AFR Head topic

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Re: AFR Head topic

Post  Straubtech on November 11th 2016, 1:57 pm

I'll just say this. The fastest turbo motor on Street Outlaws is one of the smallest in the field at under 500CID. Turbo's don't like piston speed. You want the lowest piston speed you can get for the rpm range your running.

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Re: AFR Head topic

Post  DFI429 on November 11th 2016, 3:23 pm

Straubtech wrote:I'll just say this.   The fastest turbo motor on Street Outlaws is one of the smallest in the field at under 500CID.  Turbo's don't like piston speed.   You want the lowest piston speed you can get for the rpm range your running.

Care to elaborate on the theory?  Purely curiosity.. not asking for secrets lol Wink
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Re: AFR Head topic

Post  DaveMcLain on November 11th 2016, 6:31 pm

Straubtech wrote:I'll just say this.   The fastest turbo motor on Street Outlaws is one of the smallest in the field at under 500CID.  Turbo's don't like piston speed.   You want the lowest piston speed you can get for the rpm range your running.

I can't think of a single performance attribute that is directly the result of piston speed. Piston speed in and of itself is nonsense.

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Re: AFR Head topic

Post  whatbumper on November 12th 2016, 1:18 pm

gt350hr wrote:
Scott Foxwell wrote:
octanehuffer wrote:Not pissed one bit. Just disappointed. Off topic.
I spoke with a couple people who had messaged me about the other thread offering actual help and I came to the conclusion of what to do. Ordered a Callies 4.5" crank, Oliver billet rods and Diamond 4.5" pistons. Thank you for those who actually helped! I have ZERO problem helping those who help me. All in all, I got the help I needed and was able to order a bunch of parts. Mission completed. Sad that it went the way it went though.
4.5" stroke with the turbo build?
Whoever talked you into that didn't do you any favors.

  +1 the 4.500 stroke and 20 psi is a bad choice in this application, IMHO. Good luck with getting a dished piston for less than 9-1 compression. 48cc ( approximate) dish is a challenge.

Who runs 9:1 turbo motors anymore?

2000hp in any brand of big block with boost is about like making 650 hp NA. It's not that difficult and does not take any special components other than good parts.

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Re: AFR Head topic

Post  Scott Foxwell on November 12th 2016, 4:34 pm

whatbumper wrote:
gt350hr wrote:
Scott Foxwell wrote:
octanehuffer wrote:Not pissed one bit. Just disappointed. Off topic.
I spoke with a couple people who had messaged me about the other thread offering actual help and I came to the conclusion of what to do. Ordered a Callies 4.5" crank, Oliver billet rods and Diamond 4.5" pistons. Thank you for those who actually helped! I have ZERO problem helping those who help me. All in all, I got the help I needed and was able to order a bunch of parts. Mission completed. Sad that it went the way it went though.
4.5" stroke with the turbo build?
Whoever talked you into that didn't do you any favors.

  +1 the 4.500 stroke and 20 psi is a bad choice in this application, IMHO. Good luck with getting a dished piston for less than 9-1 compression. 48cc ( approximate) dish is a challenge.

Who runs 9:1 turbo motors anymore?  

2000hp in any brand of big block with boost is about like making 650 hp NA.  It's not that difficult and does not take any special components other than good parts.
There are better ways to do things, and worse ways...

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Re: AFR Head topic

Post  Scott Foxwell on November 12th 2016, 4:36 pm

DaveMcLain wrote:
Straubtech wrote:I'll just say this.   The fastest turbo motor on Street Outlaws is one of the smallest in the field at under 500CID.  Turbo's don't like piston speed.   You want the lowest piston speed you can get for the rpm range your running.

I can't think of a single performance attribute that is directly the result of piston speed.  Piston speed in and of itself is nonsense.

Piston speed is nonsense? LOL...
Piston speed is EVERYTHING.
More specifically, piston acceleration, piston demand,...ie: piston speed.
I can't think of a single performance attribute that is directly the result of piston speed.
I can't think of one that isn't. Wink


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Re: AFR Head topic

Post  Scott Foxwell on November 12th 2016, 4:43 pm

DFI429 wrote:
Straubtech wrote:I'll just say this.   The fastest turbo motor on Street Outlaws is one of the smallest in the field at under 500CID.  Turbo's don't like piston speed.   You want the lowest piston speed you can get for the rpm range your running.

