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?

bottom paint and performance boats is like fire and ice,they just dont mix.get the bottom paint off and you will loose a lot of drag,that will equate to more speed.:party-smiley-004:

Why anyone whould put bottom paint on a performance boat is beyond me....

Dave @ Wesco knows his chit ,listen to what he's telling you BIG Daddy :drink::drink::drink:

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.

This boat should be around 12-14% slip. Right now I'm at 26% slip. I should be around 67 mph so somewhere I'm loosing 10 mph!

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.

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!!!

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.

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

I've been personally helping with this engine and the Crane ignition is set to 34 degrees advance at WOT, it is firing on all 8 and the wires are properly seperated and routed away from excessive heat and abrasion. the four barrels do tend to "stick" at idle and I suspect the base gasket is interfering. The outdrive is a Bravo. ALL speed checks are done via GPS this boat has a sweet Livorsi GPS speedo. I will hook my fuel gauge up to the fuel rail and monitor the psi at WOT...This power issue is only present with the 25 pitch the less demanding 21 has no issue with power but this engine should be spinning way more prop than a 21. ALL fuel lines are 3/8" and the check valve outlet from the tank has been replaced with a straight through version and all elbows are radius type tube and not restrictive "street elbows".

I suspect the 25 is a little too much and won't let the engine get into its real power band. The 21 is probably a little light and the engine torque is starting fall off hard in the 5500rpm range.

The thing is, all these numbers may change once the bottom is back to 100% and then the 25 may be the right prop.

He bought that prop from me....and in our old boat ( a heavy '89 Chris Craft 245 Limited..with a slightly warmed up 502 ), we turned that prop 5200 rpms @ 66.7 mph on the GPS with a half tank of fuel and two 250 lb guys on it. I think hes running outta fuel on the top end. We had a bigger Holley mechanical pump on the 502. He indicated that it seemed to be running out of power at 2/3 throttle. As an example..drag cars that seem to "lay down" about 3/4 track are notorious for not having enough fuel volume AND pressure. I would definately get a fuel pressure gauge on it. In my opinion..that carb seems a bit large. We had a 9022 800 Holley on our 502. What jets are you running ? Any black soot (at all) on the back of the boat ? Could be running way rich too. Just things to consider. :drink:

sounds like fuel and carb might be to big for the small heads, bottom paint = 3 to 5 mph my friend has 550hp in a superboat 24 with trs and bottom paint that combo costs him about 6 to 9 mph he gets 76 at 5600 and would break 80 easy with b1 drive and no bottom paint. also when I BUILT MY 585HP WE WENT TO 1/2'' LINES EVERYWHERE AND THE BIG KE gen 5 fuel pump which worked on the 595hp motor and 650hp motor carbs were 850bg with 84 jets the 670hp motor ran1050 .

Thanks for all the info and opinions on this..... I'm currently stripping the bottom paint off the bottom. Hopefully I'll have most if not all the paint off the bottom tomorrow and report what results I get. As far and the heads and carb go, the AFR's I'm running may have small ports but they flow similar to a Dart pro 1 310. The carb was custom built to the flow of the heads, intake, ect. I think the carb is fine but i do feel that the fuel pump is to weak for my combo. I'll check the pressure when i get the boat back in the water.

The bottom is 98% stripped which added another 5 mph. So I'm now at 62 mph @ 5900 rpms, which is where Bob told me to prop the engine. Prop slip dropped to 21% but its still a little high. I haven't checked the fuel pressure yet but I think that is part of issue. When I was at WOT the engine hit 5900 and then started dropping rpms at which point I backed off the throttle. However I wasn't able to replicate it again. All of this was at max trim and tabs up with the old 21 mirage.

The Mirage prop will slip a lot. Sometimes it's still the fastest on top end but it is a fuel waster in the midrange. See if you can borrow a 22 or 24 Bravo 4 blade from someone.

The last time out I was having issue with running out of power at 3/4 throttle agian. I could get up to 5000 rpms and then the boat would loose power, as I pulled back on the throttle the engine would come back to life. What i don't understand is why does it do this from time to time and not all the time?

When was the last time you changed your fuel/water seperator? Maybe you have some Sh!t in your tank that keeps cloggin your seperator ???

I have 16 hours on the engine and everything was new when the engine went in. I did run the old fuel out through it so its quite possible the old gas had sediments in it that is clogging the filter. I'll try a new seperator and see what happens.

It sure doesn't seem you should see a 1300 rpm drop going from a 21 Mirage to a labbed 25 Mirage plus. 5700 to 5900 seems like too much rpm for that comination. My old engine was a 468 with the 731 cam and a 750 carb. It ran great in the 5300 - 5400 range. I am guessing that a 23 M+ is going to be closer to the right prop once all the bottom paint is gone. You didnt say if you changed exhausts. If you haven't, you are choking the engine. I think your boat is going to be to heavy to pull a 25.

I'm running stainless marine exhaust manifolds. For the most part the paint is off the bottom and I picked up just about 5 mph. The current 21 I'm running is in fair shape and I know I'm loosing a few mph by using it. I always thought that a labbed 25 would be equal to a non labbed 23 as far as what the engine sees? Am I wrong on this?

Slip is high? Did you check you numbers carefully? Are you trimmed out too much??? Slip number is also affected by more than the prop as you figured out with the paint. Do you have a hook in the hull??

Yes the formula 242 hull has a hook. My last 242 also had the hook but the slip was closer to 13% which IMO is normal. The prop is only in fair condition so that is adding to the slip. I'm going to try the 25 again tomorrow along with a fresh fuel/water seperator and see what happens.

