Generation IV Internal Engine - LS7 head flow numbers: 348 int/219 exh @.600 lift




DrkPhx
02-23-2005, 09:55 PM
Check out this link. These numbers are almost exactly what is posted in the new issue of Corvette Fever. Incredible numbers. but they are flowed at 4.125 bore. I find it hard to believe any tuner can improve on these heads. Mike Chapman who is a revered head porter in the Mopar circles worked with GM on these. Judging by the tone of his post, I'm led to believe this is him or someone who access to this information.

http://www.gearchatter.com/viewtopic11202.php

They also have a pretty cool Gen III cam database of specs that is pages long. something *ahem* we could use here. :)


11 Bravo
02-23-2005, 10:07 PM
Crazy numbers for GM castings out of the box. But I'm sure thay could be improved uopn. My 6.0l heads flow almost 30cfm more on the exhaust at .600 with a smaller 1.60 valve.

DrkPhx
02-23-2005, 10:40 PM
Also notice how they peak at 359 cfm at .700 lift. This engine is begging for a big cam.


stik6shift93
02-23-2005, 11:14 PM
Crazy numbers for GM castings out of the box. But I'm sure thay could be improved uopn. My 6.0l heads flow almost 30cfm more on the exhaust at .600 with a smaller 1.60 valve.
Was your exhaust flowed with a tube? Also if they're indeed c5r casting like i've heard them to be they still have a lot left. Porters have pulled 390-400 out of c5rs.

ChucksZ06
02-24-2005, 11:14 AM
Yea and it is only going to dyno 440 rwhp....I may be eating crow but I tell you this thing is underrated or the valve timing is incredibly tame. What would those heads and that cam do on a 346?

2001CamaroGuy
02-24-2005, 06:25 PM
not impressed with the 219 exhaust flow at all........most stg 3 heads get about 240+ (mine did).......intake numbers looks good though....

Big-DEN
02-24-2005, 08:29 PM
Those numbers are great for a factory head, but are poor for a head
with a 2.2" intake valve.

My guess is they come up strong with porting, prolly near 300CFM@.4"
and 350CFM@.5"...

John B
02-24-2005, 09:26 PM
Those numbers aren't very impressive at all for a 4.125" bore with a 2.20" intake and a 1.615" exhaust valve on a CNC'd head! My LPE CNC'd LS6 heads with 2.02"/1.57" valves flowed 301 CFM at 0.500" on a small bore versus the LS7's 315cfm on a large bore and my exhaust numbers were 218CFM at 0.500" vs 207cfm for the LS7. I hope the production LS7 heads are a heck of a lot better than that!!!

DrkPhx
02-24-2005, 10:08 PM
Those numbers aren't very impressive at all for a 4.125" bore with a 2.20" intake and a 1.615" exhaust valve on a CNC'd head! My LPE CNC'd LS6 heads with 2.02"/1.57" valves flowed 301 CFM at 0.500" on a small bore versus the LS7's 315cfm on a large bore and my exhaust numbers were 218CFM at 0.500" vs 207cfm for the LS7. I hope the production LS7 heads are a heck of a lot better than that!!!
Yeah, but what did they flow above .500? I doubt 348 cfm at .600 and they probably fell off after that. The LS7 heads just keeps going, where a ported LS1/LS6 head falls off. It's obvious this is going to be a high revving engine that will really wake up with a bigger cam and maybe some long tube headers with no cats.

texada
02-24-2005, 10:53 PM
I wonder how big the runners are on these heads?

xp3nd4bl3
02-24-2005, 11:11 PM
I wonder how big the runners are on these heads?
Yeah somebody give us the port volume!

John B
02-25-2005, 04:45 PM
Yeah, but what did they flow above .500? I doubt 348 cfm at .600 and they probably fell off after that. The LS7 heads just keeps going, where a ported LS1/LS6 head falls off. It's obvious this is going to be a high revving engine that will really wake up with a bigger cam and maybe some long tube headers with no cats.For the amount of time that the motor spends above 0.500" lift, I'll take bigger numbers at this lift and below than this number and above any day of the week.