Care to elaborate on the theory?  Purely curiosity.. not asking for secrets lol Wink
It's pretty simple. Piston speed dictates the demand on the induction. We're not talking about mean (average) piston speed here (rpm), we're talking about piston acceleration. Long stroke engines with relatively short numeric rod ratios have higher piston speeds and more demand and it makes the job of the forced induction a lot harder to provide the filling. Displacement does the same thing. It takes a lot more supercharger, whether it's a turbo, centrifugal or roots, to fill cylinder with a piston that's accelerating faster from TDC than not... and the harder the supercharger has to work, the more inefficient it is. The most HP/CI you will see with boosted engines are the smallest displacements with the shortest strokes.

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Re: AFR Head topic

Post  dfree383 on November 12th 2016, 4:49 pm

Straubtech wrote:I'll just say this.   The fastest turbo motor on Street Outlaws is one of the smallest in the field at under 500CID.  Turbo's don't like piston speed.   You want the lowest piston speed you can get for the rpm range your running.

It's all about power management in that scenario.... Not piston speed. Put a  300" turbo engine against a properly fed 600" one in a proper chassis and traction then tell us how it is.
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Re: AFR Head topic

Post  DaveMcLain on November 12th 2016, 7:03 pm

Scott Foxwell wrote:
DaveMcLain wrote:
Straubtech wrote:I'll just say this.   The fastest turbo motor on Street Outlaws is one of the smallest in the field at under 500CID.  Turbo's don't like piston speed.   You want the lowest piston speed you can get for the rpm range your running.

I can't think of a single performance attribute that is directly the result of piston speed.  Piston speed in and of itself is nonsense.

Piston speed is nonsense? LOL...
Piston speed is EVERYTHING.
More specifically, piston acceleration, piston demand,...ie: piston speed.
I can't think of a single performance attribute that is directly the result of piston speed.
I can't think of one that isn't. Wink

You are incorrect.

If you have two cylinders of the same displacement one with a small bore long stroke and the other one a large bore short stroke they both sweep the cylinder at IDENTICAL rates of change per degree as long as the rod ratio is the same. The speed of the piston makes ZERO difference in the demand for airflow. Try again, I bet you can't come up with a single thing that's directly related to the speed of the piston in and of itself.


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Re: AFR Head topic

Post  DaveMcLain on November 12th 2016, 7:23 pm

Scott Foxwell wrote:
DFI429 wrote:
Straubtech wrote:I'll just say this.   The fastest turbo motor on Street Outlaws is one of the smallest in the field at under 500CID.  Turbo's don't like piston speed.   You want the lowest piston speed you can get for the rpm range your running.

Care to elaborate on the theory?  Purely curiosity.. not asking for secrets lol Wink
It's pretty simple. Piston speed dictates the demand on the induction. We're not talking about mean (average) piston speed here (rpm), we're talking about piston acceleration. Long stroke engines with relatively short numeric rod ratios have higher piston speeds and more demand and it makes the job of the forced induction a lot harder to provide the filling. Displacement does the same thing. It takes a lot more supercharger, whether it's a turbo, centrifugal or roots, to fill cylinder with a piston that's accelerating faster from TDC than not... and the harder the supercharger has to work, the more inefficient it is. The most HP/CI you will see with boosted engines are the smallest displacements with the shortest strokes.

Piston speed is not piston acceleration they are not the same thing. If you keep the rod ratios the same at a given displacement there is NO difference in the rate of change in cylinder volume between a long stroke small bore engine and vice versa of the same displacement.

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Re: AFR Head topic

Post  JBR-3 on November 12th 2016, 8:11 pm

Dave's statement about swept volume is correct.
To repeat again repeat again, the rod ratios MUST be identical.

