Not at Yates, That means I'd be joined up with Jack again, getting too old to deal with that kind of stress. I'm enjoying life with some sanity now, Thanks for welcoming me to the board, I appreciate it. Off now for the Holiday weekend, be safe, have fun and watch the cops checking for seatbelts, I've seen 2 stop point checks already.....Take care

 

Since I don't know a whole lot about heads and flow, I always thought the bigger the flow number the better. After it was explained to me and I thought about it, what you're saying really does make sense. After working at a shop and seeing first hand a head that is all hogged out vs. a head with a small inatke port and dyno numbers from both I got to see first hand what you mean. The low lift numbers make all of the difference in the world with these heads.

-Rick

 

Mid lifts is where the power is made. IMO when choosing a cam, it is best to give the flow sheet of your heads to a custom cam designer and ask for for a matching grind.

 

Your partially right here, midlift flow as i explained is very important but just as important is the low lift flow. Here's 2 places where most people get led astray, (1) if you have a cam that has max lift of .580, pretty avg. for what I've been seeing on the LS1's, that puts your mid-lift point at .290. How many people do you believe still look at that point as a low lift and not mid lift ? the majority I bet ! How many times do you see advertised flow numbers that leave out .100 and start at .200 lift but show flow charts that show peak flow as high as .700-.800 lift ? Just another advertising crime to sell a product. and now number (2) this probably iritates me more than any other statement I hear, "Send the flow sheets to the cam grinder to match your heads", aaaahhhhhhhh !!!! let me explain something here, flow bench numbers don't represent the actual flow on a motor. Flow benches are a tool to moniter changes at given lift points. that 300 cfm you see at 28" of water, that's exactly what it means, if you were to flow it at 40 " of water the cfm number would be much higher. it just like running the same head on a small motor then putting it on a much bigger motor, the bigger motor has more volume to fill and will pull more air through it, that 300 cfm number doesn't mean that's all the head will flow, it's just all it will flow at 28' of water. I'll give you one scenario that should clear this all up for you, please bear with me. Say you already have this awesome motor, 350 c.i. for example that's making 700 H.P. and you've been happy running low 9's. you know it's got great flowing heads and you have this .800 lift solid rollar grind in it and the motor seems happy, O.K. now comes this class that your car fit's into like a glove , cubes, weight, chassis and you really want to run this class but there is one problem, the class calls for un-ported heads. now you get your new heads and flow them but they're down 20 cfm down low and fifty cfm at .650 lift, What do you do for a camshaft ? and what is the cam grinder do when he sees your new horrible airflow numbers ? How is going to regrind or make a new cam to match these restrictive heads ? Do you now know what you will do...run the same cam ! I hope you would not believe that if they made a much smaller cam to match your heads that you would make more H.P. Does it make sense now ? the head is now more restricted so putting in a cam that opens less and for a shorter period of time certainly won't help you. The only time the the flow numbers will help you with your cam selection is your exh. to int. ratio, you may want more ex. duration to make up for a poor flowing port. Sorry my explanations are long but these these can't be summed up in a paragraph, just hoping this helps

 

mirrors some past discussions

https://ls1tech.com/forums/advanced-engineering-tech/214137-cylinder-head-discussion.html
https://ls1tech.com/forums/generation-iii-internal-engine/163744-camshaft-discussion-cfm-requirements-rpm.html
https://ls1tech.com/forums/generation-iii-internal-engine/256055-pp-ls6-style-head-review-flow-specs-comparison-inside.html

 

Flow #'s look fine to me. Should make an assload of power if you set everything up right.


Floyd.

 

Actually it's not... the most important part in terms of velocity and volume is the .500+ range on a cam with a high .500" lift or low .600" lift.

Mid lift is important, but the cam spends the least amount of time there without help of high velocity and high port pressure. Area under the curve is one thing but it's not the be all end all.

