I think you are going to find you are too low on compression. The std merc/gm long blocks are 8.75 to 1 with a DOMED piston and 118 cc chambers. An option might be to find some heads with smaller chambers. Lower compression in n/a engines really hurts performance. If you go with what you have, that cam is plenty big.

i agree with wetbar. some 113 cc alum heads would be the way to go. not chineseium though...

113cc heads aren't going to help much if the pistons are .025 in the hole. Discuss options with your shop to get the compression up to at least 9:1 if not there already.

You mentioned 509cid.

Are these the pistons ?


#257984
cid 509
Bore 4.500
Stroke 4.000
Rod 6.135
Deck Height 9.780
Compression Height 1.645
110cc 9.5
118cc 9.0
124cc 8.6
Dome Volume -3.0cc
Grams 690

http://www.jepistons.com/Catalogs/Au.../flat_top.aspx

with that piston&114 cc chamber you are slightly over 9 to 1 and with your existing cam i would expect 500 hp.i 100% agree that you should call bob m before proceding with this build.i have been selecting camshafts for my engine building needs for years but since i started working with bob i realize that i will make more power with his knoledge behind me.bob is a great guy and very easy to talk to.

Thats them

My build sheet says 116 cc chambers so still at least 9.0/1 .I did send Bob an email to get his opinion

With that small of a motor I would want a 112 lsa but as stated b4 you just can't beat a custom billet cam and distributor from Bob for $350. There is a big shot out there with a carb shop that builds overpriced carbs with bad fuel curves and has magical cam grinds that are ground when the stars are perfectly aligned. He charges $500 for his cams that can be bought from Erson with the identical specs for $250. Bobs cams might not be ground when the stars are in perfect alignment but you would think they were after you drop the motor in the boat and take it for a sea trial...

741

as mentioned,thats if your deck height match's the piston's spec's of (Deck Height 9.780 )...

BTW call bob,,his knowledge will smoke your mind,,