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Re: AFR Head topic

Post  whatbumper on November 13th 2016, 5:53 pm

If I was building a turbo motor for myself and I could do anything, it would be short stroke. And I've only built a few. Wink

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Re: AFR Head topic

Post  rmcomprandy on November 13th 2016, 8:28 pm

DaveMcLain wrote:

I can't think of a single performance attribute that is directly the result of piston speed.  Piston speed in and of itself is nonsense.
I bet you can't come up with a single thing that's directly related to the speed of the piston in and of itself.


Ring sealing, attributed to the velocity and weight of the piston ring; (which IS directly controlled by the speed of the piston).

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Re: AFR Head topic

Post  DaveMcLain on November 13th 2016, 9:07 pm

rmcomprandy wrote:
DaveMcLain wrote:

I can't think of a single performance attribute that is directly the result of piston speed.  Piston speed in and of itself is nonsense.
I bet you can't come up with a single thing that's directly related to the speed of the piston in and of itself.


Ring sealing, attributed to the velocity and weight of the piston ring; (which IS directly controlled by the speed of the piston).

Yes it is but that's not caused directly by the piston what if the ring package is made lighter? If you used a ring set from a model T the speed you could run the piston would be much lower than if you ran a very skinny modern ring package.

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Re: AFR Head topic

Post  Scott Foxwell on November 13th 2016, 9:25 pm

DaveMcLain wrote:
Scott Foxwell wrote:
DaveMcLain wrote:
Straubtech wrote:I'll just say this.   The fastest turbo motor on Street Outlaws is one of the smallest in the field at under 500CID.  Turbo's don't like piston speed.   You want the lowest piston speed you can get for the rpm range your running.

I can't think of a single performance attribute that is directly the result of piston speed.  Piston speed in and of itself is nonsense.

Piston speed is nonsense? LOL...
Piston speed is EVERYTHING.
More specifically, piston acceleration, piston demand,...ie: piston speed.
I can't think of a single performance attribute that is directly the result of piston speed.
I can't think of one that isn't. Wink

You are incorrect.  

If you have two cylinders of the same displacement one with a small bore long stroke and the other one a large bore short stroke they both sweep the cylinder at IDENTICAL rates of change per degree as long as the rod ratio is the same.  The speed of the piston makes ZERO difference in the demand for airflow.  Try again, I bet you can't come up with a single thing that's directly related to the speed of the piston in and of itself.

I'm not incorrect and I clarified my statement. The term "piston speed" is vague to the point you even had to clarify what YOU were referring to. I was referring, and I know Straub was as well, to piston acceleration. And even piston speed in regards to peak mean piston speed is relevant to performance. It's called RPM. You also can get into bore to stroke ratio and the effect that has on combustion and flame travel so when you say a small bore long stroke is the same as a large bore short stroke (as long as the rod ratio is the same) you're wrong.

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Re: AFR Head topic

Post  Scott Foxwell on November 13th 2016, 9:28 pm

DaveMcLain wrote:
Scott Foxwell wrote:
DFI429 wrote:
Straubtech wrote:I'll just say this.   The fastest turbo motor on Street Outlaws is one of the smallest in the field at under 500CID.  Turbo's don't like piston speed.   You want the lowest piston speed you can get for the rpm range your running.

Care to elaborate on the theory?  Purely curiosity.. not asking for secrets lol Wink
It's pretty simple. Piston speed dictates the demand on the induction. We're not talking about mean (average) piston speed here (rpm), we're talking about piston acceleration. Long stroke engines with relatively short numeric rod ratios have higher piston speeds and more demand and it makes the job of the forced induction a lot harder to provide the filling. Displacement does the same thing. It takes a lot more supercharger, whether it's a turbo, centrifugal or roots, to fill cylinder with a piston that's accelerating faster from TDC than not... and the harder the supercharger has to work, the more inefficient it is. The most HP/CI you will see with boosted engines are the smallest displacements with the shortest strokes.

Piston speed is not piston acceleration they are not the same thing.  If you keep the rod ratios the same at a given displacement there is NO difference in the rate of change in cylinder volume between a long stroke small bore engine and vice versa of the same displacement.  
Again, the term "piston speed" is a generalization and most of the people I know who do this for a living understand what we're talking about when we say "piston speed" in regards to induction. Then, there re those who like to argue semantics.
And piston acceleration can absolutely be about piston speed. Acceleration is simply defining a change in speed. It's all about piston speed.