Big-DEN
02-25-2005, 04:52 PM
Like I said, my guess is with porting 300CFM@.400" will be reality and 350CFM@.50"

400 or so will be in the .600" and greater. My guess is the meat is there to support it. Lets pray it is.

What happens is the 500HP that these things ship with, will become
head and cammed and exhausted 700HP cars.

DrkPhx
02-25-2005, 05:03 PM
My guess is the meat is there to support it. Lets pray it is.


I would agree. The reason for the offset intake rocker is to allow more material for CNC porting.

John - I agree about time spent at lower lift is where it's at for a street car. But for race or near race applications, these heads should open a whole new world for max effort cars. Time will tell.

BrentB@TEA
04-04-2005, 07:48 PM
I know of a truck head flowing 399.5 on the same bore with the same size valve.:devil:

Nine Ball
04-05-2005, 09:12 AM
The intake flow numbers are impressive for a factory out-of-the-box head, but those exhaust numbers are somewhat weak. Here is a flow sheet from my old Formula, just a set of MTI hand ported LS6 castings from over 2 years ago when I had the car.

http://users.ev1.net/~ynot_dv8/flowls6.jpg

Tony

cyphur
04-05-2005, 11:54 PM
well tony i guess we know where the aftermarket will make a good bit of their money on these heads :)

matt346ls1
04-06-2005, 06:07 AM
I know of a truck head flowing 399.5 on the same bore with the same size valve.:devil:

:bs: no way

Matt

sb427f-car
04-06-2005, 07:18 AM
I would agree. The reason for the offset intake rocker is to allow more material for CNC porting.

John - I agree about time spent at lower lift is where it's at for a street car. But for race or near race applications, these heads should open a whole new world for max effort cars. Time will tell.


I'm trying to think of the articles and pics that I've seen thus far (which isn't working right now) but when you say the rocker is offset, is it also canted like a "semi hemi's" valve would be? (Not splayed like a big block but canted). I love the speculation here, but, we'll just have to play the wait and see game. More than likely these products will be scarce @ first and hella expensive.

Fulton 1
04-06-2005, 07:42 AM
I'm trying to think of the articles and pics that I've seen thus far (which isn't working right now) but when you say the rocker is offset, is it also canted like a "semi hemi's" valve would be? (Not splayed like a big block but canted).

http://popularhotrodding.com/tech/0504phr_ls7_12_z.jpg


http://popularhotrodding.com/tech/0504phr_ls7_07_z.jpg

DavidNJ
04-06-2005, 03:35 PM
One interesting thing about the Chrysler 'Hemi', is that the valves are positioned side to side with the pushrods in the middle. The intakes would be visible in that picture.

sb427f-car
04-06-2005, 08:16 PM
One interesting thing about the Chrysler 'Hemi', is that the valves are positioned side to side with the pushrods in the middle. The intakes would be visible in that picture.


Yeah, I realise that, but what I was getting at was the "canting" around the combustion chamber. If you were to look @ the valve angle of a NASCAR Cup head, you'd see that the valve angle is not only 12* from the deck, but it is also tilted 4* degrees or so on the axis, around the combustion chamber. I'm assuming that the reasoning for doing this is to help with scavaging, allowing for a more direct path from intake valve to exhaust valve.

mnc2886
04-08-2005, 12:32 AM
Why is the exhaust flow so weak? Do you all think that the exhaust ports could be in dire need of porting? Now I've heard from a mechanic, and wont say his name because I might not be repeating this right, but could it be that the 2.20 intake is too big, something causing the airflow to slow down, therefore making the exhaust flow weaker? You might just want to shake your head at that, or maybe I did repeat it correct. Anyways, can't wait to see a heads/cam swap with these heads.

