XR7 Dave
Registered User
I want to thank everyone for your participation in our previous poll and discussion regarding a new cylinder head for the SC. We have nailed down some specific details regarding this proposed new product and are ready to share some of the info with you.
For the most part the discussion of what to do, how to approach the project, what to expect, and what will sell the best, etc. is over. As I stated before the design details are best left to the pro's and our job was complete when we let them know what we thought we were looking for. Now it remains for us to drum up the support necessary to make it a reality.
If something we present doesn't sit well with someone please feel free to speak and we will explain the whys and wherefores here in this thread. I expect this thread to carry us into production so lets keep our thoughts and comments focused on the fact that this thread is going down in history.
So. Here it is.
In the beginning some of us where a little - ok a lot - optimistic about what to expect from the new ports "out of the box." After a detailed look at the stock head as well as a fully ported version, the designers are convinced that an out of the box intake port flow number would be responsibly targeted at about 240cfm. Before anyone gets a long face about that, a quick look at the AFR 165cc Street SBF head shows 245cfm and the AFR 180cc Street SBC head flows 260cfm out of the box. To shoot for 240cfm out of the box puts us within reach of some of the best street small block cylinder heads on the market.
It was brought clearly to my attention that there are several things that we need to consider when looking at flow numbers for our heads.
1) Because we have an injector port in the head directly above the intake port, it follows that port height is limited by the need to have gasket material between the injector and the port. This limits as-cast potential.
2) Our heads are on top of a small 3.811 bore. Big flow numbers need room to work and big valves to go with them. The AFR heads refered to above all run with 2.02 valves. We can run that big of a valve but it will create shrouding problems at higher flow rates. Out of the box our heads will run smaller valves.
3) Runner volume. It is comparatively easy to get a large flow number from a large port but the problem begins when you consider that these heads will also be targeted as part of the marketing mix, at NA 3.8L engines. A large port volume would make the head useless on a normal NA 3.8.
So for these reasons it was suggested to me that we stay on the conservative side with port volume and concentrate on an efficient port that maintains better velocity.
So what is involved in an efficient port? This is where it gets good. There are so many revisions to our existing design it's almost too much to put into words so I'll start with the basics.
1) Valve angles and alignment will be retained. There is no real need to relocate any valves or change the angles. This is good when considering the number of stout shortblocks already out there not to mention those contemplating new heads for a stock pistoned motor.
2) By altering piston to valve clearance slightly and increasing deck thickness it will be possible to increase the stock short turn raduis by nearly an inch. This is a critical aspect of flow efficiency on the head. By raising the port floor we can achieve a turning of the air before it hits the cylinder. As it is now the air/fuel is simply slammed into the cylinder wall opposite the injector. By raising the the floor and initiating a turn prior to hitting the back of the valve, the mixture in the cylinder will be much more homogenous and will burn faster with less tendancy to detonate. This is one of the greatest benefits of this port design and it doesn't show up in raw flow numbers.
3) Port configuration. We have all agreed that from a marketing perspective it would be simply be asking too much to move the center port to a symetrical location. For most applications a proper redesign of that port will be sufficient. By moving the pushrod over and straightening the port we will be able to achieve a close balance between all ports. It is conceiveable that at some point through extensive porting someone will come to a point that the center port will not keep up any longer. We have kept this in mind and we have asked for (and received) the option to have the center port made symtrical with the end ports. It is something that will be designed into the molds making the change a simple matter of ordering a production run of symetrical port heads.
4) It was not felt that there is any particular need to dramatically depart from the basic exhaust port design that we already have. The welded radius exhaust ports currently in use already reflect modern exhaust port design technology and will be incorporated into these heads. No significant changes are planned and the port should flow 200cfm as cast giving us an 83% IE ratio out of the box. Stock exhaust hardware will most definitely fit.
5) Expect smaller combustion chambers. A more efficient layout with dual quench pads and a relocated spark plug are the biggest differences. Expect to raise compression by about a point over what you would have had otherwise. We feel that with a more efficient combustion chamber and better flow that higher compression will not result in any increased octane sensitivity. Driveability, fuel mileage, and throttle response should be expected to be noticably improved.
6) Valvetrain will be completely different. The valves will be longer and larger (1.94 intake and 1.60 exhaust as cast), and the rocker arm geometry we now use will not be carried over. The rockers will be stud mounted and the base for them to attach to will be a solid bar accross the entire head. It will be made in such a way to allow for a custom shaft system like T&D to be made for extreme rpm and solid roller cam applications. The heads will accept readily available hardware for cost effectiveness and servicability.
7) Most likely due to increased deck height, overall stock intake manifold height will be raised some - target is less than 1/2" raise. Of course while it will accept a stock intake, these heads are intended for an aftermarket intake and in most cases an aftermarket hood for clearance. However that will not be required for those simply using a stock intake and an M90 for that stock look.
These heads will be truely bolt on although their dimensions may differ slightly from stock and may require some slight accomodations (such as increased intake manifold height). They are made from 356 aluminum and will be heat treated to maximum hardness making them MUCH stiffer overall than the stock head.
So that's what is on the table. This is what we have been offered by the designer/manufacturer and I feel it truely represents what we have been waiting for. It will allow us to bolt on the head as is, it will allow us to develop the port for maximum flow, and it will allow us to develop other parts to compliment the heads without worrying about over-running them. The designer assured us that with this head we WILL be finding the next weakest link.
