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Hi folks. I seem to be a little perplexed about something and I hope you all can help me out.
I have a MerCruiser Gen IV 454 with a Volvo 280T outdrive. You can see the current build sheet here. http://www.supernova19.com/motor_build_ii_at_supernova19_com.htm If you look up a little on the page you will also see what I changed it from.
I say “current” because I have made many changes over the last year.
You see I have taken a junkyard motor and not wanting to do to much to it the first year I rebuilt it pretty much stock except I built it knowing I was going to do some upgrades later on. So when the motor was done last year it should have been around 330hp.
This spring I did the whole top end over again. Heads, cam, intake, you name it. Now it should be somewhere around 420hp.
Which brings me to my question. No matter what I do I can not get the motor to spin over 4900rpm’s. I mean I have done upgrades that should have added power but…. I know what you are going to say next. “It must be the prop.” I am comparing before and after the upgrades to the same props I have used before and have many notes on. And yes I have tried a couple props with the same result.
Leaving that aside for a minute I have to add this.
I have tried many, many props on this set up. Volvo aluminum 15X19L, 14X23L, 16X24L. Ellison racing prop that was a 14X22L and then reworked to a 14X24L with some cupping. A Johnson brass 15X19 cupped and a Stainless Steel 14X24L. They all have a WOT of 4900rpm’s with one exception.
The Volvo 15X19 did pop off the rev limiter once or twice. Again I know some of you are going to say, “What rev limiter?” Well even though the sticker outside of the little black box says “Thunderbolt IV” I have it on film coming out of wide waves at WOT. The motor never rev’ed over 5 grand when it should have jumped at least a couple hundred rpm’s.
What am I doing wrong?
I have a MerCruiser Gen IV 454 with a Volvo 280T outdrive. You can see the current build sheet here. http://www.supernova19.com/motor_build_ii_at_supernova19_com.htm If you look up a little on the page you will also see what I changed it from.
I say “current” because I have made many changes over the last year.
You see I have taken a junkyard motor and not wanting to do to much to it the first year I rebuilt it pretty much stock except I built it knowing I was going to do some upgrades later on. So when the motor was done last year it should have been around 330hp.
This spring I did the whole top end over again. Heads, cam, intake, you name it. Now it should be somewhere around 420hp.
Which brings me to my question. No matter what I do I can not get the motor to spin over 4900rpm’s. I mean I have done upgrades that should have added power but…. I know what you are going to say next. “It must be the prop.” I am comparing before and after the upgrades to the same props I have used before and have many notes on. And yes I have tried a couple props with the same result.
Leaving that aside for a minute I have to add this.
I have tried many, many props on this set up. Volvo aluminum 15X19L, 14X23L, 16X24L. Ellison racing prop that was a 14X22L and then reworked to a 14X24L with some cupping. A Johnson brass 15X19 cupped and a Stainless Steel 14X24L. They all have a WOT of 4900rpm’s with one exception.
The Volvo 15X19 did pop off the rev limiter once or twice. Again I know some of you are going to say, “What rev limiter?” Well even though the sticker outside of the little black box says “Thunderbolt IV” I have it on film coming out of wide waves at WOT. The motor never rev’ed over 5 grand when it should have jumped at least a couple hundred rpm’s.
What am I doing wrong?