RFD
11-21-2005, 11:59 PM
I posted something about in another thread, .. anyhow, ..

Kinda new here, .. so I hope you don't mind me butting in.

I've been working the LS7 head for racing applications, ..
drag racing, superstock, modified, etc.

We have the intake port flowing well over 420 cfm @ 28"
at .800" lift, .. and that is without making the cross section larger
so the airspeed is just as fast. I expect the highly modified ports
to go well over 435 - 440 cfm.

The exhaust ports, .. we tend to look at velocity maps through the port, ..
and at the valve seat area as more important then just a cfm number
from the flow bench. In exhaust ports, cfm numbers compared to
the intake just doesn't work the same.

Two things to remember with an exhaust port, .. when the valve cracks
off the seat the air is over 600 - 700 lbs of pressure and very hot and expanding.
Also the design of the exhaust valve seat area has to help the port flow go sonic.
There's MANY more dynamics to exhaust port flow to look at.

I think the LS7 exhaust port is a little weak too, .. but it only took a little
work to make it's power potential match the intake. ( my $0.02 worth )

Cheers,

Curtis

Wet 1
11-22-2005, 06:41 AM
Very interesting Curtis...

DrkPhx
11-22-2005, 08:40 AM
I posted something about in another thread, .. anyhow, ..

Kinda new here, .. so I hope you don't mind me butting in.

I've been working the LS7 head for racing applications, ..
drag racing, superstock, modified, etc.

We have the intake port flowing well over 420 cfm @ 28"
at .800" lift, .. and that is without making the cross section larger
so the airspeed is just as fast. I expect the highly modified ports
to go well over 435 - 440 cfm.

The exhaust ports, .. we tend to look at velocity maps through the port, ..
and at the valve seat area as more important then just a cfm number
from the flow bench. In exhaust ports, cfm numbers compared to
the intake just doesn't work the same.

Two things to remember with an exhaust port, .. when the valve cracks
off the seat the air is over 600 - 700 lbs of pressure and very hot and expanding.
Also the design of the exhaust valve seat area has to help the port flow go sonic.
There's MANY more dynamics to exhaust port flow to look at.

I think the LS7 exhaust port is a little weak too, .. but it only took a little
work to make it's power potential match the intake. ( my $0.02 worth )

Cheers,

Curtis

Wow. Those are great numbers. Especially considering the sentence I bolded about the cross-section size staying the same.

So the NHRA is going to allow the LS7 in Super Stock? That will be very interesting.

vmax1500
11-22-2005, 10:47 AM
Here are ET's flow number for thier C5R style head...

Cylinder Head: G III C5R Application: Street / Race
Port Volume: 240cc Chamber Volume: 58cc
Test Bore: 4.125" Test Pressure: 28.00" Water
Intake Valve: 2.180" Exhaust Valve: 1.625"

Valve Lift Intake Exhaust Valve Lift
.100" 66 51 .100"
.200" 153 106 .200"
.300" 216 153 .300"
.400" 277 206 .400"
.500" 325 232 .500"
.550" 343 237 .550"
.600" 363 240 .600"
.650" 376 241 .650"
.700" 388 242 .700"
.750" 397 243 .750"

Bink
11-22-2005, 12:02 PM
Curtis -what kind of numbers are you seeing @ .600" and .700"?
Thanks for the info! :D

Nate_Taufer
11-22-2005, 03:35 PM
These were flowed on a 1020 bench which will usually read about 10-12 cfm lower than an SF-600 which is industry standard.

Nate

RFD
11-22-2005, 08:30 PM
Hey gang,

A few points, . .. the 420 cfm @ 28" at .800" lift, .. yes the port has
the same cross section at the push rod pinch, .. and velocity as measured
has gone up a little over the stock head, cause it's flowing more volume.

Big point, .. this head flows VERY, VERY well from the factory up to
around .550" lift, .. then the air separates, goes turbulent and the flow
takes a dive. So my ported low lift numbers are around 10-15cfm better
then stock, .. and don't think there's much gain past that.
I'll try and see.

