What would you do if you was me? I need some advise.

by Hs1973 Thu Aug 05, 2021 6:01 am

Hi guys.

I have always gotten good info and help from you in here, so i will see if any one has an idea what to do.

I just finished putting a new driveline in my 75 chevelle ( wanda) i have a 2 problems o dont know quite how to solve at this point.

I just put in a new gm perfomance 290 horse 350 with a edelbrock intake and new edelbrock 600 cfm with Stock exhaust manifolds and 2.5 dual exhaust.
. I have a build an reinforced 700r4 with all the correct brackets for tv cable. And 2000 Rpm stall.
And a 3:23 posi rear and 275-60 15 tires.

Im happy with the way it drives around town, however when i get on the highway and reach 60mph and put in the lockup and just coast, it feels like driving a stick in 5 gear uphill. The car feels Big and heavy and kind of shaking ( engine Lugging? ) i have around 2000 Rpm in 4th with the lockup on. Turning off the lockup feels alittle better. I have lockup on a toogleswitch.

Problem 2 is tha it feels like dog out the hole until 2500 Rpm then it picks up and goes. Kickdown is fine with a seat off the pants feel, but 0 to 40 is kind off dead Feeling.

I was thinking a new 3:73 rear and maybe a 2500 Rpm stall converter would help.also planning on headders.
But im not sure how to correct this. Im happy with how it performes otherwise and cruising around town is fine and he car feels good. But i cant drive it like it is now on the highway without waiting to get off as soon as possible. So all advise is welcome.

by bracketchev1221 Thu Aug 05, 2021 7:01 am

I think I would do the gear change first and see how it does. The 3.23 is a little high in ratio for over drive in my opinion. With your trans thats like having a 2.26 gear in it when it goes into overdrive. The engine should still be around 2000 in overdrive at cruise speed.

by Joe73 Thu Aug 05, 2021 8:19 am

Im with Bracketchev1221 !! Id be switching the rear gear to 3.73. Everyone I know that has switched to an overdrive trans went with a 3.73 rear gear and 2000 stall convertor. That combo seems to be the best all around. From off the line to highway cruising. Good luck with it.

by Iggy Thu Aug 05, 2021 10:45 am

I would go even lower - 4.10's. The 290 HP crate engine is basically the L82 installed in Corvettes in the mid to late 1970's and they suffered from low compression. You are right in that the engine starts to make power around 2,500 RPM and will really wind up after that - I had a 1977 Monte Carlo years ago that actually came from the factory with that engine, TH350 and 2.56 gears and it was a complete slug below 60 MPH, once you hit 60 it would go triple digits in a hurry, could cruise @ 140 in that car! 4.10 gears will put you around 2,200 RPM cruising @ 60 MPH and 3.73 gears would put you around 2,000 RPM @ 60 MPH

by Hs1973 Thu Aug 05, 2021 1:31 pm

Thanks guys. Ill do the gear change first and see how she does. Ill stick with the 3:73 and hope it at least makes it driveble on the highway. I can live with it Being a little slow off the Line if need be. is there any gain in driveability if i change the converter also? Or is it a Waste of time. I dont know that much about it and im trying to learn. Thank you again guys.i will try soon and get some new pictures for you, since we all like pictures more than anything.

by Iggy Thu Aug 05, 2021 1:50 pm

2000 RPM stall should work out fine, I would not change the converter.

by Joe73 Thu Aug 05, 2021 2:12 pm

I wouldnt change the convertor either. A convertor should match your engine cam / power band specs.

Heres something to think about and I think it holds true. Years ago, I was told that to have a fun car you should be at 9. Meaning that if you take your trans 1st gear ratio and multiply it by the rear axle ratio, a fun driving car will be about 9.

More than 9 and driveability suffers but performance increases. But you have an overdrive trans so no issues there.

So, you currently have a 700r4 which has a 3.05 first gear and your axle ratio is 3.23. 3.05 x 3.23 = 9.80. But if you go with a 3.73 axle ratio you have 3.05 x 3.73 = 11.37.

So by going with the 3.73 axle ratio your "fun" factor for acceleration will be way better. And since you have a .69 4th gear ratio, highway driving will be improved as well. More torque multiplication out back.

by Hs1973 Mon Aug 09, 2021 1:26 pm

Thats some deep calculation there. But it looks like you are right. Ill try my luck with the rear gears and see how they are. Im so damn close to having it drive like i want to, just need the last 5 procent. Thanks for your advise.

by REVINKEVIN / Mr. 600+HP Mon Aug 09, 2021 3:02 pm

700R4+.373 gears= Happy Man

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