2008 Dodge Viper. Pics....

[NNT]

So whats the hp per litre on your advanced layout 1.6?

[1BadAction]

OHC advantages

1. You can get fit in bigger valves if they are on an angle rather than in a line. Of course the Hemi layout also accomplishes this, but the Viper engine is valves in a line.

2. Its easier to open and close the valves more aggressively with direct acting cams than with pushrods. This means you don't need so much overlap (lumpy idle) and extreme timing to make high rpm power. Check out how smoothly any random 1969 750 Honda idles vs any random 1969 big block. Then compare specific output and how high they rev.

3. A peaky power curve is much more a function of cam timing, and the intake and exhaust systems than how the valves are operated.

Sure there were OHC engines way back, but the dominant engine way back was flatheads, then pushrods, then OHC, now OHC 4 valve. There are reasons for this beyond marketing.

An old basic layout just provides some obstacles to be overcome, and the Viper and Vette engineers have done an excellent job.

For what its worth, my 1.6L is a Lotus engine. It came from the factory with tuned intake runners, twin two barrel carbs, and headers. And it was no match for any random V8 of its era, let alone a big block.

Every time I see a Hemi truck I think how much faster the engine would be in a 1000 lb lighter car A Chrysler 300 would be a fine ride. A Viper would be a ticket to losing my license.

1. a head designed correctly doesnt need gigantic valves to flow. as evidenced by the LSx Engine head flow numbers that destroy almost ANY ohc. the ohc head also weighs 2x as much. also, OHV engines CAN have 4 valves per cylinder and pent-roof combustion chambers, GM has tested them, but the results obviously weren't worth the trouble.

2. maybe in 1972, but materials and lifter design in the past 20 years make that problem a thing of the past. for example, a typical SBC "hot" cam is around 244* advertised duration and .500 lift at the valve. a typical "hot" LS cam is around .560" lift at the valve and 214* adv. duration.

3. I agree, and with an OHC there is more constraints on the profiles that will work, not to mention the problems with making an intake work correctly, CID for CID, HP for HP, they always have a more peaky power curve. as evidenced by the chevy 5.3 and the ford 5.4 in the trucks. (the only example of an equal performing pair of engines I can think of)

OHC engines are the trendy thing, but at this point they have nothing going for them other than HP per L and ultra high rpm capability. they are physically bigger, heavier, not as durable (at 100K a timing belt is DONE), more complicated, harder to service, and have more internal engine drag. a honduh might make 100HP per L, but that doesnt mean much when the 2.4L engine only weighs 150lbs less than a 7.0L V8 that makes 505hp and a whole sh1t ton more tq.

If pushrod engines are so outdated, tell me this... why does an LSx have THE best bsfc (brake specific fuel consumption) of ANY production automotive gasoline engine?

[The Big Al]

1BADACTION,
I like ya man.

But lets look at some facts.

GM's most powerful engine, per CI and MOST COSTLY ENGINE TO MANUFACTURE!! (this being the point) And it's most reliable is the NORTH-STAR Cadillac engine. And it's Dual Overhead Valve design.

The only reason the design is not used more is cost! It's the only reason.
And don't forget about that little 4 cyc Quad 4 also.

4 Camshafts and more man hours to assemble. More room for mistakes aligning 4 cams instead of 1.

________________________________________________________________

The Northstar Engine For the non-tech people who are reading this, it may be interesting to give some basic information on engine design. So what makes the Northstar engine so very special ? First of all it is of the Dual Overhead Cam (DOHC) design. That means that camshafts are not located centrally, as in a classic engine. Instead the camshafts are mounted above the valves. This means that there is no longer need for pushrods or rocker arms, eliminating a lot of internal friction and power loss. "Hey", I hear you say. "You are constantly talking about camshafts (plural ), why's that ?". You are right, "normal" engines only have one camshaft, which is centrally located in the V-block. The Northstar (and some other American and European V8's) has multiple camshafts. Each cylinder head has two camshafts, mounted above the valves. The reason for having more than one camshaft per cylinder head, is the amount of valves that are involved in the Northstar. Again, "normal" engines only have two valves per cylinder (one intake and one exhaust). In order to allow better engine breathing and better cylinder filling, the Northstar has two intake valves and two exhaust valves per cylinder, totaling 32 valves. Having only one camshaft per head, would result in this camshaft operating on 16 valves. Not only would this require a special valve layout, but it would also result in an enormous loss due to unnecessary friction. With a DOHC design, one camshaft operates the intake valves, the other one the exhaust valves. So as a matter of fact, the Northstar has four camshafts, compared to one as in a classic V8 (like the Cadillac 4.9 liter). Another reason why the Northstar is so special, is that is made completely out of aluminum. This makes the engine considerably lighter than one in cast iron. The Northstar engine weighs about 230 kg, about the same as the 4.9, despite the additional valves, camshafts and related chain-drive components. When you make a car lighter, you have less dead mass to drag with you, and you get an overall more performant machine (the so-called horsepower to weight ratio). The Northstar engine has a host of other improvements over the 4.9, amongst them a special modulating intake manifold and a special kind of distributor. A normal engine uses a device which contains a rotor or cam to close contact points and create a spark. This always implies using moving parts, subject to wear. The Northstar Engine does not have any moving parts in its iginition system. Magnetic sensors are positioned at the crankshaft and camshafts. Those sensors are triggered by notches in the crankshaft and camshaft. These generate an ON-OFF pulse wave, similar to the open-closed position of classic breaker-points. This wave is interpreted by the ignition module, containing 4 ignition coils (1 coil per 2 opposed cylinders). As the wave signal enters the ignition module, a high energy voltage is generated in the appropriate coil, resulting in two simultaneous sparks in the opposing cylinders. Since one cylinder is at its exhaust stroke, this spark will have no effect. This system is called waste spark ignition

