I called my local Gm dealer yesterday, and priced the lt4 hotcam kit, and he told me that he has installed this kit on two cars, and both of lost compression badly. Is it a problem with the cam, or did those 2 cars just have bad engines??

 

did the cars run worse? mabey the cars had less compression because the hotcam is bigger than stock and will cause less cranking compression? mabey the guy can't set up valve train's? my hotcam 383 works great i think your guy doesnt know what he is talking about!

 

A cam install will have nothing to do with compression, unless he's talking about the LT4 conversion. Even then, you'd GAIN compression (.3), not lose it.

Sounds like he's talking out his ***, personally. Why not order it from Jason Cromer?

 

What he said! The cam has nothing to do with compression. The only this is after the hotcam kit install..or any cam for that matter, you probably want to get tunning done because on the stock pcm the car will run very rich, idle poorly, and probably wont but much faster if at all.

Aaron

 

How much is the Hotcam kit from Jason Cromer?

Thanks guys, i think i'm gonna end up getting it this week. As far as programming the PCM, should I get a hypertech, or is there a better option, and what is the cost of the other options.

 

Under $500.

A Hypertech won't cut it on a cammed car. You will need programming by PCMforless, madwolf, Ed Wright, etc. A good tune can cost you anywhere from $100 to $300. A brief search of those names will net you tons of information. Good luck!

 

Sounds like the cam timing might be off. Or, the valves are adjusted too tightly. He should understand that valve timing, overlap, and duration will affect the dynamic compression ratio.

 

Installing a hot cam kit or any other cam for that matter will not change the "static" compression ratio. This is the measure of total cylinder volume with piston at bottom dead center vs total cylinder volume with the piston at top dead center. Static compression is not measured with a compression gage, it is a calculation of measurements.

Cranking compression (or Dynamic Compression) is largly effected by when the intake valve closes (usually after bottom dead center) And this changes with different Cams. The Cylinder (compressable) volume then changes to the point of when the intake valve closes vs the cylinder volume at TDC (top dead cylinder) so you would think that the Dynamic compression would always be lower than Static Compression. And this is what is being measured with a compression gage and cranking the engine over.

All that said...I am going to use some random numbers...not actual as I don't have these in front of me now....

a stock LT1 has a Cranking compression of say...190 psi and it's intake valve closes at say..20 degrees after bottom dead center.
Take the same engine and put in a GM 847 cam with the intake valve closing later say somewhere around 40 degrees and your Cranking compression will actualy be lower at say...175 psI

These are not actual numbers but can give you a reason why the the compression ratio may be lower after a cam install.

Someone may be able to explain it better, you can do a google search looking for "dynamic compression and there are alot of articles out there.

HTH
Keith

 

Thanks, exactly my point. Well said. The dynamic compression ratio is what is measured on a compression test.

If there is abnormality beyond that, then inspect cam timing and valve adjustments.

 

Thanks for all the feedback guys.