High rpm low mph
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High rpm low mph
So I was searching the site for posts about high rpm and low mph issues. My car is a 76 L-48 that is now a 4 speed with a T-10 BW. I bought it without any gauges connected except the speedo. When I test drove it, it seemed to be struggling to make 50 mph. The '68 327 engine runs great and the car will jump. The suggestion was to rotate the rear tire once, with the car in neutral, and count the revs for the driveshaft to determine the ratio. Sounds right. Mine is about 1.8 turns of the driveshaft going to the engine to 1 turn of the rear wheel. That don't sound right. What am I doing wrong?
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Intermediate
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check again
So I was searching the site for posts about high rpm and low mph issues. My car is a 76 L-48 that is now a 4 speed with a T-10 BW. I bought it without any gauges connected except the speedo. When I test drove it, it seemed to be struggling to make 50 mph. The '68 327 engine runs great and the car will jump. The suggestion was to rotate the rear tire once, with the car in neutral, and count the revs for the driveshaft to determine the ratio. Sounds right. Mine is about 1.8 turns of the driveshaft going to the engine to 1 turn of the rear wheel. That don't sound right. What am I doing wrong?
Is my vette stock?? HAHA
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That would be one really fast car if you could get it moving. it should be between 3-4. lots of gearing in between those. If your engine is producing significant power and isnt making it to the rear end you may have a slipping clutch. Did it work fine before the conversion
Is my vette stock?? HAHA
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From: Im not allowed to tell you
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not trying to imply anything, but what gear are you in when you are driving when you cant get above 50? just asking
Last edited by Rescue Rogers; Mar 16, 2017 at 12:16 PM.
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To determine an approximate rear end ratio both rear wheels have to be off the ground, the transmission in neutral, and the positraction rear has to be working so that both wheels turn at the same time. I'm confused by your statement that the car struggles to reach 55 and at the same time you state it runs great and will jump? Have you done a basic tune up? Plugs, points, condensor, air filter, fuel filter, check the cap and rotor and plug wire resistance?
Last edited by MelWff; Mar 16, 2017 at 11:00 AM.
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high rpm low mph
That would be one really fast car if you could get it moving. it should be between 3-4. lots of gearing in between those. If your engine is producing significant power and isnt making it to the rear end you may have a slipping clutch. Did it work fine before the conversion
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Thread Starter
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To determine an approximate rear end ratio both rear wheels have to be off the ground, the transmission in neutral, and the positraction rear has to be working so that both wheels turn at the same time. I'm confused by your statement that the car struggles to reach 55 and at the same time you state it runs great and will jump? Have you done a basic tune up? Plugs, points, condensor, air filter, fuel filter, check the cap and rotor and plug wire resistance?
When I say struggles to reach 55, I mean it seems wound out at 55 mph. Engine runs fine. I just bought the car. I think I will wait to start driving it before I address this. What do you think about the ratio? Is that high or low? Tranny is a Borg Warner T-10. 327 ci.
Last edited by Dan-a-rama; Mar 16, 2017 at 07:05 PM.
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Yes that sounds right. Your year had 3.08, 3.36, 3.50, 3.73 ratios. Because 4 speeds dont have overdrive they tend to spin up to the top faster and it does sound like it needs a another gear if your used to newer 5 and 6 speeds. Now if your tires arent 27" diameter then your speedometer could be off and your going faster than 55 or slower.
What rpm does your tach say your running at 55. That would be a better question.
What rpm does your tach say your running at 55. That would be a better question.
Is my vette stock?? HAHA
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From: Im not allowed to tell you
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You should be at 2300rpm in 4th gear for 55 with a 27" diameter tire. 26" tire would be 2500rpm
Thread Starter
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Yes that sounds right. Your year had 3.08, 3.36, 3.50, 3.73 ratios. Because 4 speeds dont have overdrive they tend to spin up to the top faster and it does sound like it needs a another gear if your used to newer 5 and 6 speeds. Now if your tires arent 27" diameter then your speedometer could be off and your going faster than 55 or slower.
What rpm does your tach say your running at 55. That would be a better question.
What rpm does your tach say your running at 55. That would be a better question.
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I'd get a GPS reading to really see what speeds you are running. If the trans doesn't have the right speedo gears then an indicated 50 might be 65...
I have 3.55 gears in my 73 and yes moving with traffic at 65 it's going to be turning close to 3000rpm. Even w/ extra insulation and stock exhaust it's loud.
here's a good chart for the speedo gears-
http://www.tciauto.com/tc/speedometer-gear-calculator/
Richard
I have 3.55 gears in my 73 and yes moving with traffic at 65 it's going to be turning close to 3000rpm. Even w/ extra insulation and stock exhaust it's loud.
here's a good chart for the speedo gears-
http://www.tciauto.com/tc/speedometer-gear-calculator/
Richard