got my head flowed(#'s inside)

[RedDeerGLH]

Well went to the shop yesterday and they had just flowed my head so here's the numbers tell me what you think.
It's an 85 G-head +1mm intake and exhaust.

lift intake exhaust
.100" 56.5 51.5
.200" 110.5 95.1
.300" 151.2 119.5
.400" 178.3 138.5
.500" 196.8 149.1
.600" 208.5 155.7

[tryingbe]

Pretty good. How much did the test cost?

[RedDeerGLH]

cost me $700Can. for everything. So porting, guides, backcutting valves, flow bench time, ported 2 pc intake and pretty much anything from the intake to the exhaust ports.

[crazy1eye]

Good #'s

[cordes]

Those are some pretty nice numbers for that price. Good show.

[mpgmike]

I'm betting the porting removed a bunch of material that hurt part-lift velocity. Although the high-lift numbers are good, you spend about 1/2 of the duration at less than full valve lift. Somebody obviously spent time with the head. As a comparison, here is the last stock valve head I ported.

http://powrehaus.com/2006/10/13/late...-head/#more-30

Mike

[RedDeerGLH]

damn those are good numbers mike. The guy who ported my head had never done one of our 8 valve heads so it was all new to him and i'm happy with the results. The thing i do notice with the Powre Haus is that there is barely any difference in CFM's between 400 and 500 lift which is were the cam i'm getting is going to be used for. But that may have to do with it still being stock valves. I'm just guessing here but your port velocity's are most likely alot higher than mine at lower lift but would it not become a restriction the higher the lift. And again i'm not expert just learning little by little and hope to hear your response.

thanks
Jay

[mpgmike]

Every head I do is a bit better than the last one I did. I tried some new ideas here and got it 95% there. The exhaust is perfect, but next time I will make an adjustment to the intake port to remedy that stall at .400" lift.

As is, though, the velocities are incredible. I intentionally shoot for stall at slightly above rated cam lift. If flow keeps climbing well above what the cam is capable of, then velocities are going to be horrible at cam lift. A cam expert recently told me that he designs in all the lift he can get for the duration and valve train design. Unless flow begins to drop at a certain lift, he will give the cam all it can take. Think of it this way, the valve spends typically about 1/2 of it's time at rated lift and the other half either opening up to that lift, or closing back down. Either way, the valve will be at maximum flow longer with the higher lift (according to him).

Mike

[2.216VTurbo]

Every head I do is a bit better than the last one I did. I tried some new ideas here and got it 95% there. The exhaust is perfect, but next time I will make an adjustment to the intake port to remedy that stall at .400" lift.

As is, though, the velocities are incredible. I intentionally shoot for stall at slightly above rated cam lift. If flow keeps climbing well above what the cam is capable of, then velocities are going to be horrible at cam lift. A cam expert recently told me that he designs in all the lift he can get for the duration and valve train design. Unless flow begins to drop at a certain lift, he will give the cam all it can take. Think of it this way, the valve spends typically about 1/2 of it's time at rated lift and the other half either opening up to that lift, or closing back down. Either way, the valve will be at maximum flow longer with the higher lift (according to him).

Mike

Interesting thought Mike, I'd never thought about the stall being adjusted to just above max lift Flow tests on the ported Masi heads out west show that the 'crash' (what we had been calling it) or stall doesn't happen until almost .700" of lift. Man, that's a lot of cam

[Frank]

If flow keeps climbing well above what the cam is capable of, then velocities are going to be horrible at cam lift.

I dont know where you cam up with this, but you are wrong. I have challeneged these statements in the past, but no response.

As an example, you have a head that flows 100cfm at 28" and 0.5" of lift and 110cfm at 0.55" of lift. Obviously it wants to taper off and is obvious. According to your statements, you would then want to set the lift for 0.5" other wise you will have horrible velocities downlow. What do you mean downlow? Low lift? Low rpm? If you mean low lift, wrong! The low lift is throttling the flow, and if flow is low, then velocities are low! If you mean low rpm, then wrong! Low rpms drastically reduce pressure differential at any given crank position because piston velocities are slower and when you have slower pressure differentials across the port, then you have slower velocities.

Speaking of pressure differentials and the fact that we are talking about your work on turbo cars. Turbo cars add more pressure differential across the port and valve at almost all rpms. That same 100cfm at 28" might actually be 130cfm at 40"... and most definently the original taper of 110cfm at 28" is now not previlant because you may see 155cfm at 40"! The theory while already not valid is far from being relivant here.


