3:55 gears
Thread Starter
8th Gear
Joined: Aug 2017
Posts: 8
Likes: 0
I really don't think I have a temp problem. I have an RPM problem. At 65mph the rpm's are about 3300 and the engine is screaming at 3,300. I was told there is a 3:55 gear setup but I'm starting to doubt it. The motor temp increases going 65mph but stays below the danger zone. I think I need to take it to a shop and confirm the ratio. To stay in the traffic flow I need to go 75 but wouldn't think of doing it for a long period because the rpms are getting way too high
Drifting
Joined: Oct 2005
Posts: 1,615
Likes: 150
From: Forth Worth TX
I really don't think I have a temp problem. I have an RPM problem. At 65mph the rpm's are about 3300 and the engine is screaming at 3,300. I was told there is a 3:55 gear setup but I'm starting to doubt it. The motor temp increases going 65mph but stays below the danger zone. I think I need to take it to a shop and confirm the ratio. To stay in the traffic flow I need to go 75 but wouldn't think of doing it for a long period because the rpms are getting way too high
I just drove over 1000 miles in 95*-100* heat with 3.70's (3500-4000rpm) with ZERO over heating issues. Water temps stayed in the 180*-190* range. Notice the RPM, Speed and Temperature gauge. You'll also notice a towel between my right knee and center console to keep it from burning due to the 100* temps.
You do not have an RPM problem.
Last edited by Revi; Aug 9, 2017 at 02:56 PM.
Instructor
Joined: Sep 2015
Posts: 122
Likes: 17
From: MA
I have 3.55s and went from a TH350 to a TKO-600...totally changed the car.
Race Director
Joined: May 2006
Posts: 18,695
Likes: 2,572
shop
I really don't think I have a temp problem. I have an RPM problem. At 65mph the rpm's are about 3300 and the engine is screaming at 3,300. I was told there is a 3:55 gear setup but I'm starting to doubt it. The motor temp increases going 65mph but stays below the danger zone. I think I need to take it to a shop and confirm the ratio. To stay in the traffic flow I need to go 75 but wouldn't think of doing it for a long period because the rpms are getting way too high
why do you need a shop to check the ratio. jack up the rear of the car, place the trani in neutral, parking brake off. Turn one wheel one complete revolution while counting the drive shaft rotations, a chalk mark will help. 3 1/2 turns is a 3:55, 3 3/4 turns is a 3:70. Your problem though is not the gears. I have a 3:70 and turn 3,500 at 70 and dont go that high in temperature, about 180 with a 160 thermostat
Last edited by MelWff; Aug 9, 2017 at 05:01 PM.
Melting Slicks
Joined: Oct 2008
Posts: 2,154
Likes: 69
From: Regina Sk Canada
If you have sufficient cooling components, you will get max airflow at speed, and the engine should never over heat. The first issue with a vette is the rad is laid back, and you have to direct the air into the rad. Secondly think of an engine like a power source. You create more power you create more BTU or heat very simple. The components have to match the power requirements.
GM engineers have been making and cooling the Vette for a long time, no need to reinvent the wheel. My junk makes 350 Hp very easy to look after. 3 core rad, shroud big mechanical fan and a 195 T stat. 16 lb rad cap. And just for the record. 195 is not hot. 200 is not hot thats normal operating temp for amy engine. You need to keep the water in the rad and in the engine until the stat opens the water in the rad should be cool enough to replace the hot water in the engine. stat closes water gets to cool off in the rad again. cycle repeats, pretty simple concept. You put a 160 stat in the car, that stat opens then stays open, never closes and acts as a restriction, nothing more. Not how a cooling system is intended to function.
GM engineers have been making and cooling the Vette for a long time, no need to reinvent the wheel. My junk makes 350 Hp very easy to look after. 3 core rad, shroud big mechanical fan and a 195 T stat. 16 lb rad cap. And just for the record. 195 is not hot. 200 is not hot thats normal operating temp for amy engine. You need to keep the water in the rad and in the engine until the stat opens the water in the rad should be cool enough to replace the hot water in the engine. stat closes water gets to cool off in the rad again. cycle repeats, pretty simple concept. You put a 160 stat in the car, that stat opens then stays open, never closes and acts as a restriction, nothing more. Not how a cooling system is intended to function.
