Benefits of a 32 valve heads
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From: Laguna Niguel, CA
I agree on MB engines^. Look at what they have done with the SL65 and the CL65 or even the SLR! I know those are turbo motors, but the SC MB motors are really sweet!Low revs yet tons of power and a truck load of torque off idle. I would like to see the torque from the Ferrari 430 at 1500RPMS compared to the MB at 1500 RPMS ( I know they are packaged for different uses).
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From: Arlington TX
Originally Posted by racer7088
The curtain are is a limit until a certain valve lift and then the ports cross sections come on line as a limit. The main advantage though is:
1. As Bret said the curtain area and thus lower lift flow ramps up FAST so shorter cams can be run and yet still breath very very well. This allows better street manners and more power so it's a win / win mostly.
2. Also the valves are smaller and lighter and this allows more valvetrain control and rpm etc. so that's also a win / win deal.
The downsides are hokey weird low volume castings and weird geometries when trying to still use pushrods along with weight and complexity and extra friction to open and close double the valves. Overall it's certainly a win though and that's what you see unrestricted race engines running as well of course.
At lower rpm the 2 valves aren't that far off though and allow bigger engine with much better packaging and like usual cubes are easy power. Look at the new LS7 and what it can do. It has no equal in the smaller CID multivalve NA world really and all it is basically is a big *** pushrod engine with big *** heads. Seems like that is a pretty proven approach!
1. As Bret said the curtain area and thus lower lift flow ramps up FAST so shorter cams can be run and yet still breath very very well. This allows better street manners and more power so it's a win / win mostly.
2. Also the valves are smaller and lighter and this allows more valvetrain control and rpm etc. so that's also a win / win deal.
The downsides are hokey weird low volume castings and weird geometries when trying to still use pushrods along with weight and complexity and extra friction to open and close double the valves. Overall it's certainly a win though and that's what you see unrestricted race engines running as well of course.
At lower rpm the 2 valves aren't that far off though and allow bigger engine with much better packaging and like usual cubes are easy power. Look at the new LS7 and what it can do. It has no equal in the smaller CID multivalve NA world really and all it is basically is a big *** pushrod engine with big *** heads. Seems like that is a pretty proven approach!
Lotsa good info. Are there any downsides to something like a DOHC Cobra head? Fairly easy to obtain, OHC design. Surely there must be a downside?
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size, weight, some will say complexity and "more to go wrong" but thats cr*p as most production engines run DOHC these days, cost......
another plus point is you dont need to buy aftermarket heads!!!!! most multi valve heads flow very well and generally just need a clean up/minor porting to get some really big numbers out of them!
Chris.
another plus point is you dont need to buy aftermarket heads!!!!! most multi valve heads flow very well and generally just need a clean up/minor porting to get some really big numbers out of them!
Chris.
I think people get carried away with the Hp/liter argument when arguing the 2 vs 4 valve head. A 2 valve is more efficent IMO because you can simply add cubes and still have a smaller and lighter overall engine package.
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FormerVendor
Joined: Nov 2001
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From: Houston, Tx.
Originally Posted by TurboZ28
Lotsa good info. Are there any downsides to something like a DOHC Cobra head? Fairly easy to obtain, OHC design. Surely there must be a downside?
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the EVO 8 FQ 400 used a 2.0ltr engine. and made ovre 400bhp, stock. i think HKS built the engine for extreme mtorsport (the guys that build the FQ models). pretty nice piece of kit, but lags like a b*tch!
i have never seen anything else making 200bhp per ltr, but i might be wrong?!?!?!
Chris.
i have never seen anything else making 200bhp per ltr, but i might be wrong?!?!?!
Chris.
Originally Posted by chuntington101
another plus point is you dont need to buy aftermarket heads!!!!! most multi valve heads flow very well and generally just need a clean up/minor porting to get some really big numbers out of them!
Chris.
Chris.
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From: Itasca, IL
Originally Posted by racer7088
The only downside is the mod motor is so small for being so big externally. The larger 5.4 is much better but even larger still. That's the beauty of the larger 2-valve pushrod engines because they can be very easily packaged and carry a lot of cubic inches and turn much slower rpm while making the same power (or more).
And that is why you see ALOT of LS1 and LT1 (and sorry to say it but Ford 5.0 motors too) swaps into other cars. Not a ton of cars can fit a SOHC or DOHC (Ford) motor into them very easily.
