Update: I pulled down the scan I posted a couple days ago of the 25" flow chart and inserted the new 28" flow chart that was done today. Here's a link to the original chart at 25" vacuum in case anyone wants to refer back to it: http://home.comcast.net/~grammerman/...um_low_res.jpg

Here is the link to the thread with a little more info on the porting work that was done:

http://web.camaross.com/forums/showthread.php?t=466928

The newest flow test should be an apples to apples comparison to most flow charts floating around from anytime recently. They used the radiused entry device this time around on the intake port and it really kicked up the numbers. I have a link to a magazine test of a stock LT1 that puts the intake flow at 215 peak so it's possible that a different flow bench operator might produce higher before and after numbers. I don't think you can accurately compare these flow numbers to others unless they also have a chart for the stock port to use as a baseline.

I think the difference between the ports before and after might be a more useful approach than the peak numbers because of this. I like the composite they produced by averaging the flow from .2" to .5" lift, I'll be working off of these numbers when discussing flow below.

The intake flow numbers went way up with the addition of the entry device. Looks like the bigger valves without any port work didn't really do anything to improve the flow numbers. There is a much larger improvement from the porting with the entry device in place ( 17% improvement versus original of 7% at 25" vacuum). With a intake port volume increase of 9% (165 to final of 180 cc's) I'm very pleased with a 17% increase in flow. The mid-lift numbers are close to a 20% improvement in flow so I think these should work out pretty well with the CC 268XFI cam I settled on ( 218/224 degrees at .050" lift and .570/.565 lift).

The exhaust numbers are a little strange, I would have assumed they would have gone up with the increase in vacuum but they didn't. The exhaust to intake ratio was the nearly the same between the ported and stock tests so apparently I didn't screw up the balance here. The exhaust average flow went up by 15% with a 10% increase in port volume ( 62cc's versus 68 cc's final volume).

So there it is, I went out on a limb from the start but I like climbing anyway. For those considering a project like this, be careful. This is not what I'd call a beginner level project by a long shot. I've done several sets of heads in the past, I'm a skilled machinist and experienced mechanic so be conservative in deciding whether you can tackle it. A little help from the right person might go a long way for those on the bubble experience wise.


Considering I don't have a flow bench with which to get direct feedback during the process I think it turned out pretty well. The strong midrange numbers should help level out the lack of "killer" high lift flow compared to professionally ported stuff that's out there. If the 2 cfm per HP rule of thumb I've run across is roughly correct then this port job might add around 15 HP.

Now, post away. Opinions, creative flow data analysis, suggestions, whatever. I went to the trouble and expense to put this out here so I'd like some mileage from it

Later, Michael







[/LEFT]

 

Interesting stuff. I compared your after numbers against some data i collected on various professional portjobs. It seems like in the low lift numbers (.100-.300) your heads actually flow better than aggressive stage2 type ports(+5 to +10 cfm). However, in the higher lift (.400-.600) your head seem to fall flat, whereas the professional ports get crazy on the flow(+30 to +40 cfm over yours). Still its looks that you've got definite improvement over stock.

 

http://www.fierolt1.com/lt1_lt4_headflow.htm

Stock and ported flow numbers from several shops for comparison purposes.

 

One of the big falacies is that low lift flow numbers (below .300") are a big deal, honestly they don't make much of a difference in terms of power and torque output. To explain that let me give a little lesson on engine dynamics....

For a NA motor to fill the cylinder it takes a difference in pressures. You want a lower pressure in the cylinder than in the port, it's the basic principal to how all fluids work. It's why the weather does what it does, it's how you breathe to live day to day and it's how your engine works, fluids go from high pressure to low pressure.

