Head backwards

[John B]

I have read of a developmental head used by Chrysler engineers on the 2.2 that had a smaller exhaust valve and larger intake valve that supposedly made lots of power. That seems exactly backwards to me. Our intake is forced in under considerable pressure while our exhaust is like a NA engine with the additional burden of turning a turbine wheel. The intake should be optimized for good velocity for preboost reponse, while the exhaust should be opened up for good flow while retaining reasonable velocity. This would seem to mean a larger EXHAUST valve and a smaller intake. Tell me where I'm wrong!

[22dodge]

you are wrong because the piston pushes out the spent gasses with way more force and velocity than the turbo pushes in. I did build and engine with the same size intake and exhaust valves.. really made no difference in power

[88-16V-Lebaron]

Quote:

Originally Posted by John B The intake should be optimized for good velocity for preboost reponse, while the exhaust should be opened up for good flow while retaining reasonable velocity. This would seem to mean a larger EXHAUST valve and a smaller intake. Tell me where I'm wrong!

No Cigar with that one. Just look at the Audi 5V technology for an example. 3 intake and 2 exhaust valves to cram more air in the engine and 50% of their motors are turbos. Air is compressible to there is a lag in the response for acceleration of the air to fill the cylinder, but the short distance that the compressed exhaust gasses need to flow is a fraction of the distance that air needs to flow from the exit of the turbo to the inside of the cylinder chamber.

[89acclaim]

John B, I believe you are talking about the +2/-2 head. They actually were designed for NA applications if I remember correctly. You may want to look at this thread ULTRA RARE +2-2 Head


Daniel Merrill




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[turbovanman]

I don't know if you had a typo John but the exhaust valves are always smaller than the intake. Reason as stated, its easier to push out the air then pull it in,

[John B]

No it wasn't a typo. I believe that on a forced induction engine the bottleneck is the exhaust side. I would like to try a head with the largest valve that the port flow will support, even if the intake valve has to be smaller to make room for a larger exhaust valve. Remember, unlike a NA engine, our exhaust has to drive a turbine wheel, not just go to atmosphere.

[turbovanman]

You did typo, see here-

Quote:

Originally Posted by John B I have read of a developmental head used by Chrysler engineers on the 2.2 that had a smaller exhaust valve and larger intake valve that supposedly made lots of power.

You mean larger exhaust valve and smaller intake valve-correct?

[John B]

I understand you now. I mean Chrysler engineers did a big intake / small exhaust head. I think it should be the other way around.

[lotza boost]

As a rule of thumb, just about every factory 2 valve non-crossflow head(s) are designed to have the exhaust flow at aproximately 80% of the intake. This does not mean that the you can just measure the intake valve face and then pick an 80% smaller valve though. The heads are also designed to work within the pre-determined average RPM range as well as the the cam, compression ratio, rod/stroke, bore/stroke.
You really need to get with the company that is either building or modified the head you are looking at using to see what they were wanting out of it when they waived there magic wand over it.
Hope this helps you in some way.