anesthes

iTrader: (12)

No, you are 100% correct. He was looking at it from an efficiency angle, not a total.

Rate vs sum.

-- Joe

PAFORM350

OMG "going full-retard". That's funny I don't care who you are.

antman89iroc

Yeah like any conversation it sometimes wonders off topic. Hell I've jacked my own threads before.

BadSS

I thought long and hard about an LS swap myself. Chevy finally did a lot right with that engine. The main thing being the flow and efficiency from the stock heads and the minimal cross-sectional area and length of the intake manifold.

Here’s my reasoning, which isn’t much different than the OP’s – my main thing was to make sure I made as much power under the curve as possible, which means you need to make peak torque a good bit over you shift recovery point.

Back in the 90s I called every cylinder head shop in the country with 5-axis CNC machining capability (not many back then) and I lucked up with a shop that had set up a similar program for some high dollar dirt track racing team out of Kansas. The team owner made me sign a release saying the heads were for an out of state street machine and the shop cut my heads for a pittance of $1000, but I still had close to $3000 in them when it was all said and done. I got my money’s worth out of them, serving me well over many years of use and I’m using them on the new build.

My once “special” old school 1990’s “high-tech” heads, while still decent, are not all that special now. While they have similar flow to the race ready AFR 227s that would have been a close enough fit to the criteria, the 227s are about half what I invested in my old heads back then. Specs on the AFR227s are:
2.10 valve – 2.34” MCSA – 227cc – 5” port length (45.4cc per inch)
.100---na/na
.200—148/114
.300—210/162
.400—261/204
.500—296/220
.600—312/229
.650—315/233
.700—318/237

Then there’s the stock L92 LS head - 2.16 valves – estimated 2.4” MCSA – 260cc - 5.85” port length (44.4cc per inch)
.100—74/61
.200—155/126
.300—225/162
.400—277/192
.500—313/206
.600—312/218
.650—310/221
.700—na/na

Now,, the exhaust flow is not all that on the stock L92 heads, but they respond well to porting and I’ve seen intake flow in excess of 360cfm at .7” lift on set of ported L92 heads and over 400cfm on ported LS7 heads. So there’s no question there’s MUCH more potential in the newer LS heads.

Still, if you’re comparing good flowing, $1600 SBC heads against stock L92/LS3 heads, then in theory there’s not going to be a lot of difference in the two with similar camshafts. In fact, based solely on head flow, the LS heads would need more duration on the exhaust to equal the $1600 SBC AFR227 heads, meaning you could run a milder cam (less overlap) on the SBC to get equal power.

Power curves/potential would be VERY similar with the stock L92 heads and the $1600 AFR 227s with all other parameters remaining equal (compression, ring tension, displacement, camshaft duration/lift/lobe spread, etc). The biggest difference when comparing this level of flow is in the LS intake.

Flow with stock L92 heads and a stock L76 intake bolted on is as follows. Note intake flow with a semi-long “tuned” intake is just a little less than you get from a set of race ready AFR210s without an intake. No wonder these cam only LS cars are quick huh???
.100—72/61
.200—151/126
.300—207/162
.400—249/192
.500—278/206
.600—293/218
.650—299/221
.700—na/na

From what I can gather, the length of the L76 intake is approximately 10” with a MCSA of around 2.68-2.80” (this is larger than the MCSA of the heads). This gives a total intake length including the heads of just a little under 16”. I consider a total length of 15-18” with the appropriate MCSA to be just about perfect for the majority of high performance street cars by proving an excellent compromise of “tuned” midrange and top-end power.

The problem is there isn’t an intake off the shelf for the SBC that can give you anywhere close to that. A Stealth Ram gives you about a 11” intake port with heads and a greater MSCA, but an aftermarket TPI is about a 21” total intake length. The “large” long tube 1.625” inside diameter runners have a miserable 2.1” cross-sectional area choking even further the 2.35” MCSA you can get from the base. The SuperRam can bring the total length down to around 17” but you’re still limited to MCSA of less than 2.35" and the runner to intake and intake to head transition is pretty bad.

The only SBC intake that can come close to an LS intake is a heavily ported FIRST with the runners siamesed to about the halfway point. I was working on one but due to family illnesses and a new time consuming job, I haven’t been able to finish it. However, I’m looking at it having a MCSA of around 2.68” and a total port length around a 17” with a much improved runner to intake and intake to head transition.

