Performer rpm heads

[Garys1969RR]

Just got a look at the port layout and shape of my new (used) Perf RPM Heads. I am impressed. This is the first Aluminum Cyl Head I have looked at closely. The intakes have straight and direct paths to the valve bowl. There is no hump on the floor just before it turns into the bowl on the short side radius as the 915s have. Also, at the top of the port window, the passage leads straight into the bowl, rather than jogging upward like the 906/915 intake ports do. The under valve bowl is large and deep, with large free flowing channels around the valve guide. The ex side is also impressive. Large deep bowls, with both channels around the valve guide being the same basic shape. They look really nice.

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I plan to blend the small ridge out where the chambers meet the top cut of the valve seat. This looks as if it would impede low lift flow.

 

[Meep-Meep]

I just want to point out the hump on the floor of the 915 and 906 head is not considered a restriction. I found the reply below on a Fiat forum and I think does a good job of explaining what I want to say, or have been saying about the 915/906 vs. 516/452 heads.

The real problem with any wedge port is the turn into the pocket and to get the A/F mixture to make the turn. Ford made a big effort to eliminate this turn by creating the high riser head for the 427 (pic below). Check out how high the port roof is. And of course the major benefit of the hemi valve layout was the breathing - less angle into the pocket.



Port Velocity
Most discussions about porting, talk almost exclusively about achieving greater values for airflow.
If simply having larger values for airflow were the key to maximum horsepower,
then we could expect the “bigger is better” theory to hold true, which it doesn’t.
The keys to producing the best airflow for an engine lie in port velocity and flow efficiency.

If a port is modified to produce good flow with a minimal amount of material removed,
then, since it is flowing more air through much the same sized port,
velocity must have also increased.

Though too much port velocity can limit top end power,
low velocity can reduce power throughout the power curve.

On a carburetted engine, a smaller port volume will improve throttle response
as it has less damping effect on the induction pulse.

Less damping will enhance the atomisation of fuel from the auxiliary (or second) venturi,
which in turn aids both fuel distribution and burning efficiency.

Higher port velocities also support atomised fuel better with less chance of fuel
falling out of suspension or forming into large droplets.

A small volume - hence high velocity - port will also enhance cylinder ramming at the end of the intake stroke
and this will increase volumetric efficiency. Coupled with attention to entry direction through the valve
which can promote better cylinder swirl and aiding combustion efficiency.
which all leads to what we want to achieve - more power being produced.

The exhaust port velocity is also important.
A slow exhaust port can cause an engine to have little low-end power before coming on the cam abruptly.
As the intake opens the exhaust flow provides the energy to initiate flow past the valve,
well before the piston begins to move down the bore.
If the exhaust velocity is low, effective scavenging of the combustion chamber is lost during the overlap period.

For both intake and exhaust the key to making an efficient port, is to manoeuvre air around any corners
as effectively as possible. Though light, air has sufficient mass to be affected by momentum as it moves
through the port, and requires little velocity to exhibit a tendency to go straight than around a bend.
Air arriving at too sharp a turn in the port will not negotiate the turn at the tight radius,
it will simply hug the turn at the wall of the larger radius. This makes the port flow considerably less,
and is seen by the air as a very real constriction.

The key to getting air to negotiate corners efficiently comes down to two factors.
1.Making the corner as large a radius as possible, and
2. Increasing the port cross sectional area enough to slow the air, hence enhance its ability to negotiate the turn.

Image one represents a standard port (for a twin cam Fiat but the idea is the same for any port),
from the manifold face to the valve seat.

Our aim is to move air from one end to the other with minimum flow loss or velocity reduction,
this means the best utilization of cross sectional area and a minimum of dead space.

Image 1


Image

The first key to efficiency of flow around a bend was to make the turns as large as possible.
Image two shows the short side radius was increased,
but in doing so the cross sectional area was decreased.

