I was looking up camshafts for an ls1 engine and I was looking at the Big Mutha Thumpr cam. The description told me about what I had to buy with the cam to be able to install it. It said that it needs 9.5:1 CR,2800+ stall, intake, gears, & headers, and a very rough idle. What does the 9.5:1 CR, the intake, gears and headers mean? Clearly explain what each one of them are? How much would each one be?

Landon Lippard

Asked by Jan 25, 2014 at 05:23 PM about the Chevrolet Camaro

Question type: General

3 Answers

Tim Robson

CR would be compression ratio this is the ratio between the area the piston displaces from bottom dead center and top dead center and the remaining area above it at top dead center. the intake is everything before the heads i.e. from your air filter to the manifold bolted to the heads, in this case i would assume they are talking about the manifold, but it may just require a less restrictive way for the air to get in like an over the radiator intake piping. The gears i assume is the timing gears. they are gears on the crank and the cam that make sure the cam turns in time with the crank (1 time for every 2 of the crank). The headers (also called extractors) are the first part of the exhaust from the head to where it all becomes 1 main pipe. The price is very hard, because there are so many different types/manufacturers/quality for eg the headers on my ls1 are ceramic coated stainless ones and are around $2500 but some can be bought for as little as $200 but usually have poor build quality and would not be recommended the same goes with all these parts. the best thing i could recomend would be look and when you find parts you are thinking about buying look around and see if others have had any complaints praises ect before you make the leap. But a general guide for a good set up i would think the whole job should be around the $3500 mark without headers (thats what it would cost here in aus not sure what the price difference would be where you are. hope this helps.

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Best Answer

That cam is for a forced induction set up. From the factory your motor is 11.1 CR. You will need new aftermarket heads or dished pistons to lower the compresion. To make that cam work you need about $8000 to get started. Then your at 800 HP and everything starts to brake. Good luck

John Carson

When I built my Corvette 350/350, I used flat top pistons, a wild street cam and high flow heads to keep it at a 10-1 CR so I could use pump gas. When my timing gear, gear drive broke, I had to rebuild from scratch. I had a professional builder do the job. He called me and told me the cam, pistons and heads didn't match up. At top dead center, (piston all the way to the top) the valves were open and I had a 0.001 of an inch clearance. One missed shift or a back fire would cause contact an destroy the motor. I had to d-tune the cam, to give me 0.003 clearance because I kept the same pistons and heads. I had a custom cam made from a NASCAR Race builder, called American Cam in Chino CA. I lost at least 10 HP and didn't have the massive rock and roll rumble. So if you do want to use a monster cam, make sure everything you use will match up. Don't let Jimmy behind the counter with the pimples, tell you what you need. Go to a VERY reliable engine builder and make sure what your building will work. The jury is our on changing cold air forced intakes for more HP or cooler air intake. Make sure you get what will work, not what "Jimmy" said will be "cool dude". My mistake by doing this cost me an additional 10 grand to do it right, and I used as many of the parts I could salvage. That was the crank, turned 0.010, the Edelbrock high flow heads, the pistons and rods, intake and dual 500 cfm Edelbrock quads. I had to get an entire new 350 block as the old one that was magnifiluxed showed three major cracks in the block. So do your homework, write out a plan, get it checked over by a pro, and if you build it, do it right and enjoy. I have built engines before, but I spent the extra money to have a pro race car engine builder do it right. The motor is strong, and puts out 1.5 HP per CI. I also did a 400 crank and bored it 0.0040. I used long ceramic headers from Hooker that was not that expensive. From scratch, you will spend around $8 grand to $12 grand depending on your toys. If you can, I might suggest looking at EFI set ups. There are a lot of good ones from the factory, to great aftermarket ones that can be set up to marry with what you have inside the engine. Good luck and have fun.

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