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73-87 Chevy _ GMC Trucks => Performance => Topic started by: Sprinkler-Man on April 04, 2016, 12:45:50 pm
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I friend of mine had gotten a hold of a rebuilt high performance short block Chevy 350. There was no spec on the cam but everything in it was hi-perf so I finished building the engine. It turns out that the cam is pretty radical and the engine produces very little vacuum. After talking to some transmission rebuilders they have basically told me that with my rear end gear ratio (3.73 I think) and large tires (40) the engine will not run well because of the low RPMs. They suggested a rear end ratio of about 5.38 Should I get a new set of gears or replace the cam and lifters? They also suggested dumping the TH350 for a TH400 to handle the power better but then I would have to change that transfer case input and adapter......Ugh...Any suggestions?
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If you are going to do a trans swap, go to a 700R4 but if your cam is too aggressive, swap it out for a milder cam
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With 40's 5.38 gears wouldn't be a bad idea anyway.
TH400 has a higher first gear than 350 or a 700 making your problem worse.
700 has the lowest.
Your going to be unhappy with a large cam with your setup. Your going to need higher stall converter to get power down low and that means heat for the trans.
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Will a 700R4 work for a 1980 GMC? I am not up on my transmissions and the electronics they may need.
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Will a 700R4 work for a 1980 GMC? I am not up on my transmissions and the electronics they may need.
It doesn't need electronics. Just s TV cable instead of a kickdown cable. Personally, I wouldn't run one with that much tire. That's a lot of extra stress on a known weak trans. A 4L60 is the electronic version and the 4L80 is the beefy electronic overdrive trans. Now, a 4L80 with a transmission controller would be as bulletproof as you can go. A built 200r4 is better than the pos 700r4, but I don't think they ever made a 4wd version. I would stick with what you have or go with the 4L80. If your truck is used for more than mall crawling or makes any power at all, you will end up with a pile of 700r4 parts and a hatred for them. There is a reason people have replaced them with 350 and 400's ever since they came out.
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If you have a 205 transfer case the 700 needs an output shaft change I believe.
The 700's were in front of 208 and 241 if I recall.
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Will a 700R4 work for a 1980 GMC? I am not up on my transmissions and the electronics they may need.
It doesn't need electronics. Just s TV cable instead of a kickdown cable. Personally, I wouldn't run one with that much tire. That's a lot of extra stress on a known weak trans. A 4L60 is the electronic version and the 4L80 is the beefy electronic overdrive trans. Now, a 4L80 with a transmission controller would be as bulletproof as you can go. A built 200r4 is better than the pos 700r4, but I don't think they ever made a 4wd version. I would stick with what you have or go with the 4L80. If your truck is used for more than mall crawling or makes any power at all, you will end up with a pile of 700r4 parts and a hatred for them. There is a reason people have replaced them with 350 and 400's ever since they came out.
There is no 4L80 only 4L80E, the 4L60 is a 700R4, the 4L60E is the electronic version, it' a 2004R and is not advantageous to run in one of these trucks. I have ran the 700R4/4L60 behind big blocks and high output small blocks with great success for many years so I would not call it a POS. If you take a stock unit out of a junker and stick it behind a powerhouse yes it will fail & by comparison to the TH400 which was essentially bullet proof can be put behind a stout engine without modification and will likely survive. If you want to limit your streetability then that is the cheapest way out. If you want to maximize your street performance then look at the 4 speed options. 700R4 is easily upgraded and affordable. Nevertheless, the trans isn't the issue here, you shouldn't build your driveline around a camshaft that you didn't select.
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me personally i would swap out the cam for one that is going to give you more power down in the lower rpms. if the cam is really that radical than no matter what transmission you go with you are going to need a high stall converter as said above and thats getting into alot more work than a simple cam change
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me personally i would swap out the cam for one that is going to give you more power down in the lower rpms. if the cam is really that radical than no matter what transmission you go with you are going to need a high stall converter as said above and thats getting into alot more work than a simple cam change
Agreed ^^^
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You running 40s and 3:73s ?
How do you get it to start moving ?
I assume stock Dana 44 front and 10 bolt rear?
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Running 35's with 3.73 right now but wanted to step it up to 40's. I was running a 2500 stall until the TH350 stopped working. The truck never felt like there was any power to it, probably because the motor was never in it's power range. I am going to take out the cam and replace it with something more street worthy and some low end torque. So it looks like the order I need to proceed is 1)pick out a new cam 2)pick out a transmission 3)with all this known pick out the correct set of gears to keep the motor in the power range at highway speeds?