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Thread Starter
8th Gear
Joined: Aug 2017
Posts: 8
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I have a 74 corvette with a zz4 crate engine (about 365HP) I can idle it in the heat and it stays below 200 degrees. However, on the highway even going 65 MPH has the RPMS over 3,000 - it's screaming and going above 200 degrees. I know I would lose some power but would I be better off with a 3:36 or so? It's running a 3:55 now
Pro
Joined: Apr 2014
Posts: 614
Likes: 186
From: Orlando, Dundee, Val-des-Monts PQ
Now that's funny, seeing how you responded to yourself. Out of curiosity did you ever check temp with an infrared temp gun? Is your fan shroud correct? Correct water pump? Chevrolet small blocks are made to scream. When you come down on ratio don't expect much wheel spin coming out of the hole unless you side-step. Mark
Thread Starter
8th Gear
Joined: Aug 2017
Posts: 8
Likes: 0
Now that's funny, seeing how you responded to yourself. Out of curiosity did you ever check temp with an infrared temp gun? Is your fan shroud correct? Correct water pump? Chevrolet small blocks are made to scream. When you come down on ratio don't expect much wheel spin coming out of the hole unless you side-step. Mark
Race Director
Joined: Feb 2001
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From: Grapevine Tx
2018 C3 of Year Finalist
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Here is a chart you can play with
http://www.angelfire.com/fl/procrastination/rear.html
You may have a 3.70 rear end.
http://www.angelfire.com/fl/procrastination/rear.html
You may have a 3.70 rear end.
Last edited by F4Gary; Aug 10, 2017 at 11:28 AM.
Racer
Joined: Jan 2008
Posts: 441
Likes: 22
From: Northeast OH
I have a 4.11 rear and (while it's indeed annoying on the highway) I never see my temps go out of the normal zone. Even on an hour-long drive in the summer and a bra probably messing with the airflow a little.
Gets hot as anything in the cabin though!
Gets hot as anything in the cabin though!
Team Owner
Joined: Oct 2004
Posts: 81,241
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From: altered state
St. Jude Donor '05
I just drove over 1000 miles in 95*-100* heat with 3.70's
Try 4.56 on the fwy going to work with a 4500 stall
you almost hope for traffic
Last edited by cv67; Aug 10, 2017 at 01:23 PM.
Le Mans Master
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From: Colorado
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I agree it's not in your rear end. I have a stock L-82 with a close ratio M21 4 speed, and 3.55 rear. I'm at 3500 rpm at 75 mph. Never above 200 degrees. I'm at 3200 rpm at 70, and 3000 rpm at 65. Yes, compared to more modern cars with 5 & 6 speed gear boxes, the engine is screaming.
Look at your cooling system. What kind of thermostat do you have? At what temp does it open up? What kind of radiator? I have a Dewitt's dual core aluminum, and it's great.
Look at your cooling system. What kind of thermostat do you have? At what temp does it open up? What kind of radiator? I have a Dewitt's dual core aluminum, and it's great.
Last edited by Rky Mtn C6; Aug 10, 2017 at 02:47 PM.
Parts Sherpa
Joined: Feb 2017
Posts: 520
Likes: 98
From: ICE boneyard, Pa
BTW im running a 180 thermostat. That was they first project and someone had already installed one.
Last edited by EarlyC34me; Aug 10, 2017 at 03:50 PM.
Burning Brakes
Joined: Jun 2010
Posts: 1,165
Likes: 93
From: Bellmore NY
Im with Revi... its the cooling system, not the gear.
Ive got a 454, that even with my belt currently slipping, is a 1/4" shy of 200 on my temp gauge in the heat. Yes I do have o.d, and Im sure it helps, but I can cruise around in 4th and the temp doesn't change much.
Stewart water pump is my secret
Last edited by Big Block Dave; Aug 10, 2017 at 09:50 PM.
Le Mans Master
Joined: Dec 2009
Posts: 6,397
Likes: 649
From: Saskatoon Saskatchewan
I had an overheating problem in one of my cars. Had the rad re-cored put in new thermostat, replaced the trans, never could solve it. I told my husband about it and he said "Did you ever check the temperature gauge to see if it was accurate?" 
Le Mans Master
Joined: Apr 2011
Posts: 6,284
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From: Hermosa
Back when I was having problems with my cooling system I purchased one of these;
https://www.summitracing.com/parts/m...SABEgLb1fD_BwE
It's accurate and useful to see at a glance how hot or cool the fluid is without having to go inside the vehicle. So far my inside gauge and this radiator cap have always agreed. Verified with non-contact temp gun.
https://www.summitracing.com/parts/m...SABEgLb1fD_BwE
It's accurate and useful to see at a glance how hot or cool the fluid is without having to go inside the vehicle. So far my inside gauge and this radiator cap have always agreed. Verified with non-contact temp gun.