Speed Issue
08-04-2010, 08:30 AM
#1
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Speed Issue
I'm having a real issue with the speed I'm getting out the new engine I had built. Here are the specs:
'87 Formula 242
427 BBC bored +.060 (440 ci)
Mandera Cam 234/242 w/ .61/.64 lift
9.9 compression ratio
AFR 265 CNC Oval port heads
Pro System 830 CFM carb (holley hp 950)
Weiand Stealth Intake
This combo was supposed to put out 550+ hp.
The boat I'm only able to get 58 mph out of it with a 21 mirage @ 5700 rpms. That works out to a slip number of 26%, which is much to high. The bottom is painted and it really bad shape but the gel is in perfect shape underneath. i've been stripping it but I still don't have it all off. The fuel system is all stock with an old school AC Delco Marine fuel pump. The one with the over flow jar. Bob said the factory fuel pump is too small, Dave at Wesco Racing said he's made 675 hp with stock fuel systems?
I had a 25 Mirage Plus that is labbed but all I could get is 4400 rpms and 50 mph. The boat seemed to be running out of power past 2/3 throttle.
So can the bottom be cutting speed by 10 mph? Is my fuel pumps lines the problem? There is just no way this engine should be only going as fast as a stock 454 mag? So what are your suggestions to look for here?
'87 Formula 242
427 BBC bored +.060 (440 ci)
Mandera Cam 234/242 w/ .61/.64 lift
9.9 compression ratio
AFR 265 CNC Oval port heads
Pro System 830 CFM carb (holley hp 950)
Weiand Stealth Intake
This combo was supposed to put out 550+ hp.
The boat I'm only able to get 58 mph out of it with a 21 mirage @ 5700 rpms. That works out to a slip number of 26%, which is much to high. The bottom is painted and it really bad shape but the gel is in perfect shape underneath. i've been stripping it but I still don't have it all off. The fuel system is all stock with an old school AC Delco Marine fuel pump. The one with the over flow jar. Bob said the factory fuel pump is too small, Dave at Wesco Racing said he's made 675 hp with stock fuel systems?
I had a 25 Mirage Plus that is labbed but all I could get is 4400 rpms and 50 mph. The boat seemed to be running out of power past 2/3 throttle.
So can the bottom be cutting speed by 10 mph? Is my fuel pumps lines the problem? There is just no way this engine should be only going as fast as a stock 454 mag? So what are your suggestions to look for here?
Last edited by endeavour32; 08-04-2010 at 08:51 AM.
08-04-2010, 08:55 AM
#4
Banned
I'm having a real issue with the speed I'm getting out the new engine I had built. Here are the specs:
'87 Formula 242
427 BBC bored +.060 (440 ci)
Mandera Cam 234/242 w/ .61/.64 lift
9.9 compression ratio
AFR 265 CNC Oval port heads
Pro System 830 CFM carb (holley hp 950)
Weiand Stealth Intake
This combo was supposed to put out 550+ hp.
The boat I'm only able to get 58 mph out of it with a 21 mirage @ 5700 rpms. That works out to a slip number of 26%, which is much to high. The bottom is painted and it really bad shape but the gel is in perfect shape underneath. i've been stripping it but I still don't have it all off. The fuel system is all stock with an old school AC Delco Marine fuel pump. The one with the over flow jar. Bob said the factory fuel pump is too small, Dave at Wesco Racing said he's made 675 hp with stock fuel systems?
I had a 25 Mirage Plus that is labbed but all I could get is 4400 rpms and 50 mph. The boat seemed to be running out of power past 2/3 throttle.
So can the bottom be cutting speed by 10 mph? Is my fuel pumps lines the problem? There is just no way this engine should be only going as fast as a stock 454 mag? So what are your suggestions to look for here?
'87 Formula 242
427 BBC bored +.060 (440 ci)
Mandera Cam 234/242 w/ .61/.64 lift
9.9 compression ratio
AFR 265 CNC Oval port heads
Pro System 830 CFM carb (holley hp 950)
Weiand Stealth Intake
This combo was supposed to put out 550+ hp.
The boat I'm only able to get 58 mph out of it with a 21 mirage @ 5700 rpms. That works out to a slip number of 26%, which is much to high. The bottom is painted and it really bad shape but the gel is in perfect shape underneath. i've been stripping it but I still don't have it all off. The fuel system is all stock with an old school AC Delco Marine fuel pump. The one with the over flow jar. Bob said the factory fuel pump is too small, Dave at Wesco Racing said he's made 675 hp with stock fuel systems?
