Title says it all. Was making myself a little less of an idiot a while ago and have been thinking about this - why are our engines pushrod? Would dual overhead cams be better for performance? (Less weight from pushrods = less wear and more range for springs - right?)

Anyone? :seeya

 

first off, im sure that push rod engines are cheaper to manufacture. that is the reason why our engines are not DOHC. Push rod engines are said to have more low end torque, while OHC set up it better for high reving engines. in my onpion, the real benefit will come when they are able to make engines with electronicly controled valves. then adjustibity will be infinite, and there will be no mechanical drawbacks.

 

pushrods lend themselves to quicker acceleration and hence more low end torque

OHC is very efficient, and eventually you may see it in a corvette. OHC engines tend to be very large because of the OHC and usually heavier than pushrod motors (though they can do alot to fix that nowadays).

However, they can rev forever and rev limiters over 9k are not uncommon, whereas it would be usually 7-8k for "normal" pushrod engine (not talking NASCAR engines, for those its a little over 9k)

The ZR1 engine is a quad-cam engine that will lose to a Z06 in the 1/4mi simply because of the Z06's pushrods-acceleration. After a 1/4mi, then the ZR1 will leave it in smoke because the ZR1 can rev much further and has an even better top end. This is why the Zr1 held the world speed endurance record for so long.

 

So the OHC engine will be perfect for the 'vette if they can get it smaller, lighter, and give it more low-end grunt? A viable option for the new 'vette?
When did OHC engines become more prevalent?

 

You've got to ask yourself what you're after. I work in a cylinder head shop and let me tell you all these 32 valve cobra heads are just plain nasty to work with, or even the 16 valve ones for that matter. Yes they will rev higher, and yes they have fewer parts, but at what cost? For the performance market it's insane. Change the cam(s) on a DOHC mustang. You've got to change 4 of them so it gets expensive real fast. You've also got 4 cams that you have to be sure are timed right.

GM hasn't used the DOHC on many V-8's just because the pushrod design is still working for it. Look at Ford vs. Chevy of the same / similar displacement. You would think that Ford would make more horsepower due to their 32 valve designs, really they don't. They'll put a blower on it to make it have more power, but N/A it's just not there. By all rights Ford should make more power than a Chevy motor because Ford is actively making 32 valve stuff. Apparently it's not just in having 32 valves but rather it's how you use them. Now if a whole lot of R & D is done and you do your homework you end up with an engine like the LT5, the ZR-1. It's kinda like the new Cobra and the IRS system. Sure they have IRS, but it's just so they can say they have it, it's nothing like what the Vette has.

GM can make more power out of a pushrod motor than Ford is out of their DOHC motors, and do it with better gas mileage. Why change something that is proven to work? The LS1 is king of the hill right now and GM has no less than 5 motors that use the same basic block / head design. It's amazing how well this is working for them.

I'm not trying to turn this into a Ford vs Chevy thread but rather just make some points. A good pushrod motor can be better than a fair DOHC setup.

 

While I agree with most of what you say, don't forget one thing
"cubic inches".

Ford Mustang GTs produce 260 hp out of 282 cubic inches, not too shabby.

 

maybe, but you know it costs alot of money for Chevy to do R&D on OHC engines, more than a pushrod engine. This is why the ZR1 was so much more expensive.

The Japs and Germans really got into the OHC thing, they both seem to get more hp than you would think out of them, especially the japs. But theyve been around a long time too, i know the japanese have been doing it for 30-40 years at least and probably longer

 

Now that the R&D has been done (ZR1, Ford V8's, etc.) shouldn't it be easier and cheaper for chevy to do a little bit more research and get from Ford's mediocre OHC V8 to a good (though perhaps not ZR1-great) OHC small block? A higher-revving engine has become more and more important from L98 -> LT1 -> LS1 right?

 

Best thing about pushrod engines (LT1/LT4) is when you dust someone off the line who thinks their DOHC sled is 'da bom' ('03 Cobras notwithstanding). ;)


[Modified by Lone Ranger, 9:42 PM 10/29/2002]

 

I prefer to play catch up and drive on by. It shows more muscle. :D :jester

 

You dont see many OHC engines stomping the LS1/6 do you.

Theyve said before that the C6 engine will have 2 cams in the block, which is a tech upgrade that i'm interesting in seeing.

But it still costs too much money, GM wont do it unless they have to do it, it still costs money to mass produce these things. And the Mustang will never compete with the vette, so they have nothing to worry about.

Higher revving may be important to some people, but i dont put my engine to 8000rpm on the street, i want the power when i hit the gas, not 5sec later.

