Use Rev Limiter or Let Carbs Limit Revs?
08-04-2011, 03:59 PM
#11
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So when you open the throttle all the way in neutral, it will only hit 6100?
Have you tried them under load? The carb calculations are correct for that size engine, but 750cfm should give you enough Carb to make horsepower at 5800, not choke the engine off.
If they will only free rev to 6100 you either have an intake restriction, a rev limiter already installed, or a major tuning problem. Are you sure your throttle plates are opening all the way?
Have you tried them under load? The carb calculations are correct for that size engine, but 750cfm should give you enough Carb to make horsepower at 5800, not choke the engine off.
If they will only free rev to 6100 you either have an intake restriction, a rev limiter already installed, or a major tuning problem. Are you sure your throttle plates are opening all the way?
08-04-2011, 04:04 PM
#12
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Made a quick phone call to Performance Distributors and verified that I don't have a built in rev limiter. I told them I was having troble setting timing on my port engine, but the starboard runs good. PD told me NOT to use a dial back gun. They think I just got lucky setting the timing some what on the starboard. I'm going to try and find a timing tape in the morning and just put my gun on 0*. Intake is an Edlebrock RPM Air Gap. All that said, you think maybe tuning with an emphasis on timing not correct?
Keep us posted.
08-05-2011, 01:46 AM
#13
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A 750 cfm carb will not come close to feeding a 454 at 6100rpms. Its even on the smaller side for 5500rpms.
Set the base timing at idle to 8-10* using the timing tab on the engine.
Set the base timing at idle to 8-10* using the timing tab on the engine.
Last edited by Griff; 08-05-2011 at 01:48 AM.
08-05-2011, 07:03 AM
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I'm going to try setting base timing this morning as suggested. On carbs, should I plan to up size or see how it does? I got the engines designed for 56-5800 rpm. At this point of the build carbs are cheap. 800 cfm or 850 cfm? Any particular brand?
08-05-2011, 09:33 AM
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bob told me a 750 would be nowhere near enough carb for my 454 that he designed the cam for. he told me to drop a 850 holley on mine, i was leaning 800, he said 850, guess who won!!!
what intake are you running and how big of a cam???
did you dyno this motor?
08-05-2011, 09:41 AM
#17
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I would go 850. Thats what I used on my 468 @ 6100 and what I use on my current 425HP 454's. Lot's of car guys will tell you to "throw a smaller carb on it" that doesn't work as well on a heavy breathing marine engine.
08-05-2011, 10:15 AM
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I did call Bob about carb size before buying ignitions. He told me I might need to go up from my 750 carb, but to only change one thing at a time on the engines. We decided to change the ignition system first to get over the stock 5100 rpm rev limiter. Intakes are Edelbrock RPM Air Gap. I got all the timing set correctly this morning. How do I tell if i don't have enough CFM while on the water? or am i just going to have to try an 850 CFM and "feel seat of the pants difference"? I will also call Bob now that i have new ignitions worked out. Thanks for opinions, Brian
Last edited by pitts1313; 08-05-2011 at 03:54 PM.
08-05-2011, 03:17 PM
#20
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Free revving to 6100 in neutral is a good way to blow up an engine. It won't tell you anything useful about your engine, so why do it? Maybe the valve float is getting so bad, the engine won't rev higher. Good way to break or bend something in the valvetrain.
