Super Jet Type 4 Dry Pipe and High Compression/ Max Porting?

[SN760]

Have a few questions------
First here is what I'm running for a motor. 62T cases and cyl. Cyl resleeved and bored to 84.5 mm. Cyl - heavy porting. ADA head with 28cc domes (215 psi comp.). Boysen manifold & reeds. 46 mm Team Scream carbs with X-Metal risers. MSD Enhanser and lightened flywheel. Weisco pistons.
Was running a B pipe with mod chamber, switched to a Type 4 Dry pipe no water injection - BIG Improvment - also at that time was running 33 cc domes (180 psi comp.). with 84 mm bore. No problems with the dry pipe couplers etc. etc. really liked the power increase it gave me.
Lost part of the ring lands of one piston 2 week ago, no signs of detonation, sticking, lean cond. etc. Motor had a LOT of hrs on it, also at that time was running stock yamaha 760 cast pistons.
Back to now - new crank, new Pistons (weisco) fresh bore. new domes (28cc) willing to run race gas. Finally the question --- Do I go back to the B-Pipe (kinda the way I'm leaning with the big jump in compression) or can I run the dry pipe and get the motor to live?
Talked with Factory Pipe - they said the dry pipe type 4 was made for a motor with limited porting - and the big one - low compression, in other words Don't Run It with this motor setup.
Any thoughts on this???

Thanks
Mark

 

[SN760]

Not sure I was clear about the compression issue.
Going from 180 psi to 215 psi and was wondering if this was a good idea with the dry pipe or should I go back to the B pipe. There is no doubt the dry pipe makes more power than the b pipe (at 180 lbs comp.) at least on my motor. Would like to hear from someone who has run the dry pipe with 200 plus comp. - good idea - bad idea ??

Thanks
Mark

 

[gtoking1972]

Not sure if this will help or not but here goes. I rebuilt my 62t a few weeks ago (82.5 mm, ported top and bottom, epoxied cases etc etc) I put a thrust head with 33 domes and a coffeman lightning dry pipe and the motor was putting out 230 psi of compression. I ended up ordering 37 domes and just got them in today so hopefully the compression will drop enough to not have to run full race gas. As far as your question, I don't see any problem with running 200 psi and a dry pipe as long as its cooling properly. Are you running dual cooling? I see a lot of guys running big bore A/M hulls and they are running dry pipes as well, something to consider anyway.....

 

[SN760]

Thanks for the reply.
Yes, Running dual cooling, compression is at 215 psi. Chickened out and put the B pipe (mod chamber) back on. Went to the lake yesterday and road the ski easy for 3/4 tank of gas to break in motor. Then went full throttle, must say Big Disappointment !!! after having the dry pipe on before. The motor came off the bottom super quick but hit a wall. Finally after playing with the water screws on the b pipe I ended up with the top two screws completely closed and the bottom screw open 1 turn. This setting seemed to lesson the the "hitting the wall problem" and seemed to improve performance overall. But still no comparison to the dry pipe.

One thing for sure --- The Dry Pipe Makes Lots More Power --- than the B-Pipe !

I guess the fact that the b-pipe is easier to setup than the dry pipe is why most people run them.

 

[Big Kahuna]

you keep saying hitting a wall. What prop are you running? You may be underpropped.

 

[Sospikey]

High compression combined with a dry pipe needs programmable ignition, I'd say.

 

[SN760]

Prop is a 13 - 15 concord with a 3 mill cutback. Nozzle is bored to 84.8 mm. Thought about the prop issue, maby need to load the pump more ?? Not sure, don't seem to be burning the prop.
The MSD Enhancer I'm running has a very flat timing curve. Starts out at 22 degrees and slowly tapers off to 20 degrees at 8000 rpm. Not the best setup for a dry pipe and high compression. I'm thinking that may cause some serious detonation at higher rpms ?

 

[MileHighJSC]

Vp c-12

 

[SN760]

Mixing 3 gal of c-12 to 2 gal of 93 pump gas to use with the b pipe.
Going to put the dry pipe back on tonight. Any thought as to the fuel mix I should use or do I go with straight up c-12

 

[MileHighJSC]

Go 3 to 1 and then decided if the power is worth the $. I use to have a motor at 220psi (5000 FT elev) that I ran 2 to 1 C-12 in, but I decided it was not worth it when c-12 went over 4 bucks a gallon. HA HA One can only dream of 4 buck a gallon VP

 

[chriselmore_1]

Dry pipes hit hard on low cc motors with with a real aggressive pitched prop and tl. My buddy flips a lightweight stock length Superjet splash hull with a 760. R&d dry pipe and tl with a rediculously low pitched prop. So I'd imagine a pfp would work good.

 

[MileHighJSC]

Mixing 3 gal of c-12 to 2 gal of 93 pump gas to use with the b pipe.
Going to put the dry pipe back on tonight. Any thought as to the fuel mix I should use or do I go with straight up c-12

On second thought, To be on the safe side, you may want to run straight C-12. I was just looking at your psi of 215 and not at your 28cc domes. Your exhaust port timing is very aggressive. Stock port timing with 28cc domes is around 245psi. Straight C-12.

 

[SN760]

Thanks for all the advice! : )
Didn't get the dry pipe put back on yet. Did get to the lake yesterday and tweaked on the b-pipe. Seems that the more you dry out the b-pipe the better the ski runs. Top 2 screw closed, bottom screw almost closed. Water to the stinger way reduced (keeping a close eye on water box and coupler temp). Mixing C-12, 1 to 1 - no signs of detonation.
Ski is hitting very hard on the bottom and I don't have that feeling of "hitting a wall" on the top end like I did before.
Still wanting to Install the dry pipe but may wait until I have a programmable TL ign. so I can set up the timing curve.

 

[MileHighJSC]

I agree, most of the time b pipes run best with little water. I run triple cooling to keep the pipe and motor cool, so I can inject minimal water.