Attention all Motor Guys *Advice Needed*
01-28-2009, 10:56 AM
#31
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Ding ding ding on the timing. how much diferent timing did you use on the dyno? Did you try it to 32,33,34,29,28 etc?
You could have to much or to little.
Carb should be fine. A lot of thes set ups historically used the twin 750's actually.
Roller cam is a good idea, but there is no reason he shouldn't be spinning past 5k IF he has the right spring.
Try adjusting the timing a little.
Check and make sure the belt is not slipping. Do you have the notched pulley set up or the grooved pulley set up. That could be why you are not making the proper boost.
What exhaust do you have on the boat. That could be slowing you down.
Just other factors.
If you had the arrestors off on the dyno, that is not the problem now.
You could have to much or to little.
Carb should be fine. A lot of thes set ups historically used the twin 750's actually.
Roller cam is a good idea, but there is no reason he shouldn't be spinning past 5k IF he has the right spring.
Try adjusting the timing a little.
Check and make sure the belt is not slipping. Do you have the notched pulley set up or the grooved pulley set up. That could be why you are not making the proper boost.
What exhaust do you have on the boat. That could be slowing you down.
Just other factors.
If you had the arrestors off on the dyno, that is not the problem now.
I didn't do alot of timing adjustment on the dyno. i was letting the Dyno guy take the lead when testing. I am running a 16 Rib grooved belt. Not a Cog belt so I am sure I have some slipping How much ?? I have stainless Marine exhaust
I have one of the engines out right now. Should I have My engine guy Test/look at the springs. I think I need to find a new engine builder in my area. I'm not confident with my guy as far as a blower motor he does not have alot of experience with blowers. If I switch to a Hydr. Roller cam what can I expext from that.
01-29-2009, 11:23 PM
#32
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cocktails,i put a 509 with 8.0 compression in a boat i had.i used a bds 8 71 with a pair of holley 750 carbs,msd 6m ignition,gm heads with ports cleaned up,crane 741 hyd roller&spring kit.this setup made 720 hp at 5600 rpm at 8 lbs boost,also had cmi headers,not manifolds.your 420 can easily make 8 lbs of boost.i think 32 or 33 total timing is right,i always lock the distributor advance on all blower motors so you have total timing all the time.one more thing to consider,are you getting enough air with the engine hatch closed,if i opened mine up 2 inches i picked up 2 mph.[more and cooler air]my thinking is your valve springs are to weak and won,t let the engine rev.i have seen it happen before.oh,i forgot to mention,i used[and still have]a 27 pitch 3 blade,slight cavatation until on plane,then hooked up real good.
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