Some Saturday Motor Fun
#21
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From: yorkville,il
#22
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Joined: Feb 2009
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From: NW Michigan
Not a huge differenc btwn the two. Seems like merc opened up their performance engines to 2.25 though but didn't make a huge flow difference. They start to fall off some at .600 but really noticeable at .650. So personally I think his cam lift is right in there but certainly wouldn't have gone anymore. I would imagine heads are close to stock or OP would have mentioned. That would certainly change things up a bit 15-20 hp?
#24
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Joined: Jul 2004
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From: chicago
Not a huge differenc btwn the two. Seems like merc opened up their performance engines to 2.25 though but didn't make a huge flow difference. They start to fall off some at .600 but really noticeable at .650. So personally I think his cam lift is right in there but certainly wouldn't have gone anymore. I would imagine heads are close to stock or OP would have mentioned. That would certainly change things up a bit 15-20 hp?
What matters, is what the head flows, at the valves "curtain area" . If he has a 2.19, that curtain area, where you really want the head to flow well, would be at .548 lift. If a 2.25 valve is used, than it be .563 lift. 2.30, then it be .575 lift.
At peak lift of .630, the valve is only there for a C hair of time. Its pretty irrelevant. Where the valve spends more time, esp at peak piston demand, is what counts. The valve spends way more time between .200 and .600, than it does at .630.
As I have said before, the camshaft timing, and valve diameter, are what control velocity. A small port with big valve, can have worse low rpm power, than a larger port, with smaller valve.
The valve diamter must be relative to the CSA. This is why, AFR supplies a 2.19 valve, in their 265 ovals, and a 2.3 valve, in their 325/335 heads. If you stick a 2.300 valve in the AFR 265 head, you can kiss some low speed torque away.
#25
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From: NW Michigan
#27
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From: NW Michigan
Maximum valve lift, isn't really limited to where the head stops flowing more cfm, at peak lift.
What matters, is what the head flows, at the valves "curtain area" . If he has a 2.19, that curtain area, where you really want the head to flow well, would be at .548 lift. If a 2.25 valve is used, than it be .563 lift. 2.30, then it be .575 lift.
At peak lift of .630, the valve is only there for a C hair of time. Its pretty irrelevant. Where the valve spends more time, esp at peak piston demand, is what counts. The valve spends way more time between .200 and .600, than it does at .630.
As I have said before, the camshaft timing, and valve diameter, are what control velocity. A small port with big valve, can have worse low rpm power, than a larger port, with smaller valve.
The valve diamter must be relative to the CSA. This is why, AFR supplies a 2.19 valve, in their 265 ovals, and a 2.3 valve, in their 325/335 heads. If you stick a 2.300 valve in the AFR 265 head, you can kiss some low speed torque away.
What matters, is what the head flows, at the valves "curtain area" . If he has a 2.19, that curtain area, where you really want the head to flow well, would be at .548 lift. If a 2.25 valve is used, than it be .563 lift. 2.30, then it be .575 lift.
At peak lift of .630, the valve is only there for a C hair of time. Its pretty irrelevant. Where the valve spends more time, esp at peak piston demand, is what counts. The valve spends way more time between .200 and .600, than it does at .630.
As I have said before, the camshaft timing, and valve diameter, are what control velocity. A small port with big valve, can have worse low rpm power, than a larger port, with smaller valve.
The valve diamter must be relative to the CSA. This is why, AFR supplies a 2.19 valve, in their 265 ovals, and a 2.3 valve, in their 325/335 heads. If you stick a 2.300 valve in the AFR 265 head, you can kiss some low speed torque away.
#28
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Joined: Jul 2004
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From: chicago
#29
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From: chicago
I can reduce valve size in a bbc build in the dyno simulator, and gain low end torque, at the expense of upper rpm power. Seems to make sense, as thats why Gm used small valves in their tow engines. Whoever wrote the simulation software, must also be aware of the net result of valve diamter and velocity changes
#30
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Joined: Aug 2016
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From: Reno, NV
My machinist is a great guy and worked for Larry at EPD heads until it closed. When he does my heads he really does not tell me much besides "I cleaned them up" LOL. I really do not think he did much besides port matching and he also said he cleaned up the bowls some for whatever that is worth. I also saw on another post someone was talking exhaust for a 540. I have the IMCO Thumper on my setup, and yes will have dyno headers. I am hoping these will be fine for some family boating. This was built for fun and to last. This is my first boat of any kind I have owned and I can tell I am in trouble as I am looking towards the next boat already.


