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Head info

718 Views 4 Replies 3 Participants Last post by  stripedmx5
Has anyone out there had their heads on a flow bench to see what kind of flow they have. If anyone know what an HO head flows could they let me know. I´m thinking about having some porting done and I´d like to know how well they flow beforehand.
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As a rough estimate,(not that it helps in your case), I think the 1.8L DOHC, and having the duel runner intake, my guess is 85% efficient.

For your Gen1 GT...I´m not sure at all, but here´s a rough estimate.

SOHC motors are generally 45%-65% efficient. I think it would be safe to assume a HO anything would be close to 65% if not more.

Here´s another interesting fact. It is actually possible to get more then 100% VE efficiency out of a head. I´ve actually seen a 350 chevy with 110% efficient VE, running naturally aspirated.
Thaks for the input Blade, but I was hoping for some actual numbers, i.e. what it will flow at different lift points. My other reason bhind wanting these numbers is because I´ve been messing around with my Descktop Dyno 2000 and there is a place in there where you can put in flow data, and I wanted to see if porting would have much effect on "Paper" before I decided to go through with it. I have the flow data for my Mustang heads (Trick Flow Twisted Wedge) because I had them done on the Flow bench at UTI when I was going to school there. I used that data and the data from several readily available 302 cams to choose the cam I´m going to use for my next engine build for my Mustang. I found a few cams for the 1.9 also that I wanted to run through the desktop dyno and try out, but I want the data to be as acuate as possable. And with the expeirence I´ve had with desktop dyno, the more accurate the info you put in the more realistic info you´ll get back.
Well I did pencil pushing on my 1.8L. Here´s what I found.

By increasing my VE by 10% (95%) efficiency. And replacing the springs to get my rev up 1k rpms, and of course doing new valves and seals. I could produce 233% more power (about 71hp) under boost, then by stroking the 1.8 to a 3.75" stroke.
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I still have a few numbers from my flowbenching work. I had a shop port and polish the head, but I was not happy with their conservative approach. Since I had a grinder and flowbench and computer at my disposal, I decided to learn the art and go to town. With that in mind, my base numbers are from a mildly ported 1.8 head, which, I assume, are better than stock. To simplify things, my potential intake flow (I can´t find my exhaust numbers, but most power will be found on the intake side) will be given at valve openings of .050, .10, .15, .20, .25, .30, .35, .40, with no intake manifold attatched, but with a short clay velocity stack to smooth the flow. Base corected flow/Final flow, 19.4/21.9, 37.4/39.6, 58.1/59.3, 76.2/76.8, 89.9/92.0, 99.0/106.0, 104.7/111.2, 108.2/114.5. Base Potential flow/Final flow (in %), 60.8/68.7, 61.2/64.8, 67.0/68.4,70.1/70.7, 70.7/72.4, 69.8/74.7, 68.4/72.7, 67.4/71.3.

Not huge numbers, to be sure, but it is hard to find big improvements on this head. I think Mazda already figured out the secret by raising the intake port openings to give a straighter shot to the chamber. I found the downward curve of the intake port to be the limiting factor. Still the results speak for themselves. My car is plenty strong and the hogged-out ports have not really hurt the bottom-end, as I had expected. I have a CD with pics of the ports, before, during and after my hand work, and many of my projects, but have not taken the time to label the items. One of these days, I will do so and get it to the webmaster to post.

Hope this gives you some food for thought.

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