12:1 on pump gas???

[rollie]

I've always ran my 300 on half 93 half 110 but im trying to sell it and i was wondering of the engine can run on 93 pump gas???

[Cody_300ex]

Nope, no way. Will detonate, and cause you to lose power.

[bwamos]

You have a 250x.

A 250x can get away with up to 12:1 max.

A 300ex because of the longer stroke I'm assuming, causes issues above 11:1.

MY 330ex at 11:1 is borderline on Premium Pump.

It also appears you're running a stock cam which is VERY mild.

[honda250xrider]

yes u can I had one and ran it hard on pump gas 94 with 12:1 compression for years and never had one problem, this is with a webcam also with a mild port job, i'd say try it out and see if it detonate's if so well just run higher octane

[2muchquad]

Yes you can run pump with 12:1 comp.Im actually a bit higher and 93 oct is fine.Compression seems to be one of the most misunderstood topics.While im not going to go too into detail as i cant type so i dont feel like writing everything,but there is a such thing as valve overlap where both intake and exhaust valves are open at the same time therefore reducing actual compression.So with your wisecohigh comp piston you'll be fine on premium pump.;)

[dork]

overlap has nothing to do with compression, its all about the intake valve's closing point. if you had 2 cams with the same intake closing point, but different overlap, they would have the same psi reading. more overlap does however provide more egr effect which cools temps. also a longer stroke typically allows for a bit more compression all things being equal.

also i'd be cautious running a true 12:1 setup in an aircooled motor with a stock cam. the reason some people say they don't have problems is because many aftermarket 12:1 or whatever pistons sit too far down in the bore causing excessive squish clearance, and or they're running a longer duration cam.

[2muchquad]

overlap has nothing to do with compression

Sure it does.The nano second that the exhaust valve is open at the tail end of the exhaust stroke the intake is starting to open for the intake stroke,therefore there will be some pressure loss.We are talking minute amounts here.Thats why some cams work best with high compression.i guess it would be similar to a 2 stroke where ACTUAL compression doesnt start until the piston clears the exhaust port or powervalve.;)

[dork]

when the intake valve is open, the cylinder is filling, not building compression. the point i'm trying to make is actual cylinder compression doesn't start until the intake valve closes. if anything more overlap can increase intake scavenging by exhaust gas which would increase your dynaminc compression ratio when reversion stops. its the same reason late intake closing points can 'supercharge' the engine at high rpms. good debate either way:D

[2muchquad]

I'll give you that point Dork since your one of the few that i have seen that knows what they are talking about.i thought i knew it all.:D