Engine rpm

[whale]

I have a question; when you reach a rpm of say 5000 and you have pedal left but you cant get any more speed or rpm out of the engine, what is wrong ?

[RiverRacer]

Elementary my dear Watson, you ran out of motor!.:D

[Flatmvn]

That is a loaded question.

Guess 1, Ran out of cam maybe.
2 Big gear and prop and that is all the engine can pull.
3 To small of a carb and not enough air flow to get any more air and fuel.

Just some of the suggestions I have. I am sure there are more things that can cause it but that is all I have for now.

[whale]

Could be Art, but with 22 gears the engine would turn 6200 and have a little pedal left. Put in some 15 gears and a taller prop and lost speed and rpm ?

[RiverRacer]

Could be Art, but with 22 gears the engine would turn 6200 and have a little pedal left. Put in some 15 gears and a taller prop and lost speed and rpm ?

Ok, so you dropped a gear and put a big prop on, is that what you're saying???. if so that's the problem, "ONE CHANGE AT A TIME", you should have tried it with the same prop first!..:D

[whale]

I agree, but when the 22's were in I had very little pedal left at the top. When I put the 15's I have a lot of pedal left at the top.

[RiverRacer]

Yeah, but what about WOT that's what counts. What is the motor good for?, what rpm range is the cam, how good are the springs, I could go on!...

[whale]

OK her is what I have. LS-6, 454/450hp with L-88 cam, 2x4's (660 center flows) ,Bassetts ,Vertex mag. Engine is in a Rayson Craft 19.6 GN with a wood deck. The boat is a little heavy and it does have a velvet drive in it ( ski boat). The problem may be the intake ( old cross ram ).

[RiverRacer]

So, you're talkin about the GN huh, ok!. Well, old cross rams are high rpm intakes only nothing on bottom and mid range and you don't have any torque and that's what you need for that boat, how about the cam??, is it compatible with the intake??? may have to change your combination here???..

[whale]

Thanks Art , I will play with some changes and get back to you on this...........wayne

[poncho]

OK her is what I have. LS-6, 454/450hp with L-88 cam, 2x4's (660 center flows) ,Bassetts ,Vertex mag. Engine is in a Rayson Craft 19.6 GN with a wood deck. The boat is a little heavy and it does have a velvet drive in it ( ski boat). The problem may be the intake ( old cross ram ).

Did you jet the center squirter's square? same thing happened to me when i dropped to too small jet all the way around would speed up by letting off a little,just a thought

[hm66Howard]

Is it possible your pulling too much advance and experiencing detonation? I know it can be hard to hear over the pipes. Check your plugs. :confused: Usually that shows as a slow drop in RPM not just "no more". Just a thought. ;)

[RiverRacer]

None of that makes a difference with that manifold. I tried that manifold on my ski boat once because they are cool looking, anything but high rpm and WOT does not work for $hit it's the design!..

[whale]

Louis, I did not see your post until now. Thanks for the help, Cam is an old chevy L88, carbs are 660 with stock jetting, and the prop was too big. It is just that it runs out of anything at 6000. I think it is the intake and will change to a weiand hole shot. Pulgs look a little lean but not much. Poncho; the carbs are stock, I am not sure what they are stock ( jetting wise ) hm66Howard; total advance is at 38 degrees, runing a mix of 93 and 114. The lower gear gives more free pedal that the 22s do. Which brings down the torque curve I think, which would be the cam and the intake............thanks to all wayne

[RiverRacer]

If they are untouched, the primaries are 76 and a #12 secondary plate!..

[poncho]

If they are untouched, the primaries are 76 and a #12 secondary plate!..

Yep thats what mine had and tried to get away with 71`s to stretch fuel mileage and got bit and ended up with 74`s and 6 pounds pressure which worked pretty good could turn the ditch pump up to 7000 without hurting anything

[rich]

Louis, I did not see your post until now. Thanks for the help, Cam is an old chevy L88, carbs are 660 with stock jetting, and the prop was too big. It is just that it runs out of anything at 6000. I think it is the intake and will change to a weiand hole shot. Pulgs look a little lean but not much. Poncho; the carbs are stock, I am not sure what they are stock ( jetting wise ) hm66Howard; total advance is at 38 degrees, runing a mix of 93 and 114. The lower gear gives more free pedal that the 22s do. Which brings down the torque curve I think, which would be the cam and the intake............thanks to all wayne
I my be wrong but is'nt the total 38 to high I was total try to stay around 31-34 for top end just a thought.

[pwderman]

Wayne, who's crossram are you using? I'm looking for an M/T for a nostaliga piece. If that's what you have and want to sell it let me know...:D I just need the manifold as I've got plenty of carbs...:eek: Jon

[gfinishline]

You did not say anything about the motor "miss firing" at 5000. Your tune up my be off, but I would take off 2 or 3 valve springs and measure them. Sounds like you are running out of spring. You said it "went slower" with the prop and gear change, but I assume it ran the same 5000 RPMs? You changed "the load" on the motor with the different prop AND gears, so was there an RPM change too? If it still ran 5000, I would look at the springs first.