1.7L exhaust cutaway pics; I'm shocked!!

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Thu May 27, 2004 8:31 am

Great work! They look better than mine do!

Now you can see the differences in porting between the two head styles.

Square ports flow!

dstar · Post by **dstar** » Thu May 27, 2004 8:44 am

MASSIVE TYPE IV wrote:Great work! They look better than mine do!

Now you can see the differences in porting between the two head styles.

Square ports flow!

And I got beat up by some folks when I posted THAT
3 years ago....(not you Jake!)

Don

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Thu May 27, 2004 8:47 am

Straighten those ports out and use some common sense, and things go wild...

dstar · Post by **dstar** » Thu May 27, 2004 8:52 am

MASSIVE TYPE IV wrote:Straighten those ports out and use some common sense, and things go wild...

I agree Jake.

What *I* would like to know, is if we can get away with
shortening the guides ANY at all, to decrease the turbulancce
and *let it all out*!
(As opposed to let it all HANG out, as we did back in the 70s...)

BTW, notice how little of a flycut either of those heads can take
without intruding on the exh stud?

What is the smallest cc you have been able to get a
combustion chamber Jake?

Don

Wally · Post by **Wally** » Thu May 27, 2004 2:27 pm

Nice shots!
Very informative.

However when you think the extension of the square exhaustport away, the oval and squareport look identical to me in crossection.

Am I missing s/th here?

Now, who will bite the bullet and saw a 914 2.0 ltr head in parts

Walter

Bobby74 · Post by **Bobby74** » Thu May 27, 2004 3:09 pm

Thats just too cool Nate!! Great work!

I thinned my guide boss's quite a bit, but left about 3/16" around the thicker parts and took the thin side down to about 1/8". I also shortened the guide very slightly, like .020". I also ground a taper into the end of the guide since the air will be basically comming down towards the guide..wich is cut with a 90 degree face. I have about 45 degree angles to the face, but kept the grind VERY short to help keep the guides from soaking heat out of the valves or absorbing heat from the exhaust gases. Its like the width of a valve seat 30 degree angle cut.

I can post more pics when I get home..

raygreenwood · Post by **raygreenwood** » Thu May 27, 2004 3:28 pm

Interesting part is that the 1.7 has a less restrictive intake and a more restrictive exhaust. That hump in the middle of the 2.0 intake should be removed. The bowl in the large curve of the 1.7 exhaust should be smoothed and slanted with the guide. Ray

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Thu May 27, 2004 4:03 pm

I'll see if I can get Len to come add some thoughts here... I just finished the strongest 2270 we have ever dynoed just a few minutes ago!

Damn near 180 ponies at 10.3:1 even with little old tiny valves!

mnsKmobi · Post by **mnsKmobi** » Thu May 27, 2004 5:58 pm

Thanks, Nate. Very informative, and rather you than me sawing the first head by hand!!!

Are you going to put the pictures up on your site for posterity?

aircooledtechguy · Post by **aircooledtechguy** » Thu May 27, 2004 6:02 pm

raygreenwood wrote:Interesting part is that the 1.7 has a less restrictive intake and a more restrictive exhaust. That hump in the middle of the 2.0 intake should be removed. Ray

That hump is half of the air "deflector", for lack of a better word, that starts the air splitting around the guide. The photo from that angle is a little deceiving.

I am going to try and do some thinning of the exhaust guide bosses and create more of a knife edge to the boss so that the flow more or less gets "sliced" as it hits the corner. I'm also going to thin the end of the guide as well so that it's almost a knife edge, but not quite. I'm going to use the square ports as well. Not just because of ths or anyone else's recommendations, but just because that's what I have got.

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Thu May 27, 2004 6:15 pm

Its not the size of that intake port that matters at all! Its all in the shapes, and patterns inside the port.

Remember that on a Type IV, the exhaust can NEVER be made good enough.

Some of my latest and greatest combos have had very little intake material removed... The more you do to that intake port, the worse it is on getting your 80% back out the exhaust!

Thats why a 48mm valve is worthless.

Racer Chris · Post by **Racer Chris** » Thu May 27, 2004 6:39 pm

Those pics are somewhat deceptive, and don't really show where material can be removed to improve flow in the 1.7 exhaust port.
There is enough material on the sides of the port to remove and divert the flow around both sides of the guide boss. If it is shaped well the oval port exhaust will equal the square port. It just takes more time and talent that's all.
My tapered stub pipes and a well executed port job will equal the best square port heads for exhaust flow.
Racing is where the limits get tested.

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Thu May 27, 2004 6:46 pm

The square port has alot of potential... The nicest curves I have made have been with a square port with a reshaped chamber.

aircooledtechguy · Post by **aircooledtechguy** » Thu May 27, 2004 7:20 pm

Who said anything about the intakes. . . I couldn't care less about anything other than blending the seats and removing any casting imperfections on the intake side. The EXHAUST is where I plan to do all my work. There is a LOT of meat on these heads to either side (fore & aft) of the exhaust ports that could be blended right before the curve and could allow you to create a better flow around the exhaust guide boss as well as thinning of the boss itself. I'm not talking hogging it out but just slightly deepening/widening the pockets to either side of the guide boss. This area can't be seen in these photos. This may be the area where Chris was saying they are a little deceptive. I tried to catch these in the photos looking straight down the ports of the two heads mated up.

MASSIVE TYPE IV · Post by **MASSIVE TYPE IV** » Thu May 27, 2004 7:30 pm

Absolutely- BUT almost all the huge heads you see have tons of intake port work done... Thats what hurts performance..

Good luck Nate, I like your approach for sure!