phragle

iTrader: (3)

Not reinventing the wheel,just making a basic 525 sc. A lot of things have improved since it was designed, The 731 cam is supposed to be a nice improvement and I have one of those. Using a merc mag bottom end freshened up. A lot of posts and discussion has stated the original compression ratio was exceedingly low and that something around 8.5;1 would work a lot better so I am aiming in that direction. (making about 5 psi boost on top of that)

Now the heads. I have some mag heads, but head tech has changed dramatically. With heads like EQ cast irons and Promaxx aluminum not being a whole lot more that completely going thru my old heads.

What are the pros and cons of each? Assuming that properly sized either would outperform oem.....

mike tkach

iTrader: (3)

your thread title confused me as i have never seen a steel head then i figured you might have meant aluminum.anyway,i am one of the dumb guys who still feels that their are advantages to using an aluminum head other than the weight saving.i do believe that the eq head is a lot of bang for the buck espically for the budget builds.i am building an engine right now that is going to have a set of them.i know nothing about the promaxx but we have a guinnie pig[getrdunn] experimenting with some so we will get some good information about them soon,the are looking like they may be ok but time will tell.imo a crane 731 cam,8.5-1 c/r eq heads would be a good combination for a 177 blown deal.i will be watching your build and i hope it makes good power.

phragle

iTrader: (3)

Fixed, thanks Mike...

vintage chromoly

iTrader: (3)

Getting closer on the title. If you give it just one more shot, I bet you nail it.

tommymonza

Isn't that 177 a tiny blower that needs to be Overdriven?

getrdunn

iTrader: (7)

How much power you looking to achieve? 731 is a good cam for that 177 combo but are you going to run intercooler? I see there was a couple for sale on swap recently. That actually raises a question though that I personally have no experience with. But just shedding some light on the subject. Intercoolers are used to lower air temps/charge correct. So in a sense would aluminum heads help keep the temps down as well. Another scenario what if you have both aluminum heads and intercooler. I'm just pondering this but it does make sense if you just think about a little. I know MT did a bunch of temp testing so and recently post but I'm not so sure about intercooler with aluminum heads. Again what's mercury doing on their sc builds. Their R&D has to be astronomical.

phragle

iTrader: (3)

No intercooler. Powerwise, Somewhere slightly north of 550.

From what I understand on what I have read, on the 177 an intercooler adds some restriction, so you need to speed up the blower even more to compensate creating more heat. So my mind sees that as somewhat of a wash. Also by raising the static compression about a point over what merc ran in the 525sc, I can run the same boost and make more power

While we are thinking of such things, the alum head will take a point more of compression from what I am told. Now would alum heads allow me to run run 91 vs 93? I have a 60 gallon tank and would like to be gas dock friendly if possible,

getrdunn

iTrader: (7)

Yes true on intercoolers. Would definitely wanna research what one to get if you did. Your goal of 550 plus will be achieved easily with cam and static comp bump. They run extremely fat also if your running stock 525 sc 1050 carb. You'd have to tune a bone stock 525 sc to come close to actually 525.

mike tkach

iTrader: (3)

the merc 525sc makes 525 at the flywheel according to mercury marine.with a static c/r of 7.5.1they still required premium fuel.imo,with a good tuneup 89 oct would work just fine.i never understood why they wanted premium fuel,maybe old school thinking,maybe to get it past the warranty period.

phragle

iTrader: (3)

DAve said the ones in the Donzi would ping on 89 but only if you really leaned into the boost for a stretch. His opinions on the motors after running them for several trouble free years has been one of the deciding factors going that way. Also why I not trying to get more out of them per say, just updating them with the tech thats avail today. A lot has changed in 15-20 years.