B.W.

iTrader: (3)

Cause you know, hp/L is what it is all about

ProductionS14

This should be badass, I was hoping the C6 Z06 was DOHC, although I am happy with the LS7 motors. It is a bit sad to me that they had to supercharge the motor to get 600hp out of a 6-liter quad cam... Maybe just to meet emissions standards. Let's hope that motor has some bad *** potential. Otherwise I will have little reason anymore to think that DOHC motors more than marginally superior to OHV.

Haha, some of the folks on Digital Corvette seem to think DOHC motors are inferior to their pushrod power producers that are "easily wrenchable by the enthusiast"... "I think the LT5 had to be pulled and sent back to the factory for any more than a plug change" ...if you're too much of a bitch to do it yourself. One guy even bashes the sound of a properly tuned DOHC motor... hahaha... what a moron.

Edit: In response to the argument of weight of the LS9 affecting the ability of the Corvette SS, I honestly would assume that 600bhp is a modest output claim, but even if the motor weighed 150 or 200lbs more, it would take somewhere around another 750lbs to nullify the effects of an increase of 95bhp.

macky

It is NOT going to be OHC.

I <3 80057

iTrader: (1)

True, they decided not to go a DOHC platform before the LS1 was introduced.

pkincy

iTrader: (1)

Long legs on the top end but it handled a bit like a pig since it had an extra 200 lbs on the front end.

OK on a road race course but was pretty worthless to autox.

Perry

cam91z

iTrader: (1)

You dont need 2 cams to run 3 vavles. There are 3 valve heads out for gen 1 sbc.

DavidNJ

No, hp/L is irrelevant unless you have tax or insurance laws or racing rules based on displacement.

What matters is emissions, economy, power, power curve, packaging, and cost. Those last two help help keep inline valve pushrod motors alive.

The first (emissions) is at the root of many forced induction solutions; you need to keep the cam timing to conservative to produce power without. For example, the LS7s tortured cam timing (211/230/121) in order to prevent intake from flowing out the exhaust.

State of the art? BMW's new direct injection, 4 valve, continously variable intake and exhaust centerline and lift, turbo-charged 3.0L. Ridiculous state of tune though with only 306hp and 295 (undoubtly computer limited) lbf-ft of torque available from 1500rpm. Very compact packaging, and very light weight. Probably clean as a whisper also. I would expect to see a 350-400hp version within a few years.

Another interesting observation, most modern production engines (DOHC 4v) seem to be 550-600cc/cylinder and slightly undersquare with a low rod/stroke ratio (the LS7 appears to be 1.5 vs a 350 SBCs 1.63). There are very few engines with smaller cylinders (other than the smallest 4 cylinder sub-sub compact motors) and few larger (MB's new 5.5l is the only one I can think of that is larger, and that their V6 oversquare).

My guess is that is a combination of factors. However looking at the Engine Master's Challenge it may be to allow high compression ratios with limited octane.

J-Rod

See this post also.

https://ls1tech.com/forums/advanced-engineering-tech/437433-benefits-32-valve-heads.html

I think the autoblog feature sums it up nicely....

300bhp/ton

How about overhead inlet side exhaust this uses a cam that acts directly on the valves as well as using puch rods.

RussStang

Yeah, I remember reading about that in Sport Compact Car of all magazines. Seems like an interesting idea to me. Nothing will probably ever come of it though, like most of the other variations of the IC engine that have come and gone.

300bhp/ton

Funnily enough it has been well used over the years very popular in the 30's and most Rover engines right into the 70's used this setup (some even used slanted pistons as opposed to roud ones).

Such engines are meant to be very smooth but drink fuel like there's no tomorrow.

sp57supra

I havent read all 11 pages of this thread but I will say this. Overall both have there advantages, pushrod motors are smaller and sometimes lighter, plus cheaper. doch motors make more power. To me the best motor is one that is of decent size and also has doch heads.

As 300hp/ton has said, a lot of you guys look at what the ford doch motors have done as the best that can be done. here is something to think about for you lsx guys. There is much talk and rumor about a new toyota supra for 07, it will have a v8 as the top of the line model. Rumor is that it will have a 5.0 liter v8 with 450hp and 383bft. Hell the base model will have a 350hp and 275bft doch 3.5 liter v6. The v8 supra should be able to give the regular c6 vette a run with only 5.0 liters. Oh and its rumored to weigh in at 3080lbs.

The above is just to show that even though displacement is nice and needed, you cant ignore hp/liter

jRaskell

iTrader: (1)

I only got up to page 8 before I gave up reading. At that point more than 50% of the posts were of little technical content anyways, but I'll still weigh in with points I hadn't seen made to that point...

Why do so many production vehicles use OHC?