But the high lift numbers, .. big gains there as I'm sure any of the
talented porters here could find.

The development I'm doing is on a Superstock Modified, .. modified being
the key word, .. I don't know what NHRA will do with this combo for the
regular SS classes.

Nate brings up a good point, .. not all flow benches give the same
CFM number, .. so it's kind hard to make a close comparison.
I have a custom built bench that flows over 700 cfm @ 28" and
is calibrated to a SF 600.

Curtis

Bink
11-22-2005, 09:16 PM
..........................................

Big point, .. this head flows VERY, VERY well from the factory up to
around .550" lift, .. then the air separates, goes turbulent and the flow
takes a dive. So my ported low lift numbers are around 10-15cfm better
then stock, .. and don't think there's much gain past that.
I'll try and see.
.................................................. ..............................................

Curtis

LS7 Head Flow - 2.200 Int and 1.615 exh. (From GearChatter)

Valve Lift Intake Exhaust Valve Lift
.100" 60 71 .100"
.200" 145 120 .200"
.300" 222 159 .300"
.400" 271 192 .400"
.500" 315 207 .500"
.550" 332 214 .550"
.600" 348 219 .600"
.625" 350 220 .650"
.700" 359 222 .700"



You are seeing these values with your LS7 porting below .700" ? :

342 -347 @.550
358 -363 @.600
360 -365 @.625
369 -374 @.700


Here are ET's flow number for their C5R style head...(from vmax1500's post)

Cylinder Head: G III C5R Application: Street / Race
Port Volume: 240cc Chamber Volume: 58cc
Test Bore: 4.125" Test Pressure: 28.00" Water
Intake Valve: 2.180" Exhaust Valve: 1.625"

Valve Lift Intake Exhaust Valve Lift
.100" 66 51 .100"
.200" 153 106 .200"
.300" 216 153 .300"
.400" 277 206 .400"
.500" 325 232 .500"
.550" 343 237 .550"
.600" 363 240 .600"
.650" 376 241 .650"
.700" 388 242 .700"
.750" 397 243 .750"



I guess for most of us, not building to class restrictions, the ET C5R head is a better value in sub .700" Lift - compared to a pro-ported LS7 head??


Thanks for info!! :D

vmax1500
11-22-2005, 09:36 PM
And my numbers are right off ET's webpage... by the looks of it, the ET LS7 (or C5R style) head is going to be hard to beat! The difference between the C5R and LS7 head from ET will be the type of intake it will work with... the LS7 head from ET will bolt on to the GM LS7 intake... it will be very interesting to see what kind of numbers this combination will make!
http://www.etheads.com/mainpage.htm

RFD
11-23-2005, 09:06 AM
Guys,

You're comparing different flow benches for a few CFM, ..
Comparisons have to be done on the same bench.
The entry radius, bore adaptor etc all effect the flow test.

But, .. yes I would agree, .. if you're looking for a street or mass
produced cylinder head then it looks like ET is a great value.

Just to be clear, .. I didn't come onto this board to try to sell porting
( 4 months behind now ) or get attacked by people from another
porting shop, .. I just saw the post and thought I could offer something.
We don't mass produce CnC ported heads and never will, .. not what
our shop does. We are an engineering firm working on IHRA & NHRA
pro stock, Comp elim, superstock, 4 cylinder road race & SB2.2 heads.

There are choices in porting, .. you guys know this, .. the LS7 with
much work, .. 50 or 55 degree valve seats, .. etc are all for getting
high end flow without changing the low lift numbers.

That's what I really liked about this head, .. we picked up the low lift
numbers but have great high numbers up around .800" - .900"
For the combination we are working on, .. 358" ci, .. 9800 rpm peak
power, .. comp eliminator style engine in a super stock ( SS / modified )
This ISN'T a street head !

