The making of cylinderheads for an Okrasa engine on steroids

[Alstrup]

Yes.
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https://www.thesamba.com/vw/forum/viewtopic.php?t=435993

[Alstrup]

Soo. A year and a half later I got around to get the heads done. there have been a few changes in the project too. the main thing is that the displacement has been increased to 78 x 83 mm. so 1690 cc. in order to sort of make the power, but make the car more driveable in regular traffic.
I was initially goiung with 37,5 x 33 valves, but varius obsticles with delivery prevented me from that, so we opted for 36,5 x 32 From Ray (Speedwell) That turned out to be a good thing as such because the 37,5 x 33 combination would have left very little space between the valves. To the point of it being dangerous.
Also, Once the heads were at the stage I settled for we found out that the exhaust port, once again, basicly outflowed the intake in spite of the fact that the valve is on only 32 mm and that I basicly only cleaned up the throat to match the 32 mm valve seat.
The intake did NOT meet my expectations. It is about 10 cfm down compared to what I expected. After a couple of hours of investigation and playing with the pitot tubes on the flow bench we realized that these intake ports have an issue with having enough throat area ½ to 3/4" into the port where it turns rather abrupt "downward". the aprupt turn is no help either though. In these castings there were very little material to work with on the long radius so I could not increase the bend radius much even if I wanted to. (Come winter, and I will try to increase that throat area on a set of test heads in order to figure out where I would have to add material on the back side to get to where I´d like to be.
After the decission with going 83 x 78 I set my nose up for 120 hp, but thats not gonna happen. Theoretical peak is approx 117 hp. Real life will most likely be around 110. One positive aspect of the restrictive intake is that the port velocity is incrediblky high. Over 400 fps and slowing down to the 325 fps range just above the valve. That should give the engine the ability to pull good lower and midrange power, i.e- more driveable.
As mentioned, the exhaust port is crazy efficient. I could probably have settled for a 30 mm and gotten the flow needed. But I didnt. So in order to compensate for that we will be running 1,4/1,25 rockers, kinda 356 style. This will give an I/E ratio in the range of 90-95%. Still on the high side, but better than 100%. The beneficial side effect of doing it this way is that the engine sees the valve motion as the cam is a split dur. So i think the engine will pull good overall torque.
Cam will be an Elgin 7208-17 ground on a tiny base circle to clear the rods.
Pistons will be out a Honda Motorcycle IIRC. CR will be around 9,4-1, to be figured out exactly when the deck height and slight dome on the pistons are measured out.

So, from now on the project will be taken over by Hans Biesmann (Speedshack) in Belgium. With a little luck he will continue this thread once he gets the bits´n bobs figured out.)

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https://www.thesamba.com/vw/forum/viewtopic.php?t=435993

[grueni]

Not been here for a Long Long Time. (Mymedusa)
Torben, you should have talked to Andreas Hendl or me or read the old stuff from flow Bench Numbers here(Tom Bruch vor example)
The exhaust Port in the 36hp Heads is extremly good in compare to intake in Stock and even in okrasa heads.38/30mm is a good Combo that worked Well in okrasas or even 38/28 in single Ports. This big Missmatch in Ports makes the 36 Heads a good Kompressor or turbo head. With 78mm crank it is hard to get lift in the camshaft, Hope you have that in mind. But possible with very small rod big end Diameter.

Enjoy the build.
Chris
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1960 1584cc turbocharged, 35,5/32 (11,117s 1/4mile )

[Alstrup]

There is some truth in that.
Yes, cam ground on 20 mm base circle, 0,333" lift, and will be multiplied with 1,45 on intake and 1,25 on exhaust. - Speedwell rocker arms on a custom shaft.
rods are VW type 4 w. 50 mm journals. The smallest off the shelf rods we could find within reason.

But the slightly conservative flow numbers are not the fault of the valve and seat, but the upper part of the port. I am not sure there is enough meat to improve that without welding. I will look into this come winter.
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https://www.thesamba.com/vw/forum/viewtopic.php?t=435993

[grueni]

Funny i have on my shelf also a 76mm with smaller typ4 rods plus a 74/81combo. The Port is the Problem for Sure but the exhaust valve should have been smaller and same time you have more meet in between or can use a bigger valve...but it is how it is, i would weld and improve it. So much work that this should be done too. Sadly you are so far in Progress, i would have done it before valve seats so you could weld the chambers Up. AS i remember right Andreas Hendl Had 95isch HP Out of a 1582cc single Port with 38/28 valves. Did Not Tom Bruch Had 156hp from a 16xx in the old days. Maybe Talk to him or search what they have done to reach that.
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1960 1584cc turbocharged, 35,5/32 (11,117s 1/4mile )