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

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

Post by Shockwave » Thu Oct 12, 2017 11:46 pm

V Remian wrote:
Thu Oct 12, 2017 11:40 pm
What intake manifold are you going to use?
I have a ported super victor with an Accufab 4150 on my Dart 225s right now.

Im most like going with either a Holley Hi ram or a Mast single plane.

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

Post by BILL-C » Fri Oct 13, 2017 6:39 am

Go with the l-92 heads . Both intakes good. I'm getting excited about this build and it's not even mine! We have 4 LS builds going on in shop now. Turbocharged L-92 in a land speed racer, supercharged 427lsx with cnc ported cathedrals, LQ-4 with cnc ported cathedrals going into S-10 drag truck, and another LQ-4 with cnc ported cathedrals going into 70 nova. This platform is really starting to grow on me.
Carlquist Competition Engines

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

Post by mag2555 » Fri Oct 13, 2017 6:49 am

That Catherdral shape becomes a hinderence when looking to do as you are shockwave, you really want a Aftermarket LS type head with a rectangular port in my opinion!

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

Post by Shockwave » Fri Oct 13, 2017 8:39 pm

BILL-C wrote:
Fri Oct 13, 2017 6:39 am
Go with the l-92 heads . Both intakes good. I'm getting excited about this build and it's not even mine! We have 4 LS builds going on in shop now. Turbocharged L-92 in a land speed racer, supercharged 427lsx with cnc ported cathedrals, LQ-4 with cnc ported cathedrals going into S-10 drag truck, and another LQ-4 with cnc ported cathedrals going into 70 nova. This platform is really starting to grow on me.
Yeah, I think thats the direction I'm going to have to go.
Friends are telling me they feel the Darts would probably work, but would be heading towards their upper limit on this type of build.

Now im weighing whether to sell off the GM castings and buy the Dart Pro 1 LS3 castings, which are 750/head bare. Its an incredible deal, but the runners are HUGE. 280cc as cast. Seems too big for what I'm doing, but the casting itself seems to be much better all around that my GM castings.

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

Post by swampbuggy » Fri Oct 13, 2017 11:07 pm

Hey Shockwave, I am currently working out my intake port for my engine 371 C.I., 8500 RPM, 18 Deg. engine. If you are gonna spin your 408 even 7800 to 8000 i am pretty sure the Dart LS-3 head will NOT be too big of a port. Keep in mind the liquid fill of the port (280cc) does NOT tell you the whole story, you HAVE to know the MCSA (Minimal Cross Sectional Area) which is the MORE important number (measurement). I figure that i will need a MCSA of 2.90 sq. in. + or - a tad. So i think the Dart head would work pretty darn good, also remember if the port is too small your air speed CAN be too great creating atomization problems. I hope something said here helps you. Mark H.

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

Post by Shockwave » Sat Oct 14, 2017 12:00 am

swampbuggy wrote:
Fri Oct 13, 2017 11:07 pm
Hey Shockwave, I am currently working out my intake port for my engine 371 C.I., 8500 RPM, 18 Deg. engine. If you are gonna spin your 408 even 7800 to 8000 i am pretty sure the Dart LS-3 head will NOT be too big of a port. Keep in mind the liquid fill of the port (280cc) does NOT tell you the whole story, you HAVE to know the MCSA (Minimal Cross Sectional Area) which is the MORE important number (measurement). I figure that i will need a MCSA of 2.90 sq. in. + or - a tad. So i think the Dart head would work pretty darn good, also remember if the port is too small your air speed CAN be too great creating atomization problems. I hope something said here helps you. Mark H.
It aboslutely does. I don't have the formulas in my notes to calculate airflow/CSA requirements for displacement/RPM, so it does help. I try and determine it from my old SAM notebook, guesstimating from other combos I've been a part of re:airflow, displacement, and RPM.

Most of what I've seen has either been 7000ish RPM street motors, or things like our 9500rpm CR5 headed 434. I havent dealt with a whole lot of in between, so I lack the experience to know what is too big/too small for this type of build. Seems like alot of the race motors I've seen have had MCSAs of 3.5ish sq in.

Ive always sized ports by using the throat as a percentage of valve size (I always go small, 85-88%, rather than the 90% my notes recommend), and then use taper to work out the rest of the port. I always remember Darins lectures saying going small and focusing on airspeed will generally produces better results. Since I don't have a bench, I always try and go by that rule and it seems to have worked out OK for the small amount of heads that Ive done in my private life.

But thats always been just based off of a head I have to work with. I've never had to try and determine an airflow requirement of an engine before and determine what CSA is required to move that air.