Now the reason that low lift flow is not as important has to do with the pressure differentials and by how different they are at different lifts. As the valve opens, hopefully we have a cam and exhaust system that are trying to help us lower the pressure in the cylinder, if we do the pressure differential is HUGE initially and fades off as lift increases. It can be on the order of 5psi easily, that translates into over 100" of H2O flowbench depression. Try flowing a port at .100" lift at that depression, your going to see at LOT of volume in cfm, and this volume can be around 240-300cfm easily. The displacement in the cylinder and the inertia of the air/fuel prevent that all from being used, so the effectiveness of the port and increasing it a large amount at low lifts doesn't matter, the motor can get more than it needs. Once we get up to around .400-.600" on a street motor the pressure differential between intake port and cylinder can be less, usually 1psi but maybe 3psi at the most. At 1psi we are close to the 28" of H2O depression that we use on the flow bench. The cylinder below that port can take more air/fuel than we can supply and the air/fuel inertia is also helping it along at this point. Therefore if we reduce the restriction to the air/fuel entering the cylinder by increasing the volume that it can flow in a time period (CFM) then we can put more into the cylinder, which makes more power. As the valve closes the same thing is happening, the tuning pulses of the intake system are raising the pressure in the port to be 5, maybe 7psi higher than the cylinder (and both are increasing to maybe 20-30psi total now, but all we care about is the pressure difference) the same condition exsists on the intake valve closing as it does on the opening pressure increases as the lift decreases.

That's why the flow at higher lifts does make more of a difference. That's the basic reason as to why that happens, but it doesn't get into the geometry of valve seats and discharge coef and their impact on this. You'll see race valve jobs that instead of a 45 deg valve seat, they have a 50 or 55 deg valve seat. The steeper angles of those seats hurt low lift flow considerably, but they gain high lift flow. Sometimes you will hear that you need to tailor the seat to the lift of the cam, but even in some of those situations I've seen low lift or restricted lift setups that made more power with a steeper seat angle.

Well that's probably a little more info than is needed on the why and how of flow curves and what makes more power, but it doesn't hurt to know.

Bret

 

I Seem to remember these statements, lets review, I said in the previous post that you stated had "trash" posts in it:

"QUOTE"
I ventured into where you are once, I had a trashed stock head that West Coast cylinder head wanted to look at to do our conversion on the heads we have now, I said I would send them and give them to them(only one head was damaged) He wanted to slice and dice them to see what they were and what exactly needed to be done for the conversion...I told him I was playing around with one cylinder and I wanted him to flow it for me just to see.....I spent HOURS on that one cylinder, I had the correct tools to do it with and had seen MANY a ported head. It was beautiful(or so I thought)..it flowed so bad that he wouldnt even tell me what the numbers were....you sould have seen this intake port..I thought I was gonna kill them in California, a first timer from Alabama with a KILLER port...NOT....there is ALOT more than meets the eye....just a little 411 for ya.


And YOU said

QUOTE:

David, did you have well researched technical books or other sources of quality info. from which to shape your ports? If you thought you were going to get awesome results from simply looking at other ports and half *** copying them then things worked out as they should have. It's pretty well known that just going in and removing material from where you "think" it would do the most good usually doesn't work out too well, that's not what was done here. I think everyone except me has said something or other about a killer port, get real. Have you actually been following along or did you just read this page? I've been pretty clear that I don't have any expectation that the ports will flow 280 at 180 cc's volume but do expect to see a modest and worthwhile gain. First timer, you really nailed me there. Sorry your first port job didn't work out but so what? You didn't add anything useful from your failure that could help anyone. Here's another useless post by another "expert" that might as well be deleted. I guess it's normal to jab at other people if you couldn't get it done yourself. How exactly having a 11 or 10 or 8 second car qualifies anyone as an expert on torque oriented stout daily drivers is beyond me. There's your 411 hanging low brother

-----------------------------------------------------------------------
The above statements and the numbers you posted.....speak for themselves.


BTW send them to this guy, spend $500 and have some DAMN nice heads. He is in south Ga. The LT1 heads pictured on his site were mine.

www.killiansportingservice.com

My heads were his first LT1's he had done, with a VERY mild cam in a six speed car that weighed 3700 lbs it ran 90 mph in the 1/8 mile. It made good power. It pays to spend a little money.

There are no "undiscovered" easy ways in the horsepower world, as it says in my sig, speed costs cubic dollars, if ya want it done right..ya gotta pay.

David

 

Let me get this right, since I recall hearing that higher flow at lower lift is more important than higher flow at higher lift.

OK---at lower lifts the cyl pressures are lower and therefore pull in more than enough A/F at low lift and therefore there doesn't need to be high CFM at the low lift.

Whereas, when the lift is higher, the cyls have lost some of the low pressure and the difference in pressure is compensated by the higher flow numbers at the higher lift allowing the cyls to be filled as well as they were at the lower lift.