I went through some of the same growing pains with my 242. The boat was very sensitive to prop setup and motor setup. I had added 50 HP in theory and slowed down from 68.7 to 66.7 with an aluminum headed 502. What I found was the boat liked a lot more fuel, spend some time out with the GPS doing fuel pressure and jetting checks. In my case I just added fuel till it quit going faster and stopped. Other thing was I tried 21 mirage pluses to get the RPMs up and the boat would not run any better, my best results were with a stock or labbed 23 mirage plus. With the hook in the hull we found adding cup for bow lift was the ticket. Tried 25s and always slower even if RPMs were in range. Test and test and don't give up

Well I got out today with the labbed 25 and a fuel pressure guage! The boat will now pull the 25 without much problem up to 4000 rpms, then the engine will stall out unless I pull back. I hooked up the pressure guage and I'm only getting 2.5 lbs from idle to 4000. At 4000 the bowls are drained! So that tell me one thing the fuel pump is junk!

Looks like that is your issue or at least part of it.

Ok after a ton of testing here is what I found.
The fuel pump was not the problem not even the wimpy 2 psi pump was a problem. I repleaced with another stock pump got 4 psi and same speeds. Replaced that with a 7 psi/120 gph and still same speeds. I then tore into the carb, there were bits of rubber hose in the secondary needle and seat. Removed and problem was solved but then it happened again. I have a feeling that the fuel rail hose may be junk.

I was still not able to pull the 25 pitch labbed mirage plus, 4400 rpms max vs the 5800 on the 21 mirage that is banged up. I'm going to get a 23 Mirage plus today. I'll report the results.

Based on your engine specs, you have a high winding engine. The cylinder heads you have flow more air than iron Chevy rect. port heads. The cam has similar timing to a HP525 cam which has 62 cubic inches more so your engine will want to rev higher.. Your builder advised you to run it at 5900 rpm's. Hopefully he set up the valvetrain correctly because you are running on the edge of valve float. He is correct that the power peak is up there. After looking at the Bam (www.go-fast.com) speed and slip calculators, I doubt if you will be able to pull more than a 23 pitch Mirage or a 22 4 blade. Any prop that slows the engine below 58-5900 will probably slow you down. You might even be faster spinning a worked 21 above 6000 if you can control the valvetrain. There's no substitute for cubic inches and you are a little low on them.

P.S.Fix the fuel system. More high perf. engines have been ruined from running lean. Get a good fuel pump and make sure you have a steady 5 lbs of pressure at all times.

as far as the fuel issue is concerned look at the anti-sih valve at the tank inlet...very restrictive...but also why would you build a 427 ? great engine but not great torque...cubic inches are key to torque in boats...if I were spending $$$ on doing a engine would have been a 468 min...the longer stroke 454 much better in a boat. now I agree with griff on the props. the other issue with that engine is the RPM thats needed to make power..upper 5000's and the drive is not going to like that all that well....

When I was talking to bob about the 439 vs the 468 he said that "long stroke equals more torque" is a myth and that its all about total cubes and not stroke length. Trust me I asked! I built the 427 because I already had the crank and quite a few people talked to said I would get a wider powerband with it. Plus my interest was having power up high and not down low. I could have easily built a bigger engine with lower quality parts and hit my goal... Instead I picked top quality parts in a small, high reving bbc. For the record, the help that I have got from Bob on this project has been second to none, and I would choose Marine Kenetics in a heart beat if/when I decide to change things. I just want that to be clear.

As far as the drive goes. Mr. Gadgets has told me that my drive is happy up to 6500 as long as the tolerences are in check!

Anyone who works on drives will tell you the same thing. They are much happier spinning a small prop at 6000rpm then turning a big prop at 5000. Torque kills drives..
Get all your rigging issues figured out, prop that thing to spin to 6k and go have fun. :drink:

Ok- I'm getting closer!!! Maybe I'll love this engine yet! I drilled 4- 1/8" holes in my thermostat (I'm running a crossover) Heating problem solved! I called patrick at prosystem and we are jetting the carb up 4 sizes and droping the air bleeds to solve the lean issue. Today with the mirage plus 23 I hit 59 mph at 4800 rpms without cracking the 4 barrels. I don't want to push it until the new jets are in. Once again, will report back!

As far as the valvetrain goes, I'm using morel lifters, the new scorpion marine endurance rockers, custom push rods, inconnel exhaust valves... I'm confident my valvetrain is perfect!

I sure hope this topic helps someone else avoid the headaches I've had fine tuning this.

What did you use to remove the bottom paint? I need to start to work on mine.

I tried everything! Petit, back to nature marine stripper, kleen strip for fiberglass, west marine stripper... The best was something I just tried for the he!! of it... Behr Priemium deck stripper from home depot! $20.00 a gallon and worked better than all the $70.00 gallon marine strippers and it had no negitive effects on the gelcoat. I applied it with a pump up sprayer and removed it with a power washer and a roto tip nozzle. If you go this route you must have the roto tip nozzle!

Ok Sounds easy. Mine should go pretty quick there is only one coat to deal with.

You are definately lucky. In many cases that would equal a hole in a piston or burned valve.

Any updates??

Ok I finally got the boat back in the water now that the ice is gone, so here is an update to my thread. Over the winter I made a few changes. 1. I removed the Stainless Marine Exhaust and installed Eickert headers. That said I picked up 200 rpms and much better throttle reponse. 2. rebuilt the raw water pump, the case was shot as was the impeller, solved the over heating issue. 3. Swapped out the old Mirage 21 non-plus, for a Mirage 21 Plus. Top speed is now 69 mph. So basically other than getting a lot of bugs worked out, the results of getting the bottom paint free and getting the correct prop on the boat I picked up a solid 12 mph, my prop slip went from 26% to 13%. Thanks for all your help guys. Now its time to get ahold of BBlades and let Bret do his magic.