Same 3.6 Running 2 Diffent Intake/Exhaust Systems?
 

I've got a 1997 993 3.6 (w/ 1995 intake) that I'm going to use for my PRC GT-L car which is under construction. The class rules dictate that I run a 3.6 (or smaller) with a stock 964 or pre-Varioram 993 intake (1995). The rules also say I need to run a 1 5/8 header. Everything else in/on the engine is free - cams, headwork, c.r., etc. These rules are designed to keep you from going all out on the engine build and keep the class somewhat affordable.

I just picked up a complete 1991 964 engine. My plan is to have two complete, running 3.6's - one for the racecar and one for my pre-smog weekend street car. The street car's engine will serve as a back up in the case of a problem with the racecar engine.

My question is how to build these engines. The long blocks need to be identical but can run different intakes and exhaust. As stated earlier, the racecar will have to run a 1995 intake and 1 5/8 header but the pre-smog street car can run anything.

Should I run cams and do corresponding headork to match the racecar's intake and exhaust. I don't know much about engine desing but keep thinking the engine(s) could be built so that racecar engine is little choked down but is breathing free on the street with a larger intake/exhaust.

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Thanks-
Craig Backer

can you clarify the varioram issue for me - I was under the impression 1995 was the only 993 year without the varioram, with the varioram being introduced in 1996? Was this an option in 1996 or did the varioram start in 1997?

You're right. I was thinking/remembering wrong. Where I said 1996, I meant 1995. I will edit the original post.

You might check in with some local experts. Rich Walton and/or Jerry Woods. Or Mat Lowrance at Sporthaus. These folks are familiar with our GTL class, and are reknowned for their skill and expertise. Rich and Mat may also be racing in GTL later this year...

If you use a Motec or Haltech system, or something similar, you can always re-map for different headers and exhausts. But I am pretty sure that you need to choose cam profiles carefully.

The '95 993 intake was the one w/o v-ram

You already have the '91?, w/ the aluminum intake? I would prefer the later plastic ones myself

For the race car the 1 5/8(ID?) headers and '95 intake will limit your cam choices, for a race car I would want mechanical lifters instead of the 993 hyd. ones, cam, either factory ss or DC22 are about the best w/ the given intake.

there is some controversy as to whether the 964 crank w/ it's wider journals or the 993 crank w/ it's stiffer design is better.

there is also some controversy about which is better, the large port/valve vram heads ot the smaller port and valve non v's. I think that it depends on the rpm that the engine will be run in and the gearing that the motor sees., the smaller ports will have better gas speed and better throttle response over a fairly wide range the big ports will want more revs and closer gearing. Given the cam restrictions smaller ports/valves might be better.

If you have a builder that you trust consult w/ him. Otherwise my 2¢ might be to use the 964 block w/ '95 non vram heads and intake. Mechanical lifters(use the 964 heads to save a few $) SS or DC22 cams, Ti retainers and a good spring set. 1 5/8" ID headers.

The vram intake can be adapted to the street motor where it is better suited.

There are differences in the way the oil lines attach to the block between early and late so you wil probably want to incliude them in your short block sets.

Thanks Bill. Some great info! I was hoping you might chime in.

To clarify, I have a complete 91 3.6 and a complete 97 3.6 with an intake that has been replaced with a 95.

Be aware, we have seen some failures with 993 cranks in the pulley area. At minumum, I'd consider adding a second pulley-locating pin.

One newer approach uses a crank from a water-cooled engine.

that(GT3 crank) would certainly be the optimal solution

Yeah.. I think this is a recent trend. I just got one.

There are some potential "tricks" for a competitive GTL engine. For example, I would not run the stock alternator.

Does anyone know if the 95 non Vram heads are different than the 964 ones.

What I'm trying to land up with is two identical (approx) longblocks - one for the racecar and one for the street car that can be used as a spare - looks like I'll need to do some buying/selling/trading of parts.

Does it make any sense to run the street one with a larger intake and exhaust for more power. I'm guessing not seeing as that the cams should probably match the intake and exhaust.

BTW, I'll probably be running the racecars engine up to the low sixes and will be using a close ratio gear box.


Thanks all-
Craig Backer

Yes, 993 M64/05 Intake port is 43mm vs 964 41.5. Otherwise ports and valve heads are the same. The 993 valves are lighter due to the 993 7.9mm stems vs 964 9mm. vram used even larger valves 50 & 43.5 and 51.5 & 43.5 on RS

The 964 rocker arms are the old style w/ the bearings cast into the carrier, 993 is the newer bolt on type.

US 993 have SAI ports cast into them, 964 and RoW do not

993 heads use a high temp resistant alloy, RR530, only the 930 heads had previously used this alloy.

Who will build the engines?

I'll probably have JWE do at least the bottom end of the first. I may take it from there - if I can find the time.

Craig Backer