Mercruiser 454/420 exhaust risers
#1
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Mercruiser 454/420 exhaust risers
Anyone have any knowledge regarding which height exhaust riser works on the mercruiser 454/420's using EMI exhaust manifolds ? They have a standard and 3" higher riser. The standard states not to be used on engines with aftermarket camshafts. These engines have the mercruiser supplied camshafts.
My question centers around reversion and also hatch clearance.
thanks, ed
My question centers around reversion and also hatch clearance.
thanks, ed
Last edited by Interceptor; 10-27-2017 at 10:29 AM.
#2
Charter Member # 55
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The 454/420's were mated to TRS drives. Is that what you have??
Reversion is more about the downward angle and length of riser. TRS risers are longer and water mixes farther down.
I ran standard long IMCO risers with a cam slightly more aggressive than the 420 cam and didn't have any issues
Reversion is more about the downward angle and length of riser. TRS risers are longer and water mixes farther down.
I ran standard long IMCO risers with a cam slightly more aggressive than the 420 cam and didn't have any issues
#3
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Standard install measurements
#4
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Thread Starter
The 454/420's were mated to TRS drives. Is that what you have??
Reversion is more about the downward angle and length of riser. TRS risers are longer and water mixes farther down.
I ran standard long IMCO risers with a cam slightly more aggressive than the 420 cam and didn't have any issues
Reversion is more about the downward angle and length of riser. TRS risers are longer and water mixes farther down.
I ran standard long IMCO risers with a cam slightly more aggressive than the 420 cam and didn't have any issues
This is in a Bravo application with silent choice.
Last edited by Interceptor; 10-26-2017 at 08:55 AM.
#5
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My 502 (415hp) was using EMI's with silent choice and I didn't quite have 13 inches up from the water with no issues. After rebuild I removed the standard risers and installed the 3 inch higher because of more hp. Still have the regular ones
EMI Thunder Exhaust System-BB Chevy With SS Silent Choice Risers Colored Finish
EMI Thunder Exhaust System-BB Chevy With SS Silent Choice Risers Colored Finish
#7
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My 502 (415hp) was using EMI's with silent choice and I didn't quite have 13 inches up from the water with no issues. After rebuild I removed the standard risers and installed the 3 inch higher because of more hp. Still have the regular ones
EMI Thunder Exhaust System-BB Chevy With SS Silent Choice Risers Colored Finish
EMI Thunder Exhaust System-BB Chevy With SS Silent Choice Risers Colored Finish
#8
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Thread Starter
So I'm still trying to understand. Has anyone run a 454/420 or engine with a similar cam (assuming the cam is the issue) using a GIL, EMI type manifold and standard riser and silent choice system and Bravo outdrive ? and did you have reversion ?
ed
ed
#9
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that 420 cam is pretty much extinct. flat tappet. a lot of duration. found old thread, so old dennis moore weighed in on it. but you should upgrade those cams instead of trying to build around them.
#10
Charter Member # 55
Charter Member
None of the parts diagrams show a short riser/tail available with the 525SC.
Personally, I wouldn't chance it and I'd run longer risers with good mufflers.