New GM LS9 Supercharged Vette ZR1 engine

[Indy]

I still maintain that the DOHC high-revving nature is in fact an illusion. DOHC setups are generally used on engines that are inherently high-strung - low strokes and large bores, due to the abilitly of the valvetrain to reliably handle higher RPM's.

With a DOHC cylinder head and appropriate geometry on a high-stroke engine, I suggest that the result would be an even MORE flat torque curve due to better cylinder filling. I agree with Will, the largest differences between the two are cost and complexity.

Just look at Porsche's recent flat sixes...DOHC 3.6 liters with a torque curve that looks like this ________________

[crzyone]

I would love to see an oversquare LSX with DOHC heads. Let is rev to 10-11000rpm. Thats what DOHC is meant for, not putting the heads on a conventional bottom end and not seing the gains that you could.

DOHC starts where pushrods end.

[The Dark Side of Will]

I still maintain that the DOHC high-revving nature is in fact an illusion. DOHC setups are generally used on engines that are inherently high-strung - low strokes and large bores, due to the abilitly of the valvetrain to reliably handle higher RPM's.

With a DOHC cylinder head and appropriate geometry on a high-stroke engine, I suggest that the result would be an even MORE flat torque curve due to better cylinder filling. I agree with Will, the largest differences between the two are cost and complexity.

Just look at Porsche's recent flat sixes...DOHC 3.6 liters with a torque curve that looks like this ________________

Exactly. Please don't confuse camming/tuning with valvegear.
Look at Toyota's truck engines... DOHC V8's with power curves essentially the same shape as GM's pushrod truck engines.

[The Dark Side of Will]

I would love to see an oversquare LSX with DOHC heads. Let is rev to 10-11000rpm. Thats what DOHC is meant for, not putting the heads on a conventional bottom end and not seing the gains that you could.

DOHC starts where pushrods end.

Except that emissions regulations level the playing field. I would freaking love for a Lotus Elise to have a 2 litre engine that made 350 HP N/A at 14,000 RPM, but even with the best variable cam phasing available, it would still be too dirty for the EPA to bless.

[FieroWanaBe1]

350hp, is 350hp at what ever RPM your at, so 350hp of air AND FUEL will be burned.

[Indy]

At 14,000 RPM you have to consider where this air and fuel is going. Just because you're making 350 HP DOESN'T mean that your only putting in 350 horsies-worth of air and fuel.

A camshaft that's going to be able to support that kind of speed will have likely have a lot of overlap and other extreme features, a good portion of what's going in will never be burned...

[FieroWanaBe1]

At 14,000 RPM you have to consider where this air and fuel is going. Just because you're making 350 HP DOESN'T mean that your only putting in 350 horsies-worth of air and fuel.

A camshaft that's going to be able to support that kind of speed will have likely have a lot of overlap and other extreme features, a good portion of what's going in will never be burned...

I know but what i said was 350hp worth will be burned, not consumed. But still.

I realy apreciated the level of engineering GM is doing on thier LS series engine, I think the torque curves is very good, and not typical of past sbc designs from gm.

[Aaron]

I don't think the EPA much cares about how clean the car is at WOT, at redline. Hell all of the high output foreign cars I've driven smoked pretty good (Diesel like), at WOT because the factory runs them on the rich side.

But with the cam profiles needed to sustain 14,000rpm, let alone make climbing power to those levels, the idle and part throttle, low RPM emissions are what takes a big hit. And as Will said, even with the new VVT and phasing, 500 lift is 500 lift, there's no getting around that. So the cams may do better than your SBC cams, but getting them to pass new car emissions is still a chore.

And after all that time and development, you're left with a motor that not many people will appreciate (Look at the S2000).

How do today's sportbikes pass emissions with their wild, high RPM engines? I don't think the EPA is the only reason for cars not having 14,000rpm engines. I think a lot of it is durability. Your 200hp/l sportbike engines aren't made to last 200,000 miles, half of that under warranty. They're made to last 20,000, if that. And change your oil all you want, 16,000rpm does not make for a long lasting engine at the technology we have, and can afford at the still mass-produced levels sportbikes are.

[crzyone]

And after all that time and development, you're left with a motor that not many people will appreciate (Look at the S2000).

The S2K has a cult like following, much like the fiero. You won't see people trading in their camaros for one but they are a wicked car.

I find the cars with the highest rpm are the most fun to drive. 8k in my GTR is just wicked.

[Kohburn]

the v-tec system with dual cam lobes would be the easiest to maximize both fuel economy/emissions and high end power. the low end lobes can be ground to maximize the emissions during the rpm range that most daily commuting and highway cruising would be done at , and the second lobe could be ground to maximize potential power.

