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Any possibility of introducing DOHC as against push rod technology in C6 ???



Hey gang,

I am new to this group but don't own a Corvette quite yet. Let's just say I am planning on getting into one in a year or two. However, I am a car buff and have always wondered why have they not moved to overhead cam technology on this machine ? This worked very well on the ZR1 engine but they moved back to push rod on the C5 motor. Could we start a discussion on that ???

Thanks all.
Welcome to the club Aspiring.

The story behind the LT5 is that it's an engine designed by Lotus and built by Mercury Marine. While it is a DOHC engine, it was excedingly complex and difficult to work on. I think that while the pushrod engine design is about 50 years old, the simplicity of it makes it a prime choice for development. And take a look at the 2002 LS6, a pushrod 350 pumping out 405hp. Those are ZR-1 numbers. If GM keeps pulling stuff like that out of their bag of tricks I think the pushrod V-8 has a long life ahead of it.

Heck, if for no other reason, the pushrod should stick around a while more just because of tradition. LIke the flip up headlights, and twin round tail lights, a monster pushrod V-8 is part of the Corvette image.:)

Pushrod, pushrod, rah rah rah! So much for a discussion. I love my pushrod, have you hugged yours today:love.

- Eric
It is very true that pushrod has had a history and it has worked out very well for everyone. But can you imagine how much better the motor would be if it goes OHC ?? It is like getting into the NSX arena with smooth revs and refined response up the wazzoo. I can bet you Chevy would attract buyers that are going the euro route in a heart beat.

But perhaps the current demand does not warrant this change over. In any case, I am a big fan .. no matter how they get to the cams. Make mine in Black please with a 6 speed tranny.
Wouldn't the factor of repair cost on a DOHC vs. Pushrod be a factor. That's probably the biggest factor of all.
Well, although I'm quite partial to the LT5 engine, there are couple things to take into consideration.

First of all the ZR-1's LT5 engine was a joint venture between GM Powertrain and Lotus in Hethel, England. At the time, GM owned Lotus. Because the construction of the engine was going to be mostly aluminum, GM didn't have a lot of experience building all aluminum engines. As a result, they looked at several outside sources for manufacturing and chose Mercury Marine; a very well known, reputable outboard manufacturing company located in Stillwater, OK. The idea/concept of the LT5 engine actually began in 1985 as the Corvette engineers had the insight to realize that a very serious threat was coming from overseas. Hence, the LT5/ZR-1 project began.

At the time, a DOHC was the way to go to create the high revs and power necessary to push the Corvette into exotic car performance territory.

As the ZR-1 matured from 1990 to 1995, so to did GM's ability to massage more power out of the pushrod motor. Hence, the birth of the LT1 engine in 1992. The LT1 engine put out 300 horsepower; 75 hp less than the 1992 LT5. Even though the engine lacked the 75 extra horses, the LT1 powered Corvette also lacked some of the ZR-1s extra weight. Over the years, the ZR-1's weight increased to just over 3500 lbs I believe (see http://corvetteactioncenter.com/specs/c4/zr1/zr1specs.html for exact details). The difference in performance grew smaller between the LT1 and ZR-1.

It wasn't long that the writing was finally seen on the wall: nearly similar performance could be had out of an engine with much less moving parts which cost much less to manufacture. As a result, the LT5/ZR-1 program was killed in 1993 as the last LT5 engine rolled off the assembly line in November 1993 (shedding a tear here....). The extra engines saw their way into 448 1994 ZR-1s and 448 1995 ZR-1s. The rest were stockpiled for spares.

The rest is history....the LT1 led to the LT4 and in 1997, the LS1; an all new "small block" pushrod motor unlike the previous generation small block debuted. For the 2002 model year, we have the LS6 and I wouldn't be the least bit surprised if the LS6 engine was capable of producing even more power with minor modifications. Basically, we have LT5 engine output coming out of a much smaller motor (in a packaging and number of moving parts standpoint) for much lower production costs. From a number standpoint, it just makes sense.

The other thing to keep in mind is that by nature, DOHC engines are not torque monsters contrary to popular belief. Their forte lies in their heavy breathing capability which is why the LT5 engine is capable of breathing as deeply as it does in the upper rpm range and propels the ZR-1 to its 180 mph top speed.

Although I haven't done a seat to seat comparison, I have heard many people state that the L98 engine actually felt more "torquey" than the LT5 engine. I wouldn't be surprised. The ZR-1 is certainly no slouch by any stretch of the imagination. It definitely produces enough torque to suck your eyeballs back into their sockets, but the "ole pushrod V8 engine is just as capable if not more than capable of producing that same kind of suction.