I can offer more info about the combo I'm working on if you like, ..

Curtis

MadBill
11-23-2005, 06:15 PM
I....Two things to remember with an exhaust port, .. when the valve cracks
off the seat the air is over 600 - 700 lbs of pressure and very hot and expanding....
Curtis
That would be a little low for a Top Fuel engine, but for most N/A gasoline engines, the cylinder pressure is more like 60 to 90 psi at EVO...

RFD
11-24-2005, 12:21 PM
That would be a little low for a Top Fuel engine, but for most N/A gasoline engines, the cylinder pressure is more like 60 to 90 psi at EVO...

Oooops, .. my bad, .. was trying to refer to velocity, .. long day and tired.

Referring to the blow down process and the possibility of super sonic flow
as the reason just looking at raw flow numbers from a flow bench isn't
a good judge for an exhaust port's ability to make power.

If you look at the requirements for supersonic flow in critical flow nozzles the flow cannot go supersonic until the pressure ratio across the orifice exceeds 1.89:1.

I think it would be pretty clear that the pressures inside the cylinder would be more than 1.89x the header pressure. In the book "Scientific Design of Exhaust and Intake Systems" on page 78 that at exhaust valve opening there were cylinder pressures of 70 psi.

So at least in the early part of the blow down process the flow has to hit the speed of sound at the valve seat or throat. If the port shape from the throat is of diverging shape and does not cause flow separation, I think its a pretty good bet that for at least the first .200 - .300 of exhaust valve lift, you have the potential for supersonic flow.

Curtis

abbaskhan
11-24-2005, 05:01 PM
wouldnt port velocity/size and valve size have a a bigger effect on the low end than just flow numbers at a certain amount of lift. to look at just wat the head flows is doing all manufactures of these heads a disservice. i think most people make the mistake of geting the largest flow numbers they can and dont bother to consider the lowlift #'s and the importantance port velocity plays in a motor. and wouldnt keeping the importance of exhaust flow numbers at a minimum be a hinderance by causing excessive backpressure and heat build up in the heads they are as important as intake numbers... i wish i could build a streetable 9000rpm turbo monster with those 420cfm .750 lift heads but lets be real it would be a PITA to drive around

thanks curtis for the insight on the potential of these heads glad to see they are workin out well

fact is thers so many choices (wonderful for the consumer) that we can pick and choose (and also screw up) a great basis for power potential in any arena we choose street or otherwise

RFD
11-24-2005, 11:01 PM
abbaskhan,

Oh yea, .. you've hit a little "nerve" with me, .. as you are right.
Looking at flow numbers and only flow numbers is completely wrong.
Like you say, port cross section, air speed, discharge coefficient, etc, ..
are far more important to look at then just a raw flow number.

That is one thing that got me regarding the LS7 head, .. I got flow numbers
over 400 cfm with a very high air speed. these could be driven on the street, ..
but I really wouldn't advise it.

As for the exhaust port, .. yes you have to look at flow numbers as they relate
to the intake flow, .. but my previous post was making the same point you did
about intake flow numbers, . .. there's much more to it then just a CFM number.
Exhaust ports more so then intake ports can really fool you on the flow bench, ..
it's easy to make an exhaust port flow, .. just make it big and it'll flow.
But that doesn't make power, what does make power in an exhaust port
is velocity, .. and the LS heads have it. I made this point because some one
pointed out the low exhaust flow numbers, .. but I don't see a problem myself.
The numbers aren't low enough to cause any of the problems you suggest.

I have more development to do on these heads, .. I've only just started to scratch
the surface of what these heads can do. And if you're interested I'll continue to
post my findings.

There are many choices for parts / heads, .. I had someone call me from this
forum that only wanted "the most flow" and really didn't listen to reason.