The reality is that each will always have its own advantage if money is still put towards the research.

 

GM does have the Northstar though, which is a development of the LT5.

I dont think theyll ever stick a DOHC in a vette, theyll go straight to the electro-pnumatic, hopefully for C7s.

 

In all reality it is 2 different ways of accomplishing the same thing. But for some to say that a DOHC motor has nothing in the low RPM is just crazy. Remember torque gets you moving horsepower keeps you moving. The LT5 has just as much or even more torque down low as the L98/LT1/LT4/LS1/LS6. The ZR-1s biggest achilles heal is the 3500+lb weight. Which is what really makes it a tad slower than a Z06 off the line, not the fact that the LS6 has pushrods. Put the LT5 in a 3100 lb car and see what happens. That is what I will be looking into doing after I finish the minor mods to the motor(Intake P&P, Exhaust). I am going to see what I can do to get my Z down to ~3100lbs. It won't be easy.


[Modified by BiZ, 11:14 PM 10/29/2002]

 

If they wouldve just removed that iron from the block so they didnt have to machine AL and Iron at the same pass, the weight wouldve been less and it wouldve been cheaper to make the LT5s.

 

Oh Boy, where to even start here.......

Some of you guys are saying stuff that you are really just guessing at or are completely wrong about.

First and foremost , power is all about flow. Displacement , head flow, valve timing etc. How the valves are opened and closed physically , by what mechanical process, is important but not necessarily what makes a given engine have alot of low end power or accelerate quickly.

"pushrods lend themselves to quicker acceleration and hence more low end torque" - huh? First, quicker acceleration doesnt necessarily have to do with low end torque. There are many very quick accelerating peaky(relatively) engined cars out there.

"The ZR1 engine is a quad-cam engine that will lose to a Z06 in the 1/4mi simply because of the Z06's pushrods-acceleration."

That statement is absolutely ridiculous. First your comparing a ZR1 engine to a Z06 car.....I guess you mean car v. car. The ZR1 would lose to a (presumably 02+) Z06 because its heavier, less aerodynamic, and has less optimal gearing for 1/4 mile racing - NOT because it has a DOHC engine!
Take a look a heavily modded LT5's - They can make almost 600 rwhp on pump gas . The very hottest LS6's are just matching that but with 10-20 more cubic inches and a MUCH newer design. They have lumpier idles and are big solid roller motors. The LT5's are much sweeter and safer to rev.

Here is another beauty : "After a 1/4mi, then the ZR1 will leave it in smoke because the ZR1 can rev much further and has an even better top end. This is why the Zr1 held the world speed endurance record for so long."

The ZR1 leaves the Z06 in top speed ONLY because its geared for more top speed , PERIOD. If the Z06 was geared taller , it would pass the ZR1 because it has as much or more horsepower, can rev nearly as high , is more aerodynamic, and is lighter. The ZR1 held/holds the record for many reasons but this is not one of them.

Vader, sorry I am pickin on ya a bit , but this info is just not right. If you know , fine , but if you dont , dont say you do.

"You would think that Ford would make more horsepower due to their 32 valve designs, really they don't" - What two engines are you comparing ? A 281 cid 2001 Cobra engine typically dynos around 280 rwhp while 346 cid early LS1's dyno around 300 rwhp - GM engine is 65 cubes bigger (19%) and only makes 20 rwhp more (7%). I would say the Cobra engine is MUCH stronger for its size .....If it were a 346 , using the same power/cid it would make over 340 rwhp.....thats about what 01 Z06's make and ZR1's.

The Cobra engines are VERY mild in cam setup, compression etc. They can make alot of hp if done right. Why Ford has not made them more aggressive, I dont know but their potential is there. Size, both physically and potential cubic inches, is their biggest disadvantage to GM's engines. Otherwise , they are quite good.

Overhead cam designs control the valves more precisely. With double over head cams they also allow more exact control of intake and exhaust valves seperately . They can rev higher and a good 4 valve head is better than ANY comparable pushrod 2 valve head in terms of flow. Look at the tremendous amounts of hp current bikes make from small engines....none of which are 2 valve pushrod motors. Formula 1 is THE pinnacle of engine development and they use what they do because of its superiority.

Pushrod designs can be very good , relatively physically small, cost efficient and effective. That doesnt mean that they are the all out best.

Imagine how good a modern GM 350 cid LT5 successor could be. Dont get me wrong , I love the pushrod engine for what it is and how well they have been made to work . But dont try to say the others are no good just because they are not what you have.