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

Post by swampbuggy » Sat Oct 14, 2017 9:07 am

Shockwave, here are some formulas for figuring out appx. C.S.A. 1. Bore x Bore x Stroke x R.P.M. x .00353 divided by 613.8 = C.S.A. 2. IF you know your peak C.F.M----------C.F.M. x 2.4=______ divided by 300 feet per second (is a nice target) = C.S.A. 3.By intake valve size, example, 2.180 x .90 = 1.962 , 1.962 x 1.962 x .7854 = 3.023 sq. in. C. S. A. Hope this helps , BTW these most likely originated from D. M. Mark

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

Post by stealth » Sat Oct 14, 2017 9:18 am

Shockwave wrote:
Thu Oct 12, 2017 7:42 pm
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. :?:
There ya go....sell everything and buy complete sb2.2 (many ex cup engines with outstanding parts and years of expert development)


Rpm to 10,000 ...... done deal... :D
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Re: Thoughts on L92/LS3 vs Cathedral port for 8500rpm 408ci

Post by peejay » Sat Oct 14, 2017 9:21 am

Shockwave wrote:
Thu Oct 12, 2017 7:36 pm
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.
Not to sidetrack, but stock rods and pistons? How about the rod bolts?

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

Post by A_VAS » Sat Oct 14, 2017 10:06 am

BILL-C, fyi the L92 head would be a truck head, and no does not have the hollow stem intakes. Only the LS3 heads (car heads) get the hollow intakes.
the truck valves are more like 120g

Shockwave, if you are gonna buy heads have you checked into a LS7 head fitting this bore? smaller exh valve
a set of nice take-offs and you get the good intake valves...good port...good chamber...knock the wing out and do a valve job/guides to fix the GM crapola. yet another option to contemplate.
too lazy to make power w/o boost

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

Post by Shockwave » Sat Oct 14, 2017 7:08 pm

peejay wrote:
Sat Oct 14, 2017 9:21 am
Shockwave wrote:
Thu Oct 12, 2017 7:36 pm
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.
Not to sidetrack, but stock rods and pistons? How about the rod bolts?
Yep, stock rotating assembly. I bought the motor and T56 with 25k miles on it from the owner of SAM. It came out of his wrecked 35th anniversary Camaro.

I swapped it into a 98 V6 Firebird and drove it around as a bolt on motor while at school.

It had 40k miles on it when I pulled it to do a cam/head install. I flycut the stock pistons for valve reliefs while it was apart, reassembled with total seal rings, and clevite bearings.

Other than that, stock bottom end, including rod bolts. I spin it up to 7500 a couple times a week for the last 2,500 miles, and shes done fine so far.

Motor peaks around 7200, and it hits right around 7450 at the shift going by the data.

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

Post by Shockwave » Sat Oct 14, 2017 7:19 pm

swampbuggy wrote:
Sat Oct 14, 2017 9:07 am
Shockwave, here are some formulas for figuring out appx. C.S.A. 1. Bore x Bore x Stroke x R.P.M. x .00353 divided by 613.8 = C.S.A. 2. IF you know your peak C.F.M----------C.F.M. x 2.4=______ divided by 300 feet per second (is a nice target) = C.S.A. 3.By intake valve size, example, 2.180 x .90 = 1.962 , 1.962 x 1.962 x .7854 = 3.023 sq. in. C. S. A. Hope this helps , BTW these most likely originated from D. M. Mark
Thank you very much man. Im adding these to my notes.

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

Post by Shockwave » Sat Oct 14, 2017 8:10 pm

A_VAS wrote:
Sat Oct 14, 2017 10:06 am
BILL-C, fyi the L92 head would be a truck head, and no does not have the hollow stem intakes. Only the LS3 heads (car heads) get the hollow intakes.
the truck valves are more like 120g

Shockwave, if you are gonna buy heads have you checked into a LS7 head fitting this bore? smaller exh valve
a set of nice take-offs and you get the good intake valves...good port...good chamber...knock the wing out and do a valve job/guides to fix the GM crapola. yet another option to contemplate.
I have looked into it, but the only affordable castings are the RHS small bore LS7 heads, and theyre designed for 3.900 bore.
The GM casting wont fit my bore at 4.030

Im trying to keep it somewhat affordable as well. Im planning on doing a 4.125 bore C5R or LSx DR head in a few years, so this is a stepping stone/learning experience for me.

The Dart 280cc heads are 800/bare. Trick Flows 255cc LS3 head is 1000/bare.

The darts seem like an incredible deal.

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

Post by A_VAS » Sun Oct 15, 2017 11:28 am

i was suggesting putting a GM LS7 head on your 4.030 bore, not the "small bore" variants
if you have a take off that can be used to set on the block and take a look, I believe if you run a smaller exh valve it can be done.
too lazy to make power w/o boost

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

Post by steve316 » Sun Oct 15, 2017 12:01 pm

What ever head you choose; I would not run them on a stock short block.Rods and pistons would have to be up graded at least. As far as witch head to run; I would vote for the ls3 because of air flow and the rocker arms you have. Ti valves will let your springs last 3 times longer. This is your budget so its your call, but if it comes a part it will not matter witch heads you have on, they most likely be scrap.Good luck Steve

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