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Switch to rpm air-gap?

Ed's 1970

Well-known member
Joined
Sep 17, 2006
Messages
87
Location
SoCal
Corvette
1970 Stingray coupe
Hello everyone,
Now that I have driven my corvette around for the last few weeks, I have a better idea of what it's all about. This car is pretty fast for a small block, it revs like no tomorrow, pulls like a mofo up top but it does not have much low end torque.
I found out it has a solid lifter cam (maybe the original LT-1) and 492 camel hump heads. It has sidepipes. On top it has an old edelbrock torquer manifold with a newer 5160 holley.
Would switching to a edelbrock rpm air-gap, hotter carb (like a 650 DP), and possibly roller rockers make any difference? I have a L-88 hood so I think hood clearance is okay. I really don't know much about the torquer manifold, it looks alright.
Thanks,
Ed
 
Joined
Apr 29, 2001
Messages
2,141
Location
Rio Rancho, NM
Corvette
1981 HD Suspension; ZN1 Option
Hello everyone,
Now that I have driven my corvette around for the last few weeks, I have a better idea of what it's all about. This car is pretty fast for a small block, it revs like no tomorrow, pulls like a mofo up top but it does not have much low end torque.
I found out it has a solid lifter cam (maybe the original LT-1) and 492 camel hump heads. It has sidepipes. On top it has an old edelbrock torquer manifold with a newer 5160 holley.
Would switching to a edelbrock rpm air-gap, hotter carb (like a 650 DP), and possibly roller rockers make any difference? I have a L-88 hood so I think hood clearance is okay. I really don't know much about the torquer manifold, it looks alright.
Thanks,
Ed

First, find out if it is the original engine and if it is an LT-1. Then, if it is original and an LT-1, then perhaps there is some other problem (engine health, tuning). The LT-1 is one serious kick-butt engine, Nevertheless, the LT-1 had a 3310-Styled Holley carb in it with a Holley -36 intake.

If NOT original or LT-1, then perhaps you're not very far from making it run just right, but I doubt that the changes you mentioned will do very much good. The roller cam requires modifying your old engine to accommodate the roller lifters (I believe that the valleys have to be shaved down).

GerryLP:cool
 

Ed's 1970

Well-known member
Joined
Sep 17, 2006
Messages
87
Location
SoCal
Corvette
1970 Stingray coupe
I know it is not the original LT-1 motor, that is for sure and I wish it was. But thru some research I have done, the LT-1 motor ran the 492 camel hump head castings. The heads I have are similar, but the code on the heads indicates these were obtained over the counter from gm. Also, the cylinder block is a CE block, not the original. After pulling the valve covers, it became apparent to me that this engine has a solid (mechanical) camshaft in it by how loose the rocker arms are. If it was a hydraulic, there would be virtually no play in the valvetrain. I think it is a pretty mild camshaft though, it does have a slight lope, but idles very good. Perhaps the lack of low-end torque is due to the large diameter headers (1 7/8") and sidepipes.
 

Crimson Thunder

Well-known member
Joined
Dec 16, 2001
Messages
814
Location
Orange Park FL USA
Corvette
1970 Marboro Maroon Convertible
I had the same problem when i bought my car.The previous owner installed a Weiand single plane intake and an Edelbrock 600 carb.(I guess to go with the 300+ duration cam he used that dropped a valve in the numbers matching block)I switched to a Performer intake(hood clearance) and a 670 Holley Street Avenger and it made a HUGE difference in driveabilty.
 

Hib Halverson

Technical Writer for Internet & Print Media
Joined
Jan 10, 2001
Messages
13,453
Location
CenCoast CA
Corvette
71 04 12 19
If the car has an L88 hood, ie: a power bulge with a rearward facing intake on top of a standard big-block hood, then an Edelbrock Performer RPM will fit under it.

That's a great manifold choice provided the engine has the right heads and camshaft.

You mention that you've determined that the camshaft has mechanical lifters based on the valves being "loose". They need to not only be loose but have clearance. In some cases, you can have a hyd. cam with zero lash yet, when the lifters are on the base circle, you can still move the rockers a bit.

When you lift the intake to change it, you'll be able to determine if they are mechanical or hyd. by looking at them.
 

Ed's 1970

Well-known member
Joined
Sep 17, 2006
Messages
87
Location
SoCal
Corvette
1970 Stingray coupe
What I meant to say is not only loose, but plenty of clearance. I have a 94 Z28 with a hydraulic roller cam and the roller rockers on that motor have some play, but not nearly like the ones on the corvette motor. At first, I became alarmed and thought they were way too loose, but after thinking about it, I realized the cam is solid, not hydraulic.

I'll probably just get the rpm air-gap on it for now and see what happens.
Eventually, I want to build a nice 383 out of this motor (since I am pretty sure the block has 4-bolt mains and a forged crank) with some nice heads and possibly a roller cam. Looking for approx. 500 horse and 500 tq.
 

bradfordsvettes

Well-known member
Joined
Mar 28, 2001
Messages
549
Location
Boston, MA area
Corvette
jewel blue 61.cranberry 69 t-top.black rose 92
check your axle ratio and make sure it meets the expectations of the engine;shrug .you sure do not want a 2:73 axle ratio and expect any low end grunt :ugh . just my 2 cents Steve:upthumbs
 

Ed's 1970

Well-known member
Joined
Sep 17, 2006
Messages
87
Location
SoCal
Corvette
1970 Stingray coupe
check your axle ratio and make sure it meets the expectations of the engine;shrug .you sure do not want a 2:73 axle ratio and expect any low end grunt :ugh . just my 2 cents Steve:upthumbs
Very good point. The code on the rear axle is: 1 CAC(or maybe CAO) 12 70W
Does anyone know what this means.
 

Evolution1980

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Administrator
Joined
Feb 25, 2002
Messages
4,302
Location
Cleveland, Ohio
Corvette
ZZ4, 700R4, Steeroids rack & pinion, VB&P Brakes
Perhaps the lack of low-end torque is due to the large diameter headers (1 7/8") and sidepipes.
1 7/8" ??? :W Your primary tubes are almost 2" in diameter?!? I'm far from being a engineer, but that's probably way too much breathing room for a mild small block. Yes, that could definitely cause a loss in low-end torque, along with the side pipes. Great for upper-end HP though...
 

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