Is that close? And by lower lift are we talking half lift, 3 quarters or what? I.e, should we be looking at 300, 400, 500, 600 for the average 350---since most seem to brag about the CFM at around 500-550 rather than 300-400, etc.

thx

 

Yes your statement of

"at lower lifts the cyl pressure TO INTAKE PORT PRESSURE DIFFERENCE IS GREATER and therefore pull in more than enough A/F at low lift and therefore there doesn't need to be high CFM at the low lift.

Whereas, when the lift is higher, the cyls have lost some of the low pressure and the difference in pressure is compensated by the higher flow numbers at the higher lift allowing the cyls to be filled as well as they were at the lower lift."

Just put the same reference of difference in pressure in the low lift part and you got it. The pressure differential is greater, which means it acts like a flow bench pulling at 100" rather than one pulling at 28"
As for how you should look at the port the upper 15% of the lift curve is usually moving the most into the cylinder at lower pressure differentials on street stuff. Race stuff they have more lift so that % increases.

So basically the .100-.200 numbers don't matter much as long as they are in line with whats normal you are ok, but if someone says that their LT1 casting moves 155cfm @ .200, tell them to put the rocker stud and spark plug back in. Or as one of the funniest things I've ever heard is that they have a Martin Luther King flow bench, because it "has a dream" that it flows that much.

The .300-.400" lift numbers start to mean something, usually tells you how good of a valve job you have, but a port with a taller short side radius will have better numbers there but the port quality can go in the toilet which is much more important. 240cfm of quality flow is better than 250cfm of turbulent flow.

The .500-.600" numbers and beyond (on street stuff) give you a indication of the ports ultimate shape, to pick these numbers up you need to know what you are doing in that area.

BTW David you don't have to rub it in his face, but I do see where you are coming from, but that was a bitch slap and a half. Easy killer. This ain't a grude match on Pinks or something.

Bret

P.S. That Martin Luther King Jr reference is not ment to be offensive.

 

Bret, point taken, post amended.

I had an old guy tell me once......

Boy it's better to keep your mouth shut and let people think you are a dumb *** than to open your mouth and confirm it.


David

 

Interesting view you have on mid/low valve lift flow SStrokerAce. I'm sure you remember that my primary consideration on this build is to maximize midrange torque and part throttle response/power while retaining reasonable top end pull. I wonder if the operating dynamics are largely the same at high manifold vacuum conditions (part throttle operation) compared to WOT? Not many engine tuners/builders devote time to researching part throttle, high manifold vacuum power but in my estimation this is what makes a motor fun as a daily driver. Do you think that mid/low lift flow are of little importance when part throttle power is of high importance to the end user? What about port volume as it relates to part throttle power?

FatBoy and SStrokerAce, lets take a minute and try to be at least a tiny bit objective when comparing my flow numbers to the pro ported heads FatBoy is touting. Most pro porting outfits don't post baseline flow charts from the head before it was ported. This makes a direct comparison kind of difficult because of the lack of a starting point to level things with. The only obvious way I can see to compare my numbers with some I gathered from a well known porting shop from the web is this: Calculate a ratio from the amount the flow increased relative to the amount the port volume was increased.

Here are the numbers for a couple of pro ported heads SStrokerAce might be familiar with:

195cc port vol., 260cfm peak flow, 18% volume increase, 54cfm flow increase

205cc port vol., 275cfm peak flow, 24% volume increase, 69cfm flow increase



The % port flow increase above was calculated using an average of 206cfm for several stock LT1 heads from the link 1racerdude posted. Nice link, thanks.

Here are the numbers on my heads:

180cc port vol., 235cfm peak flow, 9% volume increase, 32cfm flow increase


The flow increase on my heads was calculated from the actual tested baseline flow before porting of 203cfm.

The two pro ported LT1 heads picked up an estimated 3cfm and 2.9cfm per 1% increase in port volume. My head picked up 3.6 cfm per point of port volume increase. This is not a standard calculation and certainly may favor a moderately ported head compared to a more heavily modified one but I think it does have some relevance. Since we don't have baseline numbers for the pro ported heads this is a guestimated comparison. The two pro ported heads differ by 10cc's in their volume but the ratio is very close between them. My heads posted ESTIMATED numbers that were 20% better than the pro ported heads. That suggests to me that if a large peak flow number was my goal that it is possible. Enlarging them into the 195 to 205cc range a peak flow of 260cfm or more might not be entirely unrealistic as FatBoy is implying. Maybe FatBoy can post links to a bunch of heads that flow 280 cfm at 180cc's of port volume. I'll pay $500 for that in a heartbeat. I'm also really in the dark about exactly how I've trashed my heads?