Image 2


Image

To compensate the port was widened as shown in Image three.
By necessity we must also have the valve stem in the air stream at the bend,
somewhere near the end of the port, this further reduces the cross sectional area.
Widening the port as in Image three also compensates for this reduction in cross sectional area,
so the room around the stem at least equals the area before its introduction to the air-flow.
The port now has all the major elements for increased efficiency.

Image 3


Image

Image four (below) is a three dimensional representation of the port in Image three.


Image

The SOHC inlet port benefits from a bias to direct the flow towards the centre of the cylinder,
and away from the port and cylinder wall. This is shown in Image 5 in an exaggerated form.


Image

The Flow Cone

This next part is a very important part of the porting / understanding flow paths concept - the Flow Cone.
I talk quite a bit about how "shrouding" will reduce the total flow thru the port considerably, well here is why.

Understanding the dynamics of airflow around an obstruction is crucial to achieving good flow through a port.
It is vital to remember that the valve head is the greatest restriction to the flow path,
as it sits right in the middle of the airstream and all flow must move around the valve head
before it enters the combustion chamber.

Smoke or water flowing thru a clear tube shows how the airflow forms a typical cone shaped path
above and below the valve head. An interesting fact is that when flow through the port becomes
better and the velocity of the flow increases, these cones become shorter.

Image

Another fact is that if anything happens to break into the area formed by these Flow Cones
on either side of the valve head- like tight cylinder wall shrouding or dropping the short side radius -
then the total flow thru the port is severely reduced.

So you can see that to achieve maximum flow through any port,
these Flow Cones must not be disturbed in any way.

Serious engine builders spend quite a bit of time ensuring that the angles and widths,
particularly of the valve face, margin and leading edge
(upper for intake, lower for exhaust) are as they want them.
This is because these factors have a strong positive influence on this Flow Cone formation.

Some factors that can have a negative influence on the Flow Cone formation,
and hence drop the total flow thru the port are...

a) Shrouding from the cylinder wall / combustion chamber walls

b) Shrouding by the valve cutout pockets / piston dome

c) Dropping the short side radius of the intake port

In the Fiat sohc cam engine the greatest factor of these three is the effect
of shrouding by the combustion chamber walls.

To get good flow on an 86/87mm bore sohc engine,
you really need to relieve the combustion chamber and deshroud the inlet valves.

Some people when fitting larger valves or porting cylinder heads
have a tendency to drop the port floor (reducing the short side radius)
in an effort to bring the flow into the backside of the valve at an oblique angle.
This is just totally wrong.

If you try and bend the flow right at the edge of the valve,
the cone doesn't form around the edge of the valve and total flow drops off considerably.

To get a uniform cone formation around the entire circumference of the valve,
we want to turn the flow well above the valve head, and let the flow come straight into the back of the valve.
There are always restrictions to what is possible, but one thing is absolutely certain,
that you should try and get the sides of the intake port dead straight and perpendicular
to the valve for as long a distance as possible.

Total flow past the primary obstruction (the valve head) can also be increased
if the Flow Cone becomes more of a Vortex.

Think back to Primary School science lessons.
Remember getting two bottles of water and inverting them to let the contents empty,
and giving one of the bottles a little swirl as you were inverting it,
the bottle that has the extra energy imparted to it forms a "whirlpool" or vortex at the mouth,
and empties considerably quicker than the tumbling flow of the "non-swirled" bottle.

Precisely this same effect can be applied to an inlet port,
and Fiat have already done it for us,
with the Port Bias that is found in the standard production ports.

The offset bias, and the transitions formed by this bias, angles the low flow (the lower portion of the port)
towards the far side of the valve, directing the airflow in such a way that a swirl effect is imparted,
and total flow increased.

If this offset bias is ignored (think of these like the little "winglets" you see all over a contemporary F1 car
which angle the airlow around obstructions) then the vortex effect is completely lost, and total flow is reduced.