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Re: AFR Head topic

Post  Scott Foxwell on November 13th 2016, 9:31 pm

DaveMcLain wrote:
rmcomprandy wrote:
DaveMcLain wrote:

I can't think of a single performance attribute that is directly the result of piston speed.  Piston speed in and of itself is nonsense.
I bet you can't come up with a single thing that's directly related to the speed of the piston in and of itself.


Ring sealing, attributed to the velocity and weight of the piston ring; (which IS directly controlled by the speed of the piston).

Yes it is but that's not caused directly by the piston what if the ring package is made lighter?  If you used a ring set from a model T the speed you could run the piston would be much lower than if you ran a very skinny modern ring package.
LOL...but it's piston speed that we're dealing with. The ring is along for the ride. The ring reacts to the piston speed.

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Re: AFR Head topic

Post  Scott Foxwell on November 13th 2016, 9:39 pm


 Try again, I bet you can't come up with a single thing that's directly related to the speed of the piston in and of itself.

I'll say it again. It's ALL about piston speed.

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Re: AFR Head topic

Post  DFI429 on November 13th 2016, 10:15 pm

Scott Foxwell wrote:
DFI429 wrote:
Straubtech wrote:I'll just say this.   The fastest turbo motor on Street Outlaws is one of the smallest in the field at under 500CID.  Turbo's don't like piston speed.   You want the lowest piston speed you can get for the rpm range your running.

Care to elaborate on the theory?  Purely curiosity.. not asking for secrets lol Wink
It's pretty simple. Piston speed dictates the demand on the induction. We're not talking about mean (average) piston speed here (rpm), we're talking about piston acceleration. Long stroke engines with relatively short numeric rod ratios have higher piston speeds and more demand and it makes the job of the forced induction a lot harder to provide the filling. Displacement does the same thing. It takes a lot more supercharger, whether it's a turbo, centrifugal or roots, to fill cylinder with a piston that's accelerating faster from TDC than not... and the harder the supercharger has to work, the more inefficient it is. The most HP/CI you will see with boosted engines are the smallest displacements with the shortest strokes.

Again I'm totally amateur hour here given the company, but would like to understand better..

I guess I'm having trouble seeing the difference in two engines having the same swept volume per cylinder.. one long stroke/small bore, one short stroke/big bore.. they breathe the same volume per revolution, correct?  I totally understand the imposed load on a super/turbocharger as engine displacement increases.. more air=more work.  But comparing two cylinders of the same volume all other things equal.. ??  As far as more and more boost (and HP) using smaller displacements.. seems to be a compromise with modern forced induction technology..
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Re: AFR Head topic

Post  rmcomprandy on November 13th 2016, 11:41 pm

DFI429 wrote:

Again I'm totally amateur hour here given the company, but would like to understand better..

I guess I'm having trouble seeing the difference in two engines having the same swept volume per cylinder.. one long stroke/small bore, one short stroke/big bore.. they breathe the same volume per revolution, correct?  I totally understand the imposed load on a super/turbocharger as engine displacement increases.. more air=more work.  But comparing two cylinders of the same volume all other things equal.. ??  As far as more and more boost (and HP) using smaller displacements.. seems to be a compromise with modern forced induction technology..

If it only was ALL mechanical volume change then there would be no difference in volume change per degree of crank rotation. However, there is other things to consider.
One thing called the combustion process and flame travel matter a whole bunch. Especially when heat of the charge and spark advance are concerned along with flame speed and octane requirements.
Some others, are simply the amount of tensile strain put upon components and inertia principles.
There are more, of less importance but, there ARE other things involved.

It is NOT all about engine breathing or just transferring air from one place to another.

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Re: AFR Head topic

Post  Scott Foxwell on November 14th 2016, 10:24 am

rmcomprandy wrote:
DFI429 wrote:

Again I'm totally amateur hour here given the company, but would like to understand better..

