Interesting interview with GM chief engineer
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Joined: Feb 2002
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Well, the C5-R doesn't do to bad in the GTS class.
i sort of wonder this. if you take a push rod and an overhead cam engine of the same cu.in.'s. Look at the overhead cam engine and its size, then look at the pushrod and imagine if you raise the height of the bores so the valve cover is level with the cover on the overhead engine.
as far as the valve arguement
3inch diameter valve = 7.1 of surface area
having 2 2 inch diameter valves will give you= 6.3 inches surface area.
i sort of wonder this. if you take a push rod and an overhead cam engine of the same cu.in.'s. Look at the overhead cam engine and its size, then look at the pushrod and imagine if you raise the height of the bores so the valve cover is level with the cover on the overhead engine.
as far as the valve arguement
3inch diameter valve = 7.1 of surface area
having 2 2 inch diameter valves will give you= 6.3 inches surface area.
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Joined: Nov 2001
Posts: 2,985
From: In a house by the bay
Originally posted by number77
as far as the valve arguement
3inch diameter valve = 7.1 of surface area
having 2 2 inch diameter valves will give you= 6.3 inches surface area.
as far as the valve arguement
3inch diameter valve = 7.1 of surface area
having 2 2 inch diameter valves will give you= 6.3 inches surface area.
Take a real example (I found specs on the LT5 so I'll use it)...
2, 1.54" valves = 3.72 in² (LT5)
1, 2.08" valve = 3.4 in²
1, 2.17" valve = 3.7 in² (large race valve)
-Mindgame
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Joined: Nov 2001
Posts: 2,985
From: In a house by the bay
You could make arguements in all directions.....
The BMW M3 for instance uses a 3.2 liter, inline 6, DOHC engine. That versus the 405hp LS6.
HP per liter
M3, 104.1
LS6, 72.3
Then look at the cost.
It's been common knowledge for some years that high VE is easier with alot of cylinder head. The big block guys have a tougher time because they can only get so much head on the motor. The bore size increases aren't getting valve size increases in proportion. Hardly ever hear of a mountain motor breaking 100% VE for that reason.
-Mindgame
The BMW M3 for instance uses a 3.2 liter, inline 6, DOHC engine. That versus the 405hp LS6.
HP per liter
M3, 104.1
LS6, 72.3
Then look at the cost.
It's been common knowledge for some years that high VE is easier with alot of cylinder head. The big block guys have a tougher time because they can only get so much head on the motor. The bore size increases aren't getting valve size increases in proportion. Hardly ever hear of a mountain motor breaking 100% VE for that reason.
-Mindgame
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Joined: Dec 1969
Posts: 1,147
From: Phila., PA
A few months back I built a PUSHROD 4.3L V6 (SBC minus a couple of slugs) for my brother to compete in Nopi's "Comp 6" 6-cylinder N/A class. No limit on displacement, engine only had to be a production based engine from the same manufacturer as the car. We figured mid 12s to be competitive, high 11s to dominate. Easy peezie, right?
Well, NOPI outlawed us before the car ever competed in a single event. They outlawed pushrod engines in the class! What's more, we have a string of emails back and forth on the subject with them- one of which explains that our pushrod/2 valve per cylinder motor would have an "unfair advantage" in torque production vs. 4 valve per cylinder engines. HAH!!! It was almost worth being outlawed just to have that email from them.
Nothing wrong with pushrod motors. 2 valves per cylinder work just fine if you lift them high enough.
Well, NOPI outlawed us before the car ever competed in a single event. They outlawed pushrod engines in the class! What's more, we have a string of emails back and forth on the subject with them- one of which explains that our pushrod/2 valve per cylinder motor would have an "unfair advantage" in torque production vs. 4 valve per cylinder engines. HAH!!! It was almost worth being outlawed just to have that email from them.
Nothing wrong with pushrod motors. 2 valves per cylinder work just fine if you lift them high enough.
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Joined: Oct 2002
Posts: 2,931
From: Upstate NY
Originally posted by Damon
A few months back I built a PUSHROD 4.3L V6 (SBC minus a couple of slugs) for my brother to compete in Nopi's "Comp 6" 6-cylinder N/A class. No limit on displacement, engine only had to be a production based engine from the same manufacturer as the car. We figured mid 12s to be competitive, high 11s to dominate. Easy peezie, right?
Well, NOPI outlawed us before the car ever competed in a single event. They outlawed pushrod engines in the class! What's more, we have a string of emails back and forth on the subject with them- one of which explains that our pushrod/2 valve per cylinder motor would have an "unfair advantage" in torque production vs. 4 valve per cylinder engines. HAH!!! It was almost worth being outlawed just to have that email from them.
