Pushrods-Purpose?

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?

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...

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. :evillol:

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

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...

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.

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

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.

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

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.

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.

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.

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

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.

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

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


My comment was not made out of spite; I merely wanted to make sure people were getting the correct information. You can have the same stroke in an OHC engine that you can have in an OHV (pushrod) engine. The design of the valvetrain does not determine your bore/stroke parameters. As for you the rest of your comment, piston speed, which is determined by rpm and stroke, has great effect on engine "revability". An engine with a shorter stroke will not have to work as hard at 9000rpm as one with a longer stroke, due to the longer distance the piston is travelling. After that, we get into connecting rod/stroke ratio and piston slap/side wall load. I'm just trying to help you out.

Jon :2cents:

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
A little tweaking? I hope that was a joke because it made me laugh. :)
Race motors don't count.

I know, no hard feelings, my bad for being a dick. That's what wanting to graduate and get the hell out of school is doing to me. Once I graduate, I plan to take some basic night automotive classes to learn basic mechanics of an engine, and how it functions. No room in the schedule with architectural engineering right now :banghead: . Soon my mechanics will match my history in the automotive world :evillol:

the stroke determines how long the valves are open

I believe the reason Chevy wen't with a pushrod engine is because it's cheap. On a V8, it's 1 cam instead of 2. Chevy made the engines make low end torque because torque engines can be made with less precision, are more fuel efficent, last longer, and are easier on the valvtrain, especially the pesky pushrods.

the stroke determines how long the valves are open
2. Chevy made the engines make low end torque because torque engines can be made with less precision, are more fuel efficent, last longer, and are easier on the valvtrain, especially the pesky pushrods.

Where do you guys get this stuff?
I don't expect people posting on here to have automotive engineering degrees but at least have some clue as to what you are talking about!! CAM DURATION determines how long valves stay open. STROKE refers to the throw of a crankshaft (how far the rod centerline is from the main centerline.)
And "torque engines" are built with no less precision than any other. If they were they would not "last longer" or be "easier on the valvetrain"... In addition, pushrod engines experience more frictional power drain making them less fuel efficient than an OHC engine, all other factors being equal.
Replies like this are the result of bolt-on horsepower. No knowledge required, just tools...

It's all good, BlkCamaro--nice car by the way, especially for a high schooler? Lucky bastard. Anyway, I agree with Murco. It would do everybody a huge favor if more people here listened to the more experienced crowd, therefore not taking up precious bandwidth with these wild assumptions. Alot of people try to make black and white out of engine mechanics/geometry. However, the more you learn about it, the more you realize that it is very much a science. A camshaft times all valve operations, and a CRANKSHAFT times the piston operations. They work together, but they are not related. Therefore, stroke (the distance the piston travels) has nothing to do with valve duration (how long they are open). As for why chevy makes pushrods, well, I'm sure it is all about the bottom line. Corporate bean-counters are always behind every decision, and I'm sure they've found it is cheaper to stay with the pushrods, given that chevy does them well enough to keep demand for newer technology low.

Jon

Murco, I'm sure you are really bright and all that, so I'll put this in terms even you will understand. Chevy used pushrods because they were cheaper. They didn't need and OHC because they weren't planning back in '55 to rev them high enough to require them. All production engines were sloppy then, the near race quality parts you get now on production engines didn't exist back then. Set for low end torque, engines have more time to burn fuel, thus better milage, lower RPM means lower lift and duration, more valveguide life, lower spring pressure, so longer seat life. Engines were doing well to break 100,000 miles. I fixed alot of them. You couldn't "bolt on horsepower" like you do on your Iroc "clone" until you did alot of machine work. There is practically no difference in friction using a pushrod cam as opposed to using 2 OHC's,especially now with GM using roller lifters. Since internal friction accounts for a small part of fuel milage, it's not an issue.

Stroke has nothing to do with valvetrain.
It does if you forget to do the math!

Ouch...

Nope, not in high school. I'm getting ready to graduate from the University of Kansas with a BS in Architectural Engineering. That's why I'll take night classes, because I'll be working at a firm during the day...

Where do you guys get this stuff?
I don't expect people posting on here to have automotive engineering degrees but at least have some clue as to what you are talking about!! CAM DURATION determines how long valves stay open. STROKE refers to the throw of a crankshaft (how far the rod centerline is from the main centerline.)
And "torque engines" are built with no less precision than any other. If they were they would not "last longer" or be "easier on the valvetrain"... In addition, pushrod engines experience more frictional power drain making them less fuel efficient than an OHC engine, all other factors being equal.
Replies like this are the result of bolt-on horsepower. No knowledge required, just tools...

no the stroke does not directly determine the valve duration, that's not what i meant. i meant that the valve duration is derived from the stroke. the valve has to be open for a certain amount of time during the intake stroke (preferably all of it to maximize the amount of mixture going into the cylinder) and that my friend is why they call it an intake stroke, its not automotive engineering its phyiscs.

P.S.- even if some of this stuff is bs or just plain wrong...that's why the frickin forum is here! so people can ask questions and get answers and learn the right stuff from the wrong.

Amen, It's all related. Murco says he has a long stroke smallblock making 520 hp. If true, that's gonna be a mighty big cam. A degree or two off either way, and he'll see just how related.

as far as chevy making an OHC V8, i think that the LT5 is about as good an argument as the camaro vs mustang, i choose to say that yes they did, because it was a chevy vehicle that used it, and was sold as production, warranteed by chevy and not lotus, and therefore is a chevy product. however, that is a can of worms and im sure many people have different oppinions that have possibly better arguments, however, i will point out that regardless of weather or not chevy made it, they went back to pushrods for the LS motors. (LS1 and LS6) as well as all the truck motors of the same design. as far as the impact on the rev range of OHV and OHC, the reason OHC are known for reving, is not for the higher range, but for the speed they can wind up. Because there is less weight in that system, and it is less prone to frictional losses, it can rev faster than the OHV counterparts. The OHV system, like all other systems with many parts, has more places for something to go wrong, and more points of friction. with high quality parts the OHV engine will last as high as youwant, look at top fuel and NASCAR engines. they run at 8000 rpm all day, so i guess its just a matter of personal preference. oh and OHC is complicated too, just in a diff way, where there are many parts to a OHV system on the inside of the engin, the OHC system has a very complicated drive system on the front of the engine. where there arejust as many things to go wrong.

um, buddhaha, i dont mean to be a dick, but you should really stop talking, murco is right. you seem to know alot of buzz words, and maybe even know alot about what they mean, but dont seem to really grasp how they go toether. trust me on this, im a chevy tech, and a mechanical engineering major. your wrong.