ledee416

I am trying to figure out what I want to do for my 928 project. I have decided to go with an SBC single or possibly twin turbo set up. I am looking at between 600 and 800 hp. My main concern is whether or not a Porsche transaxle or transmission can take that kind of power. If I go upwards of 700 hp, I am probably going to look into a vette 6 speed.

I was told that the 928 auto transmission can be shifted aggressively. I have also seen posts recently about paddle shifters. ok, so basically here are my questions:

1) what are the hp limits of both manual and auto ?

2) Are there any muscle car style shift kits available for the porsche 928 auto transmission?

3) will I be able to use paddle shifters for the 84 auto transmission in my euro, thus eliminating the need to switch to a 5 spd?

4) are there any body modifications that need to be done to switch to a manual gear box in an automatic car?

the 84 euro I have is an automatic. I have been told that the auto is markedly stronger than the manual gear box. If I could stay with the auto, but get some sort of shifting performance out of it, then I dont have to buy a 3rd 928, which would be nice. I have never really driven an auto trans car on a track that felt as fun as a 5 or 6 speed. My 350 z was triptronic or whatever you want to call it. it did not feel nearly as good in the corners, or coming down in the gears. If I can get paddle shifters that will allow me to shiuft the auto to suit track / corner purposes, then I can stick with that.

thanks in advance for your help.

77tony

What's your budget $$ for your entire conversion ? Read through links below. T

https://rennlist.com/forums/928-foru...s-manuals.html

https://rennlist.com/forums/928-foru...swap-pics.html

Lizard928

Just go with a single turbo on the original 16V with a custom intake, and standalone EFI those goals are achievable

Rob Edwards

The automatic is good for 600-ish horsepower (as seen with Andy's GTS), while the 5-speed is good up to 900 CHP (in Carl's racer).

Not sure what a muscle-car shift kit is- different torque converter? Yes, those are available. Hurst quarter stick shifters? No, not available.

I'm not aware of anyone with a paddle-shifted 928.

Switching a manual into an auto is a giant pain in the ***. Lots of threads about it in the archives.


Were I going down this road, I would start with a 5-speed car and do the LSx/Dinsbox conversion.

Speedtoys

The 928 auto is strong, because its well sized, and...the ECU retards timing between shifts, which you will have to find a way to perform as well with the conversion.

Not aware that anyone has broken an auto on HP..anywhere..yet.

5spds...lots of shatter stories.

Speedtoys

I dunno if Carls car is a good comparison..being easy shifting straight line work on the salt.

Plenty of roasted 5spds on race courses over time.

Carl Fausett

Transmissions, like clutches, are measured by the torque you can put through them, not HP. So I will relate what I know in lb ft of torque.

Most of my race experience is with the 5-spd G2813. On our customers street-driven supercharged cars that 5-speed handles the 500 ft lb range very well. Failures are uncommon, but of course that depends on the driver and the size of the rear tires. (Big, sticky tires are harder on the drivetrain than thinner tires that slip)

At torque levels above 600 lb ft of torque, on pavement, we have broken 3rd gear, 4th gear, and the spiders in the differential. Marks Anderson has broken 5th (the input) gear and the driveshaft too. It isn't immediate - it took 2 or 3 racing seasons for Mark to break a gear, and I have done it in as little as 3 weekends when running 750 lb ft of torque at the tires and fitted with 305's or 315's in the rear.

I have been told the automatics can actually handle more torque than the manual transmission can. I have not raced an automatic, and I don't know anybody running up in the high torque numbers with them that I can ask. I think Todd Tremmel has an automatic on his turbocharged 928 - you should ask him how it is doing.

Quite a few of our street-driven supercharged 928's are on automatic-equipped cars, and I have not heard of any problems. I've driven them and they do well. Get the Super-clamp, tho, and watch your Thrust bearing!

Speedtoys

Good point on Tq -vs- HP there.

Cue Kibort? *kidding*

IcemanG17

Its common knowledge that the automatic is stronger than the 5 speed...... the Mercedes 722 is universally considered to be quite robust....

I would estimate the auto can handle 500ftlbs with proper cooling (think a bit more than stock) for extended periods of time....the open road guys have proven this

The 5 speed is strong until around 400ftlbs.....once past that, in race cars it starts failing all over the place....Carl is the current dyno king with 750ftlbs...but he also has blown transmissions as well.....all the big power 5 speed racers have....Anderson-Carl-Devek-Venninger- and more.....no way around it....

terry gt

I have run 430 RWTQ at 1500 rpm on a auto , broke 2 drive shafts , had a custom one made out of 4340 with a proper taper near the splined ends. The tq converter was also welded up. Other than that its good

ledee416

thanks guys. My situation is that I have an 84 euro car in automatic. I am looking for a car I can drive on a track, or take down some twisty roads and have fun. I am just concerned that using the auto trans wont really be very fun in corners and such. Obviously, I already have the car, so if I could use the auto in a way that would be fun in corners, that would be great. Otherwise, since changing over to manual sucks, I would have to buy another 928.

My overall preference would be to keep the euro. Has anyone driven a high hp auto car on a track? I am not looking at all for a straight line car. I already have an absurdly fast (for my tastes) drag car. I want my 928 to be a cornering beast.

If someone can come out and tell me that a 700 hp automatic 928 would be as fun on a track corner ad a 5spd would, that would make me feel a little better.

Let me put it like this. If you guys were going to build a 600 hp 928 for driving on a twisty track, would you use and auto or a manual transmission? what would you guys do?

hacker-pschorr

We already know it can take 825 foot pounds with Mickey Thompson DOT slicks on the back and a very well tuned engine:

https://rennlist.com/forums/928-foru...ar-wheels.html

The problem with questions like this is power is never the only factor. Todd has separate maps strictly for controlling the engine when shifting so he doesn't send unnecessary forces through the drive-train. He has spent a considerable amount of time just tuning that aspect of his twin turbo 928.

It's like the age old question: "How much boost can a 928 engine take" - that depends on your skill level behind the laptop.

Speedtoys

People are doing DE's on automatics all the time.

DEs are for your training, not racing..I wouldn't sweat it.


Decide what you want, then do it.

rgs944

it just limits your fun a little bit.

ledee416

interesting. since I definitely will not be using a Porsche engine, I am not too concerned with that aspect. I really want to make a 928 monster, but there doesnt seem to be a convincing argument for it.

I have never owned an auto high hp car that was fun to drive in corners and such. That is my main goal. I would like to be able to run laps on an N-Ring type track and have some fun. I am just not convinced that an auto trans will get me there. The whole paddle shifting idea seems pretty cool though. I just wonder how well the paddle shifter kit will work.