I had a 25 Mirage Plus that is labbed but all I could get is 4400 rpms and 50 mph. The boat seemed to be running out of power past 2/3 throttle.
So can the bottom be cutting speed by 10 mph? Is my fuel pumps lines the problem? There is just no way this engine should be only going as fast as a stock 454 mag? So what are your suggestions to look for here?
08-04-2010, 10:03 AM
#5
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I am sure the bottom paint does not help. I think you could use some prop help. If you use a prop slip calculator you can see where you should be. I learned a lot when I started calling around about props. BBlades and Hydromotive were both very helpful. I still have to return a call to Julie at Throttle Up. I hope to do that this week.
08-04-2010, 11:01 AM
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I am sure you can make up a good bit of that with prop. I think. I am defiantly going to do something with my props this winter. I am looking at Hydro 4 blades, but will talk with anyone who is willing to help. Good luck.
08-04-2010, 11:23 AM
#8
Registered
That motor definitely needs a better fuel pump and all 3/8" lines. Here is a good one for that motor. It's 120 GPH and doesn't require a regulator. With out a big enough pump you'll lean it out at WOT and end up loosing an exhaust valve. You should also be running Inconel exhaust valves. Their good insurance.http://www.summitracing.com/parts/HLY-712-454-1/
As for a prop I'm sure you need at least a 23 Mirage Plus if not a 25.
And get rid of that paint!!!
As for a prop I'm sure you need at least a 23 Mirage Plus if not a 25.
And get rid of that paint!!!
08-04-2010, 11:29 AM
#9
Charter Member # 55
Charter Member
Where is the timing set at full advance????
You could easily have a few issues scrubbing speed.
The bottom could be costing you 5mph. I would try a 23 Mirage Plus.
I would expect 15% slip with that hull.
You could easily have a few issues scrubbing speed.
The bottom could be costing you 5mph. I would try a 23 Mirage Plus.
I would expect 15% slip with that hull.
08-04-2010, 05:37 PM
#10
Platinum Member
Platinum Member
Soda blast the paint off. Or walnut shells.
Bottom paint is like "glue" to a performance hull.
Once your bottom is slick, you can start looking for speed.
You need to put a fuel pressure gauge on the carb and have somebody watch it at wide open throttle. It should not drop below 4.5 psi. If it stays up, then you have enough fuel system. If it drops, then you don't . Period. If not, it could be anytbing from the the tank pickup, the checkballs, the filter/separator, the pump, or the feed lines. But if the pressure stays up AT THE CARB at wide open throttle, then you don't need to worry anymore about fuel system.
Are your secondaries opening fully? Do you have a large enough flame arrestor on the carb? Is the timing advancing properly? Are you certain that you are running on all 8 (sometimes plug wires can arc to metal and snuff the flame in a cylinder).
Are you running a Bravo or TRS? There can be all sorts of reasons either drive is sucking power or (in the case of the TRS tranny) slipping. Gear ratio?
Do you have hydraulic trim tabs or are they fixed? when you run WOT are you running with the tabs ALL THE WAY UP? if not, they can scrub speed like crazy. What drive angle are you seeing best speeds at?
Are you checking speed with GPS, if not, we can't believe any number your gauge says because it might be reading fast (likely) or very slow (not likely but certainly possible).
Have you verified your tachometer calibration?
get some of this figured out and post the answers and we will be able to help better.
MC
Bottom paint is like "glue" to a performance hull.
Once your bottom is slick, you can start looking for speed.
You need to put a fuel pressure gauge on the carb and have somebody watch it at wide open throttle. It should not drop below 4.5 psi. If it stays up, then you have enough fuel system. If it drops, then you don't . Period. If not, it could be anytbing from the the tank pickup, the checkballs, the filter/separator, the pump, or the feed lines. But if the pressure stays up AT THE CARB at wide open throttle, then you don't need to worry anymore about fuel system.
Are your secondaries opening fully? Do you have a large enough flame arrestor on the carb? Is the timing advancing properly? Are you certain that you are running on all 8 (sometimes plug wires can arc to metal and snuff the flame in a cylinder).
Are you running a Bravo or TRS? There can be all sorts of reasons either drive is sucking power or (in the case of the TRS tranny) slipping. Gear ratio?
Do you have hydraulic trim tabs or are they fixed? when you run WOT are you running with the tabs ALL THE WAY UP? if not, they can scrub speed like crazy. What drive angle are you seeing best speeds at?
Are you checking speed with GPS, if not, we can't believe any number your gauge says because it might be reading fast (likely) or very slow (not likely but certainly possible).
Have you verified your tachometer calibration?
get some of this figured out and post the answers and we will be able to help better.
MC
