To all 3.6 conversion gurus and tech guys

[BB911SC]

I would like some comments or suggestions regarding the use of SSI's on a 3.6 liter conversion. I know they may be too small in their stock configuration, but what if I enlarge the secondaries?

Any ideas???
Thanks

[Bill Verburg]

SSI uses 1 1/2" OD(1 3/8" ID) primaries, this small size promotes increased gas velocity in the pipes at lower revs and so is good for a mostly street driven car. B&B comes in 2 sizes 1 5/8" OD(1 1/2" ID) and 1 3/4"OD(1 5/8" ID) primaries, I have no experience with the 1 5/8" size, the 1 3/4" really brings the 3.6 to life at the top of the range and doesn't seem to harm the bottom rev range, so it is the most common recommendation. The 3.2 exhaust will also fit but it has the disadvantage of not being able to make use of the acoustic tuning effects inherent in the other pipes equal length primary tubes.

The secondary and more importantly the transition from primary to secondary is a less explored area. There is hp to be gained here. I have discussed this issue at length with some of the east coast racers who have been experimenting with these areas. The most consistatly successfull combination seems to use 18-20&deg transitions between 1 3/4" ~31" long primaries, to 2" OD ~8' long collectors.

All of this is affected by cams, mufflers and gearing so your results will vary. Small changes can have relatively large effects, when longer duration cams and open exhausts are used, however all of the effects are dramaticly masked when mufflers enter the picture.

[BB911SC]

The primaries on the SSI's match right up to the exhaust ports on the 964 heads (same size as the 3.2). I understand the benefit of the smaller tubes relating to increasing the scavenging effect, but I also have heard that the small tubes will "choke" the engine at higher revs... I don't know what the stock diameter of the secondary tube on the SSI is, but if I were to increase it, wouldn't that aid in high end performance?

[Bill Verburg]

Not appreciably.

[BB911SC]

Bill,
Thanks for your replies, let me give you some more details of my project. I would appreciate your thoughts...

3.6 liter 964 engine
Individual throttle bodies and manifolds (6)
DTA Pro8 engine management system running sequential for injection and wasted spark for twin ignition.

[Bill Verburg]

Again there is nothing wrong with stock SSI on a mostly street driven 3.6, I used them on mine for several years. But the B&B are dramaticly better at the top end and are no worse for puttering around, I would never want to go back. Given the mods on the intake side the B&B or some custom bent versions using the transitions I mentioned would be the way to go, otherwise your free flowing intakes will be wasted. I would also use a wilder cam, again for street use I have seen some very impressive results from the 993 sport cams offered by Web Cam. None of the mods discussed here work to their fullest extent unless accompanied by the others, along with some custom chips. I also feel that Jack Olsen made some good decisions when he went for better gearing on his latest transmission.

Again all of this is dependant on the intended use of the car. For street use, moderately lower gearing(I refused the 7:31 gearing offered on my trans), B&B headers with heat, 993 sportcams, custom chip, free flowing(noisy) muffler make a very nice combination. I can't speak to the effect of you intake mod except that singly it won't be much of an improvement.

[BB911SC]

Bill,
Thanks for your reply. I was planning to do cams, but it was suggested that I drive the car with the stock motor for a while. I don't need a chip since my engine management is programmable and I will tune it on a dyno.

Concerning the difference between individual throttles and the stock 964 induction, considering the 993, I would expect a significant improvement in power and response. I'll let you know how it turns out.

Thanks