Nothing wrong with pushrod motors. 2 valves per cylinder work just fine if you lift them high enough.
A few months back I built a PUSHROD 4.3L V6 (SBC minus a couple of slugs) for my brother to compete in Nopi's "Comp 6" 6-cylinder N/A class. No limit on displacement, engine only had to be a production based engine from the same manufacturer as the car. We figured mid 12s to be competitive, high 11s to dominate. Easy peezie, right?
Well, NOPI outlawed us before the car ever competed in a single event. They outlawed pushrod engines in the class! What's more, we have a string of emails back and forth on the subject with them- one of which explains that our pushrod/2 valve per cylinder motor would have an "unfair advantage" in torque production vs. 4 valve per cylinder engines. HAH!!! It was almost worth being outlawed just to have that email from them.
Nothing wrong with pushrod motors. 2 valves per cylinder work just fine if you lift them high enough.
The Speed Record GMC Sonoma pickup of early '90s (200 +mph @ Bonneville) had about 535 NA hp from a 305 CID or so version of the 4.3. B'ville is "the great white dyno" so no gernade-style drag engine.
BTW, what heads were you using?
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Joined: Oct 2002
Posts: 6,518
Nah The Ecotec is giving most of the Import guys a beating.
That is funny that they think the pushrod motors have a unfair advantage. How about the Penske Ilmor motors that dominated CART back in the 90's. They switched to pushrod motors for more cubes and more boost and just walked all over the OHC stuff.
Bret
That is funny that they think the pushrod motors have a unfair advantage. How about the Penske Ilmor motors that dominated CART back in the 90's. They switched to pushrod motors for more cubes and more boost and just walked all over the OHC stuff.
Bret
West South Central Moderator
Joined: Oct 2000
Posts: 3,371
From: Kilgore TX 75662
Originally posted by SStrokerAce
That is funny that they think the pushrod motors have a unfair advantage. How about the Penske Ilmor motors that dominated CART back in the 90's. They switched to pushrod motors for more cubes and more boost and just walked all over the OHC stuff.
Bret
That is funny that they think the pushrod motors have a unfair advantage. How about the Penske Ilmor motors that dominated CART back in the 90's. They switched to pushrod motors for more cubes and more boost and just walked all over the OHC stuff.
Bret
Registered User
Joined: Jul 1999
Posts: 128
From: Tx
Very interesting article Mr. Krause. Thanks for posting it.
Reading through this, I knew it was only a matter of time before the Ilmor was brought in.
Penske's Ilmor engine was designed from the ground up as a pushrod engine and went from concept to winner's circle in 26 weeks. An amazing feat and I'm confident in saying the Ilmor would have remained a dominant force had the USAC not stepped in.
To answer AdioSS' question more directly
Yes, being a clean sheet engine design and considering the limitations, the pushrods were likely short.
Take care
Reading through this, I knew it was only a matter of time before the Ilmor was brought in.
Penske's Ilmor engine was designed from the ground up as a pushrod engine and went from concept to winner's circle in 26 weeks. An amazing feat and I'm confident in saying the Ilmor would have remained a dominant force had the USAC not stepped in.
To answer AdioSS' question more directly
Yes, being a clean sheet engine design and considering the limitations, the pushrods were likely short.
Take care
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Joined: Jun 2003
Posts: 964
From: Cortland NY
Im sure there is some simple reason, but i dont know alot about engine physics and such so bare with me
Why do valves have to be round? It seems like if they were more of a half circle shape you could fit 2 much larger valves into the alloted space?
Why do valves have to be round? It seems like if they were more of a half circle shape you could fit 2 much larger valves into the alloted space?
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Joined: Sep 2002
Posts: 655
I'll take a wild stab at this one and say it has alot to do with
matching the seat and valve.
I'm thinking machining the seats and valve would be a problem
going from a tubular runner into a half moon shape, as well as
matching the pattern of the seat to the valve.
matching the seat and valve.
I'm thinking machining the seats and valve would be a problem
going from a tubular runner into a half moon shape, as well as
matching the pattern of the seat to the valve.
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Joined: Feb 2002
Posts: 2,428
i see that they have to be a circle because of stated above. a circle has more surface area than anyother shape, (allowing you to get more area, while taking up less space). plus since they are symetrical all the way around they wouldn't be as hard to balance as a asymetrical type. (remember the rpm's they said above?)
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Joined: Oct 2002
Posts: 6,518
Well you would have to keep a Oval valve from rotating if you wanted it to seat properly, so after you grind the stem to size you would have to machine a grove into it and then have a tang in the guide to keep it straight. More fun stuff.
