niteridder64

Hey guys, looking for any advice on rebuilding my carbed 502 after detonation took out a couple of the pistons. Out of a 1996 Powerquest 27 lazer. This is what is on there now, maybe this set up is wrong but I want to do it right. Not looking to race but would like the max hp and still run 87 w/ some mild upgrades, best bang for the buck.
Holley 750 double pumper 4150 is this too small?
Not sure of the intake but I have added pics.
EQ stock heads that I bought 3 years ago new but will need work now.
I am at .030 over now, not sure of the cond of the cyl as I just dropped it off today and he only pulled the heads.
I think I have a 502/502 roller cam and believe specs are lift int. .527/ Ex .544 dur @.50 int.224/ ex 234 110 lsa Is this cam a good choice, I am running CMI headers, see pics.
DUI dist w/ direct battery thru a relay to power it
stock circulator pump, raw water cooling
Turning a 23 " 3 blade was maxing at 60 mph/gps 5000rpm's off gauge.
When the job is complete I will dyno to tune, out of the boat. I am hoping for 65 mph. My 2 big questions are why did it detonate and seize up and what do I need to change in order to have a reliable powerplant. I was looking at carbs, am I too small w/ the 750 and why is this carb so much cheaper than a 850 holley. ebay # 202279097010 It says marine but I noticed the vent pipes are not bent. Running a holley elec fuel pump thru a relay and micron filter after pump, no prob w/ flow.
Again any advice would be greatly appreciated, thanks.

niteridder64

If I have to buy a bigger carb I may as well buy one of these-Holley Sniper EFI Self-Tuning Fuel Injection Systems 550-510- anyone have experience w/ these? Also still looking for an opinion on cam selection 502 .060 over.

Mr Maine

How was the fuel pressure with that setup? Is the anti siphon valve still in the tank?
Those pumps dont pull fuel very well, i wonder if it starved for fuel wide open and did damage? The 750 will work but an 800-850 would be better.

niteridder64

I can't remember what press I was a t at full throttle, there is no gauge on it now but the pump if I remember had plenty of gpm. I do not have an anti siphon vlv. The pump is mounted just behind the tank about mid level.If I rum the efi and have a return line, can I return to the filter element housing, would be very easy. But does that cause the fuel to get hot running around in a circle thru the hp pump?

liberator221

Those headers are your problem. I can get rid of them for you. JK. No help just like your boat. I have a 98 270, great boats. Never seen the color scheme of yours. Looks good.

niteridder64

Thanks

niteridder64

I think I will be going w/ a hp 500 cam and have 3 questions. I will be installing a Holley efi sniper that will not control timing, would I choose the efi cam or the carbed cam and is that the 731 and 741, which one is which. My heads are the stock Eng Quest heads, I believe I would have to change all the valve springs correct? Lastly, does any one know where I can get a cam and springs.