Bret

 

Sorry Brett, your way off here. Did I read right. the most important part of velocity and volume is in the .500+ range, Where are you coming up with this stuff. Get on a computer and watch how a motor cycles on an engine analyzer program, then watch the piston speeds during the cam cycle. the piston is moving its fastest when the valve is at low to midlift, that's what creates your charge and that's one of the reasons why you need improved flow at those points, well before the piston reaches peak lift the piston is almost at a dead stop, there is nothing pulling more air fuel into the cylinder except inertia. So explain how volume is important at any lift when inertia is packing the cylinder ? Volume kills all of that. Take any motor, increase int. port volume by 20 c.c without any other change and you'll crush your entire horsepower curve PERIOD !!!! Volume is your enemy everytime. what your trying to accomplish in making more power is the same as when a muzzle loader is packing the barrel, we're trying to pack the cylinder full of air/fuel. So after the piston stops and is on it's way back up you can still fill the cylinder as long as possible with inertia and having the good low and mid lift. I tried to explain this in my first post using dyno results showing the benifit of low and mid lift flow and smaller port volumes. We need to benifit here from millions of dollars of someone elses dyno studies, these are facts, not guess work.

 

i will get a chance to test this theory after i install my new heads,if everything goes good i'll then dyno it this sat.i have good low-midlift nos. but they back up at .500 and above on the intake.here are the numbers:


int. exh.
.200 148 117
.300 210 152
.400 254 189
.450 269 197
.500 248 202
.550 251 207
.600 257 210
.650 263 212

like i said,barring any problems on the install i'll have some dyno nos. sat. night.

 

Hey 66, I believe you'll be fine. These sound like real numbers from real LS1 heads ( not to be confused with 6 litre LS1 heads that actually have an LS6 int. port ) These heads usually back up @ .490 -.530 lift. with a real good peak number being around 275 cfm. what matters is it looks like your .100-.450 lift is very sound. the good part is that the LS1 head has approx 10 c.c. smaller runner than the LS6 head which is a great benifit. I've seen motors in our shop dyno'd with the ported LS6 castings that don't back up and carry flow all the way to .700 with as much as 40 cfm differance at .550 lift but very similar low lift numbers as the LS1 head and the RWHP was hardly any differant. look forward to hearing your results

 

Tucunare,

I read your couple of other posts.... so you do know what you are talking about. We could get into a interesting talk here.... I do believe in the total area under the curve theory, but if I wanted to see a big change in a port in terms of seeing more power I would like the flow to improve on the top end of the scale more than the bottom end or midrange, but improvements in the whole curve never hurt. I would rather see improvements in the port map in terms of velocity and effective cross sectional area.... but we are talking about flow here.

BIG problem with your assumptions is that air/fuel is tied to piston movment like it was on a string.... far from it. In physics it's defined as a liquid and has inertia. This means it acts independantly of the piston, the faster the piston speed the faster the change in pressure on the port will develop (as in going to a shorter rod) but it doesn't happen instantaiously. Lots of it depends on the RPM range that the system is tuned for. In a world of set port dimensions and intake manifolds this makes your job a hell of a lot harder.

I'll take this from a post I made 2 weeks ago...

"BTW I just looked at a cam I'm doing for a motor now.... Hyd Roller over .600 lift (.630 range) medium sized duration, sub 7500rpm and a "street motor"

.000-.100 68 degs 22%
.100-.200 40 degs 13%
.200-.300 26 degs 8.5%
.300-.400 34 degs 11%
.400-.500 32 degs 10.5%
.500-.600 60 degs 20%
.600 + 44 degs 14.5%

Now making a negative change in that motors flow curve from .200-.400" lift of 4.4% nets less than a 1% loss in max power and about .4% in average power. Now if you killed the flow at the top end (.600+) 4.4% you would see a 1% loss in average power. This is with big changes in flow of 15-20cfm at the top end. That's 150% more loss in average power.

To add a little more to this the lowest pressures seen in the port (highest vacuum) at the max VE occur between .420-.520" lobe lift (opening) and the highest pressures occur between .150-.020" lift (closing), from lowest vacuum to highest pressure there is roughly a 15psi change in pressures. The highest average velocities occured for 84 degs at lifts over .500". The more flow you have in that lift area will raise the amount of duration that the motor pulls that high of a velocity given the same sized port.

So you can see the time when the port is filling the motor the fastest is around max lift, and the time it's filling it with the most pressure is around valve closing while the piston is coming up the bore.

Bret"

Looks like the valve spends:

35% of it's time below .200"
30% of it's time between .200-.500"
35% of it's time between .500-.630"

So just in time/duration (they are the same things when talking about a cam) the midlift area of the curve is the part where the valve spends the least amount of time. It's suprising that the valve spends 35% of it's time in the top .130" of travel on that camshaft. Even if you limit the valve to .600" lift on a standard LS1 setup the valve spends a significant portion of it's time there. That's a lot of time devoted to a small area of lift. It's also the most common place for a LS style head to go turbulent at very high depressions. (which you say you have seen) So MOST guys aren't filling the port effectively in that area. This is mostly due to lack of attention to the short side radius.... too much velocity in the port at this point. That's a bad thing when the highest velocities and volumes are moved thru the port at these lift points.