The only way to make the valve and seat oval would be with a CNC and that of course is going to be nice and expensive.
The runner could work with the oval valve, just port development.
Bret
The only way to make the valve and seat oval would be with a CNC and that of course is going to be nice and expensive.
The runner could work with the oval valve, just port development.
Bret
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Joined: Oct 2002
Posts: 2,931
From: Upstate NY
Originally posted by Valkyn71
Im sure there is some simple reason, but i dont know alot about engine physics and such so bare with me
Why do valves have to be round? It seems like if they were more of a half circle shape you could fit 2 much larger valves into the alloted space?
Im sure there is some simple reason, but i dont know alot about engine physics and such so bare with me
Why do valves have to be round? It seems like if they were more of a half circle shape you could fit 2 much larger valves into the alloted space?
Imagine a oval or port-shaped valve with a curved stem that ends in a pivot, like a long shaft-mount rocker arm. As the valve opened, the long side of the port could have the most valve opening, the stem could be airfoil shaped to guide flow, any you might be able to use coil springs like your gagage door does; wrapped around the shaft.
Sealing, even if the valve were round, would be a big problem as would bending loads, and of course cost. Hey, Honda (I think) tried oval cylinder bores a long while ago for various reasons, including more valve area. Big manufacturing headaches.
Keep thinking!
West South Central Moderator
Joined: Oct 2000
Posts: 3,371
From: Kilgore TX 75662
Originally posted by Mr. Horsepower
Very interesting article Mr. Krause. Thanks for posting it.
Reading through this, I knew it was only a matter of time before the Ilmor was brought in.
Penske's Ilmor engine was designed from the ground up as a pushrod engine and went from concept to winner's circle in 26 weeks. An amazing feat and I'm confident in saying the Ilmor would have remained a dominant force had the USAC not stepped in.
To answer AdioSS' question more directly
Yes, being a clean sheet engine design and considering the limitations, the pushrods were likely short.
Take care
Very interesting article Mr. Krause. Thanks for posting it.
Reading through this, I knew it was only a matter of time before the Ilmor was brought in.
Penske's Ilmor engine was designed from the ground up as a pushrod engine and went from concept to winner's circle in 26 weeks. An amazing feat and I'm confident in saying the Ilmor would have remained a dominant force had the USAC not stepped in.
To answer AdioSS' question more directly
Yes, being a clean sheet engine design and considering the limitations, the pushrods were likely short.
Take care
http://web.camaross.com/forums/showt...282#post455282
Originally posted by Nick Hayes
...Pushrods work? Of course they do, Roger Penske showed us some years back that a pushrod engine can be very competitive -given rule breaks- but the Ilmor he debuted was built specifically for that purpose and used a pushrod merely 58 mm in length. Penske knew, as any good engineer would, that designing a valvetrain with a high enough natural frequency would be the key to success in that engine. Those of you not so fortunate in building your own cylinder blocks will have a much more difficult time of it...
Cheers,
Nick Hayes
...Pushrods work? Of course they do, Roger Penske showed us some years back that a pushrod engine can be very competitive -given rule breaks- but the Ilmor he debuted was built specifically for that purpose and used a pushrod merely 58 mm in length. Penske knew, as any good engineer would, that designing a valvetrain with a high enough natural frequency would be the key to success in that engine. Those of you not so fortunate in building your own cylinder blocks will have a much more difficult time of it...
Cheers,
Nick Hayes
West South Central Moderator
Joined: Oct 2000
Posts: 3,371
From: Kilgore TX 75662
Originally posted by OldSStroker
Yeah, cost and reliability is a biggie, but who says engine valves have to be straight and slide up and down thru guides?
Imagine a oval or port-shaped valve with a curved stem that ends in a pivot, like a long shaft-mount rocker arm. As the valve opened, the long side of the port could have the most valve opening, the stem could be airfoil shaped to guide flow, any you might be able to use coil springs like your gagage door does; wrapped around the shaft.
Sealing, even if the valve were round, would be a big problem as would bending loads, and of course cost.
Yeah, cost and reliability is a biggie, but who says engine valves have to be straight and slide up and down thru guides?
Imagine a oval or port-shaped valve with a curved stem that ends in a pivot, like a long shaft-mount rocker arm. As the valve opened, the long side of the port could have the most valve opening, the stem could be airfoil shaped to guide flow, any you might be able to use coil springs like your gagage door does; wrapped around the shaft.
Sealing, even if the valve were round, would be a big problem as would bending loads, and of course cost.
Hey, Honda (I think) tried oval cylinder bores a long while ago for various reasons, including more valve area. Big manufacturing headaches.
Keep thinking!
Keep thinking!