I have a set of 177 blowers with very low hours. They were a set of take off from 525 SC's. I would like to build a set of engines for spares. I know Merc sets this reliable package up with 7.5 to 1 comp. What would be the most comp. I should set these builds up with assuming 5 pds of boost.

Thanks,
John

i would go with a flat top piston that way your not over heating the blower with a ton of boost.,make sure you use good rods tho..

flat tops with 119 cc chambers would be around 8.75 to 1 plus or minus given the variables.

I'm running SRP flat tops in my 525SC (468cid), 5psi boost with stock heads. My carb HP500 is a dog in comparison.

The merc 525SC's were 7.5:1. I believe the old Hawk 525SC's were 8.5:1. Merc used a Dominator, hawk used a 4150 style 800CFM i believe. The Hawk versions were good engines and made a little more power.

I am around 8.5, dart aluminum heads, 177 blower, roller cam, 1025 barry grant carb. Stellings headers. They run very well, and pushed my 402 Formula to 70-72mph.

SRP's catalog says 8.4 to 1 with flat tops with a zero deck hgt. Make sure you get your blocks decked or the CR will only be about 8 to 1.

I had a pair of Hawks, Thunder is correct on the higher 8.5:1 CR. They did limit timing on those motors to about 28 degrees, if I remember correctly. The carbs were reworked to flow over 900 cfm. Great motors, I upped the blower speed to give 7psi, pushed my old cat to 109mph.

I wonder how much power this would make with the higher comp?

I recall back when MY Dad and I both had 1993 Challengers with twins. He had stock 525 SC's with 1.36 drives and I had built 454's making 485 HP on the dyno with headers etc. and I had 1.50 drives. We ran neck and neck. I know the 1.36 drives may have robbed a little power however I still believe the power was over rated at least at the time on the 525 SC's. My builds where relatively mildly ported Dart ovals, 502/465HP cams, dual plane intakes, Holley 800 cfm carb and lightening headers. The only real difference between the two boats was he never skipped the opportunity to get fuel when having the chance and the much greater up front cost. Any comments on this is welcome. I think back now though and we should have tweaked his big carbs and bumped the boost. Those blowers do sound sweet...

"Those blowers do sound sweet... "

To me they sound like they are going to self-destruct at any moment, however, it does not influence my desire not to have the stick all the way forward when possible.

If I was building it and it had cast iron heads, I would shoot for about 8.5:1. If it has alum. heads, then I would shoot for about 9:1. The higher static compression will let you run less boost so as to not overwork that little blower and tear it up. I would look for about 5-6 psi with either setup. With that blower turning any harder, you will just start to make heat, especially without an intercooler. If you have an intercooler, then you should be able to get away with another 1-2 psi boost. Hope this helps.
Eddie