I guess I'm having trouble seeing the difference in two engines having the same swept volume per cylinder.. one long stroke/small bore, one short stroke/big bore.. they breathe the same volume per revolution, correct?  I totally understand the imposed load on a super/turbocharger as engine displacement increases.. more air=more work.  But comparing two cylinders of the same volume all other things equal.. ??  As far as more and more boost (and HP) using smaller displacements.. seems to be a compromise with modern forced induction technology..

If it only was ALL mechanical volume change then there would be no difference in volume change per degree of crank rotation. However, there is other things to consider.
One thing called the combustion process and flame travel matter a whole bunch. Especially when heat of the charge and spark advance are concerned along with flame speed and octane requirements.
Some others, are simply the amount of tensile strain put upon components and inertia principles.
There are more, of less importance but, there ARE other things involved.

It is NOT all about engine breathing or just transferring air from one place to another.
This is spot on. This isn't a simple air pump, it is an internal combustion engine. "Internal combustion" being the key phrase here. Think of it in exaggerated terms. What if you had a 6" cylinder but the piston only had to move 1" vs a 3" cylinder and a piston that has to move 4" (both have a volume of 28.27ci, both have the same rod ratio. same rpm, etc.). Think of the combustion process in terms of time and how that might make a difference. Think of the acceleration rate of each piston even though they both have the same rod ratio and same rpm...(one has to move 1" in 180* and the other has to move 4" in 180*) Equal amounts of air and fuel burning at the same rate, what would the difference be? Would there be a difference?
We're not even touching on the induction side of things or cam timing or port velocity or volumetric efficiency or any of those other dynamics.

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Re: AFR Head topic

Post  DaveMcLain on November 14th 2016, 10:54 am

Scott Foxwell wrote:
DaveMcLain wrote:
Scott Foxwell wrote:
DaveMcLain wrote:
Straubtech wrote:I'll just say this.   The fastest turbo motor on Street Outlaws is one of the smallest in the field at under 500CID.  Turbo's don't like piston speed.   You want the lowest piston speed you can get for the rpm range your running.

I can't think of a single performance attribute that is directly the result of piston speed.  Piston speed in and of itself is nonsense.

Piston speed is nonsense? LOL...
Piston speed is EVERYTHING.
More specifically, piston acceleration, piston demand,...ie: piston speed.
I can't think of a single performance attribute that is directly the result of piston speed.
I can't think of one that isn't. Wink

You are incorrect.  

If you have two cylinders of the same displacement one with a small bore long stroke and the other one a large bore short stroke they both sweep the cylinder at IDENTICAL rates of change per degree as long as the rod ratio is the same.  The speed of the piston makes ZERO difference in the demand for airflow.  Try again, I bet you can't come up with a single thing that's directly related to the speed of the piston in and of itself.

I'm not incorrect and I clarified my statement. The term "piston speed" is vague to the point you even had to clarify what YOU were referring to.  I was referring, and I know Straub was as well, to piston acceleration. And even piston speed in regards to peak mean piston speed is relevant to performance. It's called RPM. You also can get into bore to stroke ratio and the effect that has on combustion and flame travel so when you say a small bore long stroke is the same as a large bore short stroke (as long as the rod ratio is the same) you're wrong.

Long stroke small bore vs large bore short stroke combustion efficiency is not what you said, you said "piston speed". You didn't say acceleration, friction etc you said piston speed. If you keep the rod ratio the same both the long stroke small bore and the large bore short stroke engines sweep the cylinder at exactly the same rate per degree and therefore the volume change in the cylinder which drives the induction is exactly the same. EVERYTHING else that you are seeing and I don't deny that these effects occur is secondary and not directly the result of how fast the piston is moving. I'd like to hear one example of how the actual speed of the piston in and of itself makes any difference what so ever to engine performance.

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Re: AFR Head topic

Post  Scott Foxwell on November 14th 2016, 11:12 am

DaveMcLain wrote:
Scott Foxwell wrote:
DaveMcLain wrote:
Scott Foxwell wrote:
DaveMcLain wrote:
Straubtech wrote:I'll just say this.   The fastest turbo motor on Street Outlaws is one of the smallest in the field at under 500CID.  Turbo's don't like piston speed.   You want the lowest piston speed you can get for the rpm range your running.

I can't think of a single performance attribute that is directly the result of piston speed.  Piston speed in and of itself is nonsense.

