motor questions/opinion
 

OK guys ... Got 2 496 (stroked 454 style) motors that both seem to quit at 4900 5000 rpm. Both motors are new with identical parts except 1 has a hyd roller . New msd marine dist. no m-6 box New Demon Marine 750s DArt pro 1s 310 cc About9.7 comp. One motor dynod at 600 ft trq. but only ran dyno test to 5200. Even when I trim up rpm doesnt change much. Only running 23 mirages .Boat takes off great with all that trq. Cruises at 3800- 3900rpm 40 mph When you open it up Accelerates good 4 or 5 sec. to 60 62 mph 5000rpm then thats it? Does it need more carb? Fuel presser on dyno with new stock fuel pumps was 6psi. spark plugs look good any Ideas? thanks Dan

Do you have any comparisons to stingers with different power? I'd say you are doing good at 62mph with a 42' straight V bottom boat.

BT

I kinda agree, that is a big boat and takes alot to push, are you running TRS or Bravo? that makes a difference too.

motors
 

Yea compared to some 39 stingers (same hull as a 41) they ran about 50 mph with 454 hp about 400 hp TRS drives I think. The speed is one thing but shouldent the motors free up and increase rpm if I trim up? Just seems like it accelerats to strong and quick to just run out at 5k. My single engine boat when I trim up rpms go to 6 k if I want sure the mph slowes down .This one slows down but the rpms hardley go higher.maybe 100-200 rpm Maybe some others with same hull will chime in and get me some comparrison on props and motors. Oh yea also I scaled the boat its heavy but at 11700 it could be worse for a 40 frter. thanks

Hey redcorvette, Like full force said, Does it still have trs or bravo's. A friend of mine on here(wetpleasure) has a 41 stinger also w/420's TRS I think they are. You might PM him I know he has done a little motor work. Another guy built his org. 454 to right at 500 hp in a 30' formula '94 straight bottom, His boat does not react fast to accelaration either, But comes out of the hole great turning labbed 30 4 blades. He was turning 24 3 blades with the stock power. If you do have TRS you need to know the gear ratio. You lose more HP throught the tranny also on the TRS. I really believe you need 800 cfm carbs. I have some mild built 454's and I am running 770 cfm with steel GM heads with minor porting, And I am gonna go a little bigger to try and fine tune. You really need to take a good plug reading and see if they show anything. GOOD LUCK

whats cams ?? maybe combo off ?? heads/cam/carb...also some hulls just never went beyond a certain point and you could add 500hp and only gain 3 mph....sounds like you are close there...a friend of mine had that same boat..I will see him this weekend and ask what his ran...but as I remeber upper 50's was about the end of it...Rob

If it runs that well (no slippage) with 3 blade Mirages, the drives must be really deep. I bet your boat would really benefit from raised x and 4 blade props. 62 isn't bad for that boat, it wasn't really designed to be fast as much as comfortable.

motor
 

TRS 1.5 drives ,RPM air gap manifold,crane cams 139011 hyd roller 1.7roller rockers int.587 ex.610 intake max lift 107 atdc 226 duration ex.117 btdc 234 duration max rpm5600 valve float 6200. I could undestand if this thing took along time to get to max speed and rpm but it dont and the moters dont seem to lug at all only 3 4 sec .Also if you look at pics of boat moving not allot in the water carries the bow very well(look in lake cumberland pics) thanks

The thing is that it went 5200 on the dyno, well... in the boat with drivetrain loss he loses 200 rpm... not bad, the stock 420 cams if he is using them or anything similar will only pull 5000-5200, that is the rpm it was meant to run top end.


You are right about mph gains ond power, when you get to a certain point it takes alot of power to gain mph...

That cam will stop about that rpm...with the TRS that sounds rigt for dyno vs. boat rpm..

As far as stopping at 5000 instead of 6000 on single engine.... when you have 2 engines one can cancel out the other, if one makes more rpm then the other that will not allow the other to pull more rpm,....confused?? I am not sure how to explain it but hope you get what I mean...TRS are a deep drive no matter how it is trimmed, raising the X would help but the work involved would not pay off in MPH gains..