Curtis

abbaskhan
11-25-2005, 04:31 AM
didnt mean to touch a nerve curtis hope you didnt take it personal... didnt read to much of your last post but please keep the information comin all the expertise you guys have is appreciated

ill be in the market for heads very soon for my mext project (hopefully a c6 twin turbo big cube daily driver) so this information for me is very helpful

thanks again guys for the help any insight in this arena is welcomed

RFD
11-25-2005, 09:44 AM
didnt mean to touch a nerve curtis hope you didnt take it personal... < clip >

Oh no, .. I didn't mean you hit a nerve, ..
I ment that paying too much attention to flow numbers, ..
the way most people compare a good head to bad, peak flow numbers, ..
that also bothers me or "hits a nerve"

Your post was right on the mark!

I cringe every time someone call me about a head and asks
"how much does it flow", .. .. it's rare some one will ask what the
airspeed is or how it would be matched to their combination, .. etc.

I'm heading to the shop to work on the LS7 a little more, ..
I'll post the results tonight.

Cheers, .. ( happy thanksgiving )

Curtis

MadBill
11-25-2005, 01:53 PM
Maybe this is the time and place to resurface my "Big Bang" flow bench concept! As RFD points out, the exhaust flow must surely be supersonic, at least in the early phase of blowdown. The vast majority of benches flow at 28 "H2O, ~1.0 psi, vs. as much as 100 psi or more for a running engine at WOT. It's totally impractical to build a bench that could continuously flow a port at such a depression, but how about momentary flow?
If one constructed say an approximately engine cylinder-sized cylinder, bolted it to a chamber, pressurized it to 100 psi, then 'blipped' the exhaust valve with a solenoid or cam-like device, such that it opened to a pre-set stop (0.050", 0.100". etc.) for a fixed number of milliseconds, the resulting pressure drop in the cylinder would be proportional to the volume of escaped gas. Volume/time = CFM. Ta Dah!
Whaddaya bet we'd see some really different results flowing at a real world two thousand eight hundred inches of water?

RFD
11-25-2005, 08:59 PM
Here's the scoop as I just got done doing a "street / strip" work up of an LS7 port.
Low to mid lift flow improves an average of 6-7 cfm up to .600" lift where the stock port goes turbulent.
Porting allows the port to continue to flow up to .800" lift where it starts to level off at around 390 cfm.

In a live running engine, under dynamic conditions the turbulence we see on the flow bench at .600" lift
will happen much sooner as the air speed under running conditions is many times higher then our test air speed.

Air speed in the port is very good with average readings around 290fps and a high of 350fps over
the apex of the short turn.

here's today's flow numbers @ 28"

-------Stock intake ------- ported intake ----- difference ---- ported exhaust.
.100-------68------------------73.5-------------------5.5-------------67.1
.300-------217.4--------------224.1-----------------6.7-------------191.4
.500-------337.3--------------342.1-----------------4.8-------------260.8
.700-------331.9--------------387.9-----------------56.0-----------268.9
.800-------345.9--------------397.3-----------------51.4-----------272.1

Now a few notes about this, .. I used a 50 degree intake seat angle, ..
using a 45* might help the low numbers more but hurt the high numbers,
but I didn't get to try.

The exhaust still had the 45* seat, and exhaust ports seem to love 50*
seats, .. I'm going to try that to see if it helps it more.

Cheers gang, ..

Curtis

MadBill
11-26-2005, 02:29 PM
...Now a few notes about this, .. I used a 50 degree intake seat angle, ..
using a 45* might help the low numbers more but hurt the high numbers,
but I didn't get to try.

The exhaust still had the 45* seat, and exhaust ports seem to love 50*
seats, .. I'm going to try that to see if it helps it more.

Cheers gang, ..

Curtis

Hmmm...
Flow bench results certainly speak loudly. On the other hand, there's been discussion on the Forum about the need for good low lift flow in the engine, to allow a late EVO to harness as much energy as possible while retaining adequate blowdown and good scavenging around TDC.
(FWIW, Dynomation usually calls for significantly less EVL than IVL and it almost always shows a considerable sag in the port velocity when the lift is highest, between the blowdown phase and the overlap period.)