The problem most people don't get is that the wave tuning effect of length and cross section on a port add a natural supercharging effect "resonance tuning" to a NA motor. This will make the pressures in the head port much higher than atmosphere (5-7psi) vs. the vacuum on the port will ever reach.

Hmm, I've seen engines that will contradict that point of yours. In fact I have seen it for myself AND have had friends of mine confirm this from tests they have done doing heads for NASCAR teams. You've seen them on the other side of this, so things get very interesting here. A Yates vs. a P7 head and the carb on top of it might account for that. The right size is the best size. Sometimes it's harder to find the right size than we want it to be.

Smaller is not always better with a head port, the right size is better which we both know. That's the simple way to define it. In realitiy it's the smallest cross sectional area that has the best velocity map thru the port to get the job done. The big issue that I think we will agree on is getting the port to work at higher and higher MACH numbers. The heads we are talking about on here really don't go into that, mostly because 95% of them aren't that advanced due to the price points. If we could shrink the port down and the port could work effectively at higher MACH numbers, then yes we will find more power with less volume and flow.

The smaller is better, higher velocity is better approach is a very simplistic and wrong way to go about it. The people who work in NASCAR, Pro Stock and the record holders in the Sportsman classes of drag racing know this. The right size is better approach is the way the world works. I've seen motors that don't have enough port volume and cross section for what they are trying to do, and I have also seen ones that have too much both sides of this are a bad thing IMHO because you are far from optimum.

The post you made on the MTI heads is interesting. Problem is what we are talking about here is not the same world in terms of the quality you see. Get a sample head in from everyone who puts a ball end mill or a grinder on a LS casting and you will see what I mean.

Now if you play on a dyno all day, especially with LS1 heads. Then the statement of smaller is better, for the most part is true on these motors. They start off with a very big port and when ported it gets worse. The cross sectional area of the head is very big for the RPM and cubes under it so if you go smaller you will find even more power.

See my point now?

Bret

 

they are 5.3 heads, volume is 216cc on the intake and 81cc on the exh.i'm running the TR220 with .553 lift so for my use the heads should work ok.i had a few issues when i recieved the heads from the porter so i sent them out to another shop to have them checked out and have the combustion chambers CNCd to unshroud the valves.at this point i ran out of money so their going on as is.it would have been better to have the flow nos. carry on out to .600 but they are what they are.

 

Bret and Tucunare,i'm glad you both are posting in this thread,and keeping things civil.you guys have forgotten more about engines and cylinder head flow than i will ever know.even though you guys disagree,i'm learning a lot from your discussion.let's keep this going.

 

the LPE/GMPP ls6 cnc head bears this out,IMO.at almost 250cc intake port vloume that port is HUGE,but it's one of the best peforming ported ls style heads out there,and not just at higher rpms.

 

I agree with Brent 100%,a local shop=Hack Job.My MTI 2E's make wonderful power,infact I have one of the more powerful H/C car in my area(In dyno numbers that is) and I inspected after I ordered the from MTI and I did get what I seen in the pics.
Scott

 

The only think I would like to say is Bret has a tendency to think max effort all the time, not taking into consideration the street part of many of our setups.

 

