Confused about total comp. verses octane :/
#14
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I agree. Low compression and more boost will win the HP war, given the same overall engine setup. And also, dont let anyone tell you ''ahh, it dont matter, on a blower motor''. I can't tell you how many times I've heard this statement. From Cylinder head flow, to exhaust, to cam selections. It does matter.
Keep in mind, boost is a measure of restriction. A well built engine, with good flowing heads, proper cam, good flowing exhaust, good compression, etc, running on 5lbs of boost, will outperform your buddys same sized engine, with $hitty flowing heads, mismatched cam, and crappy exhaust running 8lbs of boost. So, What are we building!????
Properly spec the motor with good parts, and low boost, will live a long time.
Keep in mind, boost is a measure of restriction. A well built engine, with good flowing heads, proper cam, good flowing exhaust, good compression, etc, running on 5lbs of boost, will outperform your buddys same sized engine, with $hitty flowing heads, mismatched cam, and crappy exhaust running 8lbs of boost. So, What are we building!????
Properly spec the motor with good parts, and low boost, will live a long time.
#15
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Thanks again everyone for the advice. Im starting to get a better idea of my build now. But still not completely sure. I've got the zz502 w/ between 9-9.5 comp. (not ideal I know and haven't cc it yet) with the 320 RHS alum. heads. Thinking a 10-71 w/ 2 850 holleys and 6psi boost. I'll run a mix of 110 and 92 octane, since i'm looking at around 13:1 no big deal OR is the 2 psi even gonna be worth it. Haven't looked into cams yet but just ran across a thread talking about "exhaust revirsion" w/ a 502 and EMI manifolds, which is exactly what Im running?! What cam company or builder should I go w/ to pick my cam and talk about this with? And do u think I can pick a cam that will work for this 502 AND the 540 im building that will have all the "right stuff" to replace the 502 later.
AND I previously asked in another thread about using my 355cc pro 1 heads instead of the 320 RHS and was suggested to stay w/ the 320s. U agree? Once again, I won't be puttin alot of hrs nor be running this boat hard until I upgrade from my Bravo1.
AND I previously asked in another thread about using my 355cc pro 1 heads instead of the 320 RHS and was suggested to stay w/ the 320s. U agree? Once again, I won't be puttin alot of hrs nor be running this boat hard until I upgrade from my Bravo1.
#17
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Im going with the 850's because I already have them and the 10-71 because when I finish the building the 540, the 10-71 will be better suited. Kinda using this 502 as a test to see if I want to stick with this blower thing for my 540 build. I am New to the power adder/ supercharger thing. Im sure Im gonna love it though?!
#18
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Im going with the 850's because I already have them and the 10-71 because when I finish the building the 540, the 10-71 will be better suited. Kinda using this 502 as a test to see if I want to stick with this blower thing for my 540 build. I am New to the power adder/ supercharger thing. Im sure Im gonna love it though?!
Im running 850's on top of a 468 with a 420 B&M blower. Just slightly smaller than a 8-71. Engines made 804HP non intercooled and 6lbs of boost, and run perfect. Fuel Curve is great, not even boost referenced. Idle all day if I have to. Granted, 750's would work just fine for me, but the 850's sure arent hurting a thing.
Pretty much, the theory of too big a carb causing sluggish low end and soggy performance, you can throw out the window. Roots blower like lots of carb. Or let me rephrase that, they DONT like any restriction. Ever notice the twin 1050 Dominators on a merc 900SC? Merc Racing Engineers weren't dummies. A pair of 4150 style 850's might have helped it idle a little better, over the dominators, but i'd be very shocked if they made any more power over the 1050's on that engine. (540 W/10-71 and chiller). Overcarbing ( I mean like a pair of 1150's on your setup), would most likely cause tuning issues, more than anything. Too much carb causes poor signal thru the carbs, and you end up having to run alcohol jets to get a acceptable AFR.
BDS has a calculator for blower carbs. Based on a 509CI, turning 6000RPM, running 8lbs of boost, required CFM is 1364. They dont suggest more than 30% over carb needed on a blower. so 1364CFM, +30%, 1774CFM.
You see guys all the time with big roots blower stuff. They Gut their flame arrestors, put big old Pro Stock scoops on, trying to get more air into those motors. But then they want to run small carbs.
As for the 320cc RHS heads, vs the big Darts, tough call. I don't know much about the RHS Heads. While the 320CC port size works nicely for what you're doing, you need to think about flow also. I'd Talk to someone like JIMV here on the boards. If you have both sets of heads available to you, you might be able to weld up the floors on the Darts, to get the port velocity up, and smoke the RHS heads in performance. I'd hate to tell you to run the RHS heads based on the intake runner size alone. Those Darts move some air.
Figure out which heads you're gonna use on your build, and then have Bob Madera (RMBUILDER) here grind a cam for what you plan to do. If you take your time and do a nice build, I think you'll be pleasantly surprised, and make a lot of power. You may not even feel the need to spend the extra few grand to install a stroker crank and rods. The extra 30-40ci you gain, can easily be outdone with a properly set up 509. Then you can use that cash to beef up your drive.