Also, on the intake side there are proponents of using 30 degree seats to support low lift flow. David Vizard points out that at 0.050" lift, a 45 degree seat has a flow 'gap' of 0.035", vs. 0.043" for a 30 degree. To get the same curtain area, a 45 degree seat would need to be on a 2.48" valve to match that of a 2.02". Vizard uses a seat contour which I have confirmed has negligible impact on high lift flow compared to typical 45 degree cuts. He says good low lift flow allows a broader power band via shorter intake duration, as the good low lift capacity doesn't choke off the flow as badly when IVC is a little premature at high RPM.
Food for thought...

BrentB@TEA
11-26-2005, 03:04 PM
Hmmm...

Also, on the intake side there are proponents of using 30 degree seats to support low lift flow. David Vizard points out that at 0.050" lift, a 45 degree seat has a flow 'gap' of 0.035", vs. 0.043" for a 30 degree. To get the same curtain area, a 45 degree seat would need to be on a 2.48" valve to match that of a 2.02". Vizard uses a seat contour which I have confirmed has negligible impact on high lift flow compared to typical 45 degree cuts. He says good low lift flow allows a broader power band via shorter intake duration, as the good low lift capacity doesn't choke off the flow as badly when IVC is a little premature at high RPM.
Food for thought...

30 degree seats don't work in the real world, Picking a cam or tuning on an engine that has excessive low lift flow is a nitemare that doesn't seem to pay off. Looks good on paper it just doesn't pan out in the real world.
JMO

Ferocity02
11-26-2005, 03:53 PM
So from the factory, would the LS7 heads like a low lift cam (.625" range) with a traditional split and lots of duration? Still trying to see how these heads are going to work. Thanks

RFD
11-26-2005, 04:02 PM
Bill,

Interesting points, .. interesting post.
Man O man this looks like it's going to turn into one interesting discussion. ;-)

Yes there is a big discussion of low lift flow, .. and as we all know it's important.
But there are also other considerations, .. like blow-through during overlap.

In my dyno testing on engines like the DRCE or SB2.2 too much low lift
flow has netted less power, .. showed a good VE# on the dyno but some
of the VE# was going out the exhaust.

This is one reason the racing industry has migrated towards steeper
valve angles. ( there are other reasons as well )

Even in a cylinder head I build for a race series that limits valve lift to .347"
a 30* seat showed a flow gain but a loss of power. A 45* seat showed to
make the best power on the dyno and on the track, .. on a low lift engine!

I have found that the throat area and top and bottom angles on the valve job
play a much greater roll in the discharge coefficient and low lift numbers
then just the seat angle it's self. While curtain area size is important, ..
the efficiency of the curtain area or "flow window" seems to have a greater
impact on performance.

It's obvious to me there's more to the flow dynamics then just raw flow numbers.

case in point, .. the high lift turbulence seen in the LS7 head.
The air separated at a lift of around .550" to .600" on my bench.
In a dynamic situation I've had engines where the lift was as much as .100"
below this point and showed a power loss.

We had an engine with a set of 18* heads CnC ported by Mike Chapman, ..
VERY nice work, .. but the short turn separated at .800" lift.
The cam we used was only .680" lift. We reworked the heads and got the turbulence
out and didn't effect flow numbers in the lift range, .. the engine picked up
over 35 HP on the dyno.

Bill you said the flow bench results speak loudly, .. what else do you see?

Good conversation, stimulating.

Cheers,

Curtis

DAPSUPRSLO
11-28-2005, 09:07 AM
Bill,

Interesting points, .. interesting post.
Man O man this looks like it's going to turn into one interesting discussion. ;-)

Yes there is a big discussion of low lift flow, .. and as we all know it's important.
But there are also other considerations, .. like blow-through during overlap.