I don't have any problem with more comparisons of my port flow numbers to other professionally ported stuff. I do have a problem with just throwing peak flow numbers out as if they are the only consideration. For a strip only engine that never sees less than 4500 RPM's that might be true but for a DD it is not. If I grind my ports out to 230 cc's of volume I'm sure the peak numbers will be much improved. Why not stick to reasonable comparisons like average peak numbers from several different pro heads in the same volume range? I don't really think that a set of 220cc ports that flow 280 like FATBOY mentions is a very good choice for the type of engine character I'm after. I do think 235cfm with a real world baseline of 202cfm is pretty darned solid for a 180cc port and represents a very tangible improvement. Lets at least try to compare apples to apples, OK?

 

Unk-Stock GM LT1


63.0


126.0


180.0


206.0


206.0


206.0


These are the numbers for a "stock" unported head .100-.600. Any factory casting will flow within 3/4CFM of that so there is NO need to reflow every set.
From these figures ya might want to refigure your %.

Another thing if the flow falls off going to the top ya ain't going to have the cyl filling required to make that BIG torque. Ya will have to have a cam that has a max of .400 lift to do your peak numbers.Don't know if they can make lobes that tiny.
235 may be darn solid if it was @.600 lift but not at .300-.400 then going in the crapper.Just never seen or heard of heads that do that.

Unheard of.


BTW there are more than 1 person running 300@.650 an the street with NOOOOOOO problem.

 

Guess who that old guy was.

 

To back up what Bret posted. When I had my Dart Pro 1 200cc heads done by a local head porter he checked the flow starting at .300 lift and went to .600 lift the limit of my cam. I was kind of surprised as I had thought that the low lift were the important areas. He basically stated what Bret said. He does a lot of head porting for the racers here in Southern California.

 

1racerdude, 206cfm is the peak number I used to calculate the % on the pro ported heads. I used 203 cfm on mine since it was the actual tested flow. I don't have a clue what you mean by refiguring the numbers.

I thought the usefulness of baseline flow numbers before porting was obvious. All stock heads may flow within 3 to 4 cfm with the same bench, same operator, same settings. There are some porters that make flow claims that seem pretty far out there for their port volume. Having a baseline chart at least attempts to keep people honest about how their flow bench is used. I don't guess you've ever heard of a set of heads that fell significantly short of what was claimed when tested by a third party huh? From what I've seen it happens fairly often.

I do agree with you that it is strange that the flow was very strong up until .4" lift then flattened out. The radius device the shop showed me was for a port with parallel sides, the LT1 head is tapered toward the top. I also saw a bag of clay and assumed he would know to either use the clay to match up the device or use the clay in lieu of the device. From the conversation I had with them I wouldn't rule out that the radius device was improperly used and affected the higher lift numbers. I also think something's amiss with the exhaust numbers as most of them were actually lower when retested with the higher vacuum setting. That makes no sense at all to me. If I knew of anyone else in town with a flow bench I'd have them restested.

Michael

 

Did ya notice the .400=206--.500=206--.600=206 on the stock head..It didn't loose flow it maintained it. The way yours flow it is gonna kill any BIG numbers whether it be TQ or HP. Ya just won't get the proper cyl fill and when the piston starts back up ya will have reversion out the as* which is gonna kill the intake period. There will be less flow to help prevent that train of air from stopping or turning around and going back into the intake.Not to speak of velocity but that too.

Don't know what ya did but it ain't good.

Like I said they will all flow within 3/4CFM of each other.

If ya deal with the right people those BOGUS flow numbers DON'T happen,but big numbers sell heads.

 

So you're saying that .400"-206, .500"-206, .600"-206 will make more power than my numbers? According to the flow chart (which I don't have absolute faith in because of the radius device they had among other reasons) my ports lost 6 cfm above .400 lift. That's 2-1/2 % of the peak flow, not that huge a number. I'm no expert but it seems like a stretch that this would "kill" the head and cripple the torque and HP numbers. Forgive me for thinking there may be a bit of melodrama there