RPM vs Differential Question
Thread Starter
Racer
Joined: Nov 2008
Posts: 321
Likes: 2
From: Auburndale FL
RPM vs Differential Question
Hi all,
I am in dire need of some insight. I had a chance to run my car today, from a rolling start at about 40 mph I pulled it out of overdrive and floored the accelerator. The car did what you would expect, I achieved 115 mph before having to come off of the throttle.
My issue, while I hit a 115 mph with pedal to the floor my rpm's were only at 3200. So I am thinking I have to tall of gears or my tac is not right. Based upon the way the car felt I am thinking it is gears but need some insight from those of you that run your cars at higher speeds if you agree with the gear ratio as being the issue?
My car's specs.
New/Rebuilt 383
My Cam = Comp Cams 268XFI HR13 - Dur: adv in-268/ex-276 @50 218/224 Lift is .570 & .565 with lsa 113
Heads are procomp 190 cc
Highly Ported Factory base & plennum, asm large tube runners, 58mm Throttle Body
32lbs injectors
No AIR/EGR or Cats, tru-dual exhaust with hi-flo mufflers
Differential is stock D36 @ 2.73.
I have been seriously considering changing my rear-end but I have a lot of other car work that needs to be done first. Also, I haven't had a chance to dyno the car yet so I don't know what it capable of but the way it drove to day I figure it is more than I need.
I appreciate any insight you guys can provide on if my gears are the reason for the low RPMs?
Thanks in advance,
BeerMe!
I am in dire need of some insight. I had a chance to run my car today, from a rolling start at about 40 mph I pulled it out of overdrive and floored the accelerator. The car did what you would expect, I achieved 115 mph before having to come off of the throttle.
My issue, while I hit a 115 mph with pedal to the floor my rpm's were only at 3200. So I am thinking I have to tall of gears or my tac is not right. Based upon the way the car felt I am thinking it is gears but need some insight from those of you that run your cars at higher speeds if you agree with the gear ratio as being the issue?
My car's specs.
New/Rebuilt 383
My Cam = Comp Cams 268XFI HR13 - Dur: adv in-268/ex-276 @50 218/224 Lift is .570 & .565 with lsa 113
Heads are procomp 190 cc
Highly Ported Factory base & plennum, asm large tube runners, 58mm Throttle Body
32lbs injectors
No AIR/EGR or Cats, tru-dual exhaust with hi-flo mufflers
Differential is stock D36 @ 2.73.
I have been seriously considering changing my rear-end but I have a lot of other car work that needs to be done first. Also, I haven't had a chance to dyno the car yet so I don't know what it capable of but the way it drove to day I figure it is more than I need.
I appreciate any insight you guys can provide on if my gears are the reason for the low RPMs?
Thanks in advance,
BeerMe!
Team Owner
Joined: Sep 2003
Posts: 25,394
Likes: 2,741
It's difficult to help you with the information you post BUT if you had 275/17 tires, 3d gear and a 2.73 - 3200 RPM would be something maybe 90 MPH.
It should take 4100 RPM to make 115 MPH with 275/17 and a 2.73
What year? What tire?
It should take 4100 RPM to make 115 MPH with 275/17 and a 2.73
What year? What tire?
Thread Starter
Racer
Joined: Nov 2008
Posts: 321
Likes: 2
From: Auburndale FL
Car year is 87, stock 16 inch wheels with 245/50's.
As for the sound, it didn't sound like the engine was at its limits nor did it seem that it was struggling. I just thought it weird to be at that speed and only 3200 rpms'. Hence my question. I guess I expected the Tach to have a steady rate of climb since my foot was to the floor.
Thanks again.....