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Packaging and cost is the big advamtage pf the OHV design. However, with current emissions, fuel economy, and performance requirements every manufacturer (including GM) has determined that a DOHC 4V is the best setup.
So why is there an LSx and Chrysler Hemi and 8.1? For trucks, the emissions and fuel economy requirements were different, letting the cost and packaging take over. And for large high performance cars, those truck based engines provided an inexpensive way to get to high HP.
The LSx engines also provided an all aluminum engine with great power potential, very good off the shelf electonics (you don't see everyone swapping ECU for an AEM or HKS as you do in the Supra world) at a modest cost.
However, I don't know why they couldn't but the intake valve in front fo the intake port and the exhaust valve in front of the exhaust port like a Chysler Hemi. Or just cant the valves like a Chevy big block, Ford Cleveland or 429 family, or TrickFlow Twisted Wedge.
So why is there an LSx and Chrysler Hemi and 8.1? For trucks, the emissions and fuel economy requirements were different, letting the cost and packaging take over. And for large high performance cars, those truck based engines provided an inexpensive way to get to high HP.
The LSx engines also provided an all aluminum engine with great power potential, very good off the shelf electonics (you don't see everyone swapping ECU for an AEM or HKS as you do in the Supra world) at a modest cost.
However, I don't know why they couldn't but the intake valve in front fo the intake port and the exhaust valve in front of the exhaust port like a Chysler Hemi. Or just cant the valves like a Chevy big block, Ford Cleveland or 429 family, or TrickFlow Twisted Wedge.
Originally Posted by DavidNJ
However, I don't know why they couldn't but the intake valve in front fo the intake port and the exhaust valve in front of the exhaust port like a Chysler Hemi. Or just cant the valves like a Chevy big block, Ford Cleveland or 429 family, or TrickFlow Twisted Wedge.
thats actually the sole reason for the much hyped "cathedral" ports.
you'll notice that its been 10 years, (model year 97 to model year 07) and GM has finally approved angling them some... first thing done? the ports are changed.. (L92 and LS7...)
Originally Posted by DavidNJ
Why did they want the rocker arms inline? Were they trying to avoid offset rockers?
same reason they didnt run centerbolt valve covers the first 2 years..
same reason the LT1 didnt have the 8 coil pack setup.
until GM has fully proven to a very far extent the reliability of a change, they dont do it. they worried about the valvetrain durability, so one of the design peramiters became "keep the pushrods straight".
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From: England
Originally Posted by cantdrv65
I think people get carried away with the Hp/liter argument when arguing the 2 vs 4 valve head. A 2 valve is more efficent IMO because you can simply add cubes and still have a smaller and lighter overall engine package.
TVR's Speed 12 V12 engine would be one example, ok fair do it's a hand built engine based off a race engine, but hell so is the LS7.
The DOHC V12 is only 7.7 litres in capacity so one would expect it to produce similar numbers to the 7.0 litre 512bhp LS7. After all even at a 100bhp/litre specific output it would only be 70bhp difference.
But hay no the V12 'officially' makes 880bhp, and there are reports from TVR staff that some of the test engines where actually maxing out a 1000bhp/1000lb ft engine dyno. Not sure what differences there would have been, but I guess probably only fuel and tuning (although 97RON is the highest grade fuel in the UK which is about equal to your 93 octane).
Another example I can think of is the Jaguar AJV8 DOHC engine, In the SCCA Trans Am Championship I think a 4.5 litre variant makes 650bhp, compared to 630bhp for the Ford 5.0 Modular unit.
The Corvette also makes 650bhp, but I'm not certain of the engine displacement. But I think it's sufficent to say that if the Jaguar engine was the same capacity as the LS1 engine it would have the potential to produce a lot more bhp.
Could be wrong though
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Joined: Jun 2002
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From: Upstate NY
Originally Posted by 300bhp/ton
Yeah but you can also add cubes to a DOHC engine as well. You just don't happen to see it much in the real world.
TVR's Speed 12 V12 engine would be one example, ok fair do it's a hand built engine based off a race engine, but hell so is the LS7.
The DOHC V12 is only 7.7 litres in capacity so one would expect it to produce similar numbers to the 7.0 litre 512bhp LS7. After all even at a 100bhp/litre specific output it would only be 70bhp difference.
