Technical > Matt Shaff's Engine Shop

sbc HP per cubic inch

<< < (3/4) > >>

wideopen231:
I think one reason bigger bore works so well is unshrouding the valves.Another maybe that with bigger bore higher compression requires less dome hight. even on my desktop dyno hp increase with .060 bore is more than with extra stroke.

dusterdave173:
The bigger bores do unshroud the valves--it really helps
Most older "conventional wisdom " can be challenged these days but the old one about
Big Bore short stroke is still a real sweetheart
My best example is we had a truck puller--National Champ that wanted to stay that way--they had a simple CI rule
I can't remember exactly but it was not very big CI like 4-something
We built a 4.500 bore and made a custom crank to get that exact CI--it was pretty short stroke ( this being a big block Mopar) we then put a crazy big runner head( for that given CI) and cammed the heck out of it--filled with all the parts needed for happy RPM'ing we were stunned at the increase in HP over all the other things we had done in years past and he smashed the field until the rules changed.

These days most folks just put all the stroke and all the bore they can get no matter the math--some do good some are less than hoped for--now we have just opened the old rod ratio thing again-- and..I will leave that for another night. :)

dreracecar:
Personaly I believe the long rod and piston dwell is more suited for blowers since one is atifically filling the cylinder rather than pulling air in with vacuum from the piston stroke. I would go with a shorter rod to get that piston moving as much air as possible quickly and not be lazy

wideopen231:
To my understanding.The long rod  give more dwell time but also more piston speed which is also suppose to help the induction system.Faster piston speed adds to vaccume on the dwon stroke.I have read quite a few articles on subject and even tried  really long rod combo and cpl short rod combos on blower motors.My reasoning for short rod was if long rod help less than perfect intake runner and port then a blower could make use of shorter,hey what better induction sutem than one pushing 40 or 50 lbs of aire pressure into cylinder.

  Needelss to say ABA testing on this is next to impossible.I can not say there was any real on track gains.Then how often do you run blower combo in same air with same clutch,smae over drive and same jet on different weekends?

MaggiFinn:
Here's a short video on rod ratio.

 

Navigation

[0] Message Index

[#] Next page

[*] Previous page