ohmthis

Hey guys,
I'm trying to do some homework before purchasing parts. I need to know what the CR is for a stock Mercruiser 260? Would the CR be high (like 9.5-1 or more) just by swapping out the stock heads for a set of Vortec (64 cc Combustion chambers)? The cam I am looking at has a lift of .477, it is a Comp Cams marine cam. See any problems with using this cam with the heads? Any feed back would be very appreciated. Thanks!
Anthony

ohmthis

Ok, I did some homework by using the search feature here. From what I have seen My CR will be somewhere in the 10-1 to 9.5-1 range. Which is more than I am willing to run on 89 octane. I have an 86 boat so I'm assuming it has flat top pistons. I am thinking of scraping the whole vortec thing until I can get the motor out and change the bottom end. So now I may need a kick in the ass and just make a decision and get on with it. I'm going to be using the Comp Cams 262 cam and I have a performer intake and carb. I will be installing thru hull exhaust in the spring. Can I still reach 300 or more HP with this combo? Thanks for any advice I can get!
Anthony

ohmthis

I was hoping to get some feedback here!
Anthony

blkhorse

iTrader: (1)

I installed a set of vortec heads on a 355ci and am running 9.5 to 1(new pistons),performer intake,big block quadrajet,comp xm270 cam,thru hull exhaust in a baja 220 sport on 89 octane with no problems.I get 61.2gps@4800rpm so I feel I get over 300hp,but have not been dyno'd.I have even ran 87 octane on an emerg. and did not get any det. or ping,athough I had a smaller prop and the engine rpm's came up rather fast and easy and never felt like it was under a lot of load

ohmthis

Thanks Blkhorse,
I have a few questions if you don't mind answering. What year engine was it and did it have the flat top pistons previously stated? What size head gasket did you use? When you said 355 I'm assuming you rebuilt the engine. Did you size the pistons for the vortec heads. Thanks!
Anthony

David Stotz

ohmthis, I have some experience with the kind of changes you are talking about to SBC motors. However I really don't like to type. Call me at 716-583-7833 and I will try to answer some of your questions
Dave

cuda

355 is a .30 over 350.

blkhorse

iTrader: (1)

it was an 1989 mec 270.the pistons were flattop,same as stock.(if I remember correctly with the stock pistons and 64cc heads they were also 9.5 to 1).you can't go wrong upgrading to vortec heads,just keep valve lift below .470 or have guides cut down

John_S

You may want to read this current thread on BOC: Vortec Heads We got into allot of discussion on actual vs advertised compression ratio of some pre-gen+ and gen+ Merc engines.