Intake/exhaust valve diameter ratio on older OHV8s
Intake/exhaust valve diameter ratio on older OHV8s
(OP)
Let's take as a given the old SBC 2.02/1.6 I/E valve diameter ratio of .792 is the norm/golden mean. It's a given a larger intake valve usually produces more high RPM power than a larger exhaust valve.
I work primarily with Studebaker and Packard V8 engines. The Studebaker V8 used a .92453 I/E ratio and the Packard V8 used a .84375 ratio.
Is it possible that in the bad old days, a larger exhaust valve was seen as a way to reduce pumping losses at relatively low RPMs and thus increase efficiency and fuel economy.
If not, what other reason might Studebaker engineers have had for such a large exhaust valve?
jack vines
I work primarily with Studebaker and Packard V8 engines. The Studebaker V8 used a .92453 I/E ratio and the Packard V8 used a .84375 ratio.
Is it possible that in the bad old days, a larger exhaust valve was seen as a way to reduce pumping losses at relatively low RPMs and thus increase efficiency and fuel economy.
If not, what other reason might Studebaker engineers have had for such a large exhaust valve?
jack vines





RE: Intake/exhaust valve diameter ratio on older OHV8s
Hmmm does increased compression which of course leaves a smaller chamber and less exhaust to scavenge impact on this and the trend to smaller exhaust vs intake valves. Certainly the after market modern SBC heads further increase intake to 2.08" or even bigger while retaining the same 1.6" exhaust valve
Heck, I'm currently working on a SBF Yates head that has I think 2.25" inlet and 1.6 exhaust
Regards
Pat
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RE: Intake/exhaust valve diameter ratio on older OHV8s
Mike Halloran
Pembroke Pines, FL, USA
RE: Intake/exhaust valve diameter ratio on older OHV8s
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RE: Intake/exhaust valve diameter ratio on older OHV8s
That would indicate the Chevrolet engineers had decided that a larger intake was more beneficial at higher RPMs without killing low RPM velocity.
jack vines
RE: Intake/exhaust valve diameter ratio on older OHV8s
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RE: Intake/exhaust valve diameter ratio on older OHV8s
Chevy did not take the GS Corvette with the 3-valve head engine to LaMans apparently due to the infamous GM "NO RACING" edict.
The SBC exhaust port was very short, making the engine more compact. The stock header rerouted the exhaust to a downward trajectory. When used in racing, the stock header was irrelevant leaving the short, high exhaust port and free-flowing headers to reach their full potential. Compromising, even siamesing, the exhaust port was common on other engines in those days.
RE: Intake/exhaust valve diameter ratio on older OHV8s
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: Intake/exhaust valve diameter ratio on older OHV8s
RE: Intake/exhaust valve diameter ratio on older OHV8s
Almost all 350s had the 1.94.1.5 valve sizes mostly in lower compression heads.
The 2.02/1.6 was mainly only supplied as a heavy duty 'homologated" part for racing. Although they gave a rough idle and poor low rpm power in the day, I currently run aftermarket heads with 2.08/1.6 on a social ski boat and it is very calm and tractable and has impressive fuel consumption in this application which cruises mostly at 2500 to 3500rpm, but must idle at about 600rpm so the dog clutch operates smoothly.
Regards
Pat
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RE: Intake/exhaust valve diameter ratio on older OHV8s
The valve size ratios on the classic hipo SBC was out of the normal range. However, all along they also had engines with the 1.72/1.50 valve heads with lower compression than the old Powerpak heads for more pedestrian applications.
RE: Intake/exhaust valve diameter ratio on older OHV8s
Fuelie heads and a Hurst on the floor
She's waiting tonight down in the parking lot
Outside the Seven-Eleven store
Me and my partner Sonny built her straight out of scratch
And he rides with me from town to town
We only run for the money got no strings attached
We shut `em up and then we shut `em down
Tonight, tonight the strip's just right
I wanna blow `em off in my first heat
Summer's here and the time is right
For goin' racin' in the street
B. Springsteen
----------------------------------------
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RE: Intake/exhaust valve diameter ratio on older OHV8s
About like the Beach Boys Little Deuce Coupe lyrics: "Just a little deuce coupe with a flat head mill" and the next verse, "She's got a competition clutch with the four on the floor" I was there in the day and I never saw a '32 coupe rod with a flathead and a four speed. They just didn't fit together.
jack vines
RE: Intake/exhaust valve diameter ratio on older OHV8s
Springsteen may not have hot rodded 396s, but the Beach Boys were real hot rodders during the golden era.
RE: Intake/exhaust valve diameter ratio on older OHV8s
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: Intake/exhaust valve diameter ratio on older OHV8s
Sometimes song writers deliberately say something impossible or unlikely the way Chuck Berry was "...campaign shouting like a southern diplomat..." when you expected him to say "...Southern Democrat...". Poetic license.
