Chevy cams

[Clavin78]

This is a question I have always had. How come Chevy never uses or switches to and overhead cam? I think a DOHC would be considerably better (durability, performance, etc). What do you guys think? Or maybe Chevy thinks cam in block is better/cheaper?

[ZZ327]

Its actually more expensive to build and repair. Doesnt make as good of HP and Tq. And take generally more space than a regular Cam in block. OHV is more durable too. Take the New LSX engine from GMperformance parts. It can handle up to 1200hp. They were testing a design in nascar that uses shorter pushrods also. With a redline near 9K rpm

[Tucson_02Silverado]

There has been a DOHC in a production Chevy.

1990-1995 ZR1 Corvette

LT5 5.7L DOHC 375HP-405HP

Co-Designed with Lotus Engineering

Assembled by Mercury Marine

$31,000+ option to base Vette

 

vs.

2006 LS2 5.7L SOHC 400HP

2006 LS7 5.7L SOHC 500HP (crate ~$8,000)

Future LSx based up to 511CI 700HP+ (normal aspiration)

[Import Hater]

Actually a LS7 crate engine has an SRP of $15k.

 

Back in its day, the LT5 could be sold (but wasn't in the GMPP catalog) as a crate engine for $25k.

 

Chevy uses DOHC in other carlines, just no V8s. Only Cadillac and Buick get those.

[Clavin78]

Its actually more expensive to build and repair.  Doesnt make as good of HP and Tq. And take generally more space than a regular Cam in block.    OHV is more durable too.  Take the New LSX engine from GMperformance parts.  It can handle up to 1200hp.  They were testing a design in nascar that uses shorter pushrods also. With a redline near 9K rpm

 

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So you are saying pushrods are better than OHV? And now Chevy is building pushrods that can handle 8000+ rpm?

[OUMike]

Its actually more expensive to build and repair.  Doesnt make as good of HP and Tq. And take generally more space than a regular Cam in block.    OHV is more durable too.  Take the New LSX engine from GMperformance parts.  It can handle up to 1200hp.  They were testing a design in nascar that uses shorter pushrods also. With a redline near 9K rpm

 

<{POST_SNAPBACK}>

 

 

 

Actually no I don't believe thats accurate. GM builds cam in block (or OHV) because of cost. GM has been using a similar block for years and it is a really good starting point. Not to mention tradition and the reliability of of the "ol' pushrod engine". The Chevy small block motor is the most dependable engine in the world. It is tried and true, and the old gents on this group who have owned numerous of these can back me up.

 

OHC and DOHC engines are more efficient. Think about this from a physics standpoint. In a push rod engine you you have a camshaft moving rods, which moves rockers. This is very limited, and you will never see a large pushrod V8 reving past around 7 grand..and even that is high. Both of my parents have LS1 driven cars (00' Vette, 01' Z28) and both redline at about 5500.

 

The LT5 motor was really a thing of beauty. It was designed by a fellow named Geoff Jeal who designed transmissions for the Lotus F1 teams while they were affiliated with GM. DOHC naturally rev higher and produce way more torque and horsepower. The ZR-1 was capable of making horsepower all the way to 8000 rpm. Something no LTX or LSX motor can even dream of.

 

GM doesn't use DOHC motors in their cars anymore for cost. OHC motors are more expensive to maintain, and for the most part uncharted territory for them. The LSX motors are solid, and for ZR-1 fans like myself I hope no DOHC motors make it into Corvettes ever again.

 

Saying one is better than the other is probably an argument that will never be won. To obtain TQ you need displacement. Any large displacement motor is going to produce torque. However as seen by the Europeans (the best engineers in the world) other things like proper turbocharging and interesting innovations like Flat or Horizontal aspirations they've managed to keep displacement around 3 liters and still get torque figures in the 400 range.

 

DOHC will however do one thing better hands down. Horsepower and Torque curves. OHC engines produce a flatter curve through the power band and can maintain horsepower MUCH longer than pushrod engines can. Like I said before, the ZR-1 produces power as far north as 8000.

 

Chevrolet has not and will not produce a pushrod motor for the public that will make power that high. Not because GM isn't capable of it, but it is probably something used in NASCAR but mainly because the cost for something like this would be insane and drive the costs of our already expensive cars even further.