However, this Inglese intake set up for EFI might have some potential as an LS street killer.


So, since I already had decent SBC heads, snagged a FIRST for $500, and can do all the extremely time consuming port work to the intake myself, I chose to build a 10.8:1, 406 SBC that if the modified FIRST intake acts as expected, it should be able to handle a cam only LS3 – lol. Plus, I’m sure it will be somewhat of a sleeper,,, especially since it won’t look much different than a little ole 305 TPI.

ezobens

Excellent write-up!
I'm looking forward to seeing your final results!

TPIVette

I believe this is the thread you're referencing on CF.

http://www.corvetteforum.com/forums/...o-results.html

Blackdog36

iTrader: (3)

BadSS, thanks for chiming in. Good to see you're still around. You always have some porting project going on Those are some impressive heads you had built back then.

You can always keep going with $$$ to make more power. For a little more I could do the LS3 swap. Well for a little more than that I could do a Dart SHP 420 TPI build, etc. Have to draw the line somewhere. To continue on your discussion, I calculated total intake length of a stock FIRST TPI to be 21.5". Stock diameter varies but is around a gold ball at 1.68 inches. I ran my build through Pipe Max and although primarily an exhaust sizing program it gives overall useful engine information. My calculated intake length would make peak HP at 5,350 rpm. AFR 195 head minimum CSA would equal an intake velocity of 270 feet/sec per Pipe Max. If I siamese runners 1/2 inch, I would now peak at 5,500 rpm. I have some minor porting on the runners to open them up a bit and make them consistent. I may siamese them half an inch since it would match up better for the 1/4 mile but not sure yet if i will.


TPIVette, yes that is the post I was referring too! Thank you for linking it. I found it to be a very good and inspirational read.

Orr89RocZ

iTrader: (20)

The funny thing is just because two heads flow same airflow doesnt mean they make same power. Take flow numbers with a grain of salt.
Some ls3 heads in ported condition can make 360-ish cfm but do not make the power a similar ls7 head does that flows the same.
Same goes with sbc heads of various kinds. My heads have done 700+ hp on na motors but flow 340 cfm by .800-.900". Ls3 head can match that flow but dont see any 700+ all motor

BadSS

No doubt - 100% agreement. I think the LS3/L92 equipped cars respond well to a cam only or to mild porting. Although, I consider them to be "budget heads", since bang for the buck is good IF you already have them. However, if I were picking LS heads for a from scratch build or wanted to do a serious LS build, I'd definitely look at a different head - they appear to have some wet flow "issues".

Dyno Don

iTrader: (7)

Just throwing in my two cents....

My combination is as follows:

355 cu. in. /AFR 1040 heads/Jones custom cam 228/228 .570/.570/113 LSA

10.5 comp. welded up and ported 3860 base (flows 300+CFM) modified SLP runners (see pic)

1 3/4" shorty headers dual cats 3 1/2" catback exhaust 52mm TB

Has dyno #'s 400/430 RW generous or not it matches another members #'s on the same dyno same day his was 417/420

Same day at the track he ran 11.57/116.xx

I had a huge bog off the line and ran 12.45/111.xx

Point is, this is my daily driver and with standard tires, there is no way it can hold the power output of this combo on the street.

So why switch ? Maybe if you are looking for all out power at the track.

anesthes

iTrader: (12)

111mph?? That's the same as a new stock Camaro runs.

Sounds like you need new tires

-- Joe

LegacyThirdGen

All you guys that go LS, i have one thing to say to you.

You all have fun when Skynet attacks and takes over your timing.

anesthes

iTrader: (12)

Oh boy, I can't wait for this one.

Care to explain ?

-- Joe

Dyno Don

iTrader: (7)

You need a new attitude Joe...get off my case

LegacyThirdGen

It's called hyperbole.

anesthes

iTrader: (12)

Nobody is on your case. Your just over sensitive.

-- Joe

Alice89

iTrader: (6)

Orly?

LegacyThirdGen

IT'S A JOKE. JOOOOOKE.

Alice89

iTrader: (6)

No wayyy!

SixSeriesCSi

iTrader: (11)

I'm reading this just as Terminator is playing on SPIKE, how ironic!