Hehehe. One more thing I'm running a Meizere 55gph water pump. I bought it for the hp but it as it turns out it keeps the motor cool better than the factory water pump. That is worth some power.

Another thing I'm running the Mufflex 3 1/2" cat back. I recommend it on your set up. I gained 27 RWHP between the electic water pump and the Mufflex cat back.

 

Regarding the OBDll. I'm also seriously considering converting. One of the main reasons is I'm switching out my 700R4 for a 4L60E. Big thread on the subject at 3rdgen.org. Wiring harnesses available to make it easier.

 

Thanks for sharing regarding the car with the 280XFI passing Cali emissions. That was the only thing holding me back from looking at that cam. I'm trying to be very careful about not falling into the "bigger is better" trap, but I have felt all along that 230/236 would be ideal if emissions weren't a factor.

About the exhaust -- this engine will be in an 89 Corvette. I will be able to run a 3" full dual system with an x-pipe all the way back to the mufflers, so I don't have the issues with exhaust restriction like you do. My plan right now is to use Magnaflow or Corsa mufflers. C4 Corvettes have major problems with resonance inside the car with high flow mufflers (don't ask me how I know this ), so I plan to be very selective here.

BTW -- I have read your posts regarding the amount of power you're making. I'm extremely impressed. 400 RWHP with a 355 TPI and a relatively mild cam -- incredible! In fact, your posts reinforce my philosophy that it's all about making sure all the parts complement one another and sweating the little details.

This project is going to cost me a fortune but I'm sure I'll think it was worth it the first time I tromp on the gas.

 

"In fact, your posts reinforce my philosophy that it's all about making sure all the parts complement one another and sweating the little details."

Exactly. By the way my motor was almost dead nuts as to what DynoSim said it would/could be.