363 vs 370

[mandom250r]

I was just wondering why everyone shows much interest in 363s and not 370s. About two years ago everyone wanted a pro-x 370 so they could be the fastest at the dunes; at least  people that i knew. Now everyone seems to have stroker engines, the 344 and 363 being most popular. Is the 370 mostly for drag racing and the 363 more for play/dune? Is there something i dont know? Which one makes more power? are there better port numbers with the +4mm 363? i would just like to compare pro-x cylinders as i know a sphynx would make more power than a 370 pro-x.

[RIDE-RED 350r]

363 is actual displacement of a 370 on it's first bore (78mm bore on a +4 crank). It's just a play on numbers. Kind of like how a stock R engine on its first bore is 246cc actual, yet is called a 250.

I have an ESR 78mm top end on a stock crank. Actual displacement is 344cc, but it's referred to as a 350

I'm not sure there is a straight big bore that can get you to 370cc or thereabouts. As far as I am aware, 350 (344 actual) is as big as you can make an R engine with stock stroke (on first bore anyway). 370's require a stroker crank, +4mm. Unless something has changed

[etccb]

Also the use of the 4 mil stroke crank from hot rods vs having an oem stroked 5 mil.
Numbers have always been rounded a bit even from the factories. Factory 125 250 450 500 etc are not really that exact cc most of the time.

[mandom250r]

yea i know the displacement is always less that what it says but i guess my question is why is everyone going with a +4mm crank and not a +5mm crank?

[etccb]

Before the new hot rod 4 mil held together I think most "370" were 5 mil oem rebuilds. You can still get a 5 mil made up it is just a lot are going with the new hot rods 4 mil out of the box due to cost and availabilty-turn around time on a good oem crank being stroked.

[mandom250r]

but which one makes more power?

[PORTED R]

Depends on builder ,tuning ,gearing and rider
Both are fast

[mandom250r]

someone needs to get on here and explain what stroke and bore makes what CC

[PORTED R]

Most the time a 363 is a sphinx cp setup
78 bore with 76 stroke

When people say 370 most likely its a ProX or Esr cylinder at 78 bore with a 77 stoke
Comes out to 368 cc if memory serves me right

But if u go on the cp industries website u can build a 363 puma aswill

[GO OVRIT]

^^^ here are some calculator links  http://trx250r.org/threads/240-calculator-links

[mandom250r]

^^^ here are some calculator links  http://trx250r.org/threads/240-calculator-links

 awesome links!!! ok i got my answers for displacement but i guess i have one more question. Does a +4mm have an advantage over a +5mm?

[FerrinMotorsports]

Somebody from another site seems to think so....I have run a 5mm stroker crank with a ESR 350 top end for three years and have yet to see a 363 pass me on the track......

[mandom250r]

Somebody from another site seems to think so....I have run a 5mm stroker crank with a ESR 350 top end for three years and have yet to see a 363 pass me on the track......

hell yea those are the kind of answers im looking for but i wish they were built by the same builder though

[Burns363R]

A 370 is closer to square and is probably a more balanced power than a 363. But I bet it's a negligible difference from that perspective.

[FerrinMotorsports]

hell yea those are the kind of answers im looking for but i wish they were built by the same builder though

I am running the older ESR cylinder which if I remember right is the old PRO-X cylinder......FTZ ported my cylinder to match the 5mm stroke....I assembled it myself with a few other options....