Sorry for the harsh words , but sometimes the misinformation on the internut gets too deep........ :seeya

OOPS almost forgot to answer original post......our engines are pushrod because GM didnt want to change at the time our cars needed a new/updated design. GM had more knowledge of pushrod designs, also the design is what was always used in the Vettes, and it was still an effective , cost efficient way to make power and maintain image.

Yes , DOHC would be better for performance. BUT not necessarily needed , as the LS1/6 proves. Plenty of power can reliably be made from a small packaged engine that is cost efficient and still maintain image and heritage at the same time with pushrod designs.

I am sure someone will add more or correct me if I am wrong , but.......

Hope that helps..... :seeya


[Modified by Shriker, 11:43 PM 10/29/2002]

 

i'm sorry i can never remember that the ZR1 was much heavier

a guy here at Clemson with a ZR1 told me that he couldnt beat a Z06 in the 1/4mi because it has pushrods and would accelerate much quicker

 

Ok, this is going to sound like I'm beating a dead horse even more dead, but I have to ask one question. Why can't Ford make an engine that gets decent gas mileage? GM can get better mileage out of older technology and a larger displacement while making more HP at the same time. Sure Ford can make good power for their size, but for all their high technology I would expect a little more.

As you point out there are a lot more factors involved than just the engine alone, and in general Mustangs are just poor performers because of it. I don't know if it's gearing, weight, aerodynamics or what exactly but I find it amusing that a much larger F-body with a larger engine can put more power to the ground, be faster, AND get better mileage at the same time with an old pushrod motor.

Sure Ford's power output per cubic inch is decent, certainly better than anything I could make. But just look what GM came up with in the well designed LT5. The performance out of that was absolutely amazing. Look at what was available when the LT5 was first introduced, the L98. Compare these two

I borrowed these numbers from the performance registry on this forum.
Bone stock 1990 L98 - 225 hp
Bone stock 1990 LT5 - 335 hp

That's 110 horsepower out of a dual overhead cam setup on an engine that is technically a slighly smaller displacement.

Ford achieved what exactly out of the same year standard engive vs the cobra in 1991? Was there even a cobra in 1991?

All I'm saying is that the best technology in the world is useless if it's poorly implemented. There are lots of benefits to the overhead cam design, but there is no way to say one is absolutely better than another. Only now is Ford beginning to get respectable numbers out of their 32 valve Mustangs and they seem to be using a blower to do it. If GM was to make a pushrod motor of the same displacement using the LS1 head design and put a supercharger on it I promise you it would make more power.

As you said there are many improvements factors, airflow being one of them. Working at a cylinder head shop I can tell you that OHC doesn't mean anything. A ported Cobra can be ported to match that of a ported LS1. Kinda sad when you consider that they can MATCH airflow with twice the number of valves and a chunk of metal twice the size and weight and it's going to go on an engine of far less displacement.

Please don't flat out call people wrong. You never know for sure, sometimes things can be misinterpreted and it's not worth starting any serious arguments over.

 

DOHC = $$$$$$$$$$
Pushrods = LOW tech but $$$$$ savings.

The head flow, valve diameter, camshaft design all play the important role here. A DOHC vs Pushrod is ridiculous, A DOHC motor can be designed to make tons of low end power. it has 4 valves and airflow is greater.

think of this... whenever the LT5 was designed..87 or 88... it made 375 hp stock. 14 years later a pushrod motor makes 405.
Now.. if GM designed a 5.7 L DOHC motor now....... only god knows how much more that 500 hp it would make. :yesnod: :yesnod: :yesnod: :yesnod:

 

manifold design also has a lot to do with this, a long fast moving runner would produce bottom end torque in a zr1 as well. DOCH's are more suited to rpms & do hold up better with abuse. i really have no preference between the two, you can make either one bad azz

 

My Eldorado has the Northstar and that motor is just incredible...

The torque is not there at the low RPMs like on my LT1 or previous TPI motors, but once that thing runs past 3500RPM, it screams like a turbo kicked in or something all the way to 6000RPM... It feels like it takes about twice as long to go from idle to 3500RPM than it does to go from 3500RPM to 6000RPM... My LT1 is the inverse of this...

I just wish we could see a 5.7L Northstar to power our Vettes... It would be pretty impressive IMO... Or even better yet, make a larger displacement 32V motor like a 6.6L (400) to compensate for the low end... That thing would scream at the top of the RPM band...

I also noticed that people mention that the DOHC motors are more reliable... From what I'm seeing that seems pretty true with the LT5s taking abuse and smiling right back at you... The Northstar has developed this reputation as well from my readings...