Frank

[mpgmike]

OK Frank, I think I might have finally figured a way to illustrate this idea. Consider the cam lobe split into 2 functions; open the valve, and close the valve. When the valve begins to open, we can assume that the charge above the valve is fairly stagnant. When I say stagnant, pressure differential is of no value at this point. As the valve begins to open, the pressure differential takes on importance and starts to accelerate the charge. As the valve opens further, the charge accelerates even faster through the valve and through the ports. We now have a mass in motion.

Once the valve reaches max lift, it will stay there for a moment as the velocity accelerates to it's maximum. In a large port, the velocity will be slower than in a smaller port. As the piston slows toward BDC, the velocity of the charge determines to a great extent the amount of additional charge that will ram itself into the cylinder. As the valve begins to close, the velocity within the curtain area will first accelerate, then taper off.

With all that said, the greatest velocity achievable in a port is when the cross sectional area of the port is well matched to the curtain area (between the valve and seat when the valve is open). If the curtain area is the choke point, then the rest of the port will never reach the hypothetical maximum velocity. Less-than-maximum velocity will yield less-than-maximum cylinder filling at part valve lift AND at the BBDC piston positions. Pressure differential will jump start the charge as the valve opens, and work toward a higher velocity throughout the system, but velocity will keep the charge moving after the pressure differential tapers off.

Velocity is the pay-off for the choke at slightly above max valve lift.

Mike

[Frank]

I would like to first appologize for my post... made me sound like an arse. I was typing fast and didnt pay attention to the what I wrote in that concern.

OK Frank, I think I might have finally figured a way to illustrate this idea. Consider the cam lobe split into 2 functions; open the valve, and close the valve. When the valve begins to open, we can assume that the charge above the valve is fairly stagnant. When I say stagnant, pressure differential is of no value at this point.

Before my recent studies, I would agree with you because of the tendency to look at engine dynamics in a freeze frame. However this is not the case. If you look at the previous set of cycles, the air is never quite stagnant and velocity in turn is much higher then anticpated when the valve opens. That previous set of cycles has air in motion. When that valved had opened previously, that pressure differential drops because you have flow (block a water hose to reduce flow and pressure goes up, release the block and pressure goes down). Now that pressure drop is a gradient in that the most will be at the bottom of the port and the less will be at the top of the runner. So even after the valve closes, air from the intake is still flowing into the chamber all the way to the valve.

Dont get me wrong, air velocity does slow down, but it can be assumed to be stagnat. We also know that air velocity does slow down, otherwise you wouldnt need longer duration cams for the higher rev's you want to achieve.

As the valve begins to open, the pressure differential takes on importance and starts to accelerate the charge. As the valve opens further, the charge accelerates even faster through the valve and through the ports. We now have a mass in motion.

Agreed!

Once the valve reaches max lift, it will stay there for a moment as the velocity accelerates to it's maximum. In a large port, the velocity will be slower than in a smaller port. As the piston slows toward BDC, the velocity of the charge determines to a great extent the amount of additional charge that will ram itself into the cylinder. As the valve begins to close, the velocity within the curtain area will first accelerate, then taper off.

Agreed! This is because depending on port size, velocity tends to lag behind piston speed because since air has mass, it takes longer to accelerate and slower to deaccelerate when compared to piston velocity. You can have the same cfm at 0.45" of lift as 0.50" when occuring after 0.50" when looking at the system in motion because the air has momentum and wants to maintain the same mass flow since combustion chamber is still expanding.

I however wouldnt say accelerate without defining "the respect to". It is still slowing down because valve is indeed closing, however it is faster then what you would expect when compared to a more ideal system or even normal tought process.

With all that said, the greatest velocity achievable in a port is when the cross sectional area of the port is well matched to the curtain area (between the valve and seat when the valve is open). If the curtain area is the choke point, then the rest of the port will never reach the hypothetical maximum velocity.

Agreed IF the max lift is properly lined up with peak piston velocity. However the optimum and typical setup is to have max lift before this because the max piston velocity will allow for better flow past the valve while closing. Think of it as free pressure differential.

Less-than-maximum velocity will yield less-than-maximum cylinder filling at part valve lift AND at the BBDC piston positions.

Typically ya.

Pressure differential will jump start the charge as the valve opens, and work toward a higher velocity throughout the system, but velocity will keep the charge moving after the pressure differential tapers off.

Velocity is the pay-off for the choke at slightly above max valve lift.

Mike

What you have said above minus the comments I made doesnt back up nor explain that you want a taper off of cfm right after CFM. Maybe its your wording in previous posts, but that just doesnt make sense. If I ported 2 heads and its max lift was 0.5" and flow at that lift was 200cfm. If one head was still flowing 220cfm at 0.6" and the other was 240cfm at 0.6", the later head will perform better overal and will perform awesome on a boosted motor. You previous posts implied that this is either not nessecary and/or not desired. That is my disagreement.


