Here is an eye opening comparo:
Merlin 310cc Rectangle Port Big-Block Chevy Heads.
2.30" Intake and 1.88" Exhaust valves.
Flowed on a 4.25" bore with a 2.5" pipe on the exhaust.
-------I-----E
.100 74----65
.200 133---128
.300 186---179
.400 240---207
.500 285---221
.600 311--- 229
Now compare that to some TEA Stage II heads for our little LS1.
Don't know the intake runner volume; but it is no where near the 310 for the Big Block heads.
2.02" Intake and 1.60" Exhaust valves I assume.
3.9" or maybe 4.0" bore ?Pipe on the exhaust?
--------I-----E
.100 65----58
.200 135---114
.300 202---160
.400 251---200
.500 285---225
.600 296---240
Note the similar or BETTER flow numbers for the little LS1 heads up untill .600" lift even thought the LS1 heads have smaller intake volume, smaller valves(2.30/1.88 vs. 2.02/1.60), and a smaller test bore(4.25' vs. 3.90" or 4.0").

I think we have the best cylinder heads in the world. <img border="0" alt="[Fluffy]" title="" src="graemlins/fluffy.gif" />

<small>[ December 17, 2002, 09:49 PM: Message edited by: 1CAMWNDR ]</small>

 

I agree! GM went all out designing these heads. Alot of the extra flow comes from the 15 degree valve angle vs 23 degree for a traditional small block.

 

Notice that the big block heads took over at .600 lift. Ask the big block guys what kind of lifts they are running with their cams. Its apples to airplanes they arent even close to the same thing. If we could get some Dart SBC heads and the LS6 heads and test them both up to 1.000 lift with the same valves then things might get interesting.

 

Actually, most big blocks really dont run all that much lift. .550 to a little over .600 is the most youll ever see on the street. Ive seen a few 23 gen 1 heads go close to 300 cfm. But these were hogged out race heads with port cc's in the 230-240 range. Not much good for the street. If I remember correctly Scogin Dickey sells a set of race ported Brodix track 1's that flow right at 300 cfm. Also, this is at very high lifts, like .700 If you want to compare LSx heads to the old stuff you really have to look at the 18 degree heads. These are high dollar pieces that require offset solid roller lifters and shaft mounted roller rockers. These also require special intakes and may cause header problems because of the raised exhaust port. So after youve spent 5 or 6 grand to outfit you regular sbc with this stuff you still only flow maybe 15 cfm more than a set of stage 2 LS6's and you're monster solid roller cam wont idle worth ****. Plus, youve got to turn it to 8 grand because you've got a 260 cc intake port BTW, I have yet to see a gen 1 head flow even close to 295 cfm at .550 lift.

<small>[ December 18, 2002, 01:16 AM: Message edited by: CW 99 Z ]</small>

 

Not intended to be a direct comparrison.
But the Big-Block head needed a 4.25" bore AND a 2.30" intake valve to flow similar numbers.
You guys don't think it is amazing that our little heads can flow the same as RECTANGLE PORT Big-Block heads......with a SMALLER test bore and a SMALLER intake valve?
Big Block Chevys are supposed to be such sought-after motors.....I know, I wished my '69 Chevelle had come with a 396. I wonder if with just Stage II preppared LSx heads on a big inch motor (440+) we might see some VERY impressive numbers compared to a similar Gen IV, V, or VI Big-Block.

 

I think it was my friend past Popular Hotrodding or some magazine but they had a 565" big block that made 1050 hp on pump gas with no power adder. The heads flowed in the 550 cfm range. <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" /> <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" /> <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" /> <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" /> <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" /> <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" />

The motor was 35 grand. It is probably the sickest motor I have ever seen. Incredible amounts of engineering went into this thing. It had a 4.6" bore with a 4.125" stroke and still turned 7500 rpm.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by DailyAluminumBlock:
<strong>....The heads flowed in the 550 cfm range. <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" /> <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" /> <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" /> <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" /> <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" /> <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" /> ....

</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Wow. That is some monster airflow!

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by phil97svt:
<strong>Who is "We"?
</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">We, the LS1 owners/lovers as a group...

 

Yeah, ls1 heads are good. They are in the same league as bigblock heads and stock they only have 346 cubes.

It would be interesting to see how well some 4 valve heads flow. The 4v modular heads are terrible they flow less than the lt1 heads. Mostly due to the tiny bore.

 

Im gonna have to disagree on that statement. The LS1 heads are amazingly good for a GM cast head but no where near the "best head in the world"

fwiw.. my "old school" sbc heads flow just over 400cfm @.700 lift. Better than most out of the box big block heads.

Darren
--------
94Z A2, 410ci LT1, SB2.2's, EFI, and 2 stages of nitrous <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by dug:
<strong>Yeah, ls1 heads are good. They are in the same league as bigblock heads and stock they only have 346 cubes.

It would be interesting to see how well some 4 valve heads flow. The 4v modular heads are terrible they flow less than the lt1 heads. Mostly due to the tiny bore.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">i dont know the specifics of the heads but a guy i know with a heavily modded supercharged cobra told me his heads flowed like 354cfm but im not sure what the lift was.

