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.

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.

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..