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Too much exhaust duration

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Old 10-06-2024 | 11:01 PM
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Default Too much exhaust duration

I’m building a 454 with l29 heads,air gap intake and 496ho exhaust manifolds. Should be 9.5 compression

the cam I’m looking at is 539/539 lift 228/238 @.050 on a 114 LC

In an auto application I now it would run well but my concern is will the manifolds flow enough. Am I look at to much exhaust duration for my combo?
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Old 10-07-2024 | 07:34 PM
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kieth eikhart used a duration like that on his 675 + 725hp motors
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Old 10-08-2024 | 12:13 PM
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well that answers that question thank you
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Old 10-08-2024 | 07:20 PM
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just my opinion but I would bring the compression down a little. I try to stay at 9.2 or less with iron heads as the fuel you get is not always what you want and that is a bit too close to the edge of detonation for me. I had one customer not long ago that was 9.2 and told him to always run at least 91 octane, well he got 89 on a poker run and detonated a hole in one piston. in a boat always error on the side of caution. thats just me any how.
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Old 10-08-2024 | 09:57 PM
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thank you
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Old 10-09-2024 | 03:36 AM
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Many used cans like that. No biggie.

Flat tappet ? Be careful with wear….
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Old 11-07-2024 | 02:18 AM
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Originally Posted by compedgemarine
just my opinion but I would bring the compression down a little. I try to stay at 9.2 or less with iron heads as the fuel you get is not always what you want and that is a bit too close to the edge of detonation for me. I had one customer not long ago that was 9.2 and told him to always run at least 91 octane, well he got 89 on a poker run and detonated a hole in one piston. in a boat always error on the side of caution. thats just me any how.
That's a very good point and a great reminder for those of us running cast iron heads ---- Thanks!!! 👍 🇺🇸⚔️
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Old 11-09-2024 | 01:01 AM
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Originally Posted by compedgemarine
just my opinion but I would bring the compression down a little. I try to stay at 9.2 or less with iron heads as the fuel you get is not always what you want and that is a bit too close to the edge of detonation for me. I had one customer not long ago that was 9.2 and told him to always run at least 91 octane, well he got 89 on a poker run and detonated a hole in one piston. in a boat always error on the side of caution. thats just me any how.
Always better to have reasonable compression, vs always having to retard ignition IOT avoid detonation. Retarded ign timing will heat up the exh valves.
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