ls1 lm7 AFR "mongoose" heads GEN III

[zgeezer]

I have a little over 3K to upgrade my 2002 LM7 (5.3L) GEN III truck engine that will be in my Z in another month or so. The engine has only 20,000 miles, so I expect everything to be in excellent shape. It is rated at 285 hp, uses the smaller intake valves (around 1.9") than the Ls1 and has smaller combustion chambers than the LS1 (around 62cc as against 66cc or so). This drops the C/R down into 9 something from the 10 plus of the LS1

 

I have a chance to buy the new 205 AFR heads and a GMPP HOT cam and springs for the LS1 at a reasonable price. The AFR heads are CNC ported with 2.02 intake valves and are real works of art, but they also have 66cc combustion chambers and I think the loss the compression may offset any other gains they might offer over the stock LM7 heads. One of the design parameters for my Z is that it be an honest middle 11 second car that can and will be driven everywhere. I expected to do this with a mild cam and a supercharger. I would sure appreciate some input, because if these heads and cam work, it will save me a bundle on hood modifications and allow me to look just a little more stock.

 

g

[DaleMX]

Well for starters I believe the intake on the 5.3 is too tall for the hood. Lower CC's raise the CR also. I have a set of ported 5.3 heads for my LS1 and they raise the CR to around 10.8:1. I would worry about the valve size being too big for the bore and getting shrouded. It may not be a problem but I think that Tony Mamo at AFR can answer all your questions. If you do a search for AFR and Tony over on LS1Tech.com you can get your questions answered.

 

Here's a thread he's in http://www.ls1tech.com/forums/showthread.php?t=313038

[zgeezer]

Tony

 

Thanks for the link. The 4.8 truck bores are too small and will not clear the valves or so I've been told by a shop selling AFR, but the same source "thinks" the 5.3 is ok. I will contact AFR.

 

The truck intake is too tall, but that can be cured by either swapping over to an LS1 intake.... and that is not entirely w/o problems of its own or pretending I own a '73 240 Z with an overheating problem and cut a BFH in the hood and cover it with something resembling the hood vent Datsun sold over the counter in '73 or so. It looks like a scoop, but vents to each side.

 

g