Big bore throttle bodies

[adamnitti]

how much of a difference do they make on a stock 3.2? i've been thinking about getting mine bored or swapping for one. is their potential more easily reached by going with a chip or sport exhaust?

[89911]

I would think in the big scheme of things, not much alone or with one or two mods. If it isthe only thing that you haven't done and have done everything else, (MAF, SSI's, exhaust, higher fuel pressure), it can only help. The best price I've seen is Big Bore Throttle Body in the back of Pano. About $200. We are talking minimal increase at best even so.

[RSupdate]

If you look at my sig below, you can see what's been done to my 3.2.... basically opened up the intake & exhaust capabilties and a chip.

Would a BB throttle body be a waste of time? Just a passing thought. A MAF is quite a bit more $$$, so Just want to know my options.

Thx.

[mm86911]

Adam,

It's worth at least 40 hp. . . . if you add a tuned exhaust system, MAF, chip, ported heads, etc. Seriously, I don't think you will notice any difference by itself but as part of a package it should add a few extra ponies. BTW, I have one - was done by Big Bore Throttle Body as 89911 described.

[Steve W]

I'll probably second what 89911 says. May help a little bit in conjunction also with extrude honing the intake manifolds, which BA found produces an extra 7hp at the top end. The circumference of the throttle body has a bit of a lip around the bore which can impede the flow. After I had my mods done, I did have mine bored out. Cost was about $165 and it added about 3 mm to the diameter and cleaned out the bore.

[skinnerd]

Like everyone else above is saying, in conjunction with other mods (chip, exhaust, etc), it probably helps a bit. Is what you get from the larger throttle body worth the $200 bill? That's subject to debate. I believe a chip, SSI's and exhaust help more than the throttle body. All of the above including throttle body are installed on my car, and the engine hooked to a 915 with 7:31 ring & pinion really scoots.

[RSupdate]

Doug,

I have almost the same setup as you, except for the B.B. throttle body & 7:31 r/p. Based on yr experience, would you think any improvement could be noticed by me if I were to add the B.B. Throttle body? The $200 is no big deal, heck it's a 911, right?

I just want to feel a bit more scoot when I depress the pedel.

Thx.

[skinnerd]

Honestly, I don't think you'll be able to notice it. In fact, when I first had the 3.2 Motronic engine installed into the 75 Carrera, it only had SSI's with factory exhaust, the larger throttle body and the stock 8:31 R&P. I was disappointed in the performance of the car. I eventually tracked down a NOS 7:31 R&P and had it installed with a Quaiffe and chip. Holy cow, the car was transformed into a rocket sled! I'm sure the R&P accounted for most of the HUGE difference. I added a taller 5th gear for good mileage on the highway. Although somewhat expensive (~$1000 for the 7:31, installation extra), it is a lot of bang for your buck. You'll notice more difference with gearing changes than most of the "add-ons" you can install on the engine. Just my thoughts....

[RSupdate]

Thanks a bunch Doug. I appreciate yr feedback.

You bring up another issue which has been bugging me the last month or so... and that's my gearing. I'm running an '84 915 trans and it's bone stock.....

I do most of my running around with the RGruppe boys and their 2.7 RS spec motors and I'm lacking "oommphh" in the gearing dept for sure.

So based on what you have shared with me a 7.31 ring & pinion with a quaife Ltd slip will do the trick ehh? A slightly taller 5th couldn't hurt either.

Thanks again.

[skinnerd]

John:
I think you'd be amazed at what a 7:31 will do for your car. It's like installing a close ratio box, and if you go with the taller fith gear to give you the same revs/speed, you'll get good cruising (and gas mileage) out on the highway. I put a Quaiffe in to harness all that new low end grunt for autocrossing. Like I said I think you can still find good 7:31's for around $1000, the fifth gear will run you a couple a hundred, Quaiffes are not cheap, and then someone has got to put it all together for you. I think I went through a $2600 bill pretty quick. But the end result is worth it! Good luck.

[Kemo]

skinnerd,
When you say 7:31, do you mean you can buy a complete gearbox for a $1000 or is that the cost to convert an 8:31? Was the 7:31 an option or was it only available on certain cars or certain years?
As always, any comments are appreciated.

[RSupdate]

Thanks Doug, yr help is greatly appreciated !!!!!!!

[skinnerd]

$1000 was the cost of the 7:31 ring & pinion alone (and this was 3 years ago). Mine was a NOS, so it was basically new. I'm not sure you can get a used one for much less these days (due to supply & demand), but definitely shop around. They are getting more scarce these days. A complete 915 transmission in good shape with a 7:31 already in it would be a great way to go. Cost for this is dependant on the overall shape of the transmission, but I wouldn't be surprised if some people are asking $1500 or more. Again supply and demand. If you are patient, you can probably find a good deal somewhere, but it will take some looking. Again this is for a gearbox with 7:31 in very good condition.

I believe that 74/75 were the cutoff years. All 1974 and early 915 gearboxes will have the 7:31, and all 1975 and later gearboxes will have the 8:31. If you do find a 7:31, it will cost you at least $6-700 to get it installed. Figure removal of engine/trans, trans disassembly, set-up of the ring & pinion (not so trivial), and reassembly/reinstallation. As you can see, it's not a cheap endeavor, but one that I think is well worth the effort. Obviously, if you can find a good deal on the necessary parts and can do most if not all the work yourself, you'll save lots.

Hope this answers some questions, and is not information overload.

[adamnitti]

for what it's worth, i replaced the r&p in my tranny when it was rebuilt (not a 7:31; the stock one) and the cost was $1200 just for that part.

[RSupdate]

Doug, I'm not too worried about the $$$ as thw wife has worked in the P-car biz since '78 and at the same independent Porsche garage for almost 19 of those yrs.

Yeah It'll cost me, but I get the office mgr. discount

I like the concept of everything you've shared!! Ican't wait.