The Flow Path. Inlet manifolds and Carburettors

When you talk about improving the output of an engine,
you must consider the entire path of the intake / exhaust gases as they dynamically cycle through the cylinder head,
so the cylinder head and inlet manifold need to be considered as a single unit at this point.

The extent of any porting and valve and seat modifications will depend on the choice of manifolding and fuel delivery. Fortunately for the SOHC there is a load of choice.


(Image 1-5; Ford high riser intake port)




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[Garys1969RR]

Interesting reading, Meep. I find the science of cyl head airflow to be a fascinating subject. I am far from being an expert on this, but I love to experiment and try different ideas. Thanks for your help.

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Meep Meep, dont you think that the rise on the floor of the 915/906 port can "launch" the airstream at higher valve lifts? Is this what causes the port to stall at lifts above .500"? Or are there other contributing factors. Just trying to learn a little about port design and air flow. Thanks.

 

[67Satty]

The guy I've been talking to about porting some 906s says that he doesn't like the 452s because he says the 452s have "no short turn to keep air attached to the runner" and that hurts the velocity of the fuel/air mixture. I know most people say after porting, the 452s can be as good as the 906/915s but he seems to really hate the 452s for this reason.

 

[Meep-Meep]

I'm no expert either but do tend to absorb as much data as possible. A few facts that are inarguable:

CFM isn't the whole story! It's a quantitative measurement describing units of air per minute. Add velocity to the equation and you have units of air per minute at a measured speed.

Fuel and air do not behave the same.

What's important is delivering the A/F mixture into the chamber in a vapor or some nicely atomized form. Whatever leaves the venturi should enter the cylinder with as little loss as possible.


About stalling the 915 port? I don't know. Stalling would imply that the A/F mixture stops or slows down to the point it's not doing much after a certain point. If one can model the 915 port exactly but scale it up in size, you might find the port would respond to more lift and have a higher flow reading. And to keep all things equal, the engine RPM required to meet the same flow and velocity (as found on the smaller port) would come at a higher RPM or the same RPM on a larger cubic inch engine.

 

[Cranky]

I like the Eddys too. Had a set of max ported 906's and the OTB Eddy flowed the same but the port config and combustion chamber design along with the angled plugs make for a superior head vs the 906's and should out perform them. My old 906's were on a mild compared to today's standards 440 that pushed a 3200 lb 68 road runner into the mid 10's.

 

[Meep-Meep]

I like the Eddys too. Had a set of max ported 906's and the OTB Eddy flowed the same but the port config and combustion chamber design along with the angled plugs make for a superior head vs the 906's and should out perform them. My old 906's were on a mild compared to today's standards 440 that pushed a 3200 lb 68 road runner into the mid 10's.

That just proves another point I like to make is that iron heads are not the death of an engine build. Sure you can get better with an aluminum head but it all depends on your ultimate goal. For a street car you can take a set of iron heads and have them done by a competent shop and have truly bolt on parts for the same or possibly less money than Eddy's or Source heads.

 

[Cranky]

That just proves another point I like to make is that iron heads are not the death of an engine build. Sure you can get better with an aluminum head but it all depends on your ultimate goal. For a street car you can take a set of iron heads and have them done by a competent shop and have truly bolt on parts for the same or possibly less money than Eddy's or Source heads.

Yes, that's true but to do a set of 906's like mine were done, it's not going to be cheap and will probably cost as much if not more (most likely more) than a set of Eddys by the time you buy the larger valves, do the guides, cut the spring seats, install hardended seats (mine didn't have them), true up the chambers and make them all even, relieve any overhang and mill......and then they might just crack first time out. However, for a mild build, stock heads will be plenty fine imo.

 

[67Satty]

The prepped iron would probably cost more than running a pair of Stealths OOTB, and maybe be as much as the RPMs OOTB but be cheaper than a pair of aluminum heads prepped to the same level, right? Wouldn't the total cost of aluminum heads prepped to the same level as getting some irons ported and gone over exceed $2000 in most cases where getting the iron ported and prepped would cost $1000-$1500 total? Of course, like you say you could be paying $1000-$1500 for something that might crack first time out.

