Head Clearance discussion

[Terry Keeley]

We've been running .008"-.010" clearance on our 45 engines, depending on weather. Like you, we like the OD 289's, but the last couple

of orders we've been getting 1-2 dead plugs from each order of 10- right out of the box. We've found the Rossi Std. and Turbo plugs to be

on par with OD, plus the Rossi's have much better selection for temp. range when going cold.

We haven't found a better pipe for the 45 engines than the NR #50901 (we drill stinger w/Z bit- .413") and we ceramic coat pipe and header,

and we run the pipe short and fat on 60%. Try one on your CMB's at 9.25"-9.5" and see what you think... I think the difference is in the

2 stage converging (baffle) cone.

For the money involved, that Bouchie pipe has nothing on NR nitro pipe with a full mod 46DD engine (we're running 193.8° Exh.).

These engines, either NR or CMB, really don't need any exotic trickery for a winning heat racer- just deburr, align things up, delay intake

closing 2°-3° and try to get as close to 28°-30° blow down as you can, without hogging on the exhaust port more than a couple of degrees.

I like those Steve Wood liner shims to test with on a day when the air is really good, too.

Thanks-

TW

You running full water to the by chance?

 

[timothy johnson]

post the picture of the pipe your talking about I’m curious. I run my 45 RS Evos with OD99’s, CMb nitro pipe at 9- 9 1/4 and it hauls ass on my twin of course. but they are full modified engines but no need to change the exhaust timing it’s stock everything else is not stock

Does the NR pipe telescope over a CMB Header?

 

[Timbo Whalen]

You running full water to the by chance?

No, we are not this time of year... we've gotten the best performance out of the Nova's by running them on the hot

side... if the air's hot and sticky we'll add clearance, add water, and run a warmer plug...seems the warmer plug

lights the charge quicker bringing the cylinder pressure up.

 

[Timbo Whalen]

Does the NR pipe telescope over a CMB Header?

Have to check...it fits the NR header perfectly, and the NR header fits some of the CMB engines.

 

[dwilfong]

post the picture of the pipe your talking about I’m curious. I run my 45 RS Evos with OD99’s, CMb nitro pipe at 9- 9 1/4 and it hauls ass on my twin of course. but they are full modified engines but no need to change the exhaust timing it’s stock everything else is not stock

Julian your heads have modified chambers. I am doing one for Eric's RS .45 EVO this week. He can not keep a plug in it also. He talked with Richie and his .45 EVO dose the same thing.

 

[LohringMiller]

My latest article discusses head design. I would love to hear criticisms from the members here.
namba.com/content/library/propwash/2019/october/4/

Lohring Miller

 

[Terry Keeley]

Good article!

Lately I've been running about 15:1 trapped C/R with 70% squish area, a flat squish band and about 0.010 - 0.014" clearance depending on the motor size. I leave the edge between the squish and bowl sharp. My standard heat racing fuel is 60% nitro and 70% for SAW.

Cut the water back by flowing the entire cooling system to about the same as the needle to start, run hotish plugs and a little on the rich side and you can make great power without hurting parts.

Here's an old post with some on-line calculators: https://www.intlwaters.com/threads/on-line-head-volume-calculator.74796/

 

[dwilfong]

My latest article discusses head design. I would love to hear criticisms from the members here.
namba.com/content/library/propwash/2019/october/4/

Lohring Miller

That is a very comprehensive article.
I feel it is better to keep things simple when making head buttons. The trapped compression is most important in a easy to tune eng. Then the MSV calculations come in to play after you get the CR to between 8.8 to 9.2. You can go higher but then it gets in to the plug taking problems with a good MSV to mix things up. It is a balance between MSV and CR that keeps the plug good. More CR less MSV or less CR and more MSV. Nitro % will dictate what you do More CR less Nitro.
Flat squash with 3% angle I found work good. then the clearance and % of squash area need to be set for good MSV. Around 50 to 60 MPS have bin as high as 77 or 80 but only on low CR set ups (8 to 1) on high nitro %. This set up will REV to the moon.
A flat chamber top with a full radius corner that intersects the top of the chamber and exits in to the cylinder at 90% I have found to work best.
Keep it simple and pay attention to all the factors mentioned and it will make tuning much lest pain full.
This is not the holy grail just what I have found works for me in testing.

 

[LohringMiller]

Thanks. A lot of different factors effect head design. I tried to present all the different things people have tried and the reasons behind the design. I think scavenging of the head button is often ignored, but the keep it simple approach seems to work well.

Lohring Miller

 

[dwilfong]

Thanks. A lot of different factors effect head design. I tried to present all the different things people have tried and the reasons behind the design. I think scavenging of the head button is often ignored, but the keep it simple approach seems to work well.

Lohring Miller

Scavenging of the button can be done with the right boost angle. The chamber design also play a part with the flat top and full radius in the corner. This keeps the chamber shallow to clear out better with the boost flow. I feel a wide shallow chamber will clear out quicker.
I know Marty made a chamber that was very small and deep. May be he will post some results he found testing this. He was the one who showed me how to make a button and chamber design that I use to this day with just a few small tweaks.