What thinks you??
David
For the most part the discussion of what to do, how to approach the project, what to expect, and what will sell the best, etc. is over. As I stated before the design details are best left to the pro's and our job was complete when we let them know what we thought we were looking for. Now it remains for us to drum up the support necessary to make it a reality.
If something we present doesn't sit well with someone please feel free to speak and we will explain the whys and wherefores here in this thread. I expect this thread to carry us into production so lets keep our thoughts and comments focused on the fact that this thread is going down in history.
So. Here it is.
In the beginning some of us where a little - ok a lot - optimistic about what to expect from the new ports "out of the box." After a detailed look at the stock head as well as a fully ported version, the designers are convinced that an out of the box intake port flow number would be responsibly targeted at about 240cfm. Before anyone gets a long face about that, a quick look at the AFR 165cc Street SBF head shows 245cfm and the AFR 180cc Street SBC head flows 260cfm out of the box. To shoot for 240cfm out of the box puts us within reach of some of the best street small block cylinder heads on the market.
It was brought clearly to my attention that there are several things that we need to consider when looking at flow numbers for our heads.
1) Because we have an injector port in the head directly above the intake port, it follows that port height is limited by the need to have gasket material between the injector and the port. This limits as-cast potential.
2) Our heads are on top of a small 3.811 bore. Big flow numbers need room to work and big valves to go with them. The AFR heads refered to above all run with 2.02 valves. We can run that big of a valve but it will create shrouding problems at higher flow rates. Out of the box our heads will run smaller valves.
3) Runner volume. It is comparatively easy to get a large flow number from a large port but the problem begins when you consider that these heads will also be targeted as part of the marketing mix, at NA 3.8L engines. A large port volume would make the head useless on a normal NA 3.8.
So for these reasons it was suggested to me that we stay on the conservative side with port volume and concentrate on an efficient port that maintains better velocity.
So what is involved in an efficient port? This is where it gets good. There are so many revisions to our existing design it's almost too much to put into words so I'll start with the basics.
1) Valve angles and alignment will be retained. There is no real need to relocate any valves or change the angles. This is good when considering the number of stout shortblocks already out there not to mention those contemplating new heads for a stock pistoned motor.
2) By altering piston to valve clearance slightly and increasing deck thickness it will be possible to increase the stock short turn raduis by nearly an inch. This is a critical aspect of flow efficiency on the head. By raising the port floor we can achieve a turning of the air before it hits the cylinder. As it is now the air/fuel is simply slammed into the cylinder wall opposite the injector. By raising the the floor and initiating a turn prior to hitting the back of the valve, the mixture in the cylinder will be much more homogenous and will burn faster with less tendancy to detonate. This is one of the greatest benefits of this port design and it doesn't show up in raw flow numbers.
3) Port configuration. We have all agreed that from a marketing perspective it would be simply be asking too much to move the center port to a symetrical location. For most applications a proper redesign of that port will be sufficient. By moving the pushrod over and straightening the port we will be able to achieve a close balance between all ports. It is conceiveable that at some point through extensive porting someone will come to a point that the center port will not keep up any longer. We have kept this in mind and we have asked for (and received) the option to have the center port made symtrical with the end ports. It is something that will be designed into the molds making the change a simple matter of ordering a production run of symetrical port heads.
4) It was not felt that there is any particular need to dramatically depart from the basic exhaust port design that we already have. The welded radius exhaust ports currently in use already reflect modern exhaust port design technology and will be incorporated into these heads. No significant changes are planned and the port should flow 200cfm as cast giving us an 83% IE ratio out of the box. Stock exhaust hardware will most definitely fit.
5) Expect smaller combustion chambers. A more efficient layout with dual quench pads and a relocated spark plug are the biggest differences. Expect to raise compression by about a point over what you would have had otherwise. We feel that with a more efficient combustion chamber and better flow that higher compression will not result in any increased octane sensitivity. Driveability, fuel mileage, and throttle response should be expected to be noticably improved.
6) Valvetrain will be completely different. The valves will be longer and larger (1.94 intake and 1.60 exhaust as cast), and the rocker arm geometry we now use will not be carried over. The rockers will be stud mounted and the base for them to attach to will be a solid bar accross the entire head. It will be made in such a way to allow for a custom shaft system like T&D to be made for extreme rpm and solid roller cam applications. The heads will accept readily available hardware for cost effectiveness and servicability.
7) Most likely due to increased deck height, overall stock intake manifold height will be raised some - target is less than 1/2" raise. Of course while it will accept a stock intake, these heads are intended for an aftermarket intake and in most cases an aftermarket hood for clearance. However that will not be required for those simply using a stock intake and an M90 for that stock look.
These heads will be truely bolt on although their dimensions may differ slightly from stock and may require some slight accomodations (such as increased intake manifold height). They are made from 356 aluminum and will be heat treated to maximum hardness making them MUCH stiffer overall than the stock head.
So that's what is on the table. This is what we have been offered by the designer/manufacturer and I feel it truely represents what we have been waiting for. It will allow us to bolt on the head as is, it will allow us to develop the port for maximum flow, and it will allow us to develop other parts to compliment the heads without worrying about over-running them. The designer assured us that with this head we WILL be finding the next weakest link.
What thinks you??
David
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