In my dyno testing on engines like the DRCE or SB2.2 too much low lift
flow has netted less power, .. showed a good VE# on the dyno but some
of the VE# was going out the exhaust.

This is one reason the racing industry has migrated towards steeper
valve angles. ( there are other reasons as well )

Even in a cylinder head I build for a race series that limits valve lift to .347"
a 30* seat showed a flow gain but a loss of power. A 45* seat showed to
make the best power on the dyno and on the track, .. on a low lift engine!

I have found that the throat area and top and bottom angles on the valve job
play a much greater roll in the discharge coefficient and low lift numbers
then just the seat angle it's self. While curtain area size is important, ..
the efficiency of the curtain area or "flow window" seems to have a greater
impact on performance.

It's obvious to me there's more to the flow dynamics then just raw flow numbers.

case in point, .. the high lift turbulence seen in the LS7 head.
The air separated at a lift of around .550" to .600" on my bench.
In a dynamic situation I've had engines where the lift was as much as .100"
below this point and showed a power loss.

We had an engine with a set of 18* heads CnC ported by Mike Chapman, ..
VERY nice work, .. but the short turn separated at .800" lift.
The cam we used was only .680" lift. We reworked the heads and got the turbulence
out and didn't effect flow numbers in the lift range, .. the engine picked up
over 35 HP on the dyno.

Bill you said the flow bench results speak loudly, .. what else do you see?

Good conversation, stimulating.

Cheers,

Curtis

RFD, I think I understand the logic behind the head which stalls out at any lift costs power as the vacuum seen on the engine is much much greater which will cause what stalled out at 28" of depression to stall out much sooner at 100" or whatever depression is seen while operating on the motor. Now, that being said, if one is to run a much much more efficient intake setup which will not restrict the incoming air charge as much wouldn't this cause the intake port of the motor to see less depression then one with a more restrictive intake setup. Wouldn't this effectively reduce the problems that arise by running a head which eventually stalls out on flow at 28" of depression even with a cam that never produces gross lift past the stall point at 28"s. Just a question, you guys sound like the one's to ask though.

treyZ28
11-28-2005, 09:32 AM
flow numbers aren't the half of it. dont start flow bench racing just yet ;)

RFD
11-28-2005, 11:47 PM
RFD, I think I understand the logic behind the head which stalls out at any lift costs power as the vacuum seen on the engine is much much greater which will cause what stalled out at 28" of depression to stall out much sooner at 100" or whatever depression is seen while operating on the motor. Now, that being said, if one is to run a much much more efficient intake setup which will not restrict the incoming air charge as much wouldn't this cause the intake port of the motor to see less depression then one with a more restrictive intake setup. Wouldn't this effectively reduce the problems that arise by running a head which eventually stalls out on flow at 28" of depression even with a cam that never produces gross lift past the stall point at 28"s. Just a question, you guys sound like the one's to ask though.

The simple a quick answer is NO, .. regardless of the intake the choke
or sepperation will still happen in the head.
The intake can make it happen sooner but rarely make it later.

I'll explain more later, .. right now it's late and I gotta get some sleep.

The biggest thing with these heads besides the flow numbers, ..
as the post above points out, .. is the velocity and cross sectional area, .
and wet flow.

There IS MUCH more to a cylinder head then CFM flow numbers!

Curtis

treyZ28
11-28-2005, 11:55 PM
The modern internal combustion engine is way too dynamic to look at flow through a single port under a single, constant pressure differential and declare a winner.

The only thing flow numbers are good for is knowing if you fucked up or did better. IE: If your cross section remains the same and velocity numbers go down- you fucked up.

If you port them out and velocity goes up, good work. Its better than before. Not better than the head next to it, in front of it or on top of it- just better than before.

dont get me wrong, A 220cc heads, one flowing 120cfm at .550 lift intake side is clealry fucked. and one flowing 300cfm is probobly better. Its ok for general deductions and such- but flowbench racing is a no-no when its even remotely close.