cylinder heads what works?

[mightymulhern]

I would recommend that no one get too over-excited and take a dremel to their heads based soley on what they read in a book, 2 books, or on the internet. The odds of you radically improving performance are about as good as the odds that you'll win the lottery. If you go conservative you might make some small gains. If you go nuts you'll more than likely kill power or at least destroy the low end.

Having seen Ed at work on his flow bench, I can attest that what appears to be obvious isn't. Often times, "clearly this will flow better" doesn't. In an hour of watching him, I quickly figured out that to do it without a bench and without measuring air velocity would an effort in futilty. It's really a black art and not something to charge boldly into on a weekend with the one set of heads you intend to put back on your car.

...just my 2 cents.

[RoadWarrior222]

They say that it takes about 10 sets of heads to get anywhere near okay at it, so I figure if I start with these on my spare motor, I'll have a really quick car in 2023 or so.

By the way, our heads are CROSSFLOW, do not do combustion chamber side mods intended for SWIRL heads or you'll probably screw 'em up. I figure the best clues will come from DOHC porters, since those are practically always crossflow.

Myself I'm not going to be flying totally blind, I'm hoping to import port shapes into a fluid dynamics simulator and work on them in that. Then when I've got something that works, make templates, and then try to wreak that shape on the head.

I hear that one big mistake that people make is forgetting that you can often direct air more effectively with a short side radius than a long side radius. The flow will attach to a correctly formed SSR. Doing as much flow control as possible with a SSR will cause a lot less resistance than doing it on the long side. One really needs to get a firm grasp of basic fluid dynamics, "conventional wisdom" will fail you. That's probably why a lot of people who really know their stuff won't attempt to explain everything on internet forums, they get fed up of being ambushed by flash mobs of redneck engineers who'll drown the signal with cries of "Everyone knows that...." yeah sure, that's why everyone gets a BSc in physics on completing junior kindergarten. Then you get into argument on fundamentals like "I don't have to blow between two strips of paper to see whether they come together or not because it's plain common sense that they'll blow apart." .... sure whatever Bubba.

So, finding the right info is hard, best to read up on the basic physics of everything first, that will help you develop a serviceable BS filter.

RW222

[TimTona]

thats true everybody thinks they know everything, isnt the purpose of this group to learn because im sure everybody has something to add to things that somebody else doesnt know so we all learn more then we have to take what we learn as fact or fiction right?

[Tim_K]

What are good numbers for port velocities, both intake and exhaust, on our V6 heads? And what units are velocities measured in? Feet per second of airflow or something else?

I have a set of 1990 V6 heads that I've cleaned up and done some work on. Nothing crazy, just got the rough casting surfaces in the ports smoothed out, took out some obvious sharp casting edges, and used sanding drums in my Dremel grinder to smooth everything nicely.

Before I spend the money to replace the valve guides and do a nice valve job, I'm going to have new valve guides put in ONE cylinder (a center one most likely, for ease of setting it up on a flowbench), and have a 3 or 5 angle valve job done on that one cylinder, and take it to a good engine builder I know of and have flow tests and air velocity measurements done. The guy has been in business for many years, and races 6 second drag racing cars that he builds, so I think he knows what he's doing. Last time I asked a few years ago he had a Superflow 600 flow bench.

What are some stock flow numbers and air velocity numbers for unmodified V6 heads? At 28 inches of vacuum, which I think is still the standard, right?

[c2xejk]

What velocity you target depends on how good you are... Ideal is around 300 feet/sec... At the same time you need to watch velocities on the short side radius... Too fast and the flow can become disconnected... Remember in a running engine the velocities can go much higher.

28" is the standard, but many people are doing testing at higher pressures... I have done some testing at 40" and 60"

Stock flow numbers (peak) are ~183 and ~103 CFM. I havn't tested the velocity of the stock heads.

[c2xejk]

Probably a better question might be, at what RPM do you want to achieve peak torque... Do you want a stump puller or do you want to wind the engine out to 7000 or 8000 RPM? Combine that with your realistic hp goals and you can determine a lot of the sizing...