[Clavin78]

Its actually more expensive to build and repair.  Doesnt make as good of HP and Tq. And take generally more space than a regular Cam in block.     OHV is more durable too.   Take the New LSX engine from GMperformance parts.  It can handle up to 1200hp.  They were testing a design in nascar that uses shorter pushrods also. With a redline near 9K rpm

 

<{POST_SNAPBACK}>

 

 

 

Actually no I don't believe thats accurate. GM builds cam in block (or OHV) because of cost. GM has been using a similar block for years and it is a really good starting point. Not to mention tradition and the reliability of of the "ol' pushrod engine". The Chevy small block motor is the most dependable engine in the world. It is tried and true, and the old gents on this group who have owned numerous of these can back me up.

 

OHC and DOHC engines are more efficient. Think about this from a physics standpoint. In a push rod engine you you have a camshaft moving rods, which moves rockers. This is very limited, and you will never see a large pushrod V8 reving past around 7 grand..and even that is high. Both of my parents have LS1 driven cars (00' Vette, 01' Z28) and both redline at about 5500.

 

The LT5 motor was really a thing of beauty. It was designed by a fellow named Geoff Jeal who designed transmissions for the Lotus F1 teams while they were affiliated with GM. DOHC naturally rev higher and produce way more torque and horsepower. The ZR-1 was capable of making horsepower all the way to 8000 rpm. Something no LTX or LSX motor can even dream of.

 

GM doesn't use DOHC motors in their cars anymore for cost. OHC motors are more expensive to maintain, and for the most part uncharted territory for them. The LSX motors are solid, and for ZR-1 fans like myself I hope no DOHC motors make it into Corvettes ever again.

 

Saying one is better than the other is probably an argument that will never be won. To obtain TQ you need displacement. Any large displacement motor is going to produce torque. However as seen by the Europeans (the best engineers in the world) other things like proper turbocharging and interesting innovations like Flat or Horizontal aspirations they've managed to keep displacement around 3 liters and still get torque figures in the 400 range.

 

DOHC will however do one thing better hands down. Horsepower and Torque curves. OHC engines produce a flatter curve through the power band and can maintain horsepower MUCH longer than pushrod engines can. Like I said before, the ZR-1 produces power as far north as 8000.

 

Chevrolet has not and will not produce a pushrod motor for the public that will make power that high. Not because GM isn't capable of it, but it is probably something used in NASCAR but mainly because the cost for something like this would be insane and drive the costs of our already expensive cars even further.

 

<{POST_SNAPBACK}>

 

 

 

 

So basically GM would probably venture into OHC if the price of doing it was not so high.

 

And, not to start any wars, OHC is better for efficiency, more power and torque, higher rpm, and keeping the curves up longer.

 

So the advantages of the cam in block are?

[OUMike]

Its actually more expensive to build and repair.  Doesnt make as good of HP and Tq. And take generally more space than a regular Cam in block.    OHV is more durable too.  Take the New LSX engine from GMperformance parts.  It can handle up to 1200hp.  They were testing a design in nascar that uses shorter pushrods also. With a redline near 9K rpm

 

<{POST_SNAPBACK}>

 

 

 

Actually no I don't believe thats accurate. GM builds cam in block (or OHV) because of cost. GM has been using a similar block for years and it is a really good starting point. Not to mention tradition and the reliability of of the "ol' pushrod engine". The Chevy small block motor is the most dependable engine in the world. It is tried and true, and the old gents on this group who have owned numerous of these can back me up.

 

OHC and DOHC engines are more efficient. Think about this from a physics standpoint. In a push rod engine you you have a camshaft moving rods, which moves rockers. This is very limited, and you will never see a large pushrod V8 reving past around 7 grand..and even that is high. Both of my parents have LS1 driven cars (00' Vette, 01' Z28) and both redline at about 5500.

 

The LT5 motor was really a thing of beauty. It was designed by a fellow named Geoff Jeal who designed transmissions for the Lotus F1 teams while they were affiliated with GM. DOHC naturally rev higher and produce way more torque and horsepower. The ZR-1 was capable of making horsepower all the way to 8000 rpm. Something no LTX or LSX motor can even dream of.

