Thread: Differential gear choice????????

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I have a 1929 Buick that I am setting up as a street rod. I am installing a 9" disc brake ford rear end from a Granada. I belive this rear end to have about a 2.75 gear as installed from the factory. I bought a set of 370s and a rebuild kit for it. This is what I really wanted to do, but am reconsidering. I am wondering if someone that is really knows what they are talking about has any opinions on this.
Right now, the intent is to put a 95 Chevy LT1 with a 383 stroker kit in this car with a 700R4. I am more concerned with driving ecomomy than power, as the stroker will have lots of torque.
Several years back, I read a tech article that GM had on a new camshaft that they had on the market. It is a full roller cam, part #10134334. I don't remember the specs on this cam or I would post them. The article read that in the test of this cam, GM bought a 350 chevy engine from a junk yard with about 100,000 miles on it to simulate a well used engine that a back yard builder might be using. They did absolutely nothing to this engine but install this cam and an aftermarket aluminum intake with a stock quadrajet carb. It dyno'd out a 345 HP.
I had no use for this cam at the time but thought I might at a later date, so I ordered one. It is still in the unopened box. I intend to replace the LT1 cam with this one and add 1.6 roller rockers, since I already have them also. I am going to run a set of pretty tall tires on this car, 235/70-R16. I don't want short tires on this car, they would look wierd because of the extra large wheel well openings. I am kind of cencerned about using the stock 275s, but really don't want to get into rebuilding the rear right now without trying it first. I know that this is a really tall gear for a 700R4 with lockup, but I was talking to someone else that had a very similar setup except it was a stock 454. He said he could run all day at 80 MPH with the air on in a very large 42 Cadillac 4 dr and still get 24 MPG.
This car is very boxey and will have a lot of wind resistance. It is not going to be a very heavy car. The final weight I don't know yet. I know that it will probably not much more than idle at 70 MPH.
What are your opinions on this?? I know that the 370s would work best, but am curious as to how it would do with the 275s. Anyone have experience in this situation?

Thanks, Ed

Here's your cam specs:

This hydraulic roller tappet is used on the 5.7-liter H.O. engine assembly for ZZZ through ZZ2 engines. Use with spring P/N 10134358. The duration at lash point in degrees (intake/exhaust) is 336/336; duration at .050" tappet lift (intake/exhaust) is 235/235; and maximum lift with 1.5:1 rocker ratio (intake/exhaust) is 480/480. Valve lash is zero/zero and lobe centerline is 114 degrees.

That's a fairly radical cam, but what the heck. You already have it. With 1.6 rockers, your lift will increase to 512. You need to make sure the springs are up to it (no coil bind), and that you have adequate valve-to-piston clearance.

With the 2.75 gears, the 700/R4 and the 31" tire, you'd be turning 1461 RPM at 70. With the 3.70 gears, it goes up to 1965 RPM. Your gas mileage would drop approximately 25% with the lower gears. My '93 Corvette with 2.70's got about 25 MPG overall (town and highway). With the 3.55's I put in, gets about 20.

There's many things to consider including what transmission you are using. If you are running an automatic you will want to consider what engine speed you will cruise at on the highway as to what stall speed converter you get. You need to know the final drive ratios and tire diameters to figure this out.

In general the 370 is a good all around ratio I would say. I set my deuce up to pull 2700 rpm at 70 mph (30" tire dia, 350 rear) which is right where the converter stops slipping.

I am very skeptical that an older 454 caddy gets 24 mpg. My '97 SFI 454 truck gets 11 mpg at 80 mph. Albeit the truck is heavier and higher drag, the 24 mpg number sounds optimistic to me.

Regards, Kitz

Jon,

He mentioned he intended to use a 700/R4.

When I bought the roller rockers I bought them on ebay. They were supposed to be aluminum self aligning 1.5s. When I received them the guy told me he was out of the aluminum and had sent stainless steel rollers in place of them. I really didn't want the stainless because of the additional weight, but kept them anyway. Several months later I was looking at them and found that they were 1.6s. It was too late to send them back. I have never used 1.6s in anything, but the Chevy parts dealer told me that the cam could be used with either 1.5 or 1.6 rollers. The best thing I see about them is that they fit underneath my short valve covers with no modification.
I have the stock aluminum heads that I bought from a speed shop that have been rebuilt. I got a good buy on them, someone had them done and never picked them up. I purchased them for the price of the work performed. I really haven't looked at them except to take them out of the crates and put them on the shelf until I get around to putting the engine together. The engine is out of a Caprice State Police car and has cast iron heads.
I have been accumulating parts as I have been able to come across them from time to time at a decent price. I am a disabled Vet and money is getting tighter all the time, so I have to kind of look out for deals. I am building three street rods and not being paid for any of them. Two of them are friends and the other one is mine. Needless to say, mine is the last one to get worked on because of funds.
I may have to put the roller rockers on ebay. I don't want a radical engine. I want to keep the cam, I can't afford to buy anything else now. The Chevy parts guy assures me that this cam will run without a stall converter. Parts for the LT1 are quite a bit more expensive than for a regular 350. I have enough parts to rebuild a couple of 350s.
Even though the tire size calculators say this tire measures 31" tall, it actually measures 29.5" tall. I am kind of glad about that. The used one that I tried on the wheel for fit filled up the wheel well really well, but looking back, was really too tall.
If your Vet had 270s, I should be able to run the 275s, although the 1.6 rollers would probably be it too radical for a forth gear lockup. I know ideally, it would be better to be in the 2000-2250 RPM range around 70 with this transmission. If the cam is too radical I would be able to feel it while in 4th gear lockup. I still have to modify the harness for the LT1 and have the computer reprogramed.
Thanks for looking up the specs on the cam, I appreciate it.

