Here's a question for you guys. I had a reagular 300 hp 454 that was in my 242. I put rectangular port heads roller rockers(gold),lifters new howard cam,high rise air gap intake holley 850, you know all the bells and whistled... No headers though. factory corsca exhaust. I was running 58mph with old motor pushing 300hp and running 61.8gps with 425hp. Somthing has got to give, you can't tell me that 125hp only bumps you 3mph, there ar 253 with 496ho mags running 70. Help me out guys....
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lots more power no more speed
- Thread starter disturbed
- Start date
Here's a question for you guys. I had a reagular 300 hp 454 that was in my 242. I put rectangular port heads roller rockers(gold),lifters new howard cam,high rise air gap intake holley 850, you know all the bells and whistled... No headers though. factory corsca exhaust. I was running 58mph with old motor pushing 300hp and running 61.8gps with 425hp. Somthing has got to give, you can't tell me that 125hp only bumps you 3mph, there ar 253 with 496ho mags running 70. Help me out guys....
vinny p.
Active member
The first question I would have to ask is do you know for a fact that you are making 125 more h.p. Was the motor dynoed? There are a lot of claims of how much extra power a particular part will add to you engine, but most are not true. All the components of an engine must match to compliment each other. Including the prop.
Can you post more particulars IE: cam profile, compression, prop #'s, rpm before and after the new power, head flow #'s, here is a big one that alot of guys forget about--the fuel system. Will the fuel system keep up with the demands of the new power. Starting from the tank pick-up to the carb bowls.
Can you post more particulars IE: cam profile, compression, prop #'s, rpm before and after the new power, head flow #'s, here is a big one that alot of guys forget about--the fuel system. Will the fuel system keep up with the demands of the new power. Starting from the tank pick-up to the carb bowls.
Everything was done right. all the way down to the fuel pump (holley 110 gph pump)4600 with rev before repower , took out rev limiter, and hit 5150 with the same prop(22 bravo 1 4 bld)but only gained 3 mph, changed props around many diffrent ones.no more speed. i think i need headers all that power cant go anywhere, the exhaust wont let it breathe. As far as the cam, dont quote me on this277/579lift. maybe not right, but i will tell you it freakin romps!!!! dont know how much torque. but the motor is making a true 425, that is my safe number, i know guys that did the same mods and dynoed higher than that.
vinny p.
Active member
Your numbers work out about right. Assuming that you have a 1.50 gear in the drive, at 5150 rpm spinning a Bravo 1 22" prop @ 10% slip nets you about 60 mph. The question is why can't you spin a bigger prop given your power? I can tell you that I had a stock 454 Magnum MPI, 385 h.p. in a 259 Convincor. I saw about 68 mph on gps spinning a labbed 26" Bravo 1 to 4950 rpm.
I don't see replacing the stock exhaust making a big difference. A stock 502 magnum from Merc makes 415 h.p. at the prop, 445 hp at the crank through stock manifolds. I am not saying that stock Merc manifolds are good, I think they are junk, they leak too easily and can cost you a motor. But, given your power, they flow enough. While you certainly would pick up a few h.p. with the headers, I just don't think that headers alone will answer your problems.
I just built a n.a. 540. It was dynoed at 679 hp and 661 ft lbs torque. I am running Gil WetOffshore manifolds and pipes. While I haven't run the boat with the new power, I am not expecting any exhaust related problems.
What is your fuel pressure at W.O.T.?
I don't see replacing the stock exhaust making a big difference. A stock 502 magnum from Merc makes 415 h.p. at the prop, 445 hp at the crank through stock manifolds. I am not saying that stock Merc manifolds are good, I think they are junk, they leak too easily and can cost you a motor. But, given your power, they flow enough. While you certainly would pick up a few h.p. with the headers, I just don't think that headers alone will answer your problems.
I just built a n.a. 540. It was dynoed at 679 hp and 661 ft lbs torque. I am running Gil WetOffshore manifolds and pipes. While I haven't run the boat with the new power, I am not expecting any exhaust related problems.
What is your fuel pressure at W.O.T.?
Welcome back Disturbed, glad to see you found your way back.
boatn70
Well-known member
what cyl. heads are you running? if stock gm, what is the casting number (to find out flow #s)
find out exactly which cam your running.
your base numbers are accurate, my 242 runs 56-57 with the 4bld hydromotive. im really interested in whats going on here so keep us up to date.
as said before, plug readings and timing can be an issue. i think exhaust couldnt hurt but its an expense, not a little one either!
kevin
find out exactly which cam your running.
your base numbers are accurate, my 242 runs 56-57 with the 4bld hydromotive. im really interested in whats going on here so keep us up to date.
as said before, plug readings and timing can be an issue. i think exhaust couldnt hurt but its an expense, not a little one either!
kevin
DONCONVINCER
Member
Cam overlap and profile ramp design cam make a big difference for the same lift and duration. HP and Torque at a specific RPM can be dramatic depending on the lobe design. Cam timing is also a big deal depending on how advanced or retarded the inital opening is to when max HP and Torque is made is made and where their peaks intersect.
ok guys, all this motor talk has confused the hell outta me. I'm going to list everything that know and maybe this will help us all figure this thing out.lets start with new parts and i will explain about each.
