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View Full Version : Supercharged v8 rear end gearing?? How to get 3.69 ??


gsracer
02-21-2014, 07:23 PM
So background I've had this car for like 5 years now. It is a v8 out of an infinity q45 with a vortech blower. Well after all this time the factory 4.08 with cusco 2 way rear end finally blew up.

I was thinking of lowering the gear ratio to 3.69 from the factory 4.08. My redline is 7000 rpm. 1st 2nd and most of 3rd is pretty useless as it can spin 315's pretty easily, and the car weighs around 28-2900 lbs

What are the drawbacks from a performance standpoint of going to a 3.69 from the 4.08?

How does one go about using the 3.69 r200 from the 97-01 q45s in an s chassis? I want to be sure i can use my existing cusco rs lsd as well obviously.

The car is used for mostly drift and street type stuff
Heres my current gear ratio and speed at redline.

RPM 7000
TIRE 25"
REAR END 4.08
1ST 3.214 40 Mph
2ND 1.925 66 Mph
3RD 1.302 98 Mph
4TH 1 128 Mph
5TH 0.75 170 Mph

with the 3.69 it should be

REAR END 3.69
1ST 3.214 44 mph
2ND 1.925 73 mph
3RD 1.302 108 mph
4TH 1 141 mph
5TH 0.75 188 mph


and heres my dyno if it matters, its the RED line.

http://img.photobucket.com/albums/v344/gsracer/intake%20manifold/Beforeintakeandafter1.jpg


and the engine and car if anyones interested.

http://img.photobucket.com/albums/v344/gsracer/Vh45de%20part%203/7BDE981B-CFCF-4CED-A93E-D327315B7091-3136-000001B6171A443B.jpg

http://img.photobucket.com/albums/v344/gsracer/Rocket%20bunny/IMG_3439.jpg

brndck
02-21-2014, 07:47 PM
I'm guessing you're using a z32 trans?
Isn't a z33 trans taller gearing with the 6th gear?

gsracer
02-21-2014, 07:49 PM
Yea I'm using a z32 tranny.

Slo_240sx
02-21-2014, 07:59 PM
Considering that your torque and hp numbers are pretty close and you have low end torque, I think it will benefit you. Those are stout numbers and if you are already blowing the tires off (I do the same which is why I run a 3.55 gear 325/50/15 drag radial) lowering the gear will help you with traction a bit. Also being FI, having a longer gear will benefit you because you will be able to stay in your power band longer.

Messing with gearing to get it in the "sweet spot" where you like it can be tricky. Theoretically, it all works on paper. Tire size/compound has alot to do with it and if you're just blowing them off, lowering the gear will help. However, this may also drop you out of your powerband. Luckily for us, we have low end torque so it won't effect us as bad as someone running an SR. I'd lower it if it were me, but then again I make over 850whp on low boost and run a drag tire. In your case, I'd lower it but I'm not sure what you need to do to swap it over.

brndck
02-21-2014, 08:02 PM
Boom.
http://zilvia.net/f/showthread.php?t=555720

Slo_240sx
02-21-2014, 08:08 PM
^Well there ya go!

gsracer
02-21-2014, 08:57 PM
yea... i had seen that. That may end up being an option. I have a 3.69 out of a 1999 q45. Just wondering if i could make it work with the q components and my 2 way.

I figured someone had done it before... and hopefully could save me a bunch of steps. If no one does, i guess it will be the typical tear everything apart and figure it out lol. Thanks though!!

RaNMaN
02-21-2014, 09:28 PM
I have a 3.69 out of a q45 in my stock s14 housing on a s14 OBX helical differential. It's not easy, I had to use a custom sized (much smaller) spacer on the pinion. I also had to move the big spacer in the back to the other side and use different shims to get it right. You have to get the differential drilled out to accept 13mm bolts at a machine shop. I used all new pinion and axle bearings.

I have recently changed up my transmission and gearing and I went with the complete q45 3.54 rear end now. I would sell you my complete ready to bolt in pumpkin if you are interested. It was a total bitch to get it to work but it worked really well with the r154 transmission that I was using.

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RaNMaN
02-21-2014, 09:31 PM
If not you might want to buy those s15 gears if the ring is on 12mm bolts. I spent a lot to get mine done but would part with it for $500.

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gsracer
02-21-2014, 09:59 PM
Ranman... thats exactly the info i was looking for. How about putting the 2 way in the q45 pumpkin, they are both r200? Do you think this is possible?

RaNMaN
02-21-2014, 10:13 PM
Ranman... thats exactly the info i was looking for. How about putting the 2 way in the q45 pumpkin, they are both r200? Do you think this is possible?

Yes, I don't know if the diff's are the same external size or not but if they are then it's probably easier to do it that way. Measure everything though first, then measure again to double check, I cannot stress this enough. You will still need to have the s14 diff holes opened up to 13mm but if the diff's are the same size and you can get the axle stubs and driveshaft to fit you should be good.

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heychris
02-22-2014, 12:50 AM
@gsracer..Jerry your car is an inspiration....Top build...

Check this out:
http://zilvia.net/f/showthread.php?t=555322

You might also run over to NRR and do search...Been seeing a few rear end threads recently...

Good luck...love to see your car in action soon.

Ch

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jr_ss
02-22-2014, 07:28 AM
If the diff has 12mm bolt holes for the ring gear, you'll have to open them up for either ring gear. The S15 ring gears have 13mm bolts as well.

Def
02-22-2014, 02:05 PM
3.69 gears would be too long, even with good bottom end IMO. I guess if you wanted a really low cruising RPM it'd be choice, but I'd personally like shorter gears for a performance application.

What about 3.96 gears out of a J30? Cheap and really easy to get ahold of. It'll take a bit of the edge off your 4.08 being a little too short, while still allowing good overall shift points when on it. Plus no issues with 13 mm ring gear bolts.

gsracer
02-22-2014, 02:50 PM
see def thats what i thought as well, but most of the ls guys drop the gear ratio, and there first and second gear are longer than the z32 tranny.

For me 1st gear at anything more than 1/2 blows the tires off, and second is better but will brake loose rolling after 4500-5000 rpm, 3rd you have to be really careful how you shift it because with the twin plate it grabs hard and once it starts spinning at bangs the limiter pretty quickly.

I spend more time off throttle than on in the first 2 gears and i was trying to mitigate this a bit. Im as wide as can go on tire right now, 315 azenis, i don't really want to run drag radials as its not a drag car.

Def
02-22-2014, 03:26 PM
Wider street tires offer zero gains in forward grip - just doesn't work at all like wrinkle wall slicks.

What's your rear camber and camber gain look like? If you've got over 1 deg rear negative camber and run a low ride height without lots of geometry correction plus streetable spring rates - that's your main problem with forward traction.

The 3.69 will help in 1-3, but will make the car much slower in 4th and 5th. Maybe that's what you really want being as it does a lot of street driving and some drifting where long gears seem to be favored. But I'm just never a fan of a car where you shift up and it feels like the thing falls on its face due to a super tall rear gear.

What do you run for tuning? Ever thought about some traction control setup?