Torque converter and 2.73 gears question
 

Good morning all! Been awhile since I posted and just getting back into my build. I have couple questions. First the truck/engine/trans/rear info I have to help :-)

1978 C15
454 .030 over mild cam, Edelbrock Air Gap intake, Demon 750 Carb.
TH400 Transmission
2.73 Rear End (this truck originally had a Diesel in it, which I assume is why the gears are as such) No I don't have the Diesel, Yes I want the 454 I built :-)

I am not looking for MPG, because I know it will suck either way LOL

This is going to be a cruiser, car show kinda car. Not my Primary Driver.

Nothing is in the truck right now except the rear of course.

The questions (finally I know)!
1- What torque converter should I put in to work for my application? I have the diesel one that I got with the truck, but I read it will not play nicely with a gasser.

2- putting everything together will this rear gear ratio work for me? Or is it better to go into the 3's somewhere? Again not looking for drag racing launches, but still want to have a bit of fun when applicable AND be able to go decent freeway speeds 65-70 without red lining. Can the 2.73s get by for now or will I damage anyhting?

I hope some of you made it to the end and can offer some advice! I don't mind changing the rear gears is absolutely necessary.

Thank you for your input!!

Re: Torque converter and 2.73 gears question
 

lose the 2.73s...at least go 3.73s or 4.10s..
convertor will be ditacted by your cam specs...need more info than "mild cam"

Re: Torque converter and 2.73 gears question
 

2.73 is pretty tall gearing for any gasser, even the torquey 454. I think it will still operate, I don't believe it's SO tall that you'll damage the engine by lugging it too low, so I think you can save that detail for later. But I would almost definitely change it some time in the future.

As for the exact ratio, and also the torque converter, I thing that depends on the specs of your engine. A "mild cam", meaning otherwise stock heads? Basic intake (not something designed for higher revs)? So you're looking at almost a stock engine, maybe a pushing the power into the higher revs just a little due to the cam?

What size tires are you planning to run?

Re: Torque converter and 2.73 gears question
 

Ok, looks like I do need some more info, sorry about that!

I can get the cam specs from the box tonight when I get home. As for tires....not too sure yet. Looking for something to look good in the well, but not huge. Going to drop the front and level her out. Not too low, but a little lower and leveled.

Re: Torque converter and 2.73 gears question
 

It depends on your tire height, but I think something like 3.42 gear are a good sweet spot for non-OD transmission. I'm thinking of something like a 31-33" tire when I say that.

If you had OD I would look at 4.10s or 3.73s.

Re: Torque converter and 2.73 gears question
 

Thank you all for your replies so far!

Here is the info that you all requested:

Comp Cam 11-242-3
Stock Oval Heads (not peanut)
Stock crank and piston length.
Edelbrock Air Gap intake
Demon 750 carb

TH400

2.73 Rear

Tires on it right now are 235-75R-15, but I will be going a little bit fuller...maybe up to 31's

The question up in the air is what Torque Converter is recommended for street use and if the rear gearing is OK for now or needs to be changed.

Re: Torque converter and 2.73 gears question
 

With 31" tires I like 3.42s. I put the numbers into a calculator and got this info:

3.42 gears

58 mph - 2208 rpm
73 mph - 2740 rpm

3.73 gears:

58 mph - 2408 rpm
73 mph - 3030 rpm

Re: Torque converter and 2.73 gears question
 

So leaving my 2.73 in there for now the RPM would be significantly lower? Will that damage anything? Also, still leaves the question of which torque converter

Re: Torque converter and 2.73 gears question
 

with your 2.73s and 31" tire and t400 you will be at 1923rpm at 65mph..the taller you go with your tire the worse (higher ratio) your final drive ratio will be....here's a rpm calculator to help you out..http://www.csgnetwork.com/multirpmcalc.html

Re: Torque converter and 2.73 gears question
 

comp cams recommends stock converter. ..http://www.compcams.com/Company/CC/c...?csid=395&sb=0

Re: Torque converter and 2.73 gears question
 

Yup tire size is a big number you need to look at. My son was complaining about gas mileage on is 84 truck with an LS/4L60. Went from a 3.73 to a 2.73 rear in the truck...but it has 26 inch tall tires.

2400 rpm was 70 mph with the 3.73, 1750 rpm with the 2.73. Stock motor and never lugged the truck.

Bubba

Re: Torque converter and 2.73 gears question
 

IMO, don't be afraid of a little gear, GM wasn't.

My C-30 has 4.10's with a 31" tire, my K-20 also had 4.10's with a 32" tire.
Highway was not real friendly, but around town they were decent.
Mileage was 11 and 13 respectively.

Just something to think of.

Re: Torque converter and 2.73 gears question
 

Have a talk with Comp Cams about your plans. Find out where your motor's happy RPM range is likely to wind up. Then plan your transmission, rear end and tire size to make that happen. Some builds will give better performance and mpg turning faster then other builds. Slower rpm not always equal to better mileage and higher rpm not always equal to snappier performance.

Re: Torque converter and 2.73 gears question
 

I really appreciate all the input on this! It has been helpful. Looks like I will stick with the gears I have for now and a stock no stall converter. I'm not racing so that should be just fine. I will definitely be going with tires that are 29 or less to keep everything happy. Its getting lowered, so the smaller tires should look ok :-)

Again, thanks!

