Mph at Redline?
Thread Starter
Racer
Joined: Jan 2020
Posts: 388
Likes: 117
From: Tacoma, Wa
Mph at Redline?
1979 L48 4 spd. Big camshaft and intake. Putting 2.5 inch dual exhaust and headers in soon.
right now I dont have a tach, I was wondering where ~5000 rpm is for each gear on the speedo. I like freeway onramp pulls and I’m not trying to break anything.
right now I dont have a tach, I was wondering where ~5000 rpm is for each gear on the speedo. I like freeway onramp pulls and I’m not trying to break anything.
Melting Slicks
Joined: Apr 2001
Posts: 3,399
Likes: 279
From: Olmsted Falls, Ohio
How could we guess that if we don't know what's in the engine. Cam for instance. Lots of variables.
I would start by getting a Tach, even it's a tach you have to mount to the steering column.
I would start by getting a Tach, even it's a tach you have to mount to the steering column.
Safety Car
Joined: Sep 2007
Posts: 4,458
Likes: 331
From: Indy Indiana
depends on your rear end ratio and presume you have a standard t-10 trans.. and what's your tire size?
then you can calculate what rpm gives you what speed in what gear using what tires and what rear ratio.
or use a speedometer app ( free) on your smart phone and a hand held tachometer (25$) in your cockpit.
then you can calculate what rpm gives you what speed in what gear using what tires and what rear ratio.
or use a speedometer app ( free) on your smart phone and a hand held tachometer (25$) in your cockpit.
Race Director
Joined: Mar 2017
Posts: 11,960
Likes: 4,516
From: Virginia
Try this calculator once you figure out your transmission and rear diff ratios.
https://spicerparts.com/calculators/...rpm-calculator
4th gear at 5000 is ~130 mph for my 80. It has 3.08 rear gears, though.
https://spicerparts.com/calculators/...rpm-calculator
4th gear at 5000 is ~130 mph for my 80. It has 3.08 rear gears, though.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
In each gear: shift when it feels like the engine is no longer pulling strong. You should not wind it "tight" in any range if you don't have an accurate tach to go by.
In 'high' gear, you can NEVER reach redline with a basically stock engine and rear gear.
In 'high' gear, you can NEVER reach redline with a basically stock engine and rear gear.
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Race Director
Joined: Oct 2008
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From: Long Island
Not true, depends on what rear is in the car.... With the 3:70 you may ..
Last edited by BLUE1972; Feb 29, 2020 at 09:02 PM.
Le Mans Master
Joined: Jun 2019
Posts: 7,668
Likes: 2,473
From: Indiana
https://spicerparts.com/calculators/...rpm-calculator
4th gear at 5000 is ~130 mph for my 80. It has 3.08 rear gears, though.[/QUOTE]
holy cow my 4sp l82 is 3.7 rear..110 mph @5000....
so basically my max 5500 rpm is 121 mph..
it already sounds like its taking off to the moon on the highway..i guess if speed limit was 55..
4th gear at 5000 is ~130 mph for my 80. It has 3.08 rear gears, though.[/QUOTE]
holy cow my 4sp l82 is 3.7 rear..110 mph @5000....
so basically my max 5500 rpm is 121 mph..
it already sounds like its taking off to the moon on the highway..i guess if speed limit was 55..
Thread Starter
Racer
Joined: Jan 2020
Posts: 388
Likes: 117
From: Tacoma, Wa
I’m just being careful until I can take the engine apart and figure out exactly whats been done.
also its my daily driver.
Last edited by Cmurray79; Feb 29, 2020 at 09:16 PM.
Thread Starter
Racer
Joined: Jan 2020
Posts: 388
Likes: 117
From: Tacoma, Wa
Thread Starter
Racer
Joined: Jan 2020
Posts: 388
Likes: 117
From: Tacoma, Wa
Try this calculator once you figure out your transmission and rear diff ratios.
https://spicerparts.com/calculators/...rpm-calculator
4th gear at 5000 is ~130 mph for my 80. It has 3.08 rear gears, though.
https://spicerparts.com/calculators/...rpm-calculator
4th gear at 5000 is ~130 mph for my 80. It has 3.08 rear gears, though.