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Will a 700R4 work for a 1980 GMC? I am not up on my transmissions and the electronics they may need.
It doesn't need electronics. Just s TV cable instead of a kickdown cable. Personally, I wouldn't run one with that much tire. That's a lot of extra stress on a known weak trans. A 4L60 is the electronic version and the 4L80 is the beefy electronic overdrive trans. Now, a 4L80 with a transmission controller would be as bulletproof as you can go. A built 200r4 is better than the pos 700r4, but I don't think they ever made a 4wd version. I would stick with what you have or go with the 4L80. If your truck is used for more than mall crawling or makes any power at all, you will end up with a pile of 700r4 parts and a hatred for them. There is a reason people have replaced them with 350 and 400's ever since they came out.
There is no 4L80 only 4L80E, the 4L60 is a 700R4, the 4L60E is the electronic version, it' a 2004R and is not advantageous to run in one of these trucks. I have ran the 700R4/4L60 behind big blocks and high output small blocks with great success for many years so I would not call it a POS. If you take a stock unit out of a junker and stick it behind a powerhouse yes it will fail & by comparison to the TH400 which was essentially bullet proof can be put behind a stout engine without modification and will likely survive. If you want to limit your streetability then that is the cheapest way out. If you want to maximize your street performance then look at the 4 speed options. 700R4 is easily upgraded and affordable. Nevertheless, the trans isn't the issue here, you shouldn't build your driveline around a camshaft that you didn't select.
Doesn't the 700R4 have a electronic locking stall converter?
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Will a 700R4 work for a 1980 GMC? I am not up on my transmissions and the electronics they may need.
Doesn't the 700R4 have a electronic locking stall converter?
Yes it is a locking trans but it is very simple to hook up plus unlike the later electronic transmissios it doesn't have to have any power to run. You could do the swap and run the truck until you decided to hook it up.
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If you decide to get a 700r-4 make sure it is 1987 and up...the casings were stringer as well as most of the internals!
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i know these guys covered the trans issue. but whats your plans for the truck? mud, trail or just a road truck or even just one that is a trailer queen?
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i know these guys covered the trans issue. but whats your plans for the truck? mud, trail or just a road truck or even just one that is a trailer queen?
Road truck for the most part but with a splash in the mud once in awhile. It is rust free from Arizona but the sun has taken it's toll on the paint and interior. Eventually I will get some paint on it but was toying with the idea of black undercoating it instead after I saw a Diesel Brothers episode where they did it to a Willy's.
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You're not going to need any fourth gear overdrive with 40's unless you install 5.13 axle gears
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Just to add to the confusion my humble opinion is to go for a four or five speed manual. Then you are in control of what gear you need. I love automatics because they allow me to drive braindead, but much prefer a manual. And changing a burnt clutch is much cheaper than changing a burnt auto. A manual box seldom to never overheats either. Autos, with big tires and a powerful engine especially, really should have some serious cooling beyond the radiator, no problem but it's still a lot of dollars both to start and to maintain. And don't forget, as soon as the mud plugs the cooler fins up it gives up a lot of it's cooling capability right when it's the most important.
Just something to consider.
And, like everyone else said, ya really need deeper gears no matter what you decide. 3.73's don't work very good with any tire over 33". Again, just my opinion.
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Ok, so I decided to go with the 700R4. After all the upgrades needed to make a TH350 work for a high HP engine it cost about the same. I plan on ordering the Revenger series from Animal Performance Transmissions. I have been searching the web and found only good stuff about them. Anyone else familiar with them? Now if I have done my reading correctly I will either have to change the output shaft or run a spacer kit to use my NP205. Otherwise I can get the stock adapter and run a 27 spline NP208. Either way I think I may have to do some drive shaft modifications for the transmission length difference. Anyone else do the TH350 to 700R4 swap that could shed some light on this? Lucky for me I found a guy that has a lot spare parts I can pick from. Still not sure what gears to use. Some say 4.56 others 5.13. I would have to change out both front and rear correct?
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Correct on both gears needing changed. I feel the gears to be used are dependent on the tire size. I believe you said 40"? I am old school so I never worried much about gas mileage like the folks today do. I had 39/15-15 Mickey T Tall Baja's (about 38-1/2" tall) back in the day and ran 4.11's with no problems but only got about 10 mpg on 96 octane. But the national speed limit was 55 mph then. There's ratio charts and all sorts of mathematics you can do to figure out what gears you need. Just google gear companies.