RWD conversion for the 911

[beantowntechy]

Guys...I was reading the weight loss thread and amongst other things, I'm giving serious thought to the RWD conversion. I'm not mechanically inclined at all, so I have some basic questions. Does it impact HP (to the ground) positively or negatively? I'm assuming no, but just wondering how the AWD distributes it and when converting to RWD, how that impacts it. Also, does it impact PSM at all, one way or the other...or does it just work the same, but only applying it to RW axle? Any other valuable feedback would be greatly appreciated too. I didn't want to ask this question on the original thread because I didn't want to get off topic. Thx.

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[TXGold]

The perceived horsepower is, IMO, effected greatly. There is less mechanical drivetrain loss and friction, so more power makes it to the ground. I improved my best 60-130 from 8.4 to a 7.92 IIRC. Among the increase in acceleration, I feel the car becomes an actual sports car with the RWD conversion. Take it easy for a few weeks with it, it is like driving a completely different car.

PSM uses brakes to control the stability of the car. My car had zero PSM issues with the change to RWD.

The AWD system shifts power around between the axles mechanically so naturally it isn't effected. I highly recommend it. If you can afford it, put in a limited slip differential, otherwise you'll enjoy it anyways.

[beantowntechy]

TX - That's great info...just what i was looking for. I can afford a limited slip differential. Which do you recommend and how much does it weigh? :-) Going RWD will also aide my cause it getting my car dyno'd on a dynapack, as the nearest AWD dynapack is in CT...which I'm not willing to drive to at this point. There are several RWD dyna in the area.

Anyone else have information worth passing along..even if it reaffirms what TX said? Thank you in advance.

[ttboost]

Originally Posted by beantowntechy

TX - That's great info...just what i was looking for. I can afford a limited slip differential. Which do you recommend and how much does it weigh? :-) Going RWD will also aide my cause it getting my car dyno'd on a dynapack, as the nearest AWD dynapack is in CT...which I'm not willing to drive to at this point. There are several RWD dyna in the area.

Anyone else have information worth passing along..even if it reaffirms what TX said? Thank you in advance.

If all you care about is the "number", why don't you just drop the driveshaft for now, to dyno. It takes about a half an hour, if you've never done it. After you dyno it, go drive around for a week or two and see how you like it. if you don't like it, half hour later, you're back to AWD, if you like it, perform the FULL mod, where you can find the DIY here if you search. Remember, with the full mod you will get the advantage of the 70lb weight loss, but these cars can be a handful if they are powerful, RWD and have stock suspension. GL

[beantowntechy]

Good point, re: dropping the F driveshaft to do the dyno.

And to make an effort on being resourceful, I just did a search after my last post and found several threads pertaining to the RWD conversion. I had no idea that this debate has been such a rage on the forum I will read the threads and get the info I need...nobody else needs to bother responding to this post and I'm sorry if I opened up a can of worms.

After reading a few posts already, I think that with my inexperience I should leave it intact (until I have a lot more seat time).

Thx.

[ttboost]

Look up "JohnD" here on the forum, he is from up your way...

[beantowntechy]

Great minds think alike. I had read his opinion already when it convinced me to stay put, and noticed he was listed as "northeast". I am in the process of typing a hello to him.

thx again my friend.

[Steve Theodore]

Not at all pretending to be an expert on this, but having my own friends ask me about it, I've been giving it some thought lately and would offer the following observations, some of which may even be valid.

1. I would not pursue a RWD conversion without being willing to go all the way and address the lack of LSD and a proper suspension and suspension corner balance.
2. I would suspect that if you enjoy driving your car hard in the corners, or if you have quite a bit more power than stock, that point 1 is even more important.
3. I would suspect that the weight distribution is going to be affected a fair amount by pursuing this mod in a thorough manner, meaning that point 1 is extremely important.

Hopefully you can spot the trend with my thinking here...I'm more concerned for people who pursue the RWD conversion the "cheap" way and am worried that they may have some trouble down the road. I've only heard positive things said about the GT2 overall (except for the lack of PSM) so would suspect that you could recreate the best of all worlds with a well done RWD conversion on a 996TT.

As for me, although the thought of losing 72 pounds sounds absurdly appealing, I know that the full RWD conversion would be expensive if done right and might actually impede my ability to enjoy and re-sell the car if in a pinch. Given some practical thought to this and my own abilities, I think staying AWD is a pretty wise decision.

[heavychevy]

There is not much more power to the ground at all, the bulk of the increase in speed is due to the weight savings and reduction in drag from the front drivetrain. If you just pull the driveshaft, you wont notice much difference, because the front wheels are still connected and you' re only about 7 lbs lighter. Take the whole thing out and it's a different story, straight line speed is enhanced a lot.

