Black 69 Dart
Well-Known Member
Ok guys and gals with turbo cars what are you using for rear gear ratio?
Turbo cars and rear gears
- Thread starter Black 69 Dart
- Start date
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HOTMOPR
Mr Horsepower
3.54 with a 315/60
srixon4406
TURBO TOAD
I'm running 2.94 with 275/9.5/15 tire the car is almost road ready and hooks pretty good on the limited drive time I've bad it out.
forced 340
Well-Known Member
3:23 w/ 325/50-15 drag radials.
CUUDAK
Well-Known Member
All depends on what your goal is! Top speed? Fast E.T.? Whatever the case, no more than 3.55 (Drag Racing). Numerically lower gear will put more "Load" on the turbo, turbo's LOVE load!!!!!
The two fastest slant six turbo cars I am familiar with (both over 500 hp) have found out that their cars run quicker quarter miles with 2.76 gears than they can with higher numerical ratios, such as 3.55s or 4.10s.
Make no sense to me, but they have the time slips to prove it.
Like the previous poster said, turbos LOVE a load!!!!
805moparkid
Slant and AFX Guy
The two fastest slant six turbo cars I am familiar with (both over 500 hp) have found out that their cars run quicker quarter miles with 2.76 gears than they can with higher numerical ratios, such as 3.55s or 4.10s.
Make no sense to me, but they have the time slips to prove it.
Like the previous poster said, turbos LOVE a load!!!!
i wonder how cam shaft duration and weight come into play on that...
I am not sure, but I know that both of these engines run VERY low duration camshafts in order to minimze overlap. I don't think either engine has much, if any, duration of either cam lobe over 220 degrees at .050"-lift.
Both racers have said that those engines are pretty much done making power by 5,500 rpm.
So, they make an astounding amount of torque at mid-range.
Insofar as weight is concerned, I don't know how that would play into it. Ryan's '66 Valiant weighs about 2,800 pounds and goes 127 mph with a 727 transmission.
Tom's '70 Dart is heavier by about 400 pounds and goes 121 mph (into a 15mph headwind!) with a 904.... so, I would guess that the two engines are probably within a very few horsepower of each other. Somewhere just north of 500, I'd bet.
Both run Holley 4bbls, not fuel injection, although Tom is said to be working on a Megasquirt system for his 225.
I wonder if a 904 would put Ryan's car over 130???
Maybe we'll get to find out this year...
Mad Dart
Nothing to see Here!
Drive a 7500 lb diesel truck, they could care less about weight. Hook a trailer to it and it runs better! My excursion feels like it wants to lift the left front tire coming out of the hole.,
I know it's diesel but still. Boost cures the weight problem, more load, quicker into boost.
Full body cars not on a diet are running in the 7's some with ac and power windows etc....Nutzzzzz
I know it's diesel but still. Boost cures the weight problem, more load, quicker into boost.
Full body cars not on a diet are running in the 7's some with ac and power windows etc....Nutzzzzz
It's all about turbo spool up. More resistance from weight or high gears means more spool up for the turbo, because the engine is working harder and expelling more exhaust. Simple as that.
In terms of practical application, then, one facet of gearing the car (slant six/turbo, in particular) is that the age-old practice of installing a final drive ratio in the differential,
of a high numerical value (like a 4.10 or 4.56:1) is not only not necessary, it's not even desirable, because the low-numerical gear will cause the turbo to spool better and make more power, overcoming the mechanical advantage of the 4.56.
The bottom line of THAT is that the 8.75" rear housing you'd need so you could have a hiway gear (2.76) AND a gear for the strip (a 4.10 or 4.56,) swapping back and forth as needed, will not be necessary. Instead, you can pull an 8.25" rear housing out of an Aspen, Volare or very late model Duster or Dart Sport, and bolt it in with minimal mods. It will probably come from the factory with gear ratio you can use (2.5:1 and up...)
If you have an A body, that one item will save you considerable money because A-body 8.75" housings are not cheap these days.
805moparkid
Slant and AFX Guy
i wonder how they would like the 2.45?? and FYI most of the a body 8.25's have 3.21's
I think they would like it even better...
And, thanks for the info on the Aspen/Volare final drive ratios. I had heard that they had ratios in the mid-2's... but maybe that was 318 cars????
rgreule
Well-Known Member
what kind of rpm are you looking to pull through the traps?
Are you asking me?
We don't have any quarter-mile drag strips here in Arkansas, so it's not a normal situation.
There is a strip that runs some of the slower cars 1,000-feet, though and that;s likely where we'll be running,
We'd like to go through the 1,000-foot traps at just over 5,000-rpm.
We have a 3.55:1 gear in it and with the 26-inch, 9"-wide Hoosier slicks, that will put us through at 4,839 @ 105mph... plus torque converter slippage.
So, if we can get this bucket of bolts to stay together for one run, we'll find out whether our rpm calculations are in the ballpark,
rayer:rayer:rayer:
70wayfarer
Well-Known Member
you guys are talking turbos here, but would the same apply to centrifugal superchargers.
cheers
cheers
1980volare
Well-Known Member
I do know 03-04 cobras pick up a bunch with a numerically lower gear. I've done 3 or 4 after I did,the swap on my buddy's. Went from 3.55 to 3.27 and it picked up .7 in the quarter. Forced induction likes a lower numerical gear, typically.
SRT_DSTRHOLC
Well-Known Member
A friend with a different car is running 4.10s and 28in tire
Has he tried a 2.76 in the car at the strip, and is it a turbocharged engine?
Which engine?
Thanks for any information.:blob:
SRT_DSTRHOLC
Well-Known Member
Well...not a mopar should have been included. It's a 700hp nissian 5 speed that's street driven and runs mid 10's
turbodart68
Well-Known Member
Turbo cars are sensitive to gear. A lot of things come into play. Cam, turbo size, cubic inch, and stall speed play into it. On top of all that you have to make it to the end of the track without running out of RPM. When you go crazy high with gear (numerically low) the converter takes a beating and will slip. So its a fine line. I run 3:73 with a 33 inch tire on my turbo car. Back when it ran I had a 28x10.5 slick with 3.91s and at 7k I was short by 300 feet of a full run at 150mph or there about. I also tried a 2.76 in my twin turbo duster with a 360 and 2 T04s and it was really lazy and not much fun. A switch to 3.23 woke it up greatly. Turbos do love to be under load but if your not able to spool it up and have a mechanical advantage that matches the power then it will never really "come on".
No, cetrifugal superchargers are linear to engine speed. They need RPM to create boost where a turbo doesn't.
No, cetrifugal superchargers are linear to engine speed. They need RPM to create boost where a turbo doesn't.
rdakota340
Well-Known Member
I have 3.23 28'' tire I run the same in my Dakota with a 360 it turned 2800RMP at 70MPH turbo's like load I'm starting out with the same gearing for the Dart I'm thinking 2.94's we will see soon!
PLEASE KEEP US POSTED.... THAT REAR-MOUNT TURBO SOUNDS veeeery INTERESTING!!!:blob:
rdakota340
Well-Known Member
Yes I will!
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