Tune up change for BIG heads.

Hi guys, changing heads from 340cc intake runner conventional style BB/C cylinder heads to the Pontiac style cylinder heads with big runners around 460cc with 516 ci. This is for circuit race boat
Tune we have now is
1471 littlefield with 34% o/d making around 26 lbs.
110 pump
hat nozzles-50,46,46,44,32
ports -50,48,44,42 @ 25lbs
main .110"
H/S .080" @ 85lbs
I would think that we need to put more fuel via bigger hat nozzles but how much
& this would drop our fuel pressure so would we need to put more fuel via main
to get our pressure back? Any ideas on getting us in the ball park for starters.

 

I went from dart 360 heads on a 565 injected motor to Big Dukes on a 632 injected motor and as I recall I used a little less fuel with the big dukes, even on the bigger motor. I believe the smaller, more efficient combustion chambers in the big duke heads did not need as much fuel as the 119cc chambers in the dart 360 heads. If nothing else leave your nozzles and jets the same and maybe fatten up your main and make a 330' run followed by a 1/8 mile pass to check your plugs. Your egt's should stay the same as your old heads, remember egt's are only telling you whats going on in the header, however, once you run them for a while you can track jet changes fairly well as long as you don't try to compare your egt's with someone elses. Let us know how it run's and good luck. Jody Stroud TD 9325

 

Thanks Jody for the reply, but I would say that being blown the bigger heads would let more air in & therefore would need more fuel. I would have thought that this site would have had more people with a bit of knowledge in this field,& I thought I knew little with lots to learn.

 

The blower determines how much air is let in, unless you're stacking boost.

You'll lose boost if you don't change the O.D., and probably pick up some power.

Your pump is marginal in size, and you have too much going through the hat nozzles, IMO.

 

Bigger yes, in the intake runners. The chambers are alot smaller and way more efficient. Let me know if you need them and I'll give you my nozzle and jet setup on my big chief/ big duke motor, although every motor is different and racing for extended periods of time is something we drag racers don't know much about. What kind of boat racing do you do? Drag or round and round.

 

Jody;

Considering he said "circuit race" in his initial post, I'd have to think it's a roundy round.

Wizbang would be an awesome source of info for him, as he does K-Boat racing up in Wash state, and I know he has Pontiac heads on his motor.

 

WJ, It's similar to the K boats only we go straight up , turn , & straight back a few times were the K boats go more on an oval course. Were's wizbang when you need him?

 

We race the K's on one pins sometimes !!!!!!!!!!!

206-795-1209 cell

 

Wizbang, world titles last year in Aus, Duff Daley & the other guy in the red boat, you guys got creamed. Anyway , they tell me you use the pontiac BB/C heads with a 14/71.how about a close tune to get us in the ballpark ?There was a rumour that a couple of our boats were coming to USA but don't know if it's still a go.

 

Check your pm !