Ed

Ed,

If you take a good cam number like that and Google it, you'll get the answer in about 2 seconds. Same thing with head or block numbers. I use it all the time. Saves looking for reference books. Give it a try.

If you're going to keep the cam, it might make sense to keep the lifters - at least until you see how they perform. If you sell them, you'll lose money, then you'll have to buy more.

When calculating RPMs, tire diameter doesn't give you an exact result. You need to use 2 x rolling radius. Since the weight of the car "squishes" the tire down a bit, the best measurement is from the center of the hub to the ground, then double it. I'm guessing a half inch or so. With a 29" tire, you're running about 1550 RPM in fourth gear locked up. That should be high enough for the cam to work.

Thanks,
BTW, are you Jack or Henry? It depends on what day it is, one day I think I will go ahead and change to the 370s and the next day I think I will try the 275s just for the heck of it to see how it runs out. It won't be a race car by no means. Just a everyday street car. Actually, I really don't have to make it a 383 stroker. I had this same basic engine in a 93 Z28 that screamed. Even in stock form the engine will be all this old car can handle.
When I got this car it had a 235 Chevy 6 cylinder with a powerglide. I really had to wrestle with myself to pull it apart. It was really smooth and you could not even hear it run. All of the wood was bad in the car or I would not have taken it all apart. Of course once it started rolling I could not stop it unless I put it in reverse. I rebuilt all of the hydraulics, shoes, wheel cylinders and all. Had to use both feet to stop and sometimes reverse. The old single stage master cylinder was just too small.
I have plenty of new parts to rebuild this engine back to stock form. It would just be nice to be able to say it was a stroker. No more than this car weighs a stock LT1 should carry it fine. I even thought about putting it in without rebuilding it but it is not very likely that will happen. I don't believe in half way doing anything.
I have been accumulating parts for almost 5 years now. All of my exterior chrome has been done by Advance Plating in Nashville. I have a complete set of Street & Performance chrome serpentine belt system. All power windows and locks, Vintage Air, and butt-loads of accessories to go on the engine, along with a new Afco radiator. It has a Scott's IFS that I installed. I have had the seats in the upholstery shop to be covered in leather. The only thing that is going to cost me is the material. I am helping the owner with his 48 Chevy truck. I gave him the engine and tranny from my car and mounted it for him. I forgot, that makes four vehicle that I am working on. I need to mount the differential and the triangle bar suspension with coilovers yet. I already have a set of Corvette 16" chrome wire spoke knock-offs with the new tires already mounted. I also have the new glass all the way around.
This old car is going to be pretty slick. It sure won't be anything to be ashamed of. Problem is that since I have had two heart attacks and two heart surgeries and had to go on disability, funds are getting tighter. I should forget the stroker kit and just rebuild it in stock form with this cam installed. It would still have more power than I would ever need.

Ed

You're going through the same decision-making process we all do. What to do . . . . what to do . . . ?

Screen name = Henry Rifle. It comes from my g.g.grandfather's civil war service. Many of the 7th Illinois Infantry carried Henry Rifles.

Real name = Jack

By the way, a 29 Buick has to be on the cool side for a street rod. There aren't many out there. The resto boys have probably put you on the hit list.

Jack,

Yeah, I know. This car would have been a premo for restoration. Body is in outstanding condition. too bad that the wood is so bad. She is still going to look pretty much stock other than the radial tires and 16" chrome spoke wheels.
I just got a notification of an ebay auction of a 383 stroker kit with pretty much the "best" for $725 and $55 shipping. Makes my decision even tougher. Like I said, money is tight.
I am a journeyman machinist and certified welder by trade. I have the capabilities of replacing the bad wood in the car with steel, I just have never got that deep in putting the steel in place of the wood before and have to figure my steps as I go. I really need to get on the stick though, my health is getting worse. If I don't get this car finished, it will wind up being practically "given away", because my wife doesn't have a clue to what everything is. I would like to have it so that my son would be interested in it after I die. He likes the more modern cars with all the technology that will turn heads. I keep telling him that this car will turn a whole lot more heads than his car EVER will and be worth a whole lot more. I wish that some of the guys that I am helping to build cars would help me. Although, doing it by myself ensures that it is done my way. It makes things go better if you have someone to help hold something or throw ideas to, or even just to talk to.
It has been a pleasure throwing comments back and forth with you and quite enjoyable. I appreciate that.

Ed