250R head

[CorvetteZ06]

hey guys, i just bought a 250R motor from a good friend of mine. Its got a new Duncan racing 265 national top end. The stock head was modified for the cylinder.... (im guessing they milled it) my eqtion is would it make more power if I ran a cool head on it? some people don't think so since the stock head was already modded for the cylnder. what do you guys think? thanx.

[zedicus00]

if they cut the head for that engine then switching to a coolhead might even hurt performance. coolheads r a 'i cut for any engine' design where that one was cut to help combustion at that engines peak. duncan does good work

[nacs400ex]

Currently I have a 19c (stock)head on my lrd265 and I have to use race fuel. Im guessing the dome has been milled down ? Anyways, I am wondering if it is possible to run a different head such as a cool head or a different stock head to achieve running the engine on premium or atleast 50/50 mix w/ race fuel. Ocassionally I will go on the local fireroads and wide trails with my quad, and I do not want to be using race gas. I have also considering purchasing another mostly stock 250R engine, and using it on the trail.

Does anyone have any suggestions?

[zedicus00]

buy a stock head off ebay they go for dirt. or depending on what yur compression is now and what gasket setup u r ranning u may b able to eek by with just putting a stock gasket under the head. basically to run pump gas yur compession needs to be 190 ish or less. thas not a hard an fast rule though depends on temperature and elevation and so fourth. so drop the compression an thin the gas down till it pings or detonates then go up on the octane one notch. expect to loose sum torqueness as u drop compression too

[wilkin250r]

Originally posted by CorvetteZ06
hey guys, i just bought a 250R motor from a good friend of mine. Its got a new Duncan racing 265 national top end. The stock head was modified for the cylinder.... (im guessing they milled it) my eqtion is would it make more power if I ran a cool head on it? some people don't think so since the stock head was already modded for the cylnder. what do you guys think? thanx.

Duncan does pretty good work. If you already have head modifications, done by a true proffesional, I highly doubt you would see significant increase by going to an aftermarket head.

[wilkin250r]

Originally posted by nacs400ex
Currently I have a 19c (stock)head on my lrd265 and I have to use race fuel. Im guessing the dome has been milled down ? Anyways, I am wondering if it is possible to run a different head such as a cool head or a different stock head to achieve running the engine on premium or atleast 50/50 mix w/ race fuel. Ocassionally I will go on the local fireroads and wide trails with my quad, and I do not want to be using race gas. I have also considering purchasing another mostly stock 250R engine, and using it on the trail.

Does anyone have any suggestions?

Certainly changing the head to lower the compression would allow you to run pump gas. However, it may not run as well, or it may have other side effects. There is more going on inside your combustion chamber than just compression. There is the squish band and tolerance, squish angle, and overall combustion chamber design to consider.

I'm not an expert on the LRD machining modifications, so I can't tell you how all of these factors will change. But I CAN tell you with absolute certainty that it's more complex than simple compression ratio. I would highly suggest you shoot the question over to LRD.

[zedicus00]

that is a good point but if he is jus going trail riding he doesnt need the max performance. u can safely run that engine on pump gas as long as u get it below 190 (i would say safely 180) pounds of compression. true it wont b a perfect setup anymore but keep the race cut head for when u race and u will b able to run it in its prime setup still.

[wilkin250r]

Originally posted by zedicus00
that is a good point but if he is jus going trail riding he doesnt need the max performance. u can safely run that engine on pump gas as long as u get it below 190 (i would say safely 180) pounds of compression. true it wont b a perfect setup anymore but keep the race cut head for when u race and u will b able to run it in its prime setup still.

Unless the squish was so far off that it could not efficiently cool the fuel/air mixture as in compressed, and thus INCREASING the likelyhood of detonation. Or there was something about the particular setup that would create a hot-spot in the engine.

I'll admit, its rather unlikely that he will run into serious problems, BUT THE CHANCE IS STILL THERE. You can't just change the head and combustion chamber at whim, there is the possibility of negative side effects. Slim as those chances may be, it's still worth shooting an email over to LRD to make sure.

What if the squish ends up being too small, and the piston is in danger of hitting the head?

[zedicus00]

its got a 19cc stock cut head now. my guess would b anything he finds is going to hav a bigger squish and or cc size especially since he is trying to lower compression. im not saying he shouldnt email them to know for sure. im jus saying if he was to gues odds are in his favor.

[deathman53]

they probably used a cr gasket, buy a stock trx gasket, its pretty thick, that should lower compression and it will only cost you about $10

[nacs400ex]

I'm going to take this question to LRD. My motor has a spacer plate. Does this mean it has an 86 piston with longer later year rod ?:confused:

This is my first R, and I bought it in peices from a fellow race buddy. Now its almost all together, havent had a chance to get rad hose, gas line and wheel bearings.

Thanks for everyones suggestions