Pushrods-Purpose?

[DavidovSpeedWRC]

I was hoping to find some experienced Chevy V8 nutheads here to answer my question.
First, do all Chevrolet V8 engines use pushrods/
Second, what are the purpose of pushrods as opposed to Overhead Cam engines? I know pushrod motors are capable of making more low end torque than OHC motors do.
Why is that?

[BlkCamaroSS]

Yes, to date they've all been pushrods.

As for pushrods versus overhead cams, overhead cam engines rev higher because they have less distance to travel. I don't know what the relationship is between this statistic and the overall torque and hp from the engine. PM Redneck383, or maybe he'll see this and answer, he's good with this stuff...

[daeckert]

well to answer your questions, yes chevrolet has made dual overhead cam V8 engines. Now pushrods are used to push on the rocker arm which in turn pushs the valve open. an over head cam engine does not use push rods because the cam is already in the head to push on the valves. I honestly dont see why the other guy would say that they rev higher. how high your engine revs depends on alot of different things the most important being your crank and rods.

[RABarrett]

The relationship between pushrod torque and overhead cam revability, is due to the valvetrain weight. Pushrod engines have a tremendous amount of weight to control, requiring larger valve springs. Inertial mass, or the amount of effective weight to control is based on velocity. The higher the velocity, or rpm, the more inertial mass generated. The resulting spring pressure required to control this mass reduces cam life due to the pressures involved. Overhaed cam engines do not have the pushrods to control, allowing less spring pressure. The resulting reduced inertial mass ALLOWS more rpm, therefore the engine can be tuned for higher rpm power. Ray

[BlkCamaroSS]

The reason that they can rev higher is because of the distance the piston has to travel. It's much shorter on an OHC engine versus a pushrod engine. This allows for it to rev to higher rpms than it's pushrod counterpart...

[DavidovSpeedWRC]

how high your engine revs depends on alot of different things the most important being your crank and rods.

That's one aspect, but like myself and the other two guys that have posted here have said, it's the cam setup that matters.

For extreme examples take the Honda S2000 vs the Dodge Viper.
Honda=9000 RPM redline AND peak power range.
Dodge=5000 RPM redline with a peak at like 2000-3000 RPMs.

Honda used Dual Over Head Cams (DOHC) .
Dodge used pushrods.

Thanks RABarrett that makes more sense. Thanks BlkCamaroSS for the help.

[BlkCamaroSS]

I don't know what help I was, just trying to regurgitate something I think I heard Redneck say some time ago...

[DVS LT1]

Small block Chevy V8 pushrod engines can be made to rev as high as you want - 6000, 7000+ RPM's. As mentioned before, a lot has to do with internal components.

A stock LT1, for instance, really loses steam after 5000 RPM but disabe the rev limiter and you can spin that baby as high as you want. You may only end up bending a pushrod. Most of the time a V8 lags in the higher RPM range because it can't breath - port out those heads, drop in a higher lift cam and higher ratio roller rockers and you'll have an engine dying for high RPM.

Again, most of the things prventing a factory small block from reving high reliably are its components. Pushrods bend, lifters collapse - replalce the valvetrain with stronger aftermarket parts along with intake & headwork and watch out VTEC - you're about to get the smackdown by good olde fashioned cubic inches.

AFR makes a "Hyrda-Rev Kit" for late model small blocks that is a type of spring reinforcing for your lifters to prevent them from collapsing and beating up the lobes of your cam, and also help eliminate valve float. An AFR kit coupled with Comp Cams lifters and hardened pushrods will make your valvetrain bulletproof up to 6500 RPM.

[GTStang]

Not all Chevy engines are pushrods. Chevy has made DOHC V-8's example ZR-1 Vette.
Pushrods like said push on the lifter and open the valve.
Pushrod engines tend to make more torque because usually smaller engines are OHC and DOHC. A major factor of torque is cubes and piston surface area.
The main reason OHC and DOHC engines can Rev higher stock is becuase there is less moving parts and friction. The cam sit right on top of the valves and open and closes them with no lifters, rushords, rockers(depending)
But like some1 also said you can make a Pushrod engine rev to the moon if you want. Soild roller lifters, Chromely pushrods, Shaft mounted Rockers, right crank and rods you could rev your BBC to 11,000rpm

[DavidovSpeedWRC]

port out those heads, drop in a higher lift cam and higher ratio roller rockers and you'll have an engine dying for high RPM.

I wasn't interested in what could happen when you modify the engine, everything changes then.
I was trying to get an idea on the stock motor.

You can build a 2.0 VTEC Honda engine to have a torque curve as flat as any small block V8, but from the factory they are probably the peakiest engines of all.

[Murco]

A V8 will always create better torque over a larger RPM range, it's simple physics. A N/A 4-cylinder punching 240hp is impressive as hell but since horsepower is a by-product of torque it is all relative. That "peaky" engine can lose a race quickly if not kept in it's sweet-spot. I ran a very healthy cam in my Camaro last fall and produced an additional 45hp but the car didn't run any better at the track since I had taken all of my midrange and traded it for top end. I'd prefer pulling harder out of the corners to a blazing straightaway speed.
As for the rev limit, I can run at 7,500 all day but the cam drops-off the power after 6,800. I'm running all Shubeck composite valvetrain components and a proprietary cam and I cannot say enough about them. I switched to Schubeck equipment last spring and was able to drop my open spring pressure by 25% and the radius lifters broadened the torque band by 1000 RPM.

[67rsLearning]

I disagree. chevy did not make the LT5 (ZR1 Motor) they just sold it in their corvette. lotus designed the motor, and mercury marine made it. I am sure chevy has made an over head cam motor, I don't belive they ever put one into production. the main reason pushrod motors don't rev high is the spring pressure on stock motors is not strong enough to keep the lifters on the cam. (and port size and cam lift and valve size etc...) with hydrolic lifters the oil pressure changes at high rpm and the valves don't close at all effecting cylinder pressure, and causing bent pushrods when the valves hit the quick rising pistons. longer stroke effects inherent rpm powerbands but does not limit the ability of an engine to rev higher. overhead cam engines ned very long cam chains or belts theese tend to strech and have inacurate timing ofter very small amounts of time. so for reliability chevy keeps it with the pushrods. I have a ZR1 and it does love to rev past 7000.

[Chevyracincamaro]

the chevy indy car has a 3.8L v-8 that revs up to 12,000 rpm...so it stands to reason that with a little tweaking a pushrod can rev to any limit

[JohnnyWash1]

Originally Posted by BlkCamaroSS

The reason that they can rev higher is because of the distance the piston has to travel. It's much shorter on an OHC engine versus a pushrod engine. This allows for it to rev to higher rpms than it's pushrod counterpart...

Stroke has nothing to do with valvetrain.

[BlkCamaroSS]

I know, nothing in the engine is related to anything else in the engine