Max head flow for 25 psi race motor

[05stroker]

First off let me say I am open to all comments and criticism here.

Okay, so I have been looking at my setup in depth today as far as where I can gain some power while the motor is down. I have decided on a Manley 11.6:1 flattop piston. I will be pushing 23 to 25 psi along with it on E85.

From what I understand a motor is like an air pump, the faster the air can get in and out the better. I have no experience in porting heads but have the resources to do the work by hand. I currently have a set of basic ported heads from Kuntz Racing. They have stock size inlets and outlets while the ports are smoothed and have the 1mm oversized valve with bronze guides spaced properly.

I was looking at them today with the marks from the intake, exhaust, and cylinder bore still on the heads since they have not been cleaned up yet. Well, that has led to a lot of questions.

1. Why not open the intake as large as possible with the boost I will be running?

2. Why would I keep the exhaust port smaller then the gasket?

3. Why not port match the exhaust port to my headers?

4. Why is the exhaust port D shaped instead of round like my headers?

5. If flow is so important then why not open the intake port at the JPC intake and the head port as big as I can and then port the delete plate to match?


Here are a few pics to explain what I am thinking about doing. I would be machining the delete plate to remove the grooves for the factory style gaskets and using a dual gasket setup like the one below that comes with the JPC intake. Doing this would only limit the size of the intake port to what the head can withstand and not need to worry about gasket placement. It would remove about 5mm from the plate so, I will have to check for any interference with the alt. and such.

I would also like to remove the material in the combustion chamber much like the FRPP heads.

You have to keep in mind, this would be a custom setup geared towards my car only and not something that is produced for the masses.

 

[skwerl]

Air will flow sort of like water. Imagine water flowing through a hose. If the hose is lumpy with fat spots and skinny spots then flow will be interrupted and the surging water will end up slowing down the overall flow. If the hose diameter is uniform all the way through then flow will be uninterrupted and will flow faster.

Now imagine gouging out big fat spots in your intake or exhaust ports. If you take out too much you can actually reduce flow. The reason ported heads are so expensive is because it takes a lot of studying and experience to make heads flow properly. Just because you own a grinder doesn't make you a porting specialist. If I buy a spray paint gun that doesn't make me an auto painter either.

 

[rcm90]

Im going to be doing the same as you. Here are the intake and exhaust runner profiles from a junk head that I cut up. I'm really focused on the exhaust ports since that's where these turd motors seem to be lacking. I'm working on a flow bench and should be able to start testing different port shapes in the next month or two.

 

[RocketcarX]

I know in the pushrod world raising the port floor (the D shape) increases port velocity and because of that increases flow.

 

[05stroker]

Air will flow sort of like water. Imagine water flowing through a hose. If the hose is lumpy with fat spots and skinny spots then flow will be interrupted and the surging water will end up slowing down the overall flow. If the hose diameter is uniform all the way through then flow will be uninterrupted and will flow faster.

Now imagine gouging out big fat spots in your intake or exhaust ports. If you take out too much you can actually reduce flow. The reason ported heads are so expensive is because it takes a lot of studying and experience to make heads flow properly. Just because you own a grinder doesn't make you a porting specialist. If I buy a spray paint gun that doesn't make me an auto painter either.

I'm not talking a bought gouging out the insides. They are smooth and slightly ported by a professional for the application they were meant for at the time. I am talking about port matching the exhaust and opening up the intake ports as much as possible. I do understand the hose analogy though. If I have 1" hose and squeeze it to 1/2" in the middle then flow will decrease.

 

[05stroker]

I know in the pushrod world raising the port floor (the D shape) increases port velocity and because of that increases flow.

That's what I was thinking here. I understand not wanting to much exhaust flow on a N/A motor but, on a high c/r, high boosted motor I feel there cannot be enough air flow. The big ass blower should be able to push the air past a single "small" spot such as the valves there selves and open it up every where else.

 

[RocketcarX]

Are the valves stock diameter? It may be pointless to open up much more if the stock valve is a restriction with your current porting. You may want to look into un-shrouding the valves and working on quench by zero decking the block to the pistons if you do have larger valves.

 

[rcm90]

That's what I was thinking here. I understand not wanting to much exhaust flow on a N/A motor but, on a high c/r, high boosted motor I feel there cannot be enough air flow. The big ass blower should be able to push the air past a single "small" spot such as the valves there selves and open it up every where else.

From what I have read that's the idea. Big open intake runners for the blower or turbo to cram air through. For my turbo build I'm shooting for the exhaust to flow 75-80% of what the intake does. Not really sure what it should be for a blower, but cannot imagine it being too far off from that.

 

[tjm73]

11.6:1 and 23-25 psi? With only e-85? That doesn't sound like it'll work. Wouldn't that require race fuel?

 

[rcm90]

11.6:1 and 23-25 psi? With only e-85? That doesn't sound like it'll work. Wouldn't that require race fuel?

No, 4cyl guys have done 11:1 and 40+lbs of boost with no problems on e85. When really pushing cylinder pressures the cam profile plays a HUGE part in controlling the dynamic compression..

 

[05stroker]

Are the valves stock diameter? It may be pointless to open up much more if the stock valve is a restriction with your current porting. You may want to look into un-shrouding the valves and working on quench by zero decking the block to the pistons if you do have larger valves.

The valves are 1mm larger. I was looking at un-shrouding the valves though. That is what I meant about the combustion chamber work like the FRPP heads. If I zero deck the block the pistons would need work for the valves that I don't want.

