The exhaust is shoved up next to the cylinder wall further than any other head. We know this from our work creating the Wiseco multifit pockets. It was moved over to get more intake valve diameter. The intake valve has 14.7 lbs or pressure pushing air in. The exhaust has a lot more that that on blowdown. most exhaust leaves the cylinder before the piston even begins to move upwards from bdc. So it's usually smarter to sacrifice exhaust flow for intake flow. the "idea" of running a 2.160 intake valve on a L92 and 2.200 on a LS7 makes no sense to most that calculate velocity numbers, but GM has CFD and Ron Sperry is da man. I met him in person once back in the 90's while I was up at Batten....a truly out of the box thinker. The cross sections are also way bigger than most people would expect for their intended rpm.(Denali truck motor spending most of it's life at 3500rpm for instance) What we think we know.... isn't. -Brian Nutter-Wiseco

 

I like this theory, maybe just because it's simple but I'm not sure. As for the cam I'm pretty sure that just has to do with the LS6 being a smaller free'er revving engine that makes power a little higher up. Compare this to the LS3 which is bigger and makes a good bit more torque down low. Also the emissions argument has to be made when comparing these two engines, just think about the production # difference.

BTW: There has to be a reason why cam manufacturer's suggest a higher minimal compression as their cams get bigger.

 

Best post so far, Brian.

CFD is a great tool, especially in the hands of someone like Ron Sperry. Discussing heads with him is fun and enlightening, to say the least. He's still very active. Saw him at PRI and at a track in 2007.

I like this quote:

"Being able to "think outside the box" presupposes you were able to think in it." --Bob Lutz



Jon

 

what is CFD?

 

CFD is computational fluid dynamics. This is a sophisticated computer-based analysis and design tool for aerodynamics. The aircraft manufacturer that I work for uses this kind of tool to analize and predict things related to external aerodynamics. Engine manufacturers like Pratt and Whitney use the tool to refine the internal aerodynamics of jet engines and cylinder head designers like the Sperry brothers, Ron and Ken at GM. The GM, FAST and Starr intake manifolds have all been designed using CFD as a primary too.

Take a look at this http://en.wikipedia.org/wiki/Computa...fluid_dynamics.

Steve

 

What's so sick about CFD is that mere mortals are starting to use it on everyday stuff. We've dome some dome/reverse dome work to enhance combustion. We've also used it to look at Aero on cars....I'd love to spend my days modeling ideas...but I've got to earn a paycheck.

 

CFD is tough ****. I get to take it next year and am kinda looking forward to it. Doing CFD equations take up like 5 pages no lie (without computers of course).

Sorry SStroker but why dont you give you .02 worth? Seems like you are the man around here, why is that? Not too familiar with some of the guys on here so please dont take offense to my questions

 

One of my head porting buddies in Mooresville has access to CFD and is pondering the 80 hours of input time needed on a "pet" project I'm building with a local friend. It's a naturally aspirated Honda S2k. 12.5:1 pump gas 1425cc. The heads flow 310 cfm stock and some have been taken them up to 360cfm and higher. Not quite sure where ours will end up. 3.504 bore, 3.897 stroke, and 5.636 rod and turning 10K rpm is some serious piston speed, but commonly done. We're looking for 280whp conservatively..might hit 300whp...we'll see. Could of done a LS1 swap for less money, but it's fun to experiment with different stuff. These engines make a wail that sounds like a trombone blast put through a distortion pedal with the amp turned to 11.

 

Jon doesn't want to spoon feed us anything we can't figure out ourselves. It's kinda like that old proverb.

Build a man a fire, he'll be warm for a night. Set a man on fire, and he'll be warm for the rest of his life.

Or something like that.....

EDIT- an S2K engine is 1.4liters? Really?

 

dont forget about ken sperry either..

 

It's more like I don't know. I do enjoy listening to the theories of why things work.

OK, I do have one theory about C5R, LS7, LS3/L92 heads: GM did this mainly to confuse the rest of autoenginedom, of which we are all a part.
With the bore and stroke mentioned it's a 1.425 L engine ONLY if it has about 1-3/4 cylinders. . I believe brian meant 2465 cc. At 300 rwhp @~9200 that's a doable 195 psi BMEP. Things have to be done fairly well, however.

FWIW, I was amazed at the mass of the S2K rocker arm system. I suspect valvetrain control @ 10K presents a challenge.


Jon

 

Aww come on Old SStroker why don't you tell them the truth....

"I could tell you but you probably couldn't afford it!" - Joe Urban

 

That made me laugh!

 

Yep, sorry. The engine was 2.0..the later s2k's had 2.2 We're putting a k24 crank in it and ERL is sleeving the block and that puts it at 2465. As for the heads....10K isn't that much for these...it's actually common with stock springs etc. The really developed ones with Ti everything turn a lot tighter. Sounds sorta impressive, but endurance V8's turning 9500rpm with flattappets is a lot more impressive.

 

Brian, is anyone doing lightweight (Ti) rocker arms for these VTEC engines? There is a lot of iron swinging there even if it is OHC. I used the UPS scale instead of the gram scale to weight the last ones I saw.

Jon

 

Not to steal the thread here Old SStroker, but I don't think so on Ti Rockers. The lost motion device used on the Vtec is pretty complex...Crane/Ferrea does some race only aluminum roller rockers that ride on the "vtec" lobe only of the b18's and h22's. The b and h series hondas use a lash pad...which also isn't an easy thing for the aftermarket to get right either.

The k series and F series use a roller in the rocker....hence I don't think the aftermarket sees that it can beat the o.e. as easily. Same with 4g63 mitsu. In my opinion, only 1/2 the rocker really moves around that much as one side is nearly motionless on the hydraulic "lifter"..which pretty much emulates a stationary pushrod tip. A friend of mine Kevin Kiggly did a spin test with a hi speed camera on the 4g63. With a completely bone stock valvetrain, it turned 10,300 before it tossed a rocker. He developed a Beehive spring package for it (being used by the heavy hitters now) that REALLY settled things down to the point it's not a problem to twist it MUCH tighter now.

Here's where it's going to get fun for tuners in the near future. The latest I-vtec systems allow 50 degrees of cam phasing in ADDITION to vtec. The problem is these 4v engines can a: crash valves into pistons b: crash valves into valves c: get the timing chain tension BETWEEN the two sprockets reduced enough to induce whip and break Chains/tensioners. This can be exagerated with quicker longer duration lobes and oversized valves.

Old SStroker, Isn't GM, ford or Chrylser rumored to be looking at dual underhead cams that can be phased seperately in the valley to optimize packaging? At Batten in '99, we machined the prototype billet block valvetrain spin test fixture for Chrysler's "new hemi". I was astounded at the beauty of the high cam then. I've bet they've come along way since!

This new level of technology is really going to seperate the men from the boys when it comes to tuning and engine building.