The 90 engine topic.

[DaveMarles]

Ouch. I thought so. Thats not good. The disc surely cannot seal correctly. It has to seal against the carb side backplate or there is no seal. A floating zimmerman disc will only seal against the carb backplate. It doesn't touch the crankcase side for sealing purposes.

Dave

 

[TimD]

Got back from testing the K90 today - here's what I found.

Timings as Ian had them on 50% - idled poorly and extremely hard to keep running on the bank - took a fair bit of 3rd channel tweaking to get it right - needed a MC8 - wouldn't run on an MC9. Showed good speed on pipe but was not friendly at all off pipe.

Next run I removed the 30thou Liner shim, fitted a 10thou in it's place and used the original head button (more volume and all tapered squish) at 12 thou clearance. Same fuel, same pipe length, prop etc. etc.

As soon as I started it it sounded different, idled and generally behaved itself. Totally different feel to the motor (much better).

Here's the killer - even with the stock head button which I don't think is right - I fitted an MC9 plug and it idled on 4:1 fuel with no warmer on the plug at all! Most engines I have will not run on 4:1 like this one did. Unfortunately my throttle servo died and ended my testing a little short but I think in this case it was the induction overlap and not the nitro content causing the poor idle and making it hard to tune.

Tim

 

[Anders_Martinelle]

Tim what do you mean with 4:1 fuel??

I`ll be back later....

Anders

 

[Ian Inverarity]

Anders,

Tim means 80% methanol, 20% oil.

Tim,

Interesting that it still needed an Mc8 to run on 50% with the 30 thou shim. Very strange...

I guess you didn't get it on the water with the 10 thou shim? Pity.

The overlap issue was the way I was betting!

Ian.

 

[Anders_Martinelle]

I`m BACK!!!!!!! B) B) .

If everything is ok that sounds VERY strange.................

You said that you have made a smaller bowl in the head????( can you take a photo and send me)

It sounds that it`s running cold......

Do you use both cooling rings or just the top one??

I use always the top cooling ring and my "home made" heads and i have never seen that problem that you need to run the MC8..

What you also did Tim is that when you removed the shim you incresed the CR and that is what i have said all the time that you need to do....

The throttle response is going to be ALOT better if you increse the CR....

How do you make your heads Ian??

Anders

 

[TimD]

I`m BACK!!!!!!! B) B) .
If everything is ok that sounds VERY strange.................

You said that you have made a smaller bowl in the head????( can you take a photo and send me)

It sounds that it`s running cold......

Do you use both cooling rings or just the top one??

I use always the top cooling ring and my "home made" heads and i have never seen that problem that you need to run the MC8..

What you also did Tim is that when you removed the shim you incresed the CR and that is what i have said all the time that you need to do....

The throttle response is going to be ALOT better if you increse the CR....

How do you make your heads Ian??

Anders

Anders,

Just to clear things up - I ran it with only the top cooled - no lower ring fitted to the case. Water went thru the case passage under the ex - port - then thru header and finally into the head. The air temp was around 35 degrees C (it was hot and humid). First run where it ran like a pig was with a HIGHER CR than the later runs.

In other words the motor performed better even though the CR had been reduced.

I feel there is more performance to be achieved with a different head button. The only reason I had to change the button was because the high CR one was set up for the 30 thou liner shim and I didn't have enough head shims to maintain the correct squish. I didn't want the piston hitting the head.

I am confident that with the type of testing I did that the induction overlap was the cause of the previous bad behavior. Unfortunately I did not get to test the 20 thou liner shim with the high CR button as my throttle servo failed for some reason but I feel that if it didn't work with the 20 thou shim the 10 thou would be more than suitable with the right head button and squish.

I do agree with you that higher CR will improve throttle response and torque.

Tim.

 

[Ian Inverarity]

Anders,

I calculate the volume of the bowl I want, model it up on CAD to work out all the dimensions and bowl shape etc that I want, detail it, print it, give the drawing, material (2011 T6), and a carton of beer to a friend of mine with a CNC lathe, and presto: One head! B)

Nitrocrazed racing: Beer gets good service.

 

[Anders_Martinelle]

Wow Ian, so mutch work to make one head......

I just go in to the garage mount a ball end mill in the lathe and KAZAM!!!

after 30 min i have one ..

idled poorly and extremely hard to keep running on the bank - took a fair bit of 3rd channel tweaking to get it right - needed a MC8 - wouldn't run on an MC9

I`m just suprised about this??

What pipe, length and prop did you use Tim?

Anders

 

[TimD]

Mac's 15cc muffled pipe, various lengths, H667 prop. Most of the issues were related to off-pipe anyway. I don't think that pipe is the right one for it either. Would like to try a Muck 80 pipe on it some day. Also would have liked to try a 1667 or a H48.

Tim

 

[Ian Inverarity]

Anders,

Sounds like more work than it actually is, since I generally know before hand what volume and shape I want, mostly i am just changing the heights so the I am acheiving the head clearance I want with whatever liner shims etc I am using. Beacuse each head is a one off for a specific engine it is made to be an excellent fit into the liner, and needs no head shims.

A-90 type heads are a bit more work than 1/2 an hour!

Go back and read about the trouble I was having with the K90 and what was proposed to be the problems. The problems I had were not related to how it ran on the water, but how it behaved on the stand. Tim's experiments seemed to have prooved that the problems were related to too great an overlap between the inlet opening and transfer timings.

Ian.

 

[Ian Inverarity]

Anders,

Much of the early discussion on this topic was done in a thread about MAC 45 carbs, I cant remmember the exact title tho.

Ian.

 

[TimD]

Anyone got a spare standard K90 drum rotor handy to try and confirm the results?

 

[Anders_Martinelle]

Ian, have you changed the timing on you rotor??

I know that the old A90 head is a lot easier to make then the new one B) .

Anders

 

[Ian Inverarity]

Anders,

Yes, I changed the K-90 drum timings to open at 150 and close at 65 ATDC.

The old A-90 head design with a seperate head button and cooling jacket had some massive heat transfer limitations! Put a servere limit on compression! I have always made one piece heads! B)

Have you run the A-45? How does it go?

Ian.

 

[Anders_Martinelle]

Ian, i got one 45 engine late last autumn and i had not the chance to test it mutch.

I had it one time to the lake and i had no small props with me so i could find "basic setup".

I will continue this summer and i think i will find the same things with that as the 90 engine.

It`s a nice made engine..

Have you tested it yeat??

Anders

 

[Ian Inverarity]

Anders,

I dont have an A-45, but I have seen the one that Craig Chenco has, he ran it at the Nationals here a couple of months ago, and it looked okay, but it hadn't had any development.

Ian.

 

[EatMyShortsRacing]

Hey Ian,

Dont you mean it hadnt been run in yet??? LOL

EMS Racing Running in is usually in heat 1

 

[TimD]

Whats that old saying?

Proper Preparation Prevents P1$$ Poor Performance.....

EMS racing: Letter P missing from Vocabulary! hehehehe - just stirring Craig!

 

[Ian Inverarity]

Craig,

You really should run that thing a bit more to see how it goes! That is the second nats I have seen it at, and still it isnt run in!!! :huh:

Nitrocrazed racing: Engines run in at home....

 

[EatMyShortsRacing]

Ian, well 2 nats that means about 6 tanks of fuel through it.... must be getting close... but only 3 runs with the new drum setup...

now to start playing with it!!!

EMS Racing I cant complain about my performance... I dont have any!!