Exhaust timing question for the gas motor guys.

[ChrisHerzog]

Just curious if anyone has checked the exhaust timing on one of Gizmos’ modified 30 cylinders cut for a motor with a 2mm crank. I’m wondering what numbers you got when you checked it.

Heck for that matter, to the guys cutting on motors, what numbers (ballpark) are you shooting for when working on the above set up. A 30cc Zenoah with a 2mm crank in it.

Thanks in advance,
Chris

 

[Mike Hughes]

196 on the 30plus I measured yesterday.

 

[Mike Hughes]

Which I think is too much. I am running against identical setups and seeing more power from the other setups. I am building one right now at 190.

 

[Dave Gilles]

ive cut 4 heads from 180 to 195 ran them back to back and noticed no difference. its kind of bored me on porting.

 

[ChrisHerzog]

196 on the 30plus I measured yesterday.

We came up with basically the same, thanks.

 

[ChrisHerzog]

ive cut 4 heads from 180 to 195 ran them back to back and noticed no difference. its kind of bored me on porting.

We have found problems getting it up on pipe coming off the turns. It doesn’t have an issue at all with a lower timing.

 

[Dave Gilles]

have you tried lengthening the pipe since the timing is so high?

 

[ChrisHerzog]

have you tried lengthening the pipe since the timing is so high?

Dave, we have tried everything that you could imagine. Pipe length, different pipes, a number of different props, strut adjustments, fuel, carbs, carb adjustments and finally different engines.

Originally the boat ran great but one of the waterlines got pinched and he burnt the motor up. He rebuilt said motor using a top end kit from gizmo and has not been able to get the boat right since.

Yes, before anyone ask, the crank is not bent, bearing are all great and when he ordered the top end kit he told them that he had a 2mm crank in the engine. He has gone over the number with gizmo and they say that his numbers are correct.

 

[Dave Gilles]

Dave, we have tried everything that you could imagine. Pipe length, different pipes, a number of different props, strut adjustments, fuel, carbs, carb adjustments and finally different engines.

Originally the boat ran great but one of the waterlines got pinched and he burnt the motor up. He rebuilt said motor using a top end kit from gizmo and has not been able to get the boat right since.

Yes, before anyone ask, the crank is not bent, bearing are all great and when he ordered the top end kit he told them that he had a 2mm crank in the engine. He has gone over the number with gizmo and they say that his numbers are correct.

I started a thread yesterday about needle settings cause all my engines whether I ported them or they're CNC ported are all running like crap lately. I dont know if its fuel or what maybe.

 

[ChrisHerzog]

I started a thread yesterday about needle settings cause all my engines whether I ported them or they're CNC ported are all running like crap lately. I dont know if its fuel or what maybe.

He was using avgas.

 

[Ronnie King]

Chris,

The GZ's I have checked are 194 to 196.


Regards,

Ronnie King
NAMBA #1223

 

[David Krienke]

He was using avgas.

Well using avgas will just make it slower. Unless you are getting into super high compression the lower the octane the more power you get. that timing seems super high he is using. I am unsure what he is thinking. I wonder what the transfers are coming in at. that is going to make a narrow band peaky engine imo.

 

[ChrisHerzog]

Well using avgas will just make it slower. Unless you are getting into super high compression the lower the octane the more power you get. that timing seems super high he is using. I am unsure what he is thinking. I wonder what the transfers are coming in at. that is going to make a narrow band peaky engine imo.

The boat is not slow at all. The problem with it is, if you try and keep the boat in lane one all the way around the coarse, it falls off the pipe in the corners. When you get back into a straight a way, it takes all the way down to you get to the entrance bouy before it starts to get on pipe. At that point you’re turning again and the cycle starts all over. Lengthening the pipe has no effect. Changing the needle settings have no effect. Dropping down in prop size has little to no effect, moving the strut has no effect.

Take the same motor (lower end) put a stock jug on it ( exhaust timing now about 178), it runs and drivers great like a bat out of hell. Like this his boat is fast but not quite as fast as his boat with a mod motor in it.

 

[Wally Duarte]

Chris , what type of boat is this ? I would have said that the engine is lacking torque , but because of all the things you’ve tried have not made any noticeable change - I’ve always said this just means your not anywhere near the problem. IMO check the less likely items , swap spark plug , pull the shaft and see if it’s spinning freely , I’m big on air delivery - this new engine may not have a strong intake tract and isn’t pulling in enough air - try running without the cowl. What does this engine have for an intake block? If it’s a stock plastic block check and see if it’s warped , has the intake block been grinded on and opened up?

