stroker kit?

[Projectp5NA]

Quick question though,the cumbustion chamber consists of the shape of the piston and head,right?so if we increase the bore would we have to machine the head to match and would i run into a valve clearance issue with th higher comp ratio?

 

[twilightprotege]

nope. you'd just get custom pistons made to suit. obviously getting the chamber as smooth as possible would be best (ie no dips etc), but that'll cost a bit

 

[Projectp5NA]

good news....hate extra work too much $$$$$$$ even if my buddy could hook up a discount at his machine shop

 

[Installshield 2]

Andy...In all honesty, the bore to stroke ratio is more or less meaningless in this sense...Plenty of undersquare engines have nice high powerbands (which goes against the ol' adage of undersquare engines have lowend torque...and thats its)...A B18C5 is undersquare...and the older F20 S2000 engines are just barely square...And both those engines breathe better than marathon runners...

What I am getting at is simply that slightly increasing the bore of the FS, will yield possibly 2-3whp after tuned...and breathe no better high up than it otherwise would...The size of the stock bore is what restricts the size of the stock valves...and with changing just the bore, the valves will still be hard pressed to let any more air in...especially with the stock cams...

Now you probably see where this is going...It won't hurt anything at all...After larger valves are incorporated, and proper cam specs to take advantage of it...you will see more substantial gains...My only point is that bringing the engine closer to square won't really affect anything...you can still get it to breathe with the stock geometry...

I am only pointing this out to show that a larger bore size will not help it breathe on its own...and it will not increase the stock redline capabilities at all...Some people try to say that the closer an engine is to square, or if its oversquare...that it will rev forever and make heaps of highend power...I am trying to illustrate that it takes a lot of other variables than just bore and stroke...

 

[twilightprotege]

fairy nuff.

on a side note, i was looking in one of the yank mags that was porting a B18C head. in stock form, it only flowed slightly more than my ported head so i guess that's pretty good because the b18 is quite a good head isnt it???

but yeah, our engines could really really do with larger exhaust valves...

 

[Installshield 2]

yeah I don't think the B18C1 (GS-R I think) and B18C5 (ITR) have the same head...I know the cam specs are different, and I am not positive about the galley and porting specs...I know the B18C5's bottem-end and valvetrain is hand assembled, and the head is hand "scuffed" (gives some bragging rights similar to the AMG crowd)...and the rest of the B-series engines are all machine built...But the ITR definately has a great powerband...and the worse the head flows...the better news for us...

 

[akhilleus]

Was anything ever discovered concerning larger exhaust valves...how much room is there to work with...any ideas. Could one increase the size to the same as the intake and use intake valves on the exhaust side.

 

[Installshield 2]

There was a dude (GreenMp3) or something, that did a full MP3 conversion, except for the engine, to an ES...And had a ton of head and mani work done...I never saw a dyno, but I have the pics of his head...the valves were HUGE...but the intake were bigger...he showed a before and after pic, and I don't even remember if he changed the exhaust valves...but either way, there is considerable room to work with...and if you bore the cylinders a little, you have even more...albeit marginally (head restrictions from what the pics look like)

One thing to keep in mind though with boring the FS...the S in FS is derived from it being a shorter block...so block strength could be a question once bored signicantly (there is not much room between each chamber)...They only offer factory pistons up to a .5 mm larger bore from what I remember...which may point to anything beyond that being over its service limit...and .5mm is nothing big...

In either case I am searching for those pics on the forum now...I will try to find a link...

EDIT: heres the pic...http://www2.msprotege.com/forum/attachment.php?attachmentid=6169

 

[Installshield 2]

Its a funny angle sort of...but you can tell they are significantly larger than stock...

 

[twilightprotege]

i'm sure there is enough room stock to make the exhaust valves the same size as the intake valves. if i ever take my head off again and feel like doing this, that's what i'll be doing.

 

[twilightprotege]

also, i think from memory he only increased the size by 1 or 2mm. it wasnt much

 

[Gen1GT]

Jamie, there's more to increasing bore than just an increase in displacement. A 90cc increase in displacement might only get a few hp like you said, but just as importantly, it unshrouds the valves. You will have 1mm on either side of the valves on the wall sides of the cylinder. When the cylinder wall is in the way, that 'tulip' airflow shape can't form perfectly. If you push the walls out a bit, it opens up the space for this to happen. You might actually be better off with stock valves, and a larger bore(the route I'm taking). Other than cleaning up the castings, the only headwork I'm doing is a 5 angle valve job and unshrouding the valves a bit.

 

[Installshield 2]

Understood...just trying to show that bringing a stock undersquare engine closer to square, by dimensions only, will yield very little in a case where displacement can only be increased marginally...stock square, or oversquare engines have all kinds of other variables incorporated to make them behave in their traditional sense, which is lots of high end power...and a little less lowed torque...It is not just the geometry of the bore by stroke on its own...