[The Dark Side of Will]

At 14,000 RPM you have to consider where this air and fuel is going. Just because you're making 350 HP DOESN'T mean that your only putting in 350 horsies-worth of air and fuel.

A camshaft that's going to be able to support that kind of speed will have likely have a lot of overlap and other extreme features, a good portion of what's going in will never be burned...

Well... within its powerband, it will obviously have good cylinder sealing and a clean exhaust, it's only outside the powerband that it has problems with cylinder sealing and blowing mixture out the exhaust.

Direct injection can work miracles in this area, though... DI should be as much better for making a wild engine streetable as port injection is better than a carb.

[The Dark Side of Will]

I don't think the EPA much cares about how clean the car is at WOT, at redline. Hell all of the high output foreign cars I've driven smoked pretty good (Diesel like), at WOT because the factory runs them on the rich side.

But with the cam profiles needed to sustain 14,000rpm, let alone make climbing power to those levels, the idle and part throttle, low RPM emissions are what takes a big hit. And as Will said, even with the new VVT and phasing, 500 lift is 500 lift, there's no getting around that. So the cams may do better than your SBC cams, but getting them to pass new car emissions is still a chore.

And after all that time and development, you're left with a motor that not many people will appreciate (Look at the S2000).

How do today's sportbikes pass emissions with their wild, high RPM engines? I don't think the EPA is the only reason for cars not having 14,000rpm engines. I think a lot of it is durability. Your 200hp/l sportbike engines aren't made to last 200,000 miles, half of that under warranty. They're made to last 20,000, if that. And change your oil all you want, 16,000rpm does not make for a long lasting engine at the technology we have, and can afford at the still mass-produced levels sportbikes are.

The EPA testing, I believe includes some WOT exercises, but I don't know the exact extent of that portion of the test, or how much it's weighted.

Also, I don't think the EPA regulates motorcycles... YET. Ever seen a crotch rocket with a catalyst?

Also, if the EPA were to assign the same emissions standards to cars as to bikes, the bikes could still get away with some really radical engines, as pollutants are measured in mass emitted per vehicle mile... a 1.3 litre 'Busa would get the same allowance as a 7 litre 'Vette or 8 litre Viper.

[Kohburn]

Also, I don't think the EPA regulates motorcycles... YET. Ever seen a crotch rocket with a catalyst?

Also, if the EPA were to assign the same emissions standards to cars as to bikes, the bikes could still get away with some really radical engines, as pollutants are measured in mass emitted per vehicle mile... a 1.3 litre 'Busa would get the same allowance as a 7 litre 'Vette or 8 litre Viper.

actually most of the new sportbikes do have cats. haven't seen any harleys with em though.

here is a pic of where one guy cut the honeycomb out of his 2005 636 header.
http://www.kawasakiforums.com/upfiles/2 ... 829CD9.jpg

[Series8217]

You guys ever see an NSX dyno graph? DOHC engines, especially low displacement Hondas, have a reputation for being gutless or having peaky powerbands.


That's pretty darn flat from 2000 RPM to 8000 RPM for being a 3.0L DOHC V6!

[crzyone]

Looks like the cams hit at 4800rpm. Beautiful. They kick in just where it looks like the torque would start to fall off.

[Aaron]

MY GOD look at that power curve. I want one.

Amazing what RPM can do, the 3.4l DOHC actually makes just about the same amount of peak torque stock, but that NSX motor simply destroys the 3.4. A stock 3.4l DOHC for comparison. The graphs actually look very similar--until 5,000rpm. Even cammed to hell, the NSX still has a better torque curve. I love it. The NSX is down on displacement some, but its compression is probably much higher than the 9.25 of the 3.4.

By the way, is the NSX motor aluminum block?



I have sudden, and very strong, inclination to build a GM 3.6l DOHC. And build as in like $10,000 build. Full ITB setup (I got those laying around...), equal length headers, 12:1 compression, cam it to high heaven, titanium rods, lightweight valvetrain, the works. A nice 400hp 9,000rpm beast would be a fucking blast. Throw it into a nice custom made tube frame car, maybe 1500lbs worth, and go have some fun in the single digits.

[crzyone]

I plan on doing everything you just said to my N*, but I'm not changing the compression ratio.

Cams, ITBs, headers... and if I can find a core I will port some heads for later instalation.

8k rpm DOHC V-8, hopefully over 400hp

[The Dark Side of Will]

If you're going to cam it, you'll want more compression.

[crzyone]

Meh, its all bench racing until I do anything. We'll see when the time comes.

[Kohburn]

what causes an engine to be peaky? simple - a less than flat torque curve. the HP will be more flat if the torque falls off in upper rpm like almost every american engine ever released from a factory.