I highly doubt that we'll see another DOHC motor in a future Vette anytime soon, but who knows....

One of the cool things about the LT5 engine is not only the amount of enginneering and history that went into building the motor, but visually, it is literally an awe inspiring piece of engineering to look at.

I spent the better part of today cleaning mine. I had the hood up and a neighbor stopped by who was out walking his dog. I happend to be on the ground cleaning the inside of the wheels and didn't even know somebody walked up. All I heard was...."holy s**t, what the hell kind of motor is that!?" When I told him, he said that it was one of the most beautiful engines he had ever seen. His eyse were like half dollars as his eyes wandered all over the plenum and valve covers.

The engine has an extremely unique sound like none other I've ever heard. It has a more metallic, deep pitched howl upon acceleration and combined with the stock exhaust, really produces an amazine growl from inside the car.

Unfortunately, I have never had the opportunity to drive a Z06 Corvette....let alone a regular LS1 Corvette. I absolutely love the Z06, the concept behind it and its fantastic powerplant. However, in all honesty, I would not trade or sell my ZR-1 to get one (although I would have absolutly no problem parking a nice bright red one next to my Vette :) ). The 2002 Z06 can somewhat outperform the ZR-1 in some areas, but that's really not much of a concern of mine. For me, the joy is in the LT5 motor - a rare engine in the overall late model scheme of things that is extremely unique in its materials and construction when looking at the entire lineup of GM engines. I don't think we'll see anything like that again for many years to come.
Aspiring4Vette said:
Hey gang,

This worked very well on the ZR1 engine but they moved back to push rod on the C5 motor. Could we start a discussion on that ???

Thanks all.

DOHC is a dead issue with the Corvette. The rest of C5 years will have engines with pushrods and the 6.0 and 6.4 liter, Gen IV engines in the C6 will have pushrod valve gear.
So the ZR-1 was a direct response to the improved performance in the European sports cars?

And how much more horsepower could they pull out of 5.7 liters?
Yes. Mazda was going to be coming out with their new RX7. There was the Mitsubishi 3000GT, and the Toyota Supra Turbo. Ferrari had the Testarossa, etc. The main goal of the ZR-1 project was to take on the European sports cars. That was one of the reasons why the car was unveiled in Geneva, Switzerland as they wanted to unveil the car on the Europeans' own turf (so the story goes).

I'm not sure I understand your second question?

Pick up a copy of Heart of the Beast by Anthony Young if you can find it. It is an amazing book that chronicles the life and death of the ZR-1 and everyone that was involved in the project. Even if you don't own a ZR-1, or don't care to ever own one, the book is definitely worth picking up in that it gives you an incredible idea of what what it took to engineer the car, what was involved to bring the project to fruition and the many sacrifices that were made by everyone who worked on the project. It is definitely in line with All Corvettes Are Red by James Schefter.

The best place to try and find the book is on Ebay as I believe that publication has been discontinued.
i think the cost of the overhead cams out weigh the benefits. sure the acura nsx is a great car but it costs like $86,000 and gets out run by the corvette that is half the price. the one thing i notice about the zr-1 is the fact that other than the motor it has almost no change from a regluar c4 corvette but cost lots more. most of that extra cost is directly related to the engine alone. a new zo6 has slightly better performance and is cheaper than the zr1 was brand new and still cheaper than a real good used zr1. it just seems like a lot of cost for a marginal performance gain.
Mmmmmmm.....yes and no. Actually the ZR-1's body work is unique starting with the doors back. From the middle part of the doors back to the rear quarters and bumper are slightly larger to accomodate the larger rear wheels. The exhaust is unique to the ZR-1 and I believe the suspension was a combination of base Corvette and Z07 suspension components. I'm not totally clear on this so Hib may be able to help clarify. The windshield on a ZR-1 is also unique in that it incorporates a special solar ray glaze to keep excess UV rays out of the interior - hence keep the interior cooler. If you look at a ZR-1 windshield at dusk or dawn, you can really see the metallic looking color jump out.

The problem with the ZR-1 is that the changes are so subtle, that to the untrained eye, it looks exactly the same as an LT1 Corvette.