From what I have read that's the idea. Big open intake runners for the blower or turbo to cram air through. For my turbo build I'm shooting for the exhaust to flow 75-80% of what the intake does. Not really sure what it should be for a blower, but cannot imagine it being too far off from that.

That is what I am thinking. With a big blower pushing and a large exhaust system, why not give it every chance to flow? Im not talking about a DD here. This is a race car in street trim.

I can understand not wanting to get to deep in the ports but, if the meat is there then why not open it up?

 

[05stroker]

11.6:1 and 23-25 psi? With only e-85? That doesn't sound like it'll work. Wouldn't that require race fuel?

No, 4cyl guys have done 11:1 and 40+lbs of boost with no problems on e85. When really pushing cylinder pressures the cam profile plays a HUGE part in controlling that.

E85 runs cooler then the C16 (117 oct) I used to run. I feel quite good about the fuel choice for my car. I think BruceH posted once about testing that was done and even at e50 they couldn't get an internal combustion engine to detonate.

 

[rcm90]

"The exhaust port is more critical on a turbo motor than the intake. Because of pressure concerns... there are limits to how aggressive you can be with your evo evo. Limited evo means limited duration. That means the exhaust port has to kick ass to evacuate the cylinder in X amount of duration.

If the exhaust port sucks... the duration has to be so long to evacuate the cylinder that the valve events end up all wrong for the turbine.

The exhaust port is the 1st step in velocity generation in the exhaust tract. I want that bitch damn near going sonic.

As far as the intake.... give me the biggest,lowest velocity on the flowbench port you can.

80% exhaust to intake ratio on the flow bench.... makes me a happy camper."

That came off the bullet from a real smart guy. A blower engine is fairly close to this as well.

 

[rcm90]

I can understand not wanting to get to deep in the ports but, if the meat is there then why not open it up?

I'm going to make a few more cuts to measure how much "meat" is there to take away on the ports. Ill post up the results in this thread and my head porting thread.

 

[05stroker]

"The exhaust port is more critical on a turbo motor than the intake. Because of pressure concerns... there are limits to how aggressive you can be with your evo evo. Limited evo means limited duration. That means the exhaust port has to kick ass to evacuate the cylinder in X amount of duration.

If the exhaust port sucks... the duration has to be so long to evacuate the cylinder that the valve events end up all wrong for the turbine.

The exhaust port is the 1st step in velocity generation in the exhaust tract. I want that bitch damn near going sonic.

As far as the intake.... give me the biggest,lowest velocity on the flowbench port you can.

80% exhaust to intake ratio on the flow bench.... makes me a happy camper."

That came off the bullet from a real smart guy. A blower engine is fairly close to this as well.

Seems to me on my setup, low duration and close to max lift, without the back pressure concerns with the turbo, I would just want max flow period though.

 

[RocketcarX]

"The exhaust port is more critical on a turbo motor than the intake. Because of pressure concerns... there are limits to how aggressive you can be with your evo evo. Limited evo means limited duration. That means the exhaust port has to kick ass to evacuate the cylinder in X amount of duration.

If the exhaust port sucks... the duration has to be so long to evacuate the cylinder that the valve events end up all wrong for the turbine.

The exhaust port is the 1st step in velocity generation in the exhaust tract. I want that bitch damn near going sonic.

As far as the intake.... give me the biggest,lowest velocity on the flowbench port you can.

80% exhaust to intake ratio on the flow bench.... makes me a happy camper."

That came off the bullet from a real smart guy. A blower engine is fairly close to this as well.

I would think a supercharger would not be near as sensitive to exhaust port velocity as a turbo or NA motor. I mean I know velocity matters, but I think after a point with that much boost you can sacrifice a little velocity for volume.

 

[rcm90]

That's what im getting from it. The exhaust is certainly not as critical, but you still want to keep velocity up to help evacuate the cylinder faster

 

[crownaviation]

That's what im getting from it. The exhaust is certainly not as critical, but you still want to keep velocity up to help evacuate the cylinder faster

Yes that could be a problem. Back to the water hose.. you pinch it and velocity increases but flow is limited. Opening up exhaust ports will increase flow but hurt velocity. In many cases velocity is a major component here and where a good head guy with a flowbench earns his money. You can easily go the wrong way unfortunately. Not that I like paying big money for ported heads and no it does not cost much to do.. you are paying for all the trial and error..

We went thru several blowers before we got any improvements. We actually lost performance on a couple initially. On one of them we opened it up a little too much and removed a small step down in the inlet. That step down was actually helping control velocity and direct air flow to another chamber (rear wall cavity). We ruined the case totally and lost major air flow as turbulence was a factor pre-rotor. Flow bench rules..

Some things are worth the money.. this is one of those. Send them to RGR

 

[skwerl]

Do you want a set of heads ported by somebody with years of experience and a proven track record, or a set of heads ported by somebody who has never ported heads before but thinks he can figure it out on his first attempt?

 

[psfracer]

If this were an N/A application we could have a very interesting discussion on port volume vs port velocity and how that affects flow numbers.

But,

With 25psi that changes the discussion completely. I don't see how velocity in the port could be a problem at 25 psi. I would be interesting if you had access to a flow bench and a couple trashed heads and see the affects of port shape yourself.

Also to consider is the valve angle, how much the port is raised, and even the valve job. I have seen big differences in flow numbers going from 45 degrees to 52 degrees, but valve life may suffer, especially when talking about titanium valves.