First i got retangular port inkanell heads(didnt dpell that right)then a howard cam ,here are the specs(intake valve lift=.570,exhaust valve lift=.581, lobe center=112+4,intake gross lift at cam=.335, intake degree of duration@.050=.226, exhaust gross lift at cam=.342, exhaust degree of duration@.050=.232), next i put in roller rocker arms(gold)push rods and lifters, then went to a edlebrock high rise air gap intake, topped with a holley 850 double pumper, jet size is 88 front and back. ok now that the motor is out of the way, and oh i think the timing is somthing like 28.
First i got retangular port inkanell heads(didnt dpell that right)then a howard cam ,here are the specs(intake valve lift=.570,exhaust valve lift=.581, lobe center=112+4,intake gross lift at cam=.335, intake degree of duration@.050=.226, exhaust gross lift at cam=.342, exhaust degree of duration@.050=.232), next i put in roller rocker arms(gold)push rods and lifters, then went to a edlebrock high rise air gap intake, topped with a holley 850 double pumper, jet size is 88 front and back. ok now that the motor is out of the way, and oh i think the timing is somthing like 28.
vinny p.
Active member
If you mean that the lobe seperation is 112* and that you have installed the cam @ 4* advanced, this will not help you. The cam would most probably work best at 0* advanced. You don't seem to know exactly where your timing is, if it is @ 28* total, that is not enough. It should be set to 34*, which is still a bit conservative. I assume you mean inconel valves, there is no such beast as an inconel head. When you added the new heads, did you have the chambers and cylinders cc'ed so you definetly know your static compression ratio? Did you go through the short block when you did the mods or did you just do the upper half? Which heads did you put on?
boatn70
Well-known member
just for the record, convincor242 said his boat ran about 78 tops gps, 74-76 all day with passengers and cooler in boat. then last time he pulled the motor he said it dynoed at 600 hp and some change. so 600 will get to 78, i dont think that 425 will see 75ish but i may be wrong. i would say you should be at 70!!!
dont get discouraged here disturbed, lotsa advice, try some of the theories, i think the cam advance and timing may be a big issue.
some cam grinders will grind a 4* advance in the cam and maybe you added another 4*?? i cant say for sure but check into that....ive heard such things as your old motor(7.4) you can just advance timing and see noticable HP gains!!!! timing is important!
keep me posted on this, i still dont have my motor together!! ill let you know how it runs in the spring, maybe we can trade out some props to test and get the right one!!
thanks
kevin
dont get discouraged here disturbed, lotsa advice, try some of the theories, i think the cam advance and timing may be a big issue.
some cam grinders will grind a 4* advance in the cam and maybe you added another 4*?? i cant say for sure but check into that....ive heard such things as your old motor(7.4) you can just advance timing and see noticable HP gains!!!! timing is important!
keep me posted on this, i still dont have my motor together!! ill let you know how it runs in the spring, maybe we can trade out some props to test and get the right one!!
thanks
kevin
hey guys,
Ok now we're gettin some where. Yah vin i mean inconnell i told you i wasn't a good speller. Ok i guess it was valves . i put on merc retangular port heads. So the timing should be set at 34? And the cam was cut with 4 advance, and i bet the cam guy that put it in advanced it 4 more. With the set up that i gave you what HP do you think it should be running?
Ok now we're gettin some where. Yah vin i mean inconnell i told you i wasn't a good speller. Ok i guess it was valves . i put on merc retangular port heads. So the timing should be set at 34? And the cam was cut with 4 advance, and i bet the cam guy that put it in advanced it 4 more. With the set up that i gave you what HP do you think it should be running?
vinny p.
Active member
I would be glad to run it through my desk top dyno for you but I need more information to get you more precise #'s. It would be best if you have actual flow numbers for the heads, but I can guess at them. I NEED the exact valve timing #'s like what degree the ivo, ivc, evo, evc points are, the valve diameters, compression and what type of cam? ie:roller hydraulic or solid, flat tappet hydraulic or solid.
Here is another thought I just had...What is the shape of the runners on that air gap intake you put on? Rectangular or oval?? The reason I ask is that there is a theory about using an oval port intake with rectangular port heads. I did this on my 540. The trick is to match up the last 2" of the intake ports to the heads. The reason for this is that we as boaters are running at a relatively low r.p.m. We will not be able to outflow a smaller oval port manifold. The benefit is that by doing this, we pick up the speed of intake velocity. This will increase torque and horsepower through out the rpm's we see.
Here is another thought I just had...What is the shape of the runners on that air gap intake you put on? Rectangular or oval?? The reason I ask is that there is a theory about using an oval port intake with rectangular port heads. I did this on my 540. The trick is to match up the last 2" of the intake ports to the heads. The reason for this is that we as boaters are running at a relatively low r.p.m. We will not be able to outflow a smaller oval port manifold. The benefit is that by doing this, we pick up the speed of intake velocity. This will increase torque and horsepower through out the rpm's we see.
boatn70
Well-known member
according to a little program i have.....if i assume his duration is 226/232, the IVO:1,IVC:45 EVC:48,EVC:4 thats also assuming both LSA and Intake CL are 112*
see what hes runnin vinny!!
my guess is 400hp at the prop, on DD, 430 at motor.
disturbed look for the casting numbers on the heads, i can try to find flow numbers.
see what hes runnin vinny!!
my guess is 400hp at the prop, on DD, 430 at motor.
disturbed look for the casting numbers on the heads, i can try to find flow numbers.