As the story goes (as I was told), then Corvette Chief Engineer, Dave McLellan wanted the bodywork of the ZR-1 to be a little more unique. Due to costs associated with tooling etc,. he kept getting shot down by the penny-pinchers. As a result, he required that the ZR-1 be equipped with the 315/35ZR17 tire/wheel combination "in order to accomodate the increased engine output". However, he knew that in order to do this, modifications to the body would have to be made in order to accomodate the increased wheel size. Hence...he was able to acquire the difference in body style, but IMHO, it wasn't drastic enough to set the car apart from the base model.
All I heard was...."holy s**t, what the hell kind of motor is that!?"
:L :L That was my brother in law's reaction when he attended the Corvette show with me earlier this year. We saw an uninstalled, still on the pallet, fresh LT5. It is one slick looking piece, to be sure. I agree, that the ZR1 body wasn't removed enough from the everyday Corvette. Have you ever seen the Larry Shinoda body kits or the John Lingenfelter bodywork? They're more acceptable for a high perfromance car, such as the ZR1. I like the way Callaway incorporated those holes in the nose with his enhanced version. The benefit of the engine design is the way it handles unobtanium speeds. For those who haven't had the pleasure of experiencing 140+mph, believe me that stability through the rev band is very important. Some cars seem to be gasping for air, while an engine like the ZR1 takes it in stride. DOHC cams may be a dead issue with the upcoming Corvettes, but it sure was a beautiful and wonderful time when it lasted. :) --Bullitt
Racer78 said:
Does the LT5 DOHC engine, have two cams per head and 4 valves per cylinder?
Any valve cover off pictures? Heads and block pictures? or link to same?
Yes, two camshafts per head, 4 valves per cylinder. You can see the attached photo of a modified LT5 (still shows the inside of the heads) as well as http://corvetteactioncenter.com/specs/c4/zr1/lt5specs.html

Great picture! I can see how that could intimidate even the most stalwart gearhead. I wouldn't mind someday owning one (ZR-1) but price would probably prohibit. Ah but life is all about the dreams.:)

- Eric
Racer78 said:
Thanks Rob :) So one cam is intake and one is exhaust?


How long has the Corvette been using the 5.7 liter displacement/350 ci for? Hasn't it been like 30 years or something like that?

I was just saying that they seem to squeeze out more and more power out of 5.7 liters and just wonder how much more could they get out of it? Is 500 HP a possibility?

This question is for everyone: Since the ZR-1 was a direct response to improved Asian/European sports cars; do you guys think GM will ever directly respond to the likes of the Porsche's, Ferrari's and Lamborghini's?
Supercars and Corvettes

It's hard to speculate if GM will ever try to take on the exotics again, Bullwinkle. Some would argue that there is no need to, while others believe it to be imperative. It comes down to economics in the end. Despite what some people want to think, the economy is taking a downturn. How far it will fall is anyone's guess. Even with Bob Lutz at the helm, GM's bean counters are legendary in their refusal of what would surely be an expensive program. For a supercar, you would have to develope a new body design to persuade current owner's of Porsches, Ferrari's and the like, that it is a sound investment. Taking a $5,000 deappreciation hit is bad for a regular car, but imagine what a $20,000 hit feels like involving prices in the $100,000 area. Dealer support and having the knowledgeable technicans available is paramount to satisfy a customer's needs. I visited a local Porsche dealer to see a new Twin Turbo earlier this year and got to talk to the only technican whom is truly qualified to work on these cars. The amount of training and experience he has takes a deep commitment from not only the manufacturer, but also from the dealer whom pays this guy's salary. Ferrari mechanics are the same. The nearest local dealer has mechanics whom have worked on Ferrari's for a long time and worked on actual race prepped Ferrari's. So it's a huge investment in design, money, dealer networking and manpower to develope and support a Supercar. A Lotus dealer once told me, "Anyone can sell a Lotus, but not just anyone can work on one." This is what it all comes down to, I suppose. --Bullitt
So Is ZR1 with OHC smoother than pushrod ??

I am just curious if the ZR1 is smoother than the pushrod engine and if so, can you tell the difference ?? I have read several mag articles going on and on about the 'easy breathing' and refinement of OHC motors and if anyone would know about this, it would be this forum.
You really have some great points there. Aren't there "certified ZR-1" dealerships out there who have the mechanics who have the extra training to work on the ZR-1's? Basically, this is what I'm getting from you and I totally agree: it takes a extra-ordinary mechanic to work on an extra-ordinary car.

9400 RPM is absolutely insane! I don't know if I could drive something like that.

America is the land of the Corvette; even Paul McCartney drove a Corvette over here! I think that's really a compliment from a European.

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