New member . just installed new motor 350 in my 81 vette making 385hp @ 5500rpm . i have a 350 th trans with 2.87 stock rear end 78 mph @3000rpm hwy but no low end power any thoughts.

 

What intake and cam do you have. 385hp @ 5500rpm doesn't mean a whole lot really as we don't drive at 5500 RPM.

 

duel plane intake camhydro roller221/226 dur .495/.502 lift

 

If its low end grunt ou want you need more torque. You can gain torque with a gear ratio change. If you go up to a 3.36:1 or higher you will start to nitice what your missing in torque. Your rear end is probably geared good for a big block but not for a small block motor

The th350 has a first gear ratio of 2.52:1

 

2.52x2.87=7.23

Your not going to go anywhere quickly with a 7.23:1 total ratio. 9:1 will feel sporty, 10:1 will feel racy, 11:1 will feel like you just snapped your neck

 

Tk is 402lbs but @ 5500rpms

 

you may want an Overdrive tranny if you change to a higher ratio as your 3000 rpm speed will drop

https://purperformance.com/p-29669-rpm-calculator.html

 

As others have said steeper gears will get your small block up much more quickly to the rpm where your 350 can make power. If you want to maximize that engine’s potential, I would go with even stiffer gears, a higher stall converter, and if the budget allowed, an overdrive trans.If an automatic, a 200 4R will require less in modifications and provide you with the optimum gearing, stall and lower rpms from the overdrive on the highway. It would be a big commitment but if it were mine and plan on keeping the car a long time, that’s what I would do. My .02

 

what is torque where you are questioning it? if its below 300 you wont get anywhere unless you have the ratio to support it. If your timing is off you will notice it doesnt have any guts also. If you are running real rich its going o be choking at lower rpm as well

 

i was thinking 3.55 gears for now. then much later new trans. but do you think i am doing any harm with the currant applacation?

 

To the engine, no I doubt it. To the tranny, maybe just from the stress. 3.55 would probably respond nicely to your power levels. I had a 327 with similar power and it was pretty fun with the 3.55 but my tranniesfirst gear was lower. Alot more fun with a 3.70 but I have an overdrive

 

what if I was to drive around in 2nd gear is keeping the RPMs high would that harm my transmission I mean 2nd gear and City 35 to 45 miles an hour bringing it up to 3500 RPM

 

Was this engine tuned on a dyno?

Jebby

 

When I was planning the drivetrain for my restomod I really wanted to keep an automatic transmission, wanted good torque, mid range and most of all I wanted to cruise down the highway at 70 with lower than 3100 rpm.
I researched all the auto overdrive transmissions and found that by the time I purchased a good OD automatic that would handle the torque and horsepower of my engine, added a custom torque converter and purchased a new driveshaft, I was in for about the same cost as doing an auto to manual transmission swap and have the best of both worlds.
I went through Silver Sport Transmissions and purchased one of their complete kits and I never looked back.
They offer several different packages and their customer service was excellent.
I was able to choose a 5 speed that had the off the line gearing I wanted and gave me the OD gearing I needed for highway cruising.
You may be able to even keep the rear end gears you have now and save some additional costs.
Have you verified your rear gears are 2.73’s?
If not there is a simple way to check them because you never know what a prior owner has done.
A few year ago I restored an 83 GMC 4X4 I purchased from the original owner who told me he ordered it with the 3.08 gearing option.
It had a 700R4 and was a complete dog on the highway with the oversized tires.
I purchased a set of 3.55’s for both differentials and found it was already equipped with 3.55’s and ended up swapping to 3.73’s.
Good luck and look at all your options before you pull the plug.

 

With that engine, you would do better with a 700R4 (or 200-4R) overdrive transmission AND a rear gear change to a 3.36 or 3.55 ratio. With that setup, you will cruise on the highway at 70 mph around 2100 rpm, get 18-21 mpg and still be able to roast the wheels from a dead stop. Acceleration from 0 mph would be 'enjoyable'. No way to really get there with swap out of only trans OR rear gear....

 

you could also tach it up to 5500 and drop it in gear.. that way it is in the power band. ok. don't do that. 81 was an epa year. gas mileage and emissions. they didn't have efi yet and same with the 700r trans. i assume you are NOT running the orig carb and distributor? 700r are going to be getting scarcer. the 4l60-80e trans are around 5-700 in junkyards. and stand alone controllers are about 500 bucks also. the 200r is rare but the same length as your t350. cheapest option is a higher stall converter. easiest is higher ratio rear. neither is really cheap or easy. at least the 3-2 kickdown on the highway is kind of satisfying.

 

Jus wondering...Are you looking for Proformance or Performance?

 

If you really want low end (low speed) power you need a higher stall torque converter and a much higher (numerically) rear gear. If you don't do a lot of highway driving, a 3.73 rear gear is very effective.
You say your HP peak is at 5,500 rpm, and you said your torque peak is at 5,500 rpm also. Was that a typo?
Also, what heads are on that engine? You have a fairly mild cam, so 385 HP output would require good, aftermarket heads.

 

I have a 383 with 2004R trans with 3.55 diff ratio. 1st is low and gives a good drivability, also the overdrive @0.67 gives great cruising. 70 mph @2100 rpm and reasonable fuel economy of 11.3 Litres/100klms.