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Discussion Starter · #1 ·
I INSTALLED A NEW VORTEC L31HD CRATE ENGINE, PN 12530283, AND A NEW 700R4 TRANSMISSION IN MY 55. REAR AXLE RATIO IS 2.93. THE COMBINATION WORKS QUITE WELL AND MY FUEL MILAGE IS MUCH IMPROVED OVER THE 305/ 350 THAT WAS REMOVED FROM THE CAR. MY QUESTION IS THIS, I EXPECTED THE ACCELERATION TO BE SOMEWHAT BETTER THAN IT IS. MY ENGINE IS CARBURATED AND NOT INJECTED. CARB IS A NEW EDELBROCK 500 CFM THAT WAS ON THE 305. I KNOW SOME MAY ADVISE TO CHANGE THE CARB TO A 600CFM BUT WILL THAT REALLY MAKE THAT MUCH DIFFERENCE? I JUST WANT GOOD PERFORMANCE WITH DECENT MILEAGE. OVERALL IT RUNS GOOD, STARTS EXCELLENT AND SO FAR HAS BEEN VERY DEPENDABLE. MAYBE I'M EXPECTING MORE THAN IS CAPABLE. I CHOSE THE VORTEC FOR THE ROLLER CAM AND THE BETTER HEADS OVER THE 290 HP CRATE ENGINE FOR ABOUT THE SAME PRICE. ANY ADVICE? THANKS.:gba:
 

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Fuel economy vs. performance.

At first blush I'd say with a 2.93 rear gear, you won't be humiliating Mustangs from the stoplights. Even with the low first gear of the TH-700R4, acceleration will be compromised. But your car should be a fuel sipper on the highway.
 

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The setup is good for fuel mileage, but the gearing isn`t good for acceleration. I have a 3:08 in my 57 with a 350/ TBI and it is good to drive. Mileage is pretty good, but take off is a bit sluggish. Going to a 3:36 or 3:55 would help.
Terry
 

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depening on the cam size

you may get better mileage with a 3.36 gear, as at 65mph, with a 26 in tall tire, your rpm is 1725 rpm, which may be under the power band for your motor,
as said, the rear gear will affect your acceleration from a stop,
a looser converter will help with acceleration also,
 

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stock gm put 3.42's in the rear gear with 700r4's in trucks and cars and 3.73's with suburbans cuz they were heavy. 3.73's would be a really nice set up streetlight to streetlight. 3.73 x 3.06 is comparable to 4.56's x 2.48 t400 first gear. freeway drops it down to like 3.0 on the freeway or so with overdrive with 3.73's. if you want more performance...get a 3.36 or 3.55's or 3.73's, either one of those gears would work great for burning the tred off the tires. had some 2.73's with my brother's 283 v8 in a 57 truck and a 700r4. it drove nice...as soon as we put some 355's inthe rear...he had burn out power and could actually use the overdrive. 2.93's was probably a good gear for the freeway with the turbo 350.
 

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I've got 2:93's for the 10 bolt for my 47, with a 350/350. I put 3:42's in the 10 bolt for my 56 with 350/700R4. You'd like 3:42's more.
 

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With the 2.93's and the 3.06 first gear on the 700R4, you have the equivalent of a Turbo 350 with 3.55's out back. But that's just in first gear...I bet your acceleration in first is decent then it really sucks in second and above. So, essentially, yes, lower gears out back would help. From experience, 3.73's with a 700R4 is pretty steep in first...I think you'd be happier with 3.42's or 3.55's.

The other thing is that L-31 motor has a tiny little cam (191/196 at .050)...so you are probably well within the engine's powerband at 1725 RPM actually. Remember, this was intended for a truck...powerband is probably 1300 RPM to 4000 RPM. It's gonna run out of breath by 5000 RPM, maybe earlier. If you really want to get some more power, you're gonna need a bigger cam, it's that simple. I'd look for a ZZ4 take-out or something similar myself. Add about 20 degrees of duration and you'd make more power and still have a pretty mild cam. Of course, you may have to swap valve springs with a bigger cam as well, but that's part of the game. Oh, and your MPG will go down with a bigger cam. A roller cam swap is super easy and you can re-use almost everything.

Do those the rear gears and a cam swap with supporting valvetrain modifications and you'll have a nice little runner. Maybe then think about a carb swap, but I doubt it'd help much now.
 

