I have a 1990 TPI LB9 that I'm changing over to a carb setup. I'm getting rid of the stock Roller cam and installing a Crane
100032 cam and lifter kit, Really I'll use the Summit brand of the same specs.

The guys at Crane said I'll need new push rods 5/16 X 7.756". I can find these but there pretty high at $90 a set. I can get 7.794" for a lot cheaper but will that cause any problems having .029" longer? Heads are stock on the LB9.

Thoughts?
thanks
Doug

 

Why did you get rid of the roller setup? There are rarely good reasons to ditch a roller cam for a flat tappet cam. Roller cams are vastly superior in performance, reliability, and technology.

You'd be a lot better off getting a factory LT1 cam, actually.

 

You need the proper length pushrods to keep proper valve train geometry. You can't really guess at the length without measuring. If 7.756" are recommended, then that's what you should use. There's no guarantee that they'll be the length you require but since everything else is still stock, they'll probably be close enough.

 

Thanks for your input. I'll find the 7.756"

Doug

 

Sorry, but there is NO Way that anyone can specify a push rod down to .001" for ANY engine without actually measuring your EXACT engine configuration. I would grab a set of high quality 7.800 (Stock Flat Tappet Length SBC) push rods and call it good! You are better off a little long, rather than a little short when it comes to push rod length. How much hydraulic lifter preload you run will affect your push rod length as well. One turn of preload on a 3/8 - 24 rocker stud moves the rocker pivot down .042, so you can use this to you advantage to make up for small variations in ideal - vs - available push rods.

What I believe they are doing is adding or subtracting the difference of the base circle of their cam and the original Chevrolet Stock Cam Base Circle to get their recommended push rod length. If you are that concerned about this, I would get some of the available measuring tools and figure out EXACTLY what you need, if that is really what you feel is necessary. In any case, you will be getting custom length push rods.

You are obviously changing to a flat tappet cam, since you are using 7.800 push rods and the roller cam engine uses 7.300 push rods. Why? You are giving up power AND reliability with a flat tappet cam. Crain 100032 is a low RPM cam and will very likely cost you power, not improve it. I have a 305 and I am using a 91 SD TPI and a stock GM L-31 (350) Roller cam, which has much better lift specs compared to this Crain cam and it is a roller cam. I cannot see the benefit to switching to this cam. What is the supposed advantage? All I can see is the "rumpity-rump" idle. Those factory roller lifters are worth 10-15 horsepower alone, cooler running oil PLUS they are super reliable with modern motor oils! You also will have to deal with the difference in the timing gears from roller to non- roller camshafts. You are making your job even more difficult.

 

Great info, Thanks I'll have to study up on it

doug