But hay no the V12 'officially' makes 880bhp, and there are reports from TVR staff that some of the test engines where actually maxing out a 1000bhp/1000lb ft engine dyno. Not sure what differences there would have been, but I guess probably only fuel and tuning (although 97RON is the highest grade fuel in the UK which is about equal to your 93 octane).
Another example I can think of is the Jaguar AJV8 DOHC engine, In the SCCA Trans Am Championship I think a 4.5 litre variant makes 650bhp, compared to 630bhp for the Ford 5.0 Modular unit.
The Corvette also makes 650bhp, but I'm not certain of the engine displacement. But I think it's sufficent to say that if the Jaguar engine was the same capacity as the LS1 engine it would have the potential to produce a lot more bhp.
Could be wrong though
TVR's Speed 12 V12 engine would be one example, ok fair do it's a hand built engine based off a race engine, but hell so is the LS7.
The DOHC V12 is only 7.7 litres in capacity so one would expect it to produce similar numbers to the 7.0 litre 512bhp LS7. After all even at a 100bhp/litre specific output it would only be 70bhp difference.
But hay no the V12 'officially' makes 880bhp, and there are reports from TVR staff that some of the test engines where actually maxing out a 1000bhp/1000lb ft engine dyno. Not sure what differences there would have been, but I guess probably only fuel and tuning (although 97RON is the highest grade fuel in the UK which is about equal to your 93 octane).
Another example I can think of is the Jaguar AJV8 DOHC engine, In the SCCA Trans Am Championship I think a 4.5 litre variant makes 650bhp, compared to 630bhp for the Ford 5.0 Modular unit.
The Corvette also makes 650bhp, but I'm not certain of the engine displacement. But I think it's sufficent to say that if the Jaguar engine was the same capacity as the LS1 engine it would have the potential to produce a lot more bhp.
Could be wrong though
The CSTV-R engine SCCA allowed GM to use was based on a pre-production LS7 destroked to 5.7L (do the math with a LS7 7.0L bore and the 4.8L stroke
). After Sebring, where one car went from last place to second (bad long-term strategy, but it got everyone's attention), they got hit with a weight penalty and a rev limit (7100 vs 7900) on their 2-valve engine. That put the max piston speed around a lazy 3900 ft/min, which is about the same as the endurance C6R. Ron Sperry had a big part in designing those engines, as well as the LS7.The DOHC 4-valvers didn't get the rev limits. Ironic.
I like your screen name 300bhp/ton. That's pretty close to a LS7/Z06 Vette.
Originally Posted by Old SStroker
Some of those sanctioning bodies limit hp with air restrictors and/or rpm limitations to keep the peak power about equal for different displacement and configuration engines. The C6R endurance Vettes produce peak power under 6000, and probably rarely get into the 6K range during a long race. That's not to say the power doesn't peak early and just hold on. Lots of area under the hp and torque curves that way.
The CSTV-R engine SCCA allowed GM to use was based on a pre-production LS7 destroked to 5.7L (do the math with a LS7 7.0L bore and the 4.8L stroke ). After Sebring, where one car went from last place to second (bad long-term strategy, but it got everyone's attention), they got hit with a weight penalty and a rev limit (7100 vs 7900) on their 2-valve engine. That put the max piston speed around a lazy 3900 ft/min, which is about the same as the endurance C6R. Ron Sperry had a big part in designing those engines, as well as the LS7.
The DOHC 4-valvers didn't get the rev limits. Ironic.
I like your screen name 300bhp/ton. That's pretty close to a LS7/Z06 Vette.
The CSTV-R engine SCCA allowed GM to use was based on a pre-production LS7 destroked to 5.7L (do the math with a LS7 7.0L bore and the 4.8L stroke
). After Sebring, where one car went from last place to second (bad long-term strategy, but it got everyone's attention), they got hit with a weight penalty and a rev limit (7100 vs 7900) on their 2-valve engine. That put the max piston speed around a lazy 3900 ft/min, which is about the same as the endurance C6R. Ron Sperry had a big part in designing those engines, as well as the LS7.The DOHC 4-valvers didn't get the rev limits. Ironic.
I like your screen name 300bhp/ton. That's pretty close to a LS7/Z06 Vette.