anyone know what is the smallest cc dome I can use for pump gas on a 72mm bore?

[jhtrx250r]

I am sick of buying race gas for my 310 PV motors, 310 stroker

My CPI sphinx has the weird CPI head and the dome size is not marked any where?

My LRD (pro cross cylinder) has a 28cc dome but it needs to be replaced, will 28cc work for pump gas? and where do I get a new head dome? will the ESR domes work?

MY LRD stroker motor (OE cylinder with 310 sleeve) has a LRD (AKA pro designs)
cool head with a 26.5 cc dome.

If there is a formula that any one knows of to calculate bore size with cc size to come up with a compression ratio ?
That would be great as well.

Thanks

[C-LEIGH RACING]

I would say no less than a 30cc dome, But, I can go ahead & tell you, you'll be sorry you switched.
Pump gas is junk & much as you have spent to get the engine like you wanted it, that engine dont deserve having to use it.
Sit back & thing good, hard & long what your about to do.
Neil

[Langbolt]

Sure!

Take your Displacement:

(Bore x Bore x Stroke x 0.7854) / 1000 = Displacement (cc's)

so

(72.0 x 72.0 x 72.0 x 0.7854) / 1000 = 293 cc's

I think 13:1 is the most you can run a 2-stroke on Pump gas

(Displacement + Dome volume) / dome volume = comp. ratio

Lets try a 25cc dome

(293 + 25) / 25 = 12.72 : 1

Lets try a 32cc dome

(293 + 32) / 32 = 10.16 : 1

You can always double check the compression value (PSI) when assembled to be safe.....don't go over 195 psi for pump fuel (93 Octane)

:devil:

[Ruf Racing]

I run a 22cc dome, on 93 octane. I have a negative deck height, pulling roughly 185psi. It's all good! :D

[jhtrx250r]

Thanks for the info guys, I guess I could stick with the 28cc dome on my LRD cylinder, dose any one know if ESR domes work with the Pro-cross head?

[derby]

Originally posted by jhtrx250r
Thanks for the info guys, I guess I could stick with the 28cc dome on my LRD cylinder, dose any one know if ESR domes work with the Pro-cross head?

You will have to machine down the spark plug area on the esr to fit into the prodesign head. Then machine a oring grove into it. The esr spark plug area is a little larger in diameter than the prodesign. Other than that it should slide right in.

Here is one forsale: http://cgi.ebay.com/ebaymotors/ATC250R-TRX250R-ATC-TRX-250R-ESR-cool-head-310-big-bore-/380306767225?pt=Motors_ATV_Parts_Accessories&hash=item588c0cbd79#ht_571wt_935

[C-LEIGH RACING]

Pro-x heads have an angled spark plug hole, so in turn they have a little divit cut into the dome edge & then one sticking out in the outer shell & you got to aline those up when putting the head & dome together.
The ESR domes are machined the same as the Pro-x far as OD, but do not have he little divit cut into the edge.
If you cut that little divit slot into the edge of the dome it will then fit right into a Pro-x outter head shell.
Pro-x domes, will drop right in to the ESR head shells.
Neil

[jhtrx250r]

Thank you Neil!
That is what I suspected but didn't have the two to compare.
Can you get those domes?

Thanks James

[TLR-Online]

I have a spare pro-x dome... i have no clue what CC it is tho. I will take a pic to show what neil is talking about tongiht.

[jhtrx250r]

I just ordered a new one from ESR $50
I do know what neil is talking about I compared my old one, to a pic of a ESR one and ESR confirmed they are the same diameter.

Thanks for the help guys, now I just need to find a good deal on a 72mm piston kit.

[jhtrx250r]

TRL , pro x domes have a part # on them the last 2 digits are the dome CC
Thats how you tell what cc they are.

[TLR-Online]

Originally posted by jhtrx250r
TRL , pro x domes have a part # on them the last 2 digits are the dome CC
Thats how you tell what cc they are.

Thanks... I never really looked at it lol. I guess its a 32cc.

[C-LEIGH RACING]

Originally posted by TLR-Online
Thanks... I never really looked at it lol. I guess its a 32cc.

Whueee, 32cc, pump gas.
Neil

[Pumashine]

Originally posted by jhtrx250r Thanks for the help guys, now I just need to find a good deal on a 72mm piston kit.

I have a new, never used 72mm wiseco piston I got a couple years ago from ESR. I would like to get 1/2 price for.$80 shipped

[jhtrx250r]

I sent you pm, and my cell, call me I'm local
Thanks James

[pdxbigfoot]

James is a pimp!!!!!
The boyz around here have been talking of starting a "we like James" group as he always comes through with whatever you need. Parts, knowledge and always a smile.

Good peeps for sure!!!!

[Pumashine]

Originally posted by pdxbigfoot
James is a pimp!!!!!
The boyz around here have been talking of starting a "we like James" group as he always comes through with whatever you need. Parts, knowledge and always a smile.

Good peeps for sure!!!!

James is a proud owner of a new never opened 72 mm wiseco piston kit he scored for 1/2 price. It will be on his doorstep tomorrow!!!!!

[jhtrx250r]

Thanks pumashine!

[ceaserthethird]

Any picture's to share of your 250R's ?

Keep us posted

[jhtrx250r]

I put a few pics up a year or two ago, right after I had the sphinx PV motor finished.
Ceaser I thought you where a ATC guy ?
Good to see you on the forum.

[ceaserthethird]

Wife own's a TRX250R, That i work on :D

[bsmith106]

Hows that sphinx working out for you? Is it the redesigned one? Trying to find out if its a better option than an esr for all around ridng.

[jhtrx250r]

The sphinx is great!, Mine was cast in 06
I dont know if that is the new design, I dont think so.
I have had to update the head, that made a huge diffrence, right out of the box it was great tons of top end but a little weak on the bottom.
last year my builder re sleeved it and changed the port timing a lot to gain power all the way through, the origonal coating was nikisil.
If your looking for a cylinder, you get what you pay for, The ESR is the cheepest and thats what you get a cheep cylinder, the old esr was better when it was the same pro x jug that CT, and LRD used, I have a LRD PV 310 from 06 its awsome, down side is that cylinder runs $1600 compaired to ESRs $600, but trust me you get what you pay for, its sort of like compairing a kia to a lexus, they both drive but one is more refined.

[bsmith106]

Its good to hear your happy with it. I was thinking about a 78mm bore stock stroke. But not too many people have expieriance with them. I think the new castings have a bigger exh port and came out around 09-10 not sure.

[jhtrx250r]

I had arlan from LED formerly LRD build mine I think he changed the size of my exhaust port because he had to get a new gate for the power valve and said my old one was too small.
I know it makes way more power than a esr 330 I used to have, I nwill try to get it on the dyno soon just dont want to pay the dyno costs. last dyno sheet I have is from befor re sleeving and it made around 55 rear wheel HP I dont remember the torque but it feels much better now.