Piston speed is nonsense? LOL...
Piston speed is EVERYTHING.
More specifically, piston acceleration, piston demand,...ie: piston speed.
I can't think of a single performance attribute that is directly the result of piston speed.
I can't think of one that isn't. Wink

You are incorrect.  

If you have two cylinders of the same displacement one with a small bore long stroke and the other one a large bore short stroke they both sweep the cylinder at IDENTICAL rates of change per degree as long as the rod ratio is the same.  The speed of the piston makes ZERO difference in the demand for airflow.  Try again, I bet you can't come up with a single thing that's directly related to the speed of the piston in and of itself.

I'm not incorrect and I clarified my statement. The term "piston speed" is vague to the point you even had to clarify what YOU were referring to.  I was referring, and I know Straub was as well, to piston acceleration. And even piston speed in regards to peak mean piston speed is relevant to performance. It's called RPM. You also can get into bore to stroke ratio and the effect that has on combustion and flame travel so when you say a small bore long stroke is the same as a large bore short stroke (as long as the rod ratio is the same) you're wrong.

Long stroke small bore vs large bore short stroke combustion efficiency is not what you said, you said "piston speed".  You didn't say acceleration, friction etc you said piston speed.  If you keep the rod ratio the same both the long stroke small bore and the large bore short stroke engines sweep the cylinder at exactly the same rate per degree and therefore the volume change in the cylinder which drives the induction is exactly the same.  EVERYTHING else that you are seeing and I don't deny that these effects occur is secondary and not directly the result of how fast the piston is moving.  I'd like to hear one example of how the actual speed of the piston in and of itself makes any difference what so ever to engine performance.  
You can repeat the same thing over and over Dave, it won't change anything. I'm sorry if you don't get it.

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Re: AFR Head topic

Post  gt350hr on November 14th 2016, 3:50 pm

500 cubic inches can be had in several ways. 4" bore , 5" stroke ( 502ish) 4.470 bore , 4" stroke ( 502ish) and 4.750 x 3.500 ( 500ish).  10,000+rpm Pro Stock engines run the latter combination. Any guess as to why they run a shorter than 9.800 deck height block?? The rod to stroke ratio was TOO much and it hurt torque. Simply shortening the rod would have made the piston too heavy for 10,000 rpm. Big bores unshroud the valves and short strokes let them rev , but 500 inches is still 500 inches , so they should all be the same right? It's just a 500 ci air pump. LOL

      I am aware of the increases in static compression ratios for turbo engines brought on by Q16 and also the increased  use of alcohol , but lots of people still use gasoline and need the lower c/r. There is also a quiet trend toward shorter rods as some feel getting the piston off of TDC faster allows more air and fuel to be introduced before it "backs up". ( High pressure in the port , opening valve and little space for the pressurized air/ fuel to go with a slow moving ( around TDC ) piston. If everybody did the same thing , they would all run the same, but they don't.

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Re: AFR Head topic

Post  BOSS 429 on November 14th 2016, 4:11 pm

gt350hr wrote:500 cubic inches can be had in several ways. 4" bore , 5" stroke ( 502ish) 4.470 bore , 4" stroke ( 502ish) and 4.750 x 3.500 ( 500ish).  10,000+rpm Pro Stock engines run the latter combination. Any guess as to why they run a shorter than 9.800 deck height block?? The rod to stroke ratio was TOO much and it hurt torque. Simply shortening the rod would have made the piston too heavy for 10,000 rpm. Big bores unshroud the valves and short strokes let them rev , but 500 inches is still 500 inches , so they should all be the same right? It's just a 500 ci air pump. LOL

      I am aware of the increases in static compression ratios for turbo engines brought on by Q16 and also the increased  use of alcohol , but lots of people still use gasoline and need the lower c/r. There is also a quiet trend toward shorter rods as some feel getting the piston off of TDC faster allows more air and fuel to be introduced before it "backs up". ( High pressure in the port , opening valve and little space for the pressurized air/ fuel to go with a slow moving ( around TDC ) piston. If everybody did the same thing , they would all run the same, but they don't.


THIS/\ IS not the main reason they use a short deck
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