DOHC vs Pushrod's

[blindeyed]

Ok, I've been trying to figure this out for a while now. From what I've learned, the F-Body's and other rear wheel drive cars from GM have one single camshaft and a pushrod system set up for the valves. I've also learned that most front wheel drive GM vehicles come with DOHC.

I understand that in a pushrod engine, the camshaft actuates long rods that go up through the block and into the head to move the rockers. And that the long rods add mass to the system, which increases the load on the valve springs. Which in turn, can limit the speed of pushrod engines.

Now, if DOHC eliminates this problem, and can achieve higher speeds and create more HP, then why didn't rear wheel drive vehicles come with this valve setup instead?

The main reason why I ask, is because my friend has a 1995 Monte Carlo. A front wheel drive vehicle, with a DOHC 3.4L V6. Now I have a 1995 Firebird with a 3.4L V6 with the single camshaft and pushrods. My engine creates around 160 HP as to his engine creating around 200 HP. I attempted to race him, thinking I would stand a chance, and he creamed me.. Now, if DOHC engines create more HP, and from what I'm assuming, create more torque as well. Then why didn't GM put them in the Firebirds as well?

This may seem like a stupid question to most of you, but I'm still learning about engines, and this question has puzzled me for a while now. If I am incorrect about anything I mentioned above, then please feel free to correct me. I appreciate any responses regarding this.

[volkerc]

Originally Posted by blindxeyed

Ok, I've been trying to figure this out for a while now. From what I've learned, the F-Body's and other rear wheel drive cars from GM have one single camshaft and a pushrod system set up for the valves. I've also learned that most front wheel drive GM vehicles come with DOHC.

I understand that in a pushrod engine, the camshaft actuates long rods that go up through the block and into the head to move the rockers. And that the long rods add mass to the system, which increases the load on the valve springs. Which in turn, can limit the speed of pushrod engines.

Now, if DOHC eliminates this problem, and can achieve higher speeds and create more HP, then why didn't rear wheel drive vehicles come with this valve setup instead?

The main reason why I ask, is because my friend has a 1995 Monte Carlo. A front wheel drive vehicle, with a DOHC 3.4L V6. Now I have a 1996 Firebird with a 3.4L V6 with the single camshaft and pushrods. My engine creates around 160 HP as to his engine creating around 200 HP. I attempted to race him, thinking I would stand a chance, and he creamed me.. Now, if DOHC engines create more HP, and from what I'm assuming, create more torque as well. Then why didn't GM put them in the Firebirds as well?

This may seem like a stupid question to most of you, but I'm still learning about engines, and this question has puzzled me for a while now. If I am incorrect about anything I mentioned above, then please feel free to correct me. I appreciate any responses regarding this.

Limit the speed of pushrod engines? Don't ask the guys in Nascar, running exactly this setup turning up to 10000 rpm in the 2005 cup cars now, traveling at 200 mph! With a single carb on top of the block!!
As far as your experience is concerned, your buddy has a lighter car and more hp. Wouldn't you think that has something to do with it?

[Twizted_3KGT]

The reason being: $$

[Philo]

A DOHC (or SOHC) can always produce more horsepower than a pushrod engine of the same size. Note that I said 'can' - they don't always. For instance show me one 500 CU IN DOHC engine that produces 6000+ HP, as the top fuel pushrod engines do. Not all manufacturers take advantage of the improvement in OHC valve operations.

Because of the lighter weight of the valve train, the DOHC engine can run higher RPMs than a pushrod engine (as you stated) giving it a much wider operating band. The basic design of the DOHC is different than the pushrod engine. Sure the valve train is different, but the stroke is usually shorter as well, since they don't rely on torque as much as a pushrod engine does. The OHC engine can more easily be equipped with multi-valve (per cylinder) heads.

GM does have a lot of OHC engines, but they still have many pushrod engines too. One of the best pushrod engines: the 3.8 used in the Buick, Pontiac and others. A very tough, reliable engine. The best pushrod engine: The Small Block Chevy.

GM, and other US manufacturers are not in business to create modern engines. They are in business to get the most mileage out of their engines while trying to provide enough power for the performance type customers to keep them coming back.

My guess is that 99% of the people in the US could not tell you why an OHC engine is better than a pushrod engine. And less that that could tell you how the two systems work and how they are different. These 99% are the people manufacturers are building most of their cars for.

I have an '04 Colorado with the 3.5 liter DOHC engine. I had a '94 S10 with the 4.3 liter pushrod engine before that. I loved the torque of the 4.3, but the 3.5 has a lot more HP and RPMs, and although it makes more noise, it runs circles around the S10.

[Mr. Luos]

Pushrod motor = cheaper.
DOHC = $$$.

I like my pushrod motor.

[blindeyed]

Originally Posted by volkerc

Limit the speed of pushrod engines? Don't ask the guys in Nascar, running exactly this setup turning up to 10000 rpm in the 2005 cup cars now, traveling at 200 mph! With a single carb on top of the block!!
As far as your experience is concerned, your buddy has a lighter car and more hp. Wouldn't you think that has something to do with it?

Well, it's a known fact that pushrods do limit the speed, despite the speeds that the NASCAR guys acheive. Check out www.howstuffworks.com. That's where I read that. I highly doubt a site like that would publish false information.

"As far as your experience is concerned, your buddy has a lighter car and more hp. Wouldn't you think that has something to do with it?"

My buddy having a lighter car and more HP was obvious to me. I even stated that actually. Obviously yes, that did have something to do with him beating me. But that was not even part of the question I was asking.