Probably not enough carburetor.

Plus, what exhaust?

With those heads and a good exhaust, I'd use something like the Crane 741. What pistons did you use? If you went from the stock dome to flat tops, you lost some CR. Where is the timing set at?

I'd borrow a set of 21's or 22's and see if that gives you some more RPM and gets you a MPH or two.

The deep drive is what it is- expensive to fix.

motor
 

Yea the drives are deep Still think should see more rpm it doesent struggle to get to 5k it goes there quick then stops even if I trim up way to much(on purpose). Stock exhaust for now but it was dynod that way wet with water pump and see pump made 520 hp at 5100 598 ft pnd torque at 3500 rpm. Seems like going to 22 would slow down mph. motor doesent bog at all from 4000 to 5000 and picks up 20 mph I think thats good isnt it?Seems like carb not big enough?A 23 pitch at 5000 rpm 1.5 drive 60 mph whats that slip ratio?

Oh yea pistons and comp are fine domes 116cc I think

Not sure on slip, could ebt he carbs, what is total timing set at?

I set the total timing a little conservitive at 34 the MSD dist has about 21 so base is 13- 14. Had detonation problems on other motors before and dont want it right out the box on a new motor. thanks Dan

One stupid question... is you trim limit set right? do the drives stop trimming too soon? bring both drives all the way up and see where they are before using trailer switch.... just a thought!!!

No not a trim issue Im not that goofy!

I hear ya, sometimes ya get all mixed up and forget stupid stuff!!

Do you have a set of carbs to try?? or like as said before, try a smaller prop, it should rev 200 or so more easily... not sure how to caculate prop slip..

Got a buddy that can figure prop slip Calling him latter As for carbs no extra big ones yet but Ill find some . Some one awhile back said the stock rochesters merc uses on ther 420 hp were just bairly enough wonder there cfm? and I got lots more cubes than them. Does your boat reach top speed and rpm quick or does it take a few more seconds .I throttle this one from 40mph and it goes you feel it set u back no it dont pin u back but you know its accelerating then its done at 5k !

420's should have had Holleys...

I have 460 CI with Melin heads, 420 cams still, Holley single plane intakes and Holley 750 (420) carbs, I just got the boat in 2 weeks ago after having issues wiping mains, all is good now but have not beat on it alot, I started to last weekend, went right to 5000 but i did not trim it much and did not hold it there long, engines are still kind of new and for the first time ever I am trigger shy.... usually I just run hard!!

I will PM you a site with all my info if interested...just search my user name..same as here.

Check vacuum at WOT, if zero, carbs are big enough.

Been working with a friend on his boat on similar issues. 35 Mistress, 522's with not ideal exhaust. About the same cam Other than the exhaust, the motors have the right parts in them.

Basically the boat is topping out at 58 at 4800 rpm. It's a little over-propped with 24 pitch Bravos. Deep X TRS boat.

Based on that, I'm thinking you're pretty close to what the boat will do.

In my example, it was close to 20%

OK lets explore the deep drive issue. If I hold a straight edge to the bottom then trim the drive paralell to that the center line of the prop is 5 inches bellow the bottom of the boat. That means with the 15 inch prop that the top blade is basicly at the bottom of the hull . Can anyone tell me the right way to check "X" dim and what is it on say maybe conrads? Also many 40 ftrs have tripples with 400hp or so there speed is around 55- 60 there "X" dim and drag has to be terrable my trq. and the hp are almost the same with waaaay less weight and waaay less drag with 2 motoers and drives . Doesent firure ???Not arguing just dont make since . OH yea also broke a drive last week at cumberland lower gears , can any one tell me if these are the" weak link " in TRS stuff ?

TRS are pretty tough in my opinion, I like mine... if you broke lower gears they were prob pitted... that is the weak link to them, I have seen many boats run decent power through a TRS, they take way more then a Bravo...