I recently purchaced a 77 elcamino classic from the supposed second owner. The original 305 was swapped out for a 454 from a pickup donor. Couple of questions: What rear end gear does my car have...it should be the one that was mated to the original 305? It still has the TH350 trans...is this stout enough to handle the 454...with modifications? Should i look at swapping a TH400 before going into the engine work? Any comments are appreciated.

Wow, I didn't know there was a lot of 4th Generation El Caminos that actually had the 305 (145 Hp LG3) engine option. Most had a 350/350 (170 Hp LM1) with the GM 10 Bolt 8.5" rear end 30 spline. I wouldn't be able to even guess at what rear end GM used on that. There is a code on the rear axel tubes that will tell you some but basically you need to look.

My "guess" is it is a 10 Bolt 7.5" 27 spline with probably a 2.73:1 gear ratio. But that is a guess. If that is actually true no, the rear end alone will not handle the pounding the 454 puts out. GM Generally uses a 12 or a 14 bolt behind the Big Blocks. In trucks it's a 12 bolt up to about 3/4 ton I think then they put in the 14 Bolt.

The 7.5" 10 Bolt doesn't hold a chance against a Big Block, even in stock hp numbers. The torque alone will eventually tear it up. If the trans is the original THM 350 that came in the El Camino with the 305 then nope it's not going to fair well ether. A THM 400 would be a better choice, that is also another thing GM put behind the Big Blocks.

Thanks for the response...do you think im safe trying to find these items(rearend and trans) at a salvage yard? I'm just trying to get a general idea of the parts list...if it gets too steep, i might just swap in an extra 350 that i have and sell the car...but we'll see.

Unfortunately you probably could locate a rear end and all that at a junk yard. I say that because it's unfortunate there are 4th generation Elkys in Junk Yards. You may not end up locating a 12 bolt you may end up settling for the 8.5" 10 bolt. Those are pretty common.

Rear ends I wouldn't worry about too much. You can open them up and inspect the gears and get a good feel of what type of shape they're in before you leave. As far as a Transmission, yeah you could get one from a junk yard too. Just rebuild it before you use it and get a new torque converter. A THM 400 in a junk yard isn't going to be real expensive. 300 to 400 at best.

Don't sell it!

Thanks again! You said i should get a new torque converter...i was wondering if you could clear something up for me: Is there a difference between a torque coverter and a stall converter. Or is a stall coverter the same-just with a later stall speed? Either way...if i get a stall converter-what stall speed should i think about getting?...or should i build the engine to what it'll be and then decide on a stall speed. Thanks!

Is there a difference between a torque converter and a stall converter. Or is a stall converter the same-just with a later stall speed?

A stall converter is just a torque converter. The stall speed is "essentially" the amount of speed in RPM of the engine where the converter is fully engaged (Fluid Lock) and it is primarily based on torque output @ a given RPM.

It is similar in thought to revving up the engine and popping the clutch in a standard.

Either way...if i get a stall converter-what stall speed should i think about getting?...or should i build the engine to what it'll be and then decide on a stall speed.

There is several ways to pick a stall converter, my experience is you need to know first the output torque curve of the engine to really get your stall speed set correctly. If you guess and guess wrong your converter will not work as it's designed and you'll be disappointed with it's performance. Worse case you can burn up a converter you just spent money on.

If you know your engine's torque curve then you know at 2500 RPM what the output is. A Converter manufacturer needs this information. You'll determine what lockup to choose.

Places like TCI and BowTie Overdrives can design the converter to what your engine's specifications are. They'll ask questions like, what CAM do you have, what Intake, Carburetor, the Heads and essentially what block and transmission, things like that. They'll plug that into some software that will help plot a curve then build to those specifications and output. There is a little more to it than that but basically that is what happens.


If you pick something like a 3300 or 3000 RPM stall speed, your Elky is not going to be very friendly at red lights doing normal every day driving. Most converters stall anyway at about 1100 RPM. That is where "generically" most engines start building decent torque. Torque is what actually moves the vehicle forward, not HP. Hp is a function of Torque.