 

GM doesn't use DOHC motors in their cars anymore for cost. OHC motors are more expensive to maintain, and for the most part uncharted territory for them. The LSX motors are solid, and for ZR-1 fans like myself I hope no DOHC motors make it into Corvettes ever again.

 

Saying one is better than the other is probably an argument that will never be won. To obtain TQ you need displacement. Any large displacement motor is going to produce torque. However as seen by the Europeans (the best engineers in the world) other things like proper turbocharging and interesting innovations like Flat or Horizontal aspirations they've managed to keep displacement around 3 liters and still get torque figures in the 400 range.

 

DOHC will however do one thing better hands down. Horsepower and Torque curves. OHC engines produce a flatter curve through the power band and can maintain horsepower MUCH longer than pushrod engines can. Like I said before, the ZR-1 produces power as far north as 8000.

 

Chevrolet has not and will not produce a pushrod motor for the public that will make power that high. Not because GM isn't capable of it, but it is probably something used in NASCAR but mainly because the cost for something like this would be insane and drive the costs of our already expensive cars even further.

 

<{POST_SNAPBACK}>

 

 

 

 

So basically GM would probably venture into OHC if the price of doing it was not so high.

 

And, not to start any wars, OHC is better for efficiency, more power and torque, higher rpm, and keeping the curves up longer.

 

So the advantages of the cam in block are?

 

<{POST_SNAPBACK}>

 

 

 

 

Honestly? None. Its an old technology that just happens to be popular with our culture. You can do everything with OHC that you can with OHV and in a smaller package. You could build and engine 3.5L and DOHC and get 400hp instead of the LS2s 6.0L and 400hp.

 

I say that costs are probably the reason, but that is really just my opinion. There is really no telling as to why the General doesn't go out into the uncharted waters of OHC.

[C & A s Dad]

I had posted my thoughts on this in another thread where someone was questioning maintenance on a timing chain.

 

Think of it this way. Take a look at Ford's 5.4, this is an OHC engine with 3 valves per cyl, that produces no more HP or TQ than the 5.3 GM and cannot compete with the GM with MPG. It contains timing chains that are miles long and as with any other OHC engine, they will need replacing much sooner than and Cam in Block design. Most (not all)OHC engines have to be spun much higher to produce the same HP and TQ that a cam in block will produce.

 

Why would you want 4 camshafts ( if DOHC), 32 valves, 2 to 4 chains or belts that can be 3 or 4 feet long or longer, multiple gears, guides and tensioners when a tried and true single camshaft engine with 16 valves will produce the kind of HP and TQ the 5.3 does and still get the MPG that we get.

 

In the Auto Parts business, it is a daily occurence that we see where someone has not replaced their timimg belts or chains in an interference style OHC engine and it breaks. This means the valves hit the tops of the pistons and the bill can easily run into the thousands of dollars. If the timing chain does get worn in a 5.3 or 5.7, it simply jumps a tooth or two and gets out of time. The bill is a couple of hundred dollars at worst.

 

For me, this was one of the reasons I bought a GM Truck. ( 1 camshaft, 16 valves, 1 chain and 2 gears, the way God Intended it ! )

 

Just for clarification in case someone may be wondering:

 

DOHC Double Overhead Camshaft

OHC Overhead Camshaft

OHV Overhead Valve (all of the engines mentioned are Overhead Valve design)

[Clavin78]

But isn't having more than 2 valves per cylinder better for efficiency and power (i.e. allow more air in and out)

 

And also, aren't you limited by push-rods?

[Import Hater]

The LT5 motor was really a thing of beauty.  It was designed by a fellow named Geoff Jeal who designed transmissions for the Lotus F1 teams while they were affiliated with GM.  DOHC naturally rev higher and produce way more torque and horsepower.  The ZR-1 was capable of making horsepower all the way to 8000 rpm.  Something no LTX or LSX motor can even dream of.

 

GM doesn't use DOHC motors in their cars anymore for cost.  OHC motors are more expensive to maintain, and for the most part uncharted territory for them.  The LSX motors are solid, and for ZR-1 fans like myself I hope no DOHC motors make it into Corvettes ever again.

 

 

<{POST_SNAPBACK}>

 

 

 

I believe I've heard Geoff himself say in interviews that if the GM brass didn't insist that the LT5 maintain 4" bore spacing like the traditional smal block, the Lotus team could have easily produced them an engine capable of the durability and mileage they wanted, and 450hp.

