700R4 and Correct Gearing

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Ozie P

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I need some tranny and gearing gurus to chime in as much as possible. Going to try and keep this short and to the point. Specs are this -84 K10, right at 500hp 5.7, NP208, and 700R4. I had originally had someone build a 700R4 setup for this motor yet, had some driveline issues and busted the case so it’s sitting under the shop. Have now replaced with another “built” but used 700R4. The gears are 4:88s front and rear with 35s. It feels as if no adjustments will fix the trans shifting. And it feels almost head back at WOT on the highway. Really looking to go to a higher gear ratio. Any input?


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bucket

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That sounds about right to me. I always recommend 4.10 or 4.56 with overdrive and 35's. A 500hp 350 isn't going to be happiest at lower rpms and 4.88's are about as mild as I would want.

What RPM are you turning at 70 mph?
 

Ozie P

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It runs about 26-2800 at 70. Not what I would like.


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bucket

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Do you have working lockup? What's the engine specs?
 

Ozie P

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After the failure from the previous trans that was built for the motor I bought this one used. The lockup doesn’t seem to be working in my opinion. It has a Fairbanks torque converter. Not even sure on stall rpm. Motor specs-5.7 Vortec block, aluminum lt1 heads, .40 over, Lunati roller cam. It’s a full roller motor. Makes decent torque and hp for a weekend truck.


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Ozie P

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Ozie P

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It’s just aggravating me that I have almost 500hp to work with and when I open it to WOT for a 4-2 shift, it feels like it’s held back extremely.


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4WDKC

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70s LT1 heads or 92-97 LT1? The converter may not have a lock up option. If the heads are to small for the cam it could be choking the flow at high rpms, along with a carb.
 

Ozie P

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It seems to be all coming now that this different trans is in it. Never had issues before with rpms. I have heard that 700R4s don’t go well with low gears though. That’s my concern. Do I need to raise the ratio?


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shiftpro

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Your gears are perfect for overdrive and 35s.
There is nothing wrong with 2700 rpm at 70 mph. Even with 500 hp you need that rpm range of you want to boot it and feel it pull hard.

Maybe you should consider a 4l80...? It will also give you a few more mph as I believe 4th ratio is 1.70 vs 700r4 with 1.75.
And you'll never break it. Stand alone controllers have dropped in price so I hear.
 

Ozie P

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Your gears are perfect for overdrive and 35s.
There is nothing wrong with 2700 rpm at 70 mph. Even with 500 hp you need that rpm range of you want to boot it and feel it pull hard.

Maybe you should consider a 4l80...? It will also give you a few more mph as I believe 4th ratio is 1.70 vs 700r4 with 1.75.
And you'll never break it. Stand alone controllers have dropped in price so I hear.
Let me rack your mind on this then. What would keep it from wanting to rev over 4K at WOT 4-2? In neutral, the motor revs great and so forth in 1st or 2nd. But when you want to “pass” someone it doesn’t want to rev more than 4K.


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shiftpro

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Let me rack your mind on this then. What would keep it from wanting to rev over 4K at WOT 4-2? In neutral, the motor revs great and so forth in 1st or 2nd. But when you want to “pass” someone it doesn’t want to rev more than 4K.


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You certainly have racked my mind. Sorry I don't have anything to say about that. Just confirming that your gear ratios/highway rpm would work
delightful for my needs.
Hang in there, we have some other guys here that will chime in...
 

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So what I'm getting from this is:
The truck runs great from a stop and runs through the gears fine.
But when cruising at speed in OD, it will kickdown like it's supposed to but then won't go past 4k and will not upsift.

Is this right?
 

bucket

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What is the full throttle upshift point? If it has no problem running through the gears, it should have no trouble doing the same thing after it has downshifted. When it holds at 4k, does it upshift when you back off the throttle?
 

Ozie P

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So what I'm getting from this is:
The truck runs great from a stop and runs through the gears fine.
But when cruising at speed in OD, it will kickdown like it's supposed to but then won't go past 4k and will not upsift.

Is this right?
You are right.....to an extent. It shifts down correctly, then back up but doesn’t want to turn more than 4K. Full pedal in OD is 4K


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