 

if your building a serious big cube motor-
http://www.sonnysracingengines.com/heads.htm
580cfm monster heads.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by CW 99 Z:
<strong> Ive seen a few 23 gen 1 heads go close to 300 cfm. But these were hogged out race heads with port cc's in the 230-240 range. Not much good for the street. If I remember correctly Scogin Dickey sells a set of race ported Brodix track 1's that flow right at 300 cfm. Also, this is at very high lifts, like .700
I have yet to see a gen 1 head flow even close to 295 cfm at .550 lift.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">http://www.weldtech.com/graphics/BrodixTrack1Chevy.gif

Welds Numbers are a little low too. I've flowed these on a bench and they are at least this. 215cc is not hogged out. This is how you make 550-600hp from a 355 to 383 SBC engine, and they are actually less than most LS1 heads.

http://www.weldtech.com/graphics/HVH231_10X.gif

Now this one is a good high HP 400+ cube SBC head and it's about in line with some of the LS6 numbers you see from most customer heads.

True the valve angle hurts the old 23 deg heads, but there is alot of time and money in these things. These heads are the easiest ones to buy that flow like this, I have seen AFR 215cc heads flow 315cfm and not a high lifts. You have to find the right people in that bussiness to build a good motor.

500+cfm is what those heads flowed on that 565 in PHR, but they were based on Pro Stock Heads. If you are going to compare BBC heads to CNC ported LS1's then you need to look at the 400+cfm CNC heads that come from Brodix, AFR, TEA. Then you are talking about then same game. I don't think you can compare a as cast BBC to a CNC ported LS6, the LS1/6 is a much better design true, it's close to the SB2 but there is always high quality stuff out there, you just have to find it.

Bret

 

Who is "We"?
Phillip

 

I'm not sure where those flow numbers came from but they cant be box stock track 1's. CHP has an excelent head flow database where all the heads are flowed on the same bech with the same operator. They only got 267 cfm at .600 lift. If you could trully get 550-600 hp out of these heads there would be buildups in the magazine articls about them. Ive yet to see one. 500hp with a big roller cam, sure. 600, I doubt it. Also, the -10 flow numbers from the link just confirm what I was saying. 231 cc intake port, you have to use offset solid roller and special rockers. Big money to flow about the same as a good set of ported LS6. I agree AFR are some of the best flowing heads out there. But Ive never seen them flow over 300, not even off of their flow bench. 285 is about it.

<small>[ December 19, 2002, 12:51 PM: Message edited by: CW 99 Z ]</small>

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">.[/QB]</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">First, the best heads have more than 2 valves.

Also you can't really compare "apple to oranges". ( The big block head does have bigger ports, but the small block was a stage 2 port.)

The LS1 heads are indeed awsome, but quite a ways from the best. But if you want to compare, here is what they are up against............

If you are talking about the factory heads, I think it has been said that Ferrari has the best with their 5 valve heads.

As far as 2 valve heads, you can't overlook , SBC2, CANTED ,SPLAYED valve, aftermarket, 18,15,14,13,12,and 11 degree SBC heads for "conventional" Small block chevy's. Some of which flow OVER 500cfm! I saw some in a 3rd gen fbody run mid 8's at I think 156 on Straight MOTOR! at about 3400lbs ! with a small block. Lower flow must have been good, because the peak power was "only" in the mid 7000rpm range. Which for an all motor small block that fast and quick is awsome. Not to forget all the bad Ford heads such as Yates either. We have a local 3000+lb ALL MOTOR 8 second mustang with a 351 if Im not mistaken.

There are 4 valve heads that you can get and will go right on an SBC including Lt1's that flow 360 to well over 400+cfm. With incredible low and mid lift flow and velocity. Some flow 300-330 at just .400 !! And the ports are about the size of some ported street 2 valve heads.

One guy on a message board had 340 cfm at just .400 !!

That' just the small block stuff. As for the big blocks. 500 cfm+ 2 valve, and 600 cfm + 4 valve stuff. But again "apples and oranges".

LS1 heads are AWSOME, but not the best.

<small>[ December 20, 2002, 05:06 PM: Message edited by: Rpm2800 ]</small>

 

this shouldnt be compared at all.ls1 heads are awesome.no doubt,air speed ,low lift #s,are awesome for a 210 cc head.but these merlin heads SUCK out the box.some idiots bolt these things on out the box,they are intended to be worked on(ported).but the key to that head is VOLUME.300+CC INTAKE RUNNERS,bbc need volume also.bolt a ls1 head to a 454 with 600 lift cam.it would run out of breath by about 5000 rpm.and most bbcs running good times usally run in the 600-700 lift range.my buddies car runs 9.60s with 720 lift 26x/27x @50 on 106-108 lobe.3000lb car.on ported STOCK rec port heads.(990 castings i think).bottem line is this apples to CUCUMBERS.

 

If "If's" and "But's" were candy and nuts, we'd all have a merry christmas! :-D

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by TAraysr:
<strong>If "If's" and "But's" were candy and nuts, we'd all have a merry christmas! :-D</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif"><img border="0" alt="[jester]" title="" src="graemlins/gr_jest.gif" /> <img border="0" alt="[jester]" title="" src="graemlins/gr_jest.gif" /> <img border="0" alt="[jester]" title="" src="graemlins/gr_jest.gif" /> <img border="0" alt="[jester]" title="" src="graemlins/gr_jest.gif" />
.....Yeah, but............

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by dug:
<strong>Yeah, ls1 heads are good. They are in the same league as bigblock heads and stock they only have 346 cubes.

It would be interesting to see how well some 4 valve heads flow. The 4v modular heads are terrible they flow less than the lt1 heads. Mostly due to the tiny bore.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">The 97-98 Cobra heads are amazing actually, I have seen some killer numbers out of them.