Re: Torque converter and 2.73 gears question
 

I'm running similair sized tires in my 68 396 with the factory 3.07s. Works great, don't think I'd wanna go any bigger on the gear. I cruise at 70mph a lot.

As far a s a converter goes, I'd call up a reputable vendor and tell them what you are looking for. Do not just pick one out of a catalog. The right converter will transform your driving experience in a good way, the wrong one in a bad way.

Re: Torque converter and 2.73 gears question
 

I ran 3.07's with a 350 no problem, 2.73's with a nice big block would be a perfect cruiser. I hated not having overdrive with the 3.07's, I'd be screaming 3k at 80mph.

Re: Torque converter and 2.73 gears question
 

That's reassuring! Thank you for the info!

Re: Torque converter and 2.73 gears question
 

I have a 396 and a turbo 350 in my 57 pick up with 3.00 gears and absolutely love it. The big block has plenty of low end torque for these gears and freeway driving is very pleasant. I have 295/40/20 and I can light em up all day long

Re: Torque converter and 2.73 gears question
 

Do you recommend I go with a stock converter with my setup? Or something with a little stall?

Re: Torque converter and 2.73 gears question
 

I can't remember what I have , it's been awhile. I do have a little more than a stock converter.

Re: Torque converter and 2.73 gears question
 

I have 2.73 gears in my 83 with a 5.3. Havent driven it yet cuz its still at my buddys shop but i was told it would be good for gas mileage with the overdrive. Guess ill see how acceleration is soon...my old 74 had 3.08s and acceleration was ok...itll probably be worse now

Re: Torque converter and 2.73 gears question
 

i would honestly leave them in there til you drive it and see where you are at. my first k5 blazer i had given to me by a friend, had 38 inch tires, a crappy 305 engine and 2.73 gears. and it actually got around kinda decently. dont get me wrong it definitly wasnt winning any drag races but had no issues driving it on the street. offroad it had its issues, a lot of times if got stuck i didnt have the powers to spin the tires in reverse even in 4low lol.

the speedometer read half of what speed i was going so you could pretty much drive like 75mph at idle.

i eventually threw in some 373s and definitly made it quicker. so if your running stock tires with a big block i would think you would have no issues getting around. especially since you dont have overdrive.

my current truck has 4.11s 33s and a th400 and is almost at like 3000rpms around 65mph so i never take it on the highway.

Re: Torque converter and 2.73 gears question
 

A buddy has an '89 Ford E150 short van with a 300 six, C6 trans., and 2.75 gears with 225/75r15's. The 300 is a little tired and the fuel injection is far from perfect but if it had just a little more power (factory rating is 145 HP/265 tq.) it would be the easiest cruising truck I've ever been in. The 300 has enough torque to drive all around town under 40 MPH and never break 1,500 RPM; on the highway, 60 MPH is about 1,900 RPM and it just floats down the road. Put anything behind it and it struggles to hold 55 on decent hills, but if you could bump the output to about 180/300 it would cruise like a dream. Best recorded mileage is almost 18 with average hwy. being around 15. With the torque a big block can put out, if it does it below 2,000 RPM 2.75's with a TH350/400 could be quite nice. FWIW

On the other hand, though, both my trucks have pretty low gears: 3.73's in the Suburban and 4.10's in the truck, which is almost exactly equalized by the difference in tire size to where they both turn 2,600-2,700 at 60. Neither go above 70 without telling me they're working for it, but up to that they're right where they need to be in the power curve of the stock engines. Suburban's best MPG is 14, truck's is 12.5.

Re: Torque converter and 2.73 gears question
 

Man I hear that! The truck this motor cam out of had 4.10s and it was almost 3k at 70. Screaming loud lol. I'm hopeful that the high gear with smaller tires will run well for now. Making sure I get the correct torque converter has me still wondering...I tried calling Comp Cams but sat on hold for 20 min...

Re: Torque converter and 2.73 gears question
 

Yeah, I think you can drive the 2.73 gearing (and I certainly wouldn't bother to change until I actually drove it) but if it's not a daily driver, I think you'd be happier with a little more pep, something like 3.42 gearing.

As for the torque converter, I wouldn't suggest a high-stall converter. Stock stall speed, but probably go with a brand name, a good reputation, something designed to handle the power that 454 will be pushing.

Re: Torque converter and 2.73 gears question
 

Stock convertor. With the low gears out back you'd just be sitting in the stall zone building heat with a high stall convertor around town.

Re: Torque converter and 2.73 gears question
 

Great information from everyone! I really appreciate all of the help and input. I may start a new build thread with pictures, this is going to be a fun build. Converting a 78 from Diesel to Gas :-). Thanks again for the help!

Re: Torque converter and 2.73 gears question
 

Well I haven't gotten the truck driving yet, but working on it! I did take the diff cover off because I wanted to for sure know the ratio. 47 Ring 17 Pinion = 2.76 Gears. I can not find much on these gears anywhere. Did GM not make them long?

Re: Torque converter and 2.73 gears question
 

2.73 and a 28 inch tall tire is an awesome combo with any torque.

Any stall would be pointless with that gear.

Re: Torque converter and 2.73 gears question
 

I'm sure the engine has enough torque to handle any converter. My current Caddy is running 2.30 gears with a little 350 and it doesn't hold up traffic. When I used to run a C10 with a lightly warmed up 350 I could not get any traction with a th400 and stock converter.

Oh yeah, I forgot what gears that C10 had. I thought it was High sped like 2.73's or maybe 3.08's.