Frank

[turbovanman²]

Great read guys.

Discuss this, is port velocity really needed on a boosted engine? I accidently remove some floor on my last swirl head, don't ask, lol, and my off boost performance wasn't affect, I also had vacuum on the highway and with my old setup, I didn't, and it made good power.

[Frank]

Great read guys.

Discuss this, is port velocity really needed on a boosted engine? I accidently remove some floor on my last swirl head, don't ask, lol, and my off boost performance wasn't affect, I also had vacuum on the highway and with my old setup, I didn't, and it made good power.

That in of itself doesnt say much. Did you remove the floor on all the ports and threw out the length of the port? Typically remove floor doesnt help much. On our heads, we like to raise the port floor to get a better radius/bend into the chamber.


Frank

[Frank]

here are some real interesting diagrams that you might like...

[turbovanman²]

That in of itself doesnt say much. Did you remove the floor on all the ports and threw out the length of the port? Typically remove floor doesnt help much. On our heads, we like to raise the port floor to get a better radius/bend into the chamber.


Frank

I asked 2 questions,


Yep, took out aprox 1/4" out of the floor on all the ports. I don't think the length changed but I definately made it larger everywhere. Kinda went hole hog, lol!


Hahhaha, thanks Frank, those diagrams are like French to me,

[mpgmike]

Great read guys.

Discuss this, is port velocity really needed on a boosted engine?

Absolutely! Boost only increases the pressure differential over naturally aspirated standards. As the piston approaches BDC, the pressure differential goes away on a boosted engine the same as it does a NA engine. Furthermore, think in terms of electricity. Watts is total electricity. It is derived from pressure (Volts) X flow/velocity (Amps). In the case of the engine, Volts would be pressure differential, or boost. Amps would be the velocity. Both are part of the equation and are necessary for total cylinder filling.

I accidently remove some floor on my last swirl head, don't ask, lol, and my off boost performance wasn't affect, I also had vacuum on the highway and with my old setup, I didn't, and it made good power.

Would that be the intake or exhaust floor? The intake floor removed will shift the flow from around the valve to over the valve. Total flow would be reduced, but the swirl effect induced would make the BSFCs go up; you'd better combust what you were able to ingest. If it were exhaust, then that might be less detrimental under boost. However, you said you gained vacuum at cruise, so...

Frank, I looked at the diagrams. Without the benefit of the context, I'd assume that the curtain area associated with these diagrams flowed more than the port; which is typical on stock heads. This is why porting improves flow and performance on stock valve heads. There were no surprises there.

Also, I AM saying that I WANT the intake ports to stall at about 0.050" above cam lift. We have been dilligently researching from different books, so to speak. There is a successful group of engine designers thinking along the lines I'm thinking and they're making at least a little more power than the camp thinking traditionally. I can't say we're talking gobs of power difference between choke at 0.050" above cam lift versus 0.150", but I can say there is gobs of power difference between the 0.050" above cam lift choke versus some of these 0.300" above cam lift choke points.

If the cam lift is 0.450" and the head is still picking up flow at 0.700", the head stinks! Period!

Mike
Mike

[GLHSKEN]

Bottom line. The 28" flow #'s are a good "base". Up the 28" # to see where flow #'s really are on a boosted engine... Try low 40's... you would be amazed... I was.. a little birdie whispered this to me...

[glhs875]

I'll throw in my .02 cents. Popular Hot Rodding put out a great porting artcle. In the article it says that the port area needs to be the area of the valve X the full lift flow efficiency, which on most well designed ports will only be in the 60 to 75% range. according to that theory would make a stock valve (1.6") need around 1.92" of area at most if I'm figuring it right. And that would be at the area before the short turn radius. For a good flowing port, it would need to grow slightly right after but before the short turn radius to slow the velocity down, build up pressure at the valve, (when velocity slows, pressure rises), while also helping the air to make the turn. And then also have a taper getting larger back towards the intake. A carb booster leg on a Holley is a good example of what the port shold basically look like. I think the area of a port needs to be a little larger than this theory on a boosted motor for max power. At least it dosen't seem to hurt from my findings.

[glhs875]

If the cam lift is 0.450" and the head is still picking up flow at 0.700", the head stinks! Period!

Mike
Mike[/QUOTE]

It could just be that the cam stinks! If would could get cams with that kind of lift for our 8V's, and had heads that could flow up there, I would gladly go that route. To get anykind of real power from what I have seen from 8V's on any engine, That is the direction to follow.