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Discussion Starter · #10 ·
FIRST, I REALLY APPRECIATE ALL THE RESPONCES TO MY QUESTION. MAYBE I SHOULD SAY THAT MY ACCELERATION ISSUE ISN'T FROM A DEAD STOP BUT RATHER MORE FROM ABOUT 25 MPH ON UP TO AROUND 60-65MPH. SOMEWHAT LIKE HUTCHENC DISCRIBED. IT MAY BE AN ISSUE I JUST HAVE TO LIVE WITH. I AM AWARE OF THE "SMALL" CAM BUT THE ENGINE IS NEW AND CHANGING THE CAM AND POSSIBILY VOIDING THE WARRANTY ISN'T SOMETHING I WANT TO DO AT THIS POINT. I HAVE CONSIDERED CHANGING THE RING AND PINION TO A LITTLE TALLER GEAR BUT THE CAR JUST ACTS LIKE IT NEEDS MORE CARBURATION. I AM PRESENTLY TRYING TO FIND A 600 CFM EDELBROCK I CAN BORROW JUST TO SEE IF IT MAKES A DIFFERENCE. I'M SURE TALLER GEARS WOULD MOST LIKELY BE THE ANSWER AND I MAY NOT HAVE A CHOICE. THANKS AGAIN FOR ALL THE ADVICE.:gba:
 

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I don't think the carb is restrictive.

here is a very good calculator for carb CFM.
http://www.wallaceracing.com/intakecfm.php
using70% efficiency, on a 350, with 5000 rpm max,
it suggests 425 to 525 cfm carb,
the drive-ability will be better with the 500 cfm than the 600.
but I kinda doubt most people would notice any difference.
 

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Discussion Starter · #12 ·
CRUZN57, I HAVE ACTUALLY SEEN AND USED THIS CALCULATOR IN HE PAST AND THIS IS PARTLY WHY I CHOSE TO KEEP THE NEW 500 CFM EDLEBROCK FOR THE 350. I THINK IT'S A COMMON MISTAKE TO OVER CARBURATE ENGINES THAT ARE USED FOR NORMAL DRIVING 98% OF THE TIME. I'M MOST LIKELY JUST CHASING MY TAIL ON THIS AND SHOULD JUST ENJOY THE ENGINE AND TRANS COMBO AS IT IS. THANKS FOR THE POSTING AND THE HELP.:gba:
 

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your welcome

and I agree, most do over carb their motors, (cause they read it in hot rod magazine, LOL)
for a street motor,you want a small venturi carb that will promote good air flow, to get the best air /fuel mixture.
which will give the best performance and economy and driveability.
but try to explain that to most people !
I run a Edelbrock 600 cfm on my 383 SBC, it makes 340 HP to the rear wheels, drives great, great throttle response, miles per gallon???????
don't know yet ,as I have added a 200R4 and haven't checked yet.
 

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The problem is the axle gears especially from 25 mph dig. Your in second gear trying to pull hard. So it will be a dog no matter what carb or efi you put on it. The L31 was rated at 255hp/330tq stock. That's plenty just need the gearing to get things going.

I would swap to 3.55 or 3.70's. or similar.

Your carb should work fine the stock l31 efi flowed around 600 cfm anyway but was less with the EGR diffuser under it. You might add some higher ratio rocker arms easier to install than a cam and should gain some lift with them. Stock was 1.5. I believe the 383 vortec they sell has 1.6 on it from gm. Adding 1.6 would be easy.
 

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Discussion Starter · #15 ·
BO185, I DID GIVE SOME THOUGHT TO INSTALLING THE 1.6 ROCKERS BUT HAVE SEEN A FEW EXAMPLES OF THE STUDS PULLING OUT OF THE HEADS WHEN DOING THIS. AGAIN, THIS ENGINE IS NEW AND HAS A WARRANTY,(FOR WHAT IT'S WORTH) AND I REALLY DON'T WANT TO DO ANYTHING TO COMPROMISE THAT. THE IDEAS ON LOWER GEARING IS MOST LIKELY SPOT ON BUT I'LL MOST LIKELY RUN WHAT I HAVE FOR THE PRESENT TIME. IF THE REAREND STARTS TO GIVE PROBLEMS IN THE FITURE I'LL TRY THE LOWER GEAR SET. IN TRUTH, THE OLD GIRL RUNS OUT GOOD. I'M PROBABLY JUST EXPECTING MORE THAN IT CAN DO. THANKS TO EVERYONE FOR THE SUGGESTIONS AND IDEAS.:gba:
 

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I've also read that the pushrod holes need to be elongated to accommodate 1.6:1 rockers on the Vortecs.

My vote is still for a cam swap...that'd really wake her up!
 
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