SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: ralph on September 06, 2011, 07:40:59 AM
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So how important are good heads on a blower motor? Without any experience to fall back on, I've been playing on Desktop Dyno (I know, I know). I've been swapping heads on a virtual 468 Chevy big block, with a Crane 302/310 duration, .621/.632 lift hydraulic roller cam, part#HR240. How about an 80hp difference at 5000rpm, and 176hp at 6000, as the poorer heads start to fall off. Is it really that bad? From 728 to 552 hp, by switching from AFR2000-315 CNC heads to Edelbrock Marine #61559. About a $2000 cost difference in the heads, too.
Ralph
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What motor parts do you have or working with? what program are you running? I just downloaded Dyno2000 and put in some generic info about my motor and came up with 700 HP with 990's.
Anybody wanna buy this boat? V
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So how important are good heads on a blower motor? Without any experience to fall back on, I've been playing on Desktop Dyno (I know, I know). I've been swapping heads on a virtual 468 Chevy big block, with a Crane 302/310 duration, .621/.632 lift hydraulic roller cam, part#HR240. How about an 80hp difference at 5000rpm, and 176hp at 6000, as the poorer heads start to fall off. Is it really that bad? From 728 to 552 hp, by switching from AFR2000-315 CNC heads to Edelbrock Marine #61559. About a $2000 cost difference in the heads, too.
Ralph
Without having all the information on your combination, including boost, it's difficult to know which of the numbers is more realisitic. 550 sounds low for a blown engine, I put together a pump gas(9.6-1) 468 that made 617 on the dyno with 990's. I didn't take the time to look up the @.050" spec on your cam, or lobe center either.
I don't spend the time messing with the desktop dyno now days, but have seen it fairly close on occasion, it depends how detailed and correct you get the details.
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It's desktop dyno 2000, but the question was more general than specific to my comination. How important are good heads on a blower motor? I was surprised at the effect better heads had on the virtual engine, and wondered if the same gains applied in the real world. So can I cheap out and go with the Edelbrocks, or am I really losing 150 hp by not buying MUCH more expensive heads? It's my 6/71 blown, .9 underdriven, lets sa y 6-7lbs boosted 468 inch, 8.5 to 1 chevy motor, currently being rebuilt. I need a new cam that I'd like to get from Barry (Obnoxiuos racing Engines), and new heads.
Ralph
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I can't speak for the DD numbers specifically (and why would anyone? :P ) but heads do indeed make a difference on a blown engine.
Just because the engine utilizes forced induction does not automatically mean that poor flowing heads are no longer poor flowing. A better flowing head will fill the cylinders better, and in fact might do so while showing less boost on the boost gauge (since the manifold/plenum is not as backed-up with the charge).
But when it comes to blown engines, there is a LOT more to consider in a cylinder head that those silly flow numbers. To this day I am perplexed at how people place so much weight in flow numbers, asking "what do they flow?" when in fact there are so many much more important factors to consider when evaluating cylinder head design for a given application. I have known of heads with lower flow numbers generating more horsepower on a shortblock than a pair of heads with higher flow numbers....thanks to the overall design of the cylinder heads with the lower max numbers. Flow schmo. But now I'm off on a tangent, lol.
Back to your question: The more radical you get with a blown engine, the more things need to be considered about a cylinder head design, and to some extent the other factors begin to rise up the ladder relative to the flow number statistics. Things such as spark plug placement, deck thickness, chamber shape, etc. are pretty important and rise in importance as boost and/or power (such as nitro) increases.
So yes, in a blown engine good heads will typically shine over not-as-good heads. That being said, in a mild blower build you might be surprised what you can do with not-as-good heads that have been properly warmed over.
LO
p.s.: this sounds like a job for your Dad's Hemi HEads. 8)
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It's desktop dyno 2000, but the question was more general than specific to my comination. How important are good heads on a blower motor? I was surprised at the effect better heads had on the virtual engine, and wondered if the same gains applied in the real world. So can I cheap out and go with the Edelbrocks, or am I really losing 150 hp by not buying MUCH more expensive heads? It's my 6/71 blown, .9 underdriven, lets sa y 6-7lbs boosted 468 inch, 8.5 to 1 chevy motor, currently being rebuilt. I need a new cam that I'd like to get from Barry (Obnoxiuos racing Engines), and new heads.
Ralph
Did you happen to plug in any larger runner heads than the AFR? Did you have all the flow numbers for both heads? Did you happen to change lobe centers on the cam with both sets of heads?
Maybe the marine Edelbrocks really do choke it down that much,, sure seems to be a huge difference. I was just asking the questions because I didn't think it would be that necessary to use the larger CNC heads on a low boost engine.