[Tim_K]

In my case, the V6 would be in my '93 Shadow ES. Hopefully with a 5 speed manual transmission. Normal everyday beater car, but of course I'll leadfoot it around as much as possible. And it'll go to the dragstrip now and then.

So I'd say the normal everyday rpm range would be 2000 to 4500 rpm. Hoping for 160-175 horsepower out of it. It'll have some mild mods like 52mm throttle body, ported intake and exhaust manifolds (don't know yet what can be done with the exhausts if anything). And a 2-1/2" exhaust system.

[mwinkle353]

Removed for stupidity

[c2xejk]

Quote:

Originally Posted by Tim_K In my case, the V6 would be in my '93 Shadow ES. Hopefully with a 5 speed manual transmission. Normal everyday beater car, but of course I'll leadfoot it around as much as possible. And it'll go to the dragstrip now and then. So I'd say the normal everyday rpm range would be 2000 to 4500 rpm. Hoping for 160-175 horsepower out of it. It'll have some mild mods like 52mm throttle body, ported intake and exhaust manifolds (don't know yet what can be done with the exhausts if anything). And a 2-1/2" exhaust system.

Ok, assuming you want the hp peak at 4500 RPM, you will need volumetric efficiency of about 115%. You will want to minimum port area to be 1.141 in^2. That will achieve a velocity of about 250 feet/sec.

The runner length should be 14.378" (3rd harmonic) or 11.317"(4th harmonic). Given that the stoc runner length is ~12.1" and you have a Shadow, taller doesn't seem like a reasonable option. So the other option would be to weld the manifold..

The other option would be to target a higher RPM peak... 175hp@5200 would yield 12.280" for the 3rd harmonic. Much more achievable...

Right now I would guess that a larger throttle body would be benifitial...

Side note, I have been assuming 175 hp at the crank. That equates to ~149 whp... If you are thinking higher, let me know.

[Tim_K]

I didn't say I wanted the horsepower peak to be at 4500, I said that in normal everyday use its normal rpm range would be 2000-4500, more or less, depending on how I feel like driving at the moment. Could be higher or lower rpms too. If the horsepower peak is at 5000 or 5200 or 5500 that is fine with me. The peak will be wherever it is. It'll have stock cams and stock compression ratio. Same mods as I have right now, 52mm throttle body and ported intake plenum.

[c2xejk]

Quote:

Originally Posted by Tim_K I didn't say I wanted the horsepower peak to be at 4500, I said that in normal everyday use its normal rpm range would be 2000-4500, more or less, depending on how I feel like driving at the moment. Could be higher or lower rpms too. If the horsepower peak is at 5000 or 5200 or 5500 that is fine with me. The peak will be wherever it is. It'll have stock cams and stock compression ratio. Same mods as I have right now, 52mm throttle body and ported intake plenum.

For 5200 RPM & 175 hp, the intake port should narrow down to 1.150 in^2 to achieve 250 fps.

The problem with moving the peak hp higher in the RPM band is the stock computer doesn't know that the engine breathes well at that RPM...

[Tim_K]

And what sort of flow / velocity numbers should the exhaust port have to handle 175 hp at 5200, or some similar numbers?

[c2xejk]

300 fps at the port exit at max lift. Sadly, the port exit is so large, that this is pretty much unattainable by convensional methods... Hence the comments I made earlier in this thread...

[RoadWarrior222]

I'm looking at 3 different fixes for that, besides welding up or fixing a block in it. One of them looks like hell but promises benefits at the supersonic speeds of initial blowdown. It'll also prolly only flow like 20cfm in reverse We'll find out how that all works in about the middle of summer, not getting there yet.

Meanwhile, plan B is "Hi-Temp Steel" putty which is meant to be good to 2000F, and is on the shelf at Canadian Tire and Part Source in Canada for $6.99 a package.

[Ondonti]

i dont think Ed has had much luck with that kind of putty.