 

[mopar12372]

remember to port to your compression ratio , anything below 11 to 1 with big *** ports is a waste and a loss in hp .

 

[Cranky]

My OTB Eddys flowed the same numbers as my max ported 906's did and we used the same bench but.....are a better design head....read post #6....

 

[Meep-Meep]

The prepped iron would probably cost more than running a pair of Stealths OOTB, and maybe be as much as the RPMs OOTB but be cheaper than a pair of aluminum heads prepped to the same level, right? Wouldn't the total cost of aluminum heads prepped to the same level as getting some irons ported and gone over exceed $2000 in most cases where getting the iron ported and prepped would cost $1000-$1500 total? Of course, like you say you could be paying $1000-$1500 for something that might crack first time out.

What is your target goal?? If for a hot street car iron heads with a mild cam (112 LSA) is fine. I got a set of 906's done by IQ52 and I sent him non cracked cores that I got for dirt cheap. He did some bowl work, hard seats, bronze guides, big valves, springs, etc.. These are truly ready to bolt on and go. If you are trying to feed 500+ inches or rev to the moon then maybe best start with a completely new aluminum head with larger ports, but in my case I'm building a 9.5:1 451 that will be a mild street engine with exhaust manifolds (engine is for a buddy). But for a hot street 440 / 383, prepped iron heads may be the best solution. Also you don't need an expensive MLS head gasket. Send Jim (IQ52) some iron and see what he can do for you.

 

[67Satty]

What is your target goal?? If for a hot street car iron heads with a mild cam (112 LSA) is fine. .

Target goal is close to 500 hp with the .534 lift 238 @ .050, 110 LSA hydraulic cam that's already in the car. I'd like to go from the current to 7.80s-7.90s in the 1/8 with my 3600 pound car to closer to 7.40s-7.50s in the 1/8. I'd like to try shifting it at somewhere between 5,500-6,000 rpm instead of it running out of steam around 5,000 like it does now with the bone stock 452s.

So I think I need heads that flow well in the .400-.500 range.

I was looking at a chart someone who flowed and compared ported iron to OOTB RPMs made and it showed them staying even until past .500 lift and then the RPMs had the advantage. Of course, like was mentioned the flow numbers aren't the only thing to look at.

 

[Garys1969RR]

remember to port to your compression ratio , anything below 11 to 1 with big *** ports is a waste and a loss in hp .

My C/R will be close to 13 to 1 with the Eddy heads and 14cc domes. So I hope they will out perform my home ported 915s. Best ET so far in a 69 RR, 3600 lbs, is 12.58@ 109. In thin air.

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That is with the 915s, 2.14/1.81 valves.

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Target goal is close to 500 hp with the .534 lift 238 @ .050, 110 LSA hydraulic cam that's already in the car. I'd like to go from the current to 7.80s-7.90s in the 1/8 with my 3600 pound car to closer to 7.40s-7.50s in the 1/8. I'd like to try shifting it at somewhere between 5,500-6,000 rpm instead of it running out of steam around 5,000 like it does now with the bone stock 452s.

So I think I need heads that flow well in the .400-.500 range.

I was looking at a chart someone who flowed and compared ported iron to OOTB RPMs made and it showed them staying even until past .500 lift and then the RPMs had the advantage. Of course, like was mentioned the flow numbers aren't the only thing to look at.

My 451 seems to drop off fairly quickly after 5000 RPM too. Running a 509 hyd cam. Would like to get a little better top end pull out of it.

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Also noticed today that the RPMs have a very noticeable jog in the side of the port right before the bowl. It extends from the floor to the roof. Is this to impart swirl to the flow? Seems like it was on the cyl wall side of the port. Have dropped them off at the machine shop for a light touch up on the seats and valves, so cant check which side for sure. I am also going to get them surfaced, because the 1009 head gaskets left a shallow round groove on the surface.