The vast majority of engine development for most car manufacturers occurs in the racing world, plain and simple. MOST of that engine development is dealing with racing regulations that place restrictions on displacement. As such, the racing development is all in OHC. All that research does not roll over to OHV readily and easily. Plain and simple.

Second, Car manufacturers give their customers what they want. Customers see race cars with DOHC, and they believe OHV is inferior. If BMW were to come out with a performance bimmer that absolutely walked all over every other bimmer ever made, but it used an OHV engine, it would be extremely poorly received, plain and simple. It really is about supply and demand. The customers demand OHC, so the car manufacturers give them OHC. The vette line has sustained OHV because it's customer base is still rooted in the OHV legacy, and thank god for that. I don't necessarily believe it's because they are more educated, it's just a heritage thing for most.

OHC engines cost more?

I don't have hard facts in the form of actual proven production costs, but I do have these hard facts. For each given cylinder, there is a substantial increase in the number of individual parts required for a 3 or 4 valve OHC engine than a 2V OHV engine. Anybody in the engineering world knows that the more parts a given product has, the more complex it is to manufacture. The more inherently unreliable it is going to be, and it will also be more expensive to manufacture and assemble.

Hp/L

Here's the very simple and easy to understand reason one this figure is worthless.

Any given displacement engine is going to have a relatively small band of capable torque it will be able to generate. Roughly speaking, nearly every engine out there will make somewhere in the range of 60-80 ftlbs of torque per liter. Regardless their total displacement, that is where they'll stand in terms of total torque output.

Where that torque is made within the rev range of the engine is directly responsible for the amount of horsepower that engine will make. The farther up the rev range you're able to push your torque, the more power you make. Simple. Now, the more displacement you have, the tougher it's going to be to build a high revving engine. We're dealing with simple mechanical limitations here. The bigger the bore, the bigger the piston. The longer the stroker, the greater the distance travelled per revolution. There is a pretty hard limit on the piston speed you'll be able to sustain in any engine, even the race varieties. Given all that, the larger the displacement, the lower the redline.

You take a Formula one engine and compare it to a similar displacement production vehicle engine. Their peak torque numbers will be the same. The difference will be that the F1 engine pull that torque to a MUCH higher RPM, and thus has MUCH higher Horsepower to boot.

Hp/L means nothing more than how high up in the RPMs you are able to make that horsepower, and it's supporters are really doing nothing more than playing off the simple physical limitations involved with displacement and piston speeds. Take any two vehicles and compare their Hp/L, the one with a higher Hp/L will almost always have a higher redline, and make their peak HP at a higher RPM, and it will also almost always have a smaller PER CYLINDER displacement as well. That's really all it ever means, nothing more.

As for comparing cars, provide me a comparison of this...

Show me any vehicle that makes similar power to any of the LS series vettes, and also gets similar gas mileage ratings. Show me any other car that can pump out 505hp and still pull 24mpg highway. I personally haven't been able to find a single vehicle that comes close.

Hp/L is a technical comparison, at best, but not even one that offers any real comparative value to speak of.

gun5l1ng3r

^ I must say that is a good post, it kinda sums every thing up!

black_knight

iTrader: (1)

Yes I can. It doesn't matter AT ALL in terms of a car's ACTUAL PERFORMANCE. It is only useful for bragging with ricer math. Get. It. Through. Your. Head.

chuntington101

sooooo what are all you guys going to do if GM decide to go ahead with it anyway?????????

are you all going to turn your backs on the future LS engines or will you imbrace them (the the tech they use) and make them as fast as you can?!?!?!?!?!?!?!

Chris.

RussStang

GM needs to do what they feel they need to do. I am not a pro OHC advocate, and I am not a pro OHV advocate. I feel they both have their place, depending on the situation. That being said, its not like I am going to have much of a say in which way GM goes with the LS9, and my only possible worry with it going OHC is how it may affect engine component compatibility with the other LS series engines. I wouldn't turn my back on a good engine simply for some stupid reason like being OHC.

I am still interested in seeing how much legitimacy there actually is to the claims of the LS9 being DOHC. The LS engines up to this point have been pretty modular thus far, moreso in many regards than Ford's "Modular" v8s, and I feel that an engine of this calibur would throw away that modular engineering idealogy.

dailydriver

Man, that's a lot of "rumored tos" . Until it comes out and kicks C6 *** (for TWICE THE $$ OR MORE ), that's all they'll be is rumors. I wonder what all of you Poopra s are gonna do when there is NO BOOST involved, and you can't just "do the fish tank mod and run 10s" (if you could even afford the "Nippon God" to begin with)! As for me, I'd take a new ZO6 anyday,anyway (for less $$) over any TOYota!!!

technical

Always look on the bright side. If GM goes D/OHC, then cams will be that much easier to change.

Snapps

iTrader: (39)

True but twice the cost then of parts