Brett, this is great discusion. I like your explanations, they have great merit. I had roush's top engineers always bringing theories to the table and Jack would always want me to try them out, many of which you explained. In the end they all made it to the shelf as bookends. With Spintron testing we saw how high we were slinging the valve, usually over .100 past actual cam lift and the lifter would land half way down the lobe on the back side, that's what really prompted Jack to want more high lift flow, but as read in my first post that wasn't the case, The motor simply couldn't make use the extra flow in that rpm range but desperatly needed it in the lowers lifts, now if we were running from 8800 rpm to 1100 rpm where the engine demanded that kind of cfm then Yes, those theories come into play. I got hit with every theory on my short track road race head why it wouldn't work. the epoxy on the floor went straight uphill and the cross section at the short turn was ridiculously small to say the least, especially when you saw a 3-D rubber of the port. My .100-.400 flow numbers didn't change a bit, the .500 was down a couple of cfm and at .600 lift we were down 15 cfm but backed up severly at that point so at .650 and .700 we were down over 35 cfm, mind you we were still slinging the valve even on the short track cam to .720 lift. did we make less peak H.P. Absolutly, but we knew we would. we were looking for worthwhile trade as we came off the hairpins at 4000 instead of 7500 like at Michigan or Charlotte. We picked up 35 foot pounds of Torque at 4000 and held those gains through 7700 but by 8800 we were down 35 H.P. who cared, by time we were at those rpm points on the track we had already gained our position, watch the in car telemetry of the tachs in those cars and you never see anybody passing with motor in those rpm ranges, it's all about getting position early, gaining ground with big torque and then going into the corners hard to hold your ground. that short track motor would be much more desireable on the street or drag strip unless of coarse it was a clutch and were only going to be in the upper rpm's. So with this example your theories do work. if what you are trying to achieve is the absolute biggest H.P. number on dyno then many of those ideals work, but you have to be willing to pay the price for the majority of your torque curve being down. I would bet that most people would would rather have that high torque motor that gets down the track faster, is way more drivable, and easier on the fuel gauge than holding that dyno sheet with one big number on it.....well maybe not...I've been reading some of these posts, LOL. Also to make one quick point, Way too many people get confused with torque and h.p. They look at peak torque and after that starts falling off they look at the H.P. because it's still climbing. They are the same thing, H.P. is torque x rpm. To make more H.P. @ 7000 rpm you have to make more torque at 7000....Very Simple and all too many forget this, Even my buddy Jack. and Thanks Brett for not taking this personal, just trying to share some valuable testing data with you guys. now let's get the BBQ's ready, have a great Memorial day and lets take a moment to salute are past veterans for making this all possible, even this website, Thanks

 

Tucunare,

If 28'' of water inflates the numbers, and 40'' of water inflates the numbers to an even greater degree, what could be done to find an accurate cfm reading?

Also, if the exhaust/intake ratios dictate the crutch of either exhaust or intake split, what dictates HOW MUCH duration is used?

 

Sportside,
great Question, there is no way to compare flow bench cfm to your motors needs real accuratly except for lots of before and after studies on the same motor. That's why winston cup motors are so efficient, we used dyno mule engines that are baselined for that day then do back to back cylinder head swaps with only one change. It may be a few c.c.s of epoxy, differant valves, changes in low or high lift flow, chamber shape, or even differant valve springs. but after every test we swap back to our original set-up to verify the change. We look at air intake, fuel consumption and changes throughout the entire curve. Then after we decide if it was better then that would be our new std. then repeat the process day after day, year after year. At that point we pretty much new what airflow we needed to maintain high end power and the sacrifices we could make with port size to cater the motor for a differant rpm range. What helped me understand the airflow needs of a motor was that we used the same yates head on winston cup, rollar cammed Craftsman truck engines that made well over 800 h.p., off road 427 ci. motors, pro stock, small 310 Trans am motors with rev limiters at 8250 rpm and of coarse the Daytona style restrictor engines. here's the interesting part. all of them wanted the same chamber shape, same valve job and valve with the great low and mid lift. even the same bowl. The biggest differance was shrinking the ports as small as possible so that the air flow loss didn't hurt that particular motor in it's operating range up top while making huge torque gains up to that point. From that I could pretty much look at any motor and decide how much it needs to make a given h.p. it would be very hard to me to ever know how to much air is needed if I didn't get to see hundreds and hundreds of A-B comparisons first hand. I wish everybody could see those studies, no one would ever look at a ported head the same again, you'd be surprised how much power you can make with a 300 cfm head, or even 250 for that matter. ex. to int. and how much cam bias you need is a whole differant topic i don't want to touch right now, again lot's of trial and error

 

Tucunare, are you affiliated with Air Flow Research in any way? I've been watching these cylinder head threads for a while now and your experiences and theories seem to support and agree with everything Tony @ AFR has been saying about how AFR develops their port designs.

Getting back to your ported vs nonported example. Have you ever seen an increase in camshaft necessary to help crutch a non flowing head, say in a nonported type class?

Or to put it another way. Some of our LS-1 brothers here have been getting good results with huge camshafts and non-ported heads. In your opinion when they switch to a high velocity ported head could they in affect have too much camshaft for the rpm range they are trying to run, based on the increased efficiency of the cylinder head? Perhaps manifesting itself with huge VE numbers and low BSAC numbers?