Boxer Rebellion

Guys,

I'm at the tail end of a full rebuild and 3.2 to 3.4L conversion on my '87 Carrera. Initially, I'm going to run Motronic induction, but down the road I'd like to run ITBs, hotter cams and aftermarket engine management. I'd like to understand how to select the appropriately sized ITBs & cams for my engine setup. What factors should I consider?

My goal is a daily driver that's streetable and fun to drive at a DE or autocross event. My engine is being built to rev up to 7k RPM. I'm running twin plugs and Mahle Motorsport "RSR" style pistons with hemispherical domes. The compression is lower than we expected at 9.6:1, but it should allow for fun ignition timing and an added margin of safety on the street. The engine is 3.4L in displacement - 98mm bore and 74.4mm stroke.

Thanks for your input!

Steve Weiner-Rennsport Systems

46mm throttles will be the right choice for such an engine.

Camshaft selection depends on many factors that include:

1) Type of use

2) Vehicle weight

3) Gearing; stock or close-ratio

4) Compression ratio

5) Piston-to-valve clearances


Beyond this, experience plays a role in making the right choice, but one rule is "less is more" when it comes to cams.

Ed Hughes

And, there you have the voice of experience, it's probably worth a call to Steve to discuss your specific needs.

race911

Which, of course, some of us had to learn the hard way...............

What's the ratio of wrong-to-right (or even close) in the cam selection area, about what compression ratio ends up being--9 or 10:1?

Boxer Rebellion

Steve - Thanks for the helpful reply. As far as the camshafts go, I think I can put some color around most of the factors you've raised:

1) Type of use - Mostly street with some DE/Autocross - probably 75% street. I really enjoy the way a stock 3.2 Carrera "comes on" at 4K RPM. My engine is limited to 7K RPM and is equipped with ARP rod bolts, EBS sport valve springs and EBS titanium retainers.

2) Vehicle weight - I don't know exactly, but it should be very close to stock for an '87 Carrera. Based upon 5 minutes' research on the forums, I'd guess 2850 lbs with a full tank of gas.

3) Gearing - Stock currently. I've considered moving to close ratios when it's time to rebuild my tranny - but hopefully that's years away. I've read that close ratios with a 3.4L can be a rocket.

4) Compression Ratio - measured at 9.6:1 after CC'ing everything. Pistons are hemispherical domed, and I'm running twin plugs.

5) Piston-to-valve clearance is set at .041" or 1.04mm

Thanks for your help!

Boxer Rebellion

Bump

Boxer Rebellion

Bump. Still looking for some direction on cams

Amber Gramps

The Gods have spoken. No further discussion is needed.

Call Rennsport Systems at 503 244 0990 and ask for Steve.

Ed Hughes

Or, call Steve. I hope he is so busy, he can't slum around here.

Amber Gramps

Speaking of Steve, there is this other guy named Weiner that is pretty good. His number is 503 244 0990....

Ed Hughes

?? That is the Steve I referred to..

Steve Weiner-Rennsport Systems

Based on your usage, I'd run a Mod-S cam in that for good power to 7K and excellent mid-range torque.

Remember now, this recommendation is for ITB's, NOT the stock intake system.

Amber Gramps

....and Steve, it is finally pay day. I'll take a set of Bilstein HD inserts for Boge and the Lemforder Turbo tie rod kit.

race911

You're no fun--was expecting you to say a '73.5 2.4T CIS grind to keep things going.

Boxer Rebellion

Thanks for your help, Steve. Now all I need to do is save some $$!