[ttboost]

Originally Posted by heavychevy

There is not much more power to the ground at all, the bulk of the increase in speed is due to the weight savings and reduction in drag from the front drivetrain. If you just pull the driveshaft, you wont notice much difference, because the front wheels are still connected and you' re only about 7 lbs lighter. Take the whole thing out and it's a different story, straight line speed is enhanced a lot.

Agreed. We tried to find this answer in an experiment which went awry. I think you might gain 2-4% going to RWD. Would you notce that? Not likely, but as heavy says you WILL and I DO notice the weight savings, which is probably more important than getting more power, as weight loss can be related to more perceived power at potentially $0 cost, other than time removing stuff. Just removing the driveshaft nets you NOTHING, except potential traction problems, trying to push all that drivetrain that just became extra weight.

[Steve Theodore]

ttboost,

I definitely hear where you're coming from, but it's not going to be easy to feel a 72 pound weight reduction on a 3400(ish) pound car with over 400 horsepower. That would be akin to feeling a noticeable difference between a full tank of gas and a quarter tank of gas. I'm guessing most of what people notice is the lack of friction from turning the driveshaft/front diff and also the lack of traction which probably comes across as more drama and more power. Needless to say I haven't done the mod myself so am just speculating here.

PS. If you're one of those people that can feel a distinct acceleration difference between the fuel levels I mentioned, more power to you! A weight loss analogy I like to use (I'm a weight weenie with cars) is to compare a car's performance with a 200 pound passenger versus when that passenger is not in the car, which I bet is something that nearly all of us could indeed notice.

[ttboost]

Originally Posted by Steve Theodore

ttboost,

I definitely hear where you're coming from, but it's not going to be easy to feel a 72 pound weight reduction on a 3400(ish) pound car with over 400 horsepower. That would be akin to feeling a noticeable difference between a full tank of gas and a quarter tank of gas. I'm guessing most of what people notice is the lack of friction from turning the driveshaft/front diff and also the lack of traction which probably comes across as more drama and more power. Needless to say I haven't done the mod myself so am just speculating here.

PS. If you're one of those people that can feel a distinct acceleration difference between the fuel levels I mentioned, more power to you! A weight loss analogy I like to use (I'm a weight weenie with cars) is to compare a car's performance with a 200 pound passenger versus when that passenger is not in the car, which I bet is something that nearly all of us could indeed notice.

I hear you Steve. Divide 70 by 3400. Now divide 70 by 3100. 2% is 2%. I agree that it won't be an earth shattering improvement, but I think it is noticable on any car at any level. There are guys here that did the RWD mod on stock cars and improved their 60-130 by over 1/2 second. That is pretty noticable IMO. I improved my 60-130 by 2.5 tenths by doing a RWD mod. While I like it, I will be going back to AWD for the winter.

[Steve Theodore]

Yeah, good point about the math. Point taken there.

The only thing I didn't like about the 60-130 comparison that was so well received is that the guy noted that he had a UMW flash and had higher octane on board during the RWD run...so in my mind that wasn't a fair comparison anymore. However, I have no doubt whatsoever that a RWD 996TT is going to outperform a similarly modified AWD 996TT in that test every time.

[heavychevy]

You will feel the weight difference, not necessarily on the butt dyno but the balance of the car. The front end will feel lighter under acceleration. I think a good test would be to compare the a car with the front diff still in but disconnected like RWD to a complete conversion with the front diff removed. That would tell if the accel is coming more from weight or from drag.

You WILL feel like you're going faster, especially on the top end where parasitic drag takes more of a toll. It's not just the weight, it's the drag too, and you can certainly feel the combination of the two, just can't say which one is more prevalent.

Seasoned drag racers and track guys will tell you that in a 3400 lb car that you can feel that 75 lbs and really you can, in the 911 it's a bit different because it feels more like liftoff under acceleration, and mid-corner push is far more prevalent. If you are not seasoned, you may not feel it in all those areas, but you will notice, even down to the steering being lighter.

[ttboost]

Originally Posted by heavychevy

You will feel the weight difference, not necessarily on the butt dyno but the balance of the car. The front end will feel lighter under acceleration. I think a good test would be to compare the a car with the front diff still in but disconnected like RWD to a complete conversion with the front diff removed. That would tell if the accel is coming more from weight or from drag.

You WILL feel like you're going faster, especially on the top end where parasitic drag takes more of a toll. It's not just the weight, it's the drag too, and you can certainly feel the combination of the two, just can't say which one is more prevalent.

Seasoned drag racers and track guys will tell you that in a 3400 lb car that you can feel that 75 lbs and really you can, in the 911 it's a bit different because it feels more like liftoff under acceleration, and mid-corner push is far more prevalent. If you are not seasoned, you may not feel it in all those areas, but you will notice, even down to the steering being lighter.

Zakly...