RE: Intake/exhaust valve diameter ratio on older OHV8s
The Mopar B and RB engines as standard had much long exhaust durations (relative to intake) from the factory and yet didn't flow significantly worse than their competitors from the other two- about mid way
http://www.moparmusclemagazine.com/techarticles/51...
From my work on the Jaguar Supercharged engines I found that a longer duration exhaust was indeed very beneficial to torque pretty much all the way through the rev range. These were fixed cam timing engines so the quote isn't distorted by optimums for VVT.
www.auto-scape.com
RE: Intake/exhaust valve diameter ratio on older OHV8s
RE: Intake/exhaust valve diameter ratio on older OHV8s
Earlier exhaust valve opening will certainly benefit the Turbo charger as more enthalpy is availiable to the turbine...IN THEORY- however with fixed cam timing this engine would potentially suffer at lower loads and lower engine speeds in terms of brake thermal efficiency- as it wouldn't be getting the most work out of the cycle.What about using variable cam phasing on the exhaust? Good idea. The other thing to bear in mind is that we're getting to stages where at WOT higher engine speeds the engines are savagely over fueled to keep the turbines cool. This indicates that there is ample energy in the exhaust stream that can't be fully utilised already and on top of that we're wastefully overfueling. For this reason earlier exhaust valve opening (lower expansion ratio) to help the turbo at higher loads and speeds may not really seems appropriate...
However with the impending implementation of COOLED EGR on GDI engines to keep exhaust temps low and mitigate knock there may be an opportunity.
If there is- it would need to be done thoroughly with extensive DOE techniques as there are SO many variables (as already touched upon) that interact with one another!
In terms of boost pressure and what the cylinder sees- supercharging and turbo charging have very similar requirements:
Design a combustion system that mittigates the onset of knock as much as possible
With the higher levels of boost on down sized boosted engines (turbo charged)- attention needs to be paid to oil control and in cylinder residual levels- to ensure 'super knock' or "megaklopf" isn't initiated.
Before such high levels of boost I was about to say that on a supercharged engine overlap is nearly always minimised to avoid short ciruiting of fresh charge.
This isn't the case on some older OEM production Turbo charged engines- such as the Porsce 993 which has quite alot of overlap- I would cite that perhaps because the back pressure is potentially higher in a Turbo charged engine this isn't such an issue. Also it's not a 4 valve engine so perhaps just looking at degrees overlap is misleading...
GDi engines can again use overlap to effect even greater scavenging taking advantage of alot superior charge cooling and the freedom of injecting whenever they want to avoid short circuiting (this is what BMW has been doing to great effect)
Again- as boost pressure start to climb further- I think we will probably see overlap minimised in certain regions of the rev range (variable cam phasing) to control in cylinder residuals and exhaust durations may start to get limited for the same reason.
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Sideways To Victory!
RE: Intake/exhaust valve diameter ratio on older OHV8s
On a turbo, the pressure in both inlet and exhaust is increased a lot. Who knows which side is highest at any one time. You might have scavenging during overlap or you might actually get exhaust flow back into the inlet port, reducing the potency of the next charge. To really know, we need data for real pressure measurements on both sides
Regards
Pat
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RE: Intake/exhaust valve diameter ratio on older OHV8s
Which brings up another question about exhaust flow. Early exhaust opening helps breathing, but costs expansion pressure and efficiency. When you consider the difference between mechanical vs turbo supercharging it appears this can be more of a help for a turbo, as stated, but does it hurt efficiency more or less in the turbo and how much does this effect contribute, if at all, to the reputed efficiency advantage of the turbo?
RE: Intake/exhaust valve diameter ratio on older OHV8s
http://xroads.virginia.edu/~music/blues/tb.html
RE: Intake/exhaust valve diameter ratio on older OHV8s
Dart Iron Eagle castings, CNC ported (both ports and chambers). Intake valve size is 2.350" and exhaust diameter is 1.800".
We have found on different race car applications that if we hurt the exhaust flow in some fashion (valve size, rocker ratio, camshaft exhaust profile, etc.) or pick up intake flow using the same methods, overall performance would pick up. Methanol engines seemed to really respond to this treatment.
Not sure if it was due to keeping heat in the motor or filling or what, it just seemed to work well.
Take care, K
RE: Intake/exhaust valve diameter ratio on older OHV8s
Not sure if it was due to keeping heat in the motor or filling or what, it just seemed to work well."
Supercharged?
"Schiefgehen will, was schiefgehen kann" - das Murphygesetz
RE: Intake/exhaust valve diameter ratio on older OHV8s