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What is your target goal?? If for a hot street car iron heads with a mild cam (112 LSA) is fine. I got a set of 906's done by IQ52 and I sent him non cracked cores that I got for dirt cheap. He did some bowl work, hard seats, bronze guides, big valves, springs, etc.. These are truly ready to bolt on and go. If you are trying to feed 500+ inches or rev to the moon then maybe best start with a completely new aluminum head with larger ports, but in my case I'm building a 9.5:1 451 that will be a mild street engine with exhaust manifolds (engine is for a buddy). But for a hot street 440 / 383, prepped iron heads may be the best solution. Also you don't need an expensive MLS head gasket. Send Jim (IQ52) some iron and see what he can do for you.

I understand the 3519 pt head gasket can be used with these heads. $20 each. .040 compressed thickness.

 

[Meep-Meep]

Target goal is close to 500 hp with the .534 lift 238 @ .050, 110 LSA hydraulic cam that's already in the car. I'd like to go from the current to 7.80s-7.90s in the 1/8 with my 3600 pound car to closer to 7.40s-7.50s in the 1/8. I'd like to try shifting it at somewhere between 5,500-6,000 rpm instead of it running out of steam around 5,000 like it does now with the bone stock 452s.

So I think I need heads that flow well in the .400-.500 range.

I was looking at a chart someone who flowed and compared ported iron to OOTB RPMs made and it showed them staying even until past .500 lift and then the RPMs had the advantage. Of course, like was mentioned the flow numbers aren't the only thing to look at.

Well, it sounds like you are more in favor of a track car. In that case you may benefit from more flow or some other radical change. Now keep in mind that a cam change can make all the difference. Perhaps a little more duration or a faster ramp rate with your existing head might get you there, or maybe the opposite. My self, I'm beginning to see that nothing is carved in stone regarding an engine build. So many variables all producing different results. The one constant, due to the cost required to alter it, would be the short block. A balanced rotating assembly should be considered a fixed asset and from there you make changes to everything above the block deck, including the cam, until you have squeezed all you can out of what you got.

 

[67Satty]

My shortblock is pretty much the same as the one in IQ52's "Pop's 440 on the Dyno" thread (also like the one in Don Dulmage's "Old Reliable" book) - so it has some long term potential I think.

 

[Meep-Meep]

But is that a low compression motor? If so, I know IQ and many others have posted big power numbers with low compression, but those are peak numbers. I personally think that big cams and high compression go hand in hand and that recipe might make more AVERAGE power throughout the RPM band. Also, a drag car that has to start from zero velocity would want to get to the power band as quickly as possible and not fall off it. The 9.5" converter might be just right - or not. You want to leave on the torque peak, and if you have a lazy engine due to low CR and big cam, that might hurt your launch. Maybe try a smaller cam to bring the cylinder pressure up. Or put in taller gears and see what happens. There are many variables in the chassis as well.

 

[67Satty]

But is that a low compression motor? .

With the TRW 2355 "6 pack" replacement pistons ending up close to zero deck, it can be configured in a few different ways depending on head choice:

9.5:1 with 90cc open chamber iron heads (452, 906, etc...)
10:1 with 84cc RPMs
10.4:1 with 80cc Stealths
10.8:1 with 75cc E Streets or Indy EZs

The 10.8:1 with 75cc heads may or may not be pushing it for pump gas, not sure, haven't tried it. I think the 80cc or 84cc would work fine for sure.

I think my launches have been pretty good so far for what it is. I've been able to get 1.68s out of it for a 60 foot. That's a little better than it should be for the ET according to calculators I've seen and it still has a lot of weight up front - iron heads, iron water pump housing, metal hood, metal bumper, battery up front, factory disc brakes. There's room for improvement in back too, I'm running cheap Monroematic shocks and I'm only running a 27" tall tire, so I could get more footpring with a taller tire. So I think it's launching good so far for what it is.