[Trent]

I only took my car to the track a few times because I knew i couldnt' drive it. But when I did, I managed a 12.2 @ 126 on the stock 3.91 88 gears. I had about 415-425rwhp at the time and ET streets on the stock MKIV wheels. Didn't have to shift to 5th.

 

[BoostAddctn]

6500rpm in 4th with 3.73 rear end is 128mph....

That's odd. where you're at should only be around 5500rpm.

Only reason it could be different is if the clutch is slipping, or your tires aren't stock size.

What size are your tires?


Have you checked the ratio of the diff?

Tire sizes = P245/50 R16 , its a 90 and I am the second owner, original owner was a old guy, it still has the stock rear end and at 192k miles it still had a stock clutch and stock timing belt and stock headgasket... aight peace

 

[BTZ]

I have an 86.5 turbo with 4.3:1. I will be testing it out at the track soon to see what it can do. If I do not like it I can put in my 3.9:1. It feels like a 10-15 mph difference in the rear ends when I compare the rev in the same gear to the speed. For example say in 4th at 4000rpm my speed would be 120km/h with the 3.9, at the same rpm with the 4.3 Im going 100km/h.

 

[Supra Guy Scotty]

Hey Jeff I see the rear ratio differences in the 1JZ cars between standard and automatic. Are the rear end ratios the same for the automatic 7M powered cars throughout the production years or do they differ aswell? Also is there a wide and close ratio R154?

With the lower gear such as 4:30 you'd get more traction with less tire spin. Taller gears equal more tire spin. I'm thinking of going R154 with the 4:30 LSD. My concern is what my RPM's will be at the end of the quarter and will I be able to finish in fourth?

From all the cars I've had,.. the 87-88 Turbos both auto and manual had 3.909's in them. All were LSD rears too. The NA 86.5-88's I've had all had 4:30's with 90% of the manuals being LSD. None of the Auto NA cars were LSD that I had. Haven't really had any 89-92s too much. The turbo '89 had a 3.73 with LSD. HTH's...


Scotty

 

[outofstep]

4.3's are gay because it makes you rip through all the gears soo fast. You get no traction with the 4.3's.

Learn how to launch on decent tires.

 

[drjonez]

Hey Jeff I see the rear ratio differences in the 1JZ cars between standard and automatic. Are the rear end ratios the same for the automatic 7M powered cars throughout the production years or do they differ aswell? Also is there a wide and close ratio R154?

http://www.mkiiitech.com/forums/viewtopic.php?t=40

With the lower gear such as 4:30 you'd get more traction with less tire spin. Taller gears equal more tire spin. I'm thinking of going R154 with the 4:30 LSD. My concern is what my RPM's will be at the end of the quarter and will I be able to finish in fourth?

you're totally backwards- higher numerical ratio = faster accel and lower topspeed, this also eqautes to MORE wheelspin. 4.30 in a 400rwhp+ car = no fun....wheelspin @ 60 mph = poor use of power.

 

[Mike 92LX]

373s in my 88 Turbo with 17"Nitto drag radials. Traps are 120-125 depending on conditions. Speedo is not far off so no worries there.
If you go with a Ford rear go with the 8.8 as mentioned. 31 spline axles,welded tubes,T/A girdle and a trac loc rear(very street able and rebuildable). Go with FRPP 373s gears. 9" is stronger but heavier. An 8.8 like that can handle 1.4 sixty foot times allday long on a stick shift car with high driveline shock.

 

[VanSupra]

http://www.mkiiitech.com/forums/viewtopic.php?t=40



you're totally backwards- higher numerical ratio = faster accel and lower topspeed, this also eqautes to MORE wheelspin. 4.30 in a 400rwhp+ car = no fun....wheelspin @ 60 mph = poor use of power.

You're right drjonez that's what I meant. But I always refer to higher numerical ratio's as lower gear and vice versa. Bad habit I guess.. Everyone seems to be saying more wheel spin with the 4:30's as opposed to 3:73 or 3:9's If this is the case why do all other drag racers(non Supra) use a higher ratio gear such as 4:88 5:13's? I'm getting ready to do a swap into my 88 NA with a 4:30 rear and am now wondering if I need a different rear end? In which case what would be the ideal ratio for strictly drag racing?
Appreciate any comments.
Thanks.

 

[Jeff Lange]

You're right drjonez that's what I meant. But I always refer to higher numerical ratio's as lower gear and vice versa. Bad habit I guess.. Everyone seems to be saying more wheel spin with the 4:30's as opposed to 3:73 or 3:9's If this is the case why do all other drag racers(non Supra) use a higher ratio gear such as 4:88 5:13's? I'm getting ready to do a swap into my 88 NA with a 4:30 rear and am now wondering if I need a different rear end? In which case what would be the ideal ratio for strictly drag racing?
Appreciate any comments.
Thanks.

Everyone refers to 4.30:1 being a lower gear than 3.73:1, it's also considered shorter gearing. It also promotes wheel spin. If you understand how gear ratios work, you'd know 4.30:1 means it's multiplying the torque by 4.30 times. Which is why a higher number results in faster acceleration (and thus, more wheelspin). But, then you add a turbocharger into the mix, which boosts faster with more engine load. You can launch with less wheelspin with a taller rear end, and have more boost earlier on in the rev range. It is also better for highway driving as your revs stay lower.

 

[drjonez]

You're right drjonez that's what I meant. But I always refer to higher numerical ratio's as lower gear and vice versa. Bad habit I guess.. Everyone seems to be saying more wheel spin with the 4:30's as opposed to 3:73 or 3:9's If this is the case why do all other drag racers(non Supra) use a higher ratio gear such as 4:88 5:13's? I'm getting ready to do a swap into my 88 NA with a 4:30 rear and am now wondering if I need a different rear end? In which case what would be the ideal ratio for strictly drag racing?
Appreciate any comments.
Thanks.

diff ratio is dictated by your power level. you want the highest (numerical) gear possible while minimizing shifts (i.e. whatever gear you'll be @ redline in 4th as you cross the end of the quarter). obviously tire height and rev limit come into play too.

your reference to other drag racers is fairly useless....what's their final gear ratio out of the trans? 1:1? overdrive? again, totally dependant on their power level, tire height, trans final drive and rev limit.

 

[drjonez]

...You can launch with less wheelspin with a taller rear end, and have more boost EARLIER on in the rev range...

fixed that. lower (numerical) gear put more load on the engine and pulls you into boost earlier.

 

[Larry_A]

My favorite rear end for a long time was this one:

It had the 3.91 & was a nice balance between the 3.73, & 4.30. I have a 3.73 in an '89 now, & the difference is measurable.

 

[Jeff Lange]

fixed that. lower (numerical) gear put more load on the engine and pulls you into boost earlier.

Oops, typo, that is what I meant.

 

[drjonez]

Oops, typo, that is what I meant.

heh. figured as much. np!