Thoughts on L92/LS3 vs Cathedral port for 8500rpm 408ci

[A_VAS]

this is interesting question

cost wise:
you already have the dart heads, super vic, and i assume rocker system
adding the cnc work, and outfitting with say 2.08/1.55 titanium valves. You could probably get away with ferrea 6000 series hollow stems as well and save a good bit vs. titanium.

vs.
outfitting the L92 with 2.165/1.59 titanium valves (I think you'd need the titanium to get the lightest pacakge and keep spring loads down)
buy L92 intake and port work for that

Dart head I'd guesstimate would come out less expensive, and you can put that money towards dry sump if you don't already have it?
No-one at SAM you can chat with about previous testing etc to see if the larger rectangle has a clear advantage?

[BILL-C]

The L-92 intake port is a nice shape except for the slightly too tall short side and the big ugly bumps in roof under the intake spring pocket and the 8 mm rocker stud boss. Playing with the short side is good, but taking out those ugly bumps makes the spring pockets thin and rocker stud bosses weaker. The stock intake valves i believe are hollow stem from factory, weighing in at 108 grams. Manley hollow stems are same weight.Alot of plusses and minuses on both sides of decision on which head to use.Sounds like the 8500 rpm is written in stone, so i won't argue against it anymore. In that rpm range, the rectangular port style heads have an advantage. Good cathredral port heads work better on the milder apps.

[Shockwave]

this is interesting question

cost wise:
you already have the dart heads, super vic, and i assume rocker system
adding the cnc work, and outfitting with say 2.08/1.55 titanium valves. You could probably get away with ferrea 6000 series hollow stems as well and save a good bit vs. titanium.

vs.
outfitting the L92 with 2.165/1.59 titanium valves (I think you'd need the titanium to get the lightest pacakge and keep spring loads down)
buy L92 intake and port work for that

Dart head I'd guesstimate would come out less expensive, and you can put that money towards dry sump if you don't already have it?
No-one at SAM you can chat with about previous testing etc to see if the larger rectangle has a clear advantage?

Yeah, Darts would require some more port work and new valves, and I may go to a larger intake, like the Hi Ram or MAST single.

L92s require all new valves, touching up the VJ, honing the guides, deck surfaced, and an intake (Hi ram or MAST)
I already have a set of Jesel Pro shaft rockers for the L92 heads.

I'm going to get in touch with my old head instructor and see what his opinion is, but at SAM (when I was there), we mostly skipped the LS3 stuff and went straight to LS7 or C5R type heads. I graduated and left before they did anything with the original head that my port is based off of.

Im curious if theres enough of a performance gain by the rectangles to justify the outlay of cost.

[Shockwave]

The L-92 intake port is a nice shape except for the slightly too tall short side and the big ugly bumps in roof under the intake spring pocket and the 8 mm rocker stud boss. Playing with the short side is good, but taking out those ugly bumps makes the spring pockets thin and rocker stud bosses weaker. The stock intake valves i believe are hollow stem from factory, weighing in at 108 grams. Manley hollow stems are same weight.Alot of plusses and minuses on both sides of decision on which head to use.Sounds like the 8500 rpm is written in stone, so i won't argue against it anymore. In that rpm range, the rectangular port style heads have an advantage. Good cathredral port heads work better on the milder apps.

8500 isn't a die hard rule. Thats just my personal upper limit financially. Id be ok with something that makes peak power around 7800-8000rpm. Im just not looking to build another 7000rpm street type engine.

I currently spin my stock bottom end 5.7l 7500rpm with the Darts and super victor on top, and It runs very well for what it is. But obviously, I want to go faster.

And thats kind of what I'm seeing too, is that theres a lot of ups and downs on both sided. It seems like the Darts are better suited to a big solid roller casting wise (spring pocket, rocker perches), but Im really concerned about whether the port would be adequate up around 8000+ rpm.

As you mentioned, seems the L92s should have the advantage at those RPM ranges. Im curious how much of a detrimental effect the bore shrouding of the large intake valve has at those higher RPM ranges, if it'll be better or worse than they are on the lower speed applications.

Sorry, I know im reiterating a lot of information.

Also, I didnt mean to come off confrontational about the RPM range. I wrote that post while I was still half asleep. Im open to suggestions, but I do have an RPM goal range that I want to work within.

[Shockwave]

A 3rd option that I havent really considered, is selling off both the L92 heads, and the Darts cathedrals, and buying something like a Dart LS3 or Mast LS3 head, with rolled valve angles and better intake valve location.

[swampbuggy]

Shockwave---the cylinder heads ARE the single most important piece of the engine in power production "(think long and hard about it") Mark.

[BILL-C]

It's both a blessing and a curse to have so many choices. Typically, when a customer comes into my shop, they have a hp, tq, or a specific performance goal in mind, and the rpm range ends up whatver it needs to be to achieve goal. Never had anyone ask for an rpm goal and not a specific power goal. That's ok. The conversation has to start someplace. Once you get a clear vision of your exact goal your options start to sort themselves out. Check out some known good builds online . When you find something you like, use it as a starting point and put your own twist on it.

[Carnut1]

Do you have any flows from these heads?

[Shockwave]

Shockwave---the cylinder heads ARE the single most important piece of the engine in power production "(think long and hard about it") Mark.

Man, Im thinking so hard my head hurts. I feel like im vastly overcomplicating things.

[Shockwave]

Do you have any flows from these heads?

The L92s flowed 355-360cfm at peak lift, which I think was .700. Been years since we flowed them.

My Dart heads I dont have flow numbers on. Very similar ones I helped a friend with flowed 310cfm@.650 lift.

Darts 250c CNC program flows around 330cfm from a 2.080 valve. They advertise 325cfm I believe, but ive seen guys flow them at 330cfm.

[Shockwave]

It's both a blessing and a curse to have so many choices. Typically, when a customer comes into my shop, they have a hp, tq, or a specific performance goal in mind, and the rpm range ends up whatver it needs to be to achieve goal. Never had anyone ask for an rpm goal and not a specific power goal. That's ok. The conversation has to start someplace. Once you get a clear vision of your exact goal your options start to sort themselves out. Check out some known good builds online . When you find something you like, use it as a starting point and put your own twist on it.

If I was going to give you a hp goal, Id say im probably looking to make ~750hp.

[1989TransAm]

Do you have any flows from these heads?

The L92s flowed 355-360cfm at peak lift, which I think was .700. Been years since we flowed them.

My Dart heads I dont have flow numbers on. Very similar ones I helped a friend with flowed 310cfm@.650 lift.

Darts 250c CNC program flows around 330cfm from a 2.080 valve. They advertise 325cfm I believe, but ive seen guys flow them at 330cfm.

That is what my CNC'd L92 heads flowed from Texas Speed. They die off around .650" lift and that is all I am lifting them.

[swampbuggy]

Have heard people say appx. 2 H.P. per C.F.M. 350 C.F.M. X 2 =700 H.P. BUTTTTTT my last engine, a 516C.I. BBC w/Dart 320's massaged that signed off at 365 CFM @ .750" net lift produced 855 H.P. at 6900 so ????????

[Shockwave]

Have heard people say appx. 2 H.P. per C.F.M. 350 C.F.M. X 2 =700 H.P. BUTTTTTT my last engine, a 516C.I. BBC w/Dart 320's massaged that signed off at 365 CFM @ .750" net lift produced 855 H.P. at 6900 so ????????

2hp/cfm is what were taught as a rule of thumb as well, but displacement, stroke (piston speed), bore size, valve layout and port design all seem to play a factor.

[V Remian]

What intake manifold are you going to use?