A good performance engine will have more torque than horse power @ a given RPM. I have, as an example a 383 that produces 500 Lb/Ft. of Torque @4300 RPM and 480 HP @ 5700 RPM. High end torque is good, what you want is a good solid torque curve all the way across the power band of your engine. Low end torque is essential to getting you moving quickly. Remember you have to overcome the inertia of a standing vehicle with around 4300 to 5000 Lb weight possibly more. You want to move that weight as quickly as possible from say 0 Mph to what ever trips your trigger.

Torque curves drop off in the higher RPM and HP numbers pick up, as you overcome the inertia and build speed. All this is determined by the CAM you choose, the Heads, their flow rates and ability to draw in air/fuel, the compression, the Intake and it's ability to Mix the Air/fuel and again draw in air/fuel, the size of the cylinder and the length of the stroke. You are limited by all those things. Again there is a little more to it than that but basically that is the things to be considered. Air flow, getting it in and getting rid of the spent gas is critical to a good performing engine.

Big Block engines produce and incredible amount of low end torque, huge numbers in some cases. The bad side of that is their weight. For every 100 Lbs of weight you loose in most vehicles you gain about a 10th of a second in quarter and 1/8th mile times. In terms of normal driving, you gain better fuel economy.

I mention this because, you need to consider the output you want when you decide to build. Once that is done, you need to be able to build the transmission, drive train to deal with that much output. Then the suspension needs to be such that you can actually use that instead of just smoking the tires at take off. You want the tires to connect to the pavement and move the vehicle not just the tires.

A stock THM 350 is capable of dealing with about 350 Lb/ft. of torque. The 7.5" 10 bolt rear end in the 5th generation Elky will deal with about 275 to 300 Lb/Ft. of torque as is. A 10 Bolt 8.5" rear is good up to roughly 375 to 400 Lb./Ft. of torque and a 12 Bolt is good to about 500 Lb/Ft. or just a bit more, generically. A 12 bolt GM Spicer and the FORD 9" is pretty close to the same as far as their ability to take a pounding. The FORD 9" will deal with a little more but you actually can loose between 2 to 6% more of your output to that rear end. It is not as efficient as the 12 bolt because of the pinion angle with respect to the Ring Gear but it's stronger because of that.

There are probably people here that will disagree with what I've said. Its cool, this is how I understand it. It is the way I put it together when I decide to do something. I'm rarely disappointed by what I've built.

Wow...awesome response...thanks.

I thought the 7.5 rear didn't start till 78 ?

Wouldn't a 77 have an 8.5 10 bolt ???

A 350 turbo and an 8.5 would be fine for a mild 454. The 75 SS454 elky I had came with a 10 bolt 8.5, it did have a 400 turbo though.

Interesting thought James. I was aware that the 305 was offered in the 4th Generation. A 10 Bolt 8.5" would be a bit much for a 305. GM, or as I understand it, has traditionally not used more than the limits of vehicle. It could have been 8.2" 10 bolt.

It is pretty easy to tell the 8.5" 10 hasn't changed in years. Just take a quick glance under it. If the rear differential has two small "ears" (best way I can describe it) on the bottom of the differential on ether side then it's an 8.5" 10 bolt. They will be square. Most all 1/2 ton pickups now days (GM) have the 8.5" 10 so if it looks like that one then it is a 8.5". The 7.5 is rounded and doesn't have them.

http://www.elcaminoplace.com/76elky/76_images/76_carrier_open_1.jpg

Look closely at the bottom, you'll see what I'm talking about. Ether side on the bottom of the housing there is a hump. They could have use a 10 bolt 8.5 or a 10 bolt 8.2 (I think most of these were BOP not Chevrolet division) and it's possible that it's a 7.5"

Here is a good article on Chebby rear ends. It will help you visually tell what you have.

http://www.chevyhiperformance.com/techarticles/49998_10_bolt_identification_guide/index2.html

The reason I'm thinking it would be an 8.5 is because 77s were still the larger 4th gen chassis. I thought the 7.5 didn't make the scene till the down sized 5th gens.

Could be an 8.2, I don't know how many years Chevy used them, but alot of 3rd gens like mine used them.

I'll check it out tomorrow...to clear up which one it is:).

Ok...it looks like the one in the picture...8.5" right? I hope so...then i'd just be looking at the trans swap for starters.