 

[Chris Haley]

I blend my own fuel. 30%, every 10% increase in Nitro add .010mm head shim on my NR .46 Purple Head. It works with the CMB .67 also. I have had 0 problems. I would rather have a day where all I have to do is clean everything, lube and store than be pushing the limits with 65% Nitro and break parts, ruin modified engines that cost a lot of money. For what? A 3 dollar plaque or trophy? A title which means nothing to the world outside of us boat racers. Everyone is out to win races, some people at all costs. Which is fine. I like my engines to last for another race. Its not all about power only but driving skill also. Throw a highly modified boat with 65% and no experience and you will will wipe them off the water with 10% and a stock engine with experience. I am enjoying this thread as I am a perfectionist in the dirt racing world also. Those engines are 20,000 to 75,000 dollars each. We changed the valve to piston angle to 11 degrees 10 years before NASCAR did. This changed the combustion efficiency dramatically. As the flame front did not have to travel over a piston dome on a 23 degree engine with the same compression ratio. Flat top piston and a very small combustion chamber. It also improve the intake and exhaust runner profile and flow rates.
Regards,
Chris

 

[Terry Keeley]

In my experience it's not nitro that hurts our motors, it's trying to make it burn with the needle. And possibly running too low of an oil content and no castor.

If the head/cooling/plug is right you can run 80% plus nitro and not hurt parts...

 

[dwilfong]

In my experience it's not nitro that hurts our motors, it's trying to make it burn with the needle. And possibly running too low of an oil content and no castor.

If the head/cooling/plug is right you can run 80% plus nitro and not hurt parts...

You hit the nail on the head Terry................

 

[dwilfong]

I will post the before and after pictures and results from a new 45 RS EVO Head modification I am doing this week.
I will include all before and after calculations of CR, MSV, CC squash size and angle changes.
Then a report from the owner on running this set up compared to the stock pug taker.
I will do this with Turbo and standard pug heads with a different set up for each style head to test.

 

[dwilfong]

The first pic is the stock heads. second is the moded heads. I used 2 different tools to make 2 different chamber with different cc but keeping every thing else the same. One tool is 1/4" and the other is 5/16". With the stock head only being 1/4" deep your hands are tied to how much you can do. Building one from scratch is a while different world.
When you can make the chamber as shallow as you want I use the 1/4" tool to make a 1/8 deep chamber.
But this is what I do with a stock head to gain cc's.
Stock heads are .32cc

 

[Chris Haley]

What did I do with My mill and lathe? I know they are here somewhere...LOL. I sure miss them.

 

[Timbo Whalen]

Julian your heads have modified chambers. I am doing one for Eric's RS .45 EVO this week. He can not keep a plug in it also. He talked with Richie and his .45 EVO dose the same thing.

Dave, a couple of us up here can't keep plugs in the 45 RS EVO with clearance tighter than .012". Thinkin' it's a matter of increasing bowl

volume to suit a .009" clearance. I guess just find the chamber volume + squish area volume and calculate out until you come up with same

overall volume with .009" squish, to start.

 

[dwilfong]

Dave, a couple of us up here can't keep plugs in the 45 RS EVO with clearance tighter than .012". Thinkin' it's a matter of increasing bowl

volume to suit a .009" clearance. I guess just find the chamber volume + squish area volume and calculate out until you come up with same

overall volume with .009" squish, to start.

Tim the .42cc chamber is the same chamber on Julian's twin RS 45 EVO eng. Thy do not take plugs running 60%.
I use the MSV as my constant. Keep it between 50-60 MPS at top RPM and you will be good.

 

[dwilfong]

What did I do with My mill and lathe? I know they are here somewhere...LOL. I sure miss them.

Only need a cheep small lathe with the tools shown in the pick.

 

[Timbo Whalen]

Tim the .42cc chamber is the same chamber on Julian's twin RS 45 EVO eng. Thy do not take plugs running 60%.
I use the MSV as my constant. Keep it between 50-60 MPS at top RPM and you will be good.

Good info, Dave... those are the SV numbers I'm shooting for- I've put your 'gift' to good use.

I haven't had mine apart yet, but does that engine have an angled squish band, or is it flat?...

If it's angled, is that squish volume part of the total volume of .42cc, or is that figure just the

bowl?... I'm thinking the latter.

My NR46 is in the same predicament- .39cc including the angled squish area. The .008" I've been running

is tearing plugs up, so we went to .011"-.012" to keep plugs in it- however, that ruins optimum SV-

It's too slow. I'm at 60.3 m/s SV with .011" clearance and assuming squish angle of 1°30' (Nova OEM)...

you mean M/S, not 'MPS', right?... we're probably talking about the same thing.

Please check your PM, Dave...

Thanks, Dave-

tw