[1BadAction]

1BADACTION,
I like ya man.

But lets look at some facts.

GM's most powerful engine, per CI and MOST COSTLY ENGINE TO MANUFACTURE!! (this being the point) And it's most reliable is the NORTH-STAR Cadillac engine. And it's Dual Overhead Valve design.

The only reason the design is not used more is cost! It's the only reason.
And don't forget about that little 4 cyc Quad 4 also.

4 Camshafts and more man hours to assemble. More room for mistakes aligning 4 cams instead of 1.

its also 150lbs heavier than an LSXs and still doesnt make as much power... which is my point. hp per CID means nothing. HP per LB means everything.

K.I.S.S.

[WILDMAN]

Bigobass just got a new hardtop GTS Viper last month. He traded his 2006 vette in on it. He says "NO COMPARISON"

[Hot Shot Merc]

Bass's must not have been the ZO6 then because all the reviews say the Vette ZO6 out performed the Viper in all aspects of the game.I watched a video of a Viper Vette comparison and the Viper looked like a fool compaired to the Vette.Handling,1/4 mile,top end etc..

[WILDMAN]

No, it was'nt a Z06. He's getting a twin turbo put on the Viper. It's supposed to be around 800hp.

[Hot Shot Merc]

Damn now thats a Viper.Theres a guy here in town that has built a few of the baddest vipers ever known.His name is Jason Hephner.Ever heard of him?I have been to his shop and Dyno.Its unreal!

[David]

My question about cam timing is how square is the lift curve. If the valves open faster you get more air in. Just because two cams open at the same time, doesn't mean the total shape of the curve is the same.

Sure you can get aggressive lift profiles with push rods. That does not negate it being easier with direct acting cams.

I still think the Viper and Vette motors are triumphs of execution. Same as Porsche 911's. No one else builds rear engine cars. No one but GM and DCX build push rod engines.

[mr.clean]

http://www.callawaycars.com/

[Action Dave]

Doesn't look much different than the current model which is a ripoff of the Vette anyway. Enter the 2008 650HP ZO7

Ummm...the newest Corvette, I guess it's the c6 is the hugest ripoff of a mopar since the F150 changed their body style to look exactly like the Ram1500. I have a buddy who is all Chevy. Always said the Viper looked silly with the really long front end. Until Chevy made their Corvette look exactly like it. Now he thinks it's the best body design ever.

[WILDMAN]

I just like the Vipers cause there's alot less around. Down here, Corvettes are as plentiful as Camaros.

[Hot Shot Merc]

http://jalopnik.com/cars/clips/zum-...mitz-227953.php

[Ted Stryker]

>{quote} Ummm...the newest Corvette, I guess it's the c6 is the hugest ripoff of a mopar since the F150 changed their body style to look exactly like the Ram1500. I have a buddy who is all Chevy. Always said the Viper looked silly with the really long front end. Until Chevy made their Corvette look exactly like it. Now he thinks it's the best body design ever.

Vette's have had long front ends for over 40 years... Actually IF it was a rip off of anything it would be a Ferrari, notta Viper...

[Cobra1racer]

http://www.microworks.net/dave/viper.html

Thats me backing up from the wall. There not made for road racing I can tell you that. There are some guys out here that race old 240Z's with some nasty 6 bangers in them, turbo yes. That will eat up a Viper or Vette on the track, and in a straight line. We even had a couple of CRX's that ran PIR with the same ET as a Vipper, Fat Alberts Vippers at that. 1:08 the same Road Course as the Rolex cars ran on.