MORE RPMs

[COBRO]

Howdy all this is my first post and this is the best site Ive found for tall hoods. Ive replaced the 402 in my 72 C-20 with a 454 and replaced the M465 with a th-400 with a GV-OD on the end of that. The engine is a .030 over just rebuilt with an Edelbrock performer cam,Edelbrock performer manifold and a 750 Edelbrock AFB. Hedman headers and 2-1/2 exhaust to the rear bumper.I put in a B&M torkconverter and the 400 trans is a fresh rebuilt.This setup is mainly for towing a travel trailer. I was turning around 2700 rpm with the 402 and stick shift at 60mph - now after getting it on the road its turning 3000 rpm at 60 mph. The rear end gearing has not been changed - still 4.10 as it was before. I cant figure what is going on here - the converter has Appox 300 to 500 rpm higher stall speed than a standard converter but wouldnt think that would cause this. Can someone please give me a clue as to whats with the extra RPMs. TIA::::::COBRO

[Stroker]

The additional 300 rpm is a result of torque converter slipping and is normal for an automatic without a lockup converter. If you still do a lot of towing be sure to add a transmission cooler to prolonge the life of you turbo 400.

[COBRO]

Thanks for the info - I knew one always got less mpg with a auto but never was sure as to why. Yes Ive got the cooler and a deep trans pan and a external 1qt. remote filter,still want to install a fluid temp guage to keep an eye on it. Thanks again::::::COBRO

[Jimbotronics]

Sounds like a nice setup Cobro!

Welcome from Florida!

[Stroker]

I missed the GV-OD. I would think the .78 OD would more than make up for converter slip. The 3000 rpm would be normal without the OD. Are you sure you're getting into OD in 3rd?

[COBRO]

Yep its going into OD and that knocks the RPMs back down to lower than I was getting with the stick,so its still a very good deal - just had it in my mind what it would be turning not knowing that the trans would let it spin up more. The older I get the more I realise how little I know about things that I thought I knew!!!!! Thanx again:::::COBRO

[69 longhorn]

have you checked the speedo calibration since the trans swap? It could be that the truck is cruising faster than it reads.....?

[krue]

Welcome to the board from South Mississippi! Board rules, gotta post pics of your truck!

[COBRO]

Longhorn that was my first idea of what was going on but after checking milepost markers with a stop watch my speedo is within 2 mph of being right and one can get that just by putting new tires on a rig. Sure wish that was it,but with running the GearVendors OD Im still in good shape. Thanks::COBRO

[69 longhorn]

Here is a calculator to play with. you can factor in tire size, converter , ect...... http://www.smokemup.com/auto_math/index.php

[dwaite72lnghrn]

My 402BB/TH400 gets to 3000rpm at 60mph with 4.1 rear end. Let me know how that gear vendors runs, I have been looking at it but the cost is keeping me from jumping into one. My truck gets about 11mgp empty at 55mph if I could drop the rpms to 2500rpms I could probably get 11mpg at 60mph. The old Qjet ran more economically I could get up to 13.5mpg with that empty at 55mph. I am still thinking of going back to the qjet.

By the way welcome to the board from PA.

[dtlilly]

My C-30 huffs pritty good good doing 55mph with the I-6 and SM465. I don't want to change a thing with mine tho, because it could pull a house off the foundation in granny low. Welcome to the board from the shadow of Lambeau Field.