 

[David Krienke]

The boat is not slow at all. The problem with it is, if you try and keep the boat in lane one all the way around the coarse, it falls off the pipe in the corners. When you get back into a straight a way, it takes all the way down to you get to the entrance bouy before it starts to get on pipe. At that point you’re turning again and the cycle starts all over. Lengthening the pipe has no effect. Changing the needle settings have no effect. Dropping down in prop size has little to no effect, moving the strut has no effect.

Take the same motor (lower end) put a stock jug on it ( exhaust timing now about 178), it runs and drivers great like a bat out of hell. Like this his boat is fast but not quite as fast as his boat with a mod motor in it.

I think your lean when in the corner, more load then out of the corner it richens when you go down the straight ,less load. you could try richening the needle and see if you can get a good balance. you might have too much prop on the straight for the engine as well. you could try bending a little cup out of the prop or barr cutting the trailing edge. as he said above the torque is what your missing and that is because of the high exh timing. with high timing you will need your pipe longer as well.

 

[Dave Gilles]

The boat is not slow at all. The problem with it is, if you try and keep the boat in lane one all the way around the coarse, it falls off the pipe in the corners. When you get back into a straight a way, it takes all the way down to you get to the entrance bouy before it starts to get on pipe. At that point you’re turning again and the cycle starts all over. Lengthening the pipe has no effect. Changing the needle settings have no effect. Dropping down in prop size has little to no effect, moving the strut has no effect.

Take the same motor (lower end) put a stock jug on it ( exhaust timing now about 178), it runs and drivers great like a bat out of hell. Like this his boat is fast but not quite as fast as his boat with a mod motor in it.

have you tried going out to 14" on the pipe? with mine around the same port timing it likes 13-3/4 to 14" there about. Just trying to spitball here.

another issue might be as another poster mentioned intake. have you measured intake timing? 155-165 degrees would where Id think it needs to be.

 

[ChrisHerzog]

Chris , what type of boat is this ? I would have said that the engine is lacking torque , but because of all the things you’ve tried have not made any noticeable change - I’ve always said this just means your not anywhere near the problem. IMO check the less likely items , swap spark plug , pull the shaft and see if it’s spinning freely , I’m big on air delivery - this new engine may not have a strong intake tract and isn’t pulling in enough air - try running without the cowl. What does this engine have for an intake block? If it’s a stock plastic block check and see if it’s warped , has the intake block been grinded on and opened up?

I’m right there with you on the lack of torque.
The hull is a wood scale hull so yes it’s a big heavy hull. However, keeping everything the same and simply swapping out just the jug on the engine with a stock jug, it’s a completely different animal. This is why I was asking what guys were getting for number on the exhaust timing on this particular kit from Gismo’s. I wanted to see if this was just a one off or if this was what he is cutting them at. It would probably be fine in a rigger just not in this hull.

I have one of their 260 top end kits on one of my back up engines. I checked it the other day just to see where it was and it’s at 184 on the button.

 

[ChrisHerzog]

I think your lean when in the corner, more load then out of the corner it richens when you go down the straight ,less load. you could try richening the needle and see if you can get a good balance. you might have too much prop on the straight for the engine as well. you could try bending a little cup out of the prop or barr cutting the trailing edge. as he said above the torque is what your missing and that is because of the high exh timing. with high timing you will need your pipe longer as well.

I wish it was that simple. We have been all over with the needles including swapping out carbs with the 30 in my own hull. Same results no matter what we do with the needles.
As for props, we have been all over the place with props as well. We we finally got to something small enough that it turned up before it would get halfway down the straight, we loose all the top end speed.
Simply just swapping out the jug on the Eng and nothing else changes everything. At this point I’m pretty much convinced that the timing is simply cut to high on this jug for this type of hull.

 

[Wasted wages]

“To finish first, you must first finish”
Stick the stock jug on it, stay in lane one, have fun.
I hate a finicky or unpredictable boat…

 

[LohringMiller]

We've done lots of engine testing. I've posted the articles here:
https://www.intlwaters.com/threads/bearing-damage.86987/page-3#post-854833

Lohring Miller