 

I think an LS7 could dream of seeing the power to 8000rpm. When the GENIV small block was in the works, GM Powertrain engineers shot their mouths off about variants with 500hp and 8000rpm rev ceilings. With the LS7's titainium con rods and other race shop engine tricks it already has, that beast could easily put out 600hp@8000rpm with the right cam and PCM burn.

 

While a DOHC may never rest under the hood of a 'Vette again, GM still has no problems using DOHC in many of it's other carlines....even trucks too. The Vortec inline engines in the Trailblazer, Envoy, Colorado, H3...all DOHC.

[OUMike]

The LT5 motor was really a thing of beauty.  It was designed by a fellow named Geoff Jeal who designed transmissions for the Lotus F1 teams while they were affiliated with GM.  DOHC naturally rev higher and produce way more torque and horsepower.  The ZR-1 was capable of making horsepower all the way to 8000 rpm.  Something no LTX or LSX motor can even dream of.

 

GM doesn't use DOHC motors in their cars anymore for cost.  OHC motors are more expensive to maintain, and for the most part uncharted territory for them.  The LSX motors are solid, and for ZR-1 fans like myself I hope no DOHC motors make it into Corvettes ever again.

 

 

<{POST_SNAPBACK}>

 

 

 

I believe I've heard Geoff himself say in interviews that if the GM brass didn't insist that the LT5 maintain 4" bore spacing like the traditional smal block, the Lotus team could have easily produced them an engine capable of the durability and mileage they wanted, and 450hp.

 

I think an LS7 could dream of seeing the power to 8000rpm. When the GENIV small block was in the works, GM Powertrain engineers shot their mouths off about variants with 500hp and 8000rpm rev ceilings. With the LS7's titainium con rods and other race shop engine tricks it already has, that beast could easily put out 600hp@8000rpm with the right cam and PCM burn.

 

While a DOHC may never rest under the hood of a 'Vette again, GM still has no problems using DOHC in many of it's other carlines....even trucks too. The Vortec inline engines in the Trailblazer, Envoy, Colorado, H3...all DOHC.

 

<{POST_SNAPBACK}>

 

 

 

 

Excellent point. I don't remember ever reading that article with Geoff, but I don't doubt it. I do recall that that 4'' bore figure you were talking about. Just imagine what the LT5 woulda looked like had they let Lotus do what they wanted.

 

I think GM really wanted the engine to be a 350. I think Geoff really saw more potential in the engine as a 6.0L hence why he started the 368 cubic inch kits. Then Ligenfelter and the gang soon followed. 368 Jeal ZR-1s are bad news...even for current ZO6s.

[Import Hater]

That's exactly what they wanted, a 350. They wound up with 349cid. They wanted something they could call a small block Chevy for the modern age. I rest most of the blame with the at the time Chevrolet motor division general manager Jim Perkins, who had a little too much "tradition" dyed in the wool of his suits.

 

I wish I'd have bought my dad's '90 ZR-1 when he sold it five years ago. I'd love to come across a fairly low mile '95 in Admiral Blue. Always loved the sound of winding that motor out.

[OUMike]

That's exactly what they wanted, a 350.  They wound up with 349cid.  They wanted something they could call a small block Chevy for the modern age.  I rest most of the blame with the at the time Chevrolet motor division general manager Jim Perkins, who had a little too much "tradition" dyed in the wool of his suits.

 

I wish I'd have bought my dad's '90 ZR-1 when he sold it five years ago.  I'd love to come across a fairly low mile '95 in Admiral Blue.  Always loved the sound of winding that motor out.

 

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I have no problem with tradition, and I do really like the LT5 being a 5.7L motor but yea your right. They really should have let Lotus do what they wanted. You can't ask an artist to paint you a picture...only on your criteria.

 

Check out www.zr1.net. They have some really really sharp 1995s all the time. After I graduate, you can bet one of them will be in my garage.

[Import Hater]

Haven't been to that site for awhile. Dave Bright, the owner of zr1.net, actually stayed in my (parents) house once when he came out to CA to run the Pony Express open road race in Nevada with my dad.

 

Glad to see the site's still going.