DavidNJ

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

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

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

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

iTrader: (4)

Very interesting Curtis...

DrkPhx

iTrader: (15)

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

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

Curtis -what kind of numbers are you seeing @ .600" and .700"?
Thanks for the info!

Nate_Taufer

iTrader: (1)

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

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

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!!

vmax1500

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

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

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

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

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

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

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

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

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?