55 mph 2nd
77 mph 3rd.
sound right?
Last edited by Cmurray79; Feb 29, 2020 at 09:46 PM.
Race Director
Joined: Mar 2017
Posts: 11,960
Likes: 4,516
From: Virginia
Not quite. A 1979 L48 should have only come with the M20, standard 4-speed, with these ratios:
1st 2.64:1
2nd 1.75:1
3rd 1.34:1
4th 1.00:1
With a final drive of 3.08:1, as best I can tell.
So, with 27" wheels (255/60R15), 5000 RPM, I get:
1st 49 mph
2nd 75 mph
3rd 97 mph
4th 130 mph
What numbers were you using? Perhaps you had a typo?
In any case, you'd want to verify these numbers with a GPS speedometer and a calibrated tachometer. You can calculate the rear gear ratio with a helper. Put the car on jackstands, and a piece of tape on the driveshaft. Have the helper count the times the tape goes around while you turn a wheel exactly once around. On a 40 year-old car, I wouldn't trust anything without measuring it, including the stamp on the differential. If you cam can be changed, so can your rear gears.
1st 2.64:1
2nd 1.75:1
3rd 1.34:1
4th 1.00:1
With a final drive of 3.08:1, as best I can tell.
So, with 27" wheels (255/60R15), 5000 RPM, I get:
1st 49 mph
2nd 75 mph
3rd 97 mph
4th 130 mph
What numbers were you using? Perhaps you had a typo?
In any case, you'd want to verify these numbers with a GPS speedometer and a calibrated tachometer. You can calculate the rear gear ratio with a helper. Put the car on jackstands, and a piece of tape on the driveshaft. Have the helper count the times the tape goes around while you turn a wheel exactly once around. On a 40 year-old car, I wouldn't trust anything without measuring it, including the stamp on the differential. If you cam can be changed, so can your rear gears.
Thread Starter
Racer
Joined: Jan 2020
Posts: 388
Likes: 117
From: Tacoma, Wa
Not quite. A 1979 L48 should have only come with the M20, standard 4-speed, with these ratios:
1st 2.64:1
2nd 1.75:1
3rd 1.34:1
4th 1.00:1
With a final drive of 3.08:1, as best I can tell.
So, with 27" wheels (255/60R15), 5000 RPM, I get:
1st 49 mph
2nd 75 mph
3rd 97 mph
4th 130 mph
What numbers were you using? Perhaps you had type?
1st 2.64:1
2nd 1.75:1
3rd 1.34:1
4th 1.00:1
With a final drive of 3.08:1, as best I can tell.
So, with 27" wheels (255/60R15), 5000 RPM, I get:
1st 49 mph
2nd 75 mph
3rd 97 mph
4th 130 mph
What numbers were you using? Perhaps you had type?
Race Director
Joined: Mar 2017
Posts: 11,960
Likes: 4,516
From: Virginia
Did you measure that? I couldn't find a source, other than this implication:
I measured 3.55 on my 79 L48 Auto, so that part is correct.
Originally Posted by https://www.corvsport.com/1979-c3-corvette/
On cars equipped with an automatic transmission, the final drive ratio was lowered from 3.08:1 to 3.55:1.
Last edited by Bikespace; Feb 29, 2020 at 10:40 PM.
Thread Starter
Racer
Joined: Jan 2020
Posts: 388
Likes: 117
From: Tacoma, Wa
Did you measure that? I couldn't find a source, other than this implication:
I measured 3.55 on my 79 L48 Auto, so that part is correct.
I measured 3.55 on my 79 L48 Auto, so that part is correct.
Corvette central and around forums is where I got 3.36. No time to measure right now. I will Monday.
Last edited by Cmurray79; Feb 29, 2020 at 10:49 PM.
Race Director
Joined: Mar 2017
Posts: 11,960
Likes: 4,516
From: Virginia
http://corvettec3.ca/axle.htm
I wouldn't lift the car just to check, but if you had it in the air anyway, it's good to confirm.
This is what I get with 3.36 at 5000 rpm
1st 45 mph
2nd 68 mph
3rd 89 mph
4th 120 mph
Last edited by Bikespace; Feb 29, 2020 at 11:00 PM.
