Pushrod vs Modern VVT DOHC engines? Which is better Really?

Forgot to say, GM LOVES its Pushrod motors, and is very loyal to them, esp in the Corvette since it is its "crown jewel" (why do you think the Buick GNs got canned?) Also, Pushrod mtrs generally tend to lose steam up top as compared to OHC engines.

Also just an FYI, the LS2 (which will be going into the C6 Vette) will have 3valves per cylinder instead of 2, but will remain OHV. Ive seen the head designs and they look kind of odd.

 

Yes, but OHC engines tend to have a higher CofG due to the fact that they are taller. IMO a DOHC probably wouldnt fit in the C5 engine bay.

 

The LS2 has 2 valves per cylinder. The LS7 will have 3 valves per cylinder.

 

1.01 times as much HP? 350rwhp/320rwhp = 1.10...

Typo?

 

Are you postive the LS2 WON'T have 3ohv? I find it hard to believe that they(GM) would release that much tecnical info even about the motor on the Z06/LS7 motor when they havent even released the C6 yet.
Heres some pics of the engine.


http://www.ls1tech.com/forums/attachment.php?attachmentid=1382
http://www.ls1tech.com/forums/attachment.php?attachmentid=1381

 

Yes, I'm positive.

 

This is an interesting discussion. I agree with most of the things that Z06Kal has said here.

A couple additional things to consider:

- Reliability: Pushrods are not only economical to manufacture, but they are also extremely reliable and cost very little to maintain.

- Durability: No doubt that pushrods are much more durable for street and racing applications. They will last much longer because there are 2 to 4 times more moving parts in a multi-cam engine. Viper Le Mans engines would last the entire season before being broken down, versus the engines being broken down every single race in the multi-cam world. Like Vette's they will go for well over 100,000 miles between reuilds.

- Torque: Traditionally multi-cam engines produce high HP and less torque. Performance pushrods traditionally make more torque than HP (or at least a 1:1 ratio). This is why most multi-cam cars need lower gears and turbo's to make them go on the bottom end.

- Power: Traditionally pushrod engines have a broad powerband and start their torque curves in the 1,200 rpm range (Vipers start at 900 rpm). Multi-cam smaller displacement engines don't enter their torque curves until 3,500+ rpm or higher.

All Corvette's are rev limited. Z06's also have low gears (which makes them perform on the low end with Vipers, but run out of it on the high end). By comparison, a Viper runs 3.07 gears (versus the Z06 which runs 3.45's) and can make the low end numbers of the Z and exceed the high end numbers. The Z06 tops out in 5th at 170's, whereas the Vipers in the mid-190's (this is restricted by aerodynamics).

Stability of the valve train? Tell that to the guys who are building pushrods out to 1,200+ HP street cars... Yeah, these cars don't rev out to 9,000 rpm, because they don't need to (in order to generate power).

If you made the modification of going from 2 throttle bodies to 10 on a Viper motor, you would get an immediate bump of 150 RWHP and 1,700 rpm on the top end redline (which would redline at 7,700 rpm). Not bad for a pushrod, and all that had to be done was increase it's intake breathing. Show me an example of this in the multi-cam world (without turbocharging or blowing).

Also keep in mind that in Europe, cars are taxed on displacement. Manufacturers had to consolidate their displacement (while increasing performance) in order to deliver a product that wasn't taxed and restricted out of the market. This trend has rolled over into the F1 and other racing series (which is a major reason why American manufacturers have stayed out).

Am I saying that pushrod is better? Absolutely not. Toss the comparisons of power per cubes and look beyond. Maybe we should compare power, cost and maintenance vs. HP/ cubic inch? The fact that Dodge dominated Le Mans for 4 years before being regulated out by the cry babies, is a testament to what pushrods can do. The fact that imports are entering the world of drag racing is also a testament to the standards that pushrods have set.

Different strokes for different folks.

 

Now I'm going to ask a stupid question, sorry.

Does the pushrod engine have more low end because of the pushrods and how the valves get moved by the cam, or is it more to the fact that it tends to be larger displacement motors that use pushrods? Also, does bore/stroke ratio, and sizes, have more to do with torque numbers then how valves get opened? Am I confused in thinking there is more to a motor then this, or is how the valves open one of the most important things? Thanks.

I agree different strokes for different folks; they both have their pos/neg and both screaming F-cars and large cam drag cars sound awesome to me.

Happy driving!

 

I am still waiting for someone to compare a 575's V12 to a pushrod zo6 V8. I think that will answer our questions on torque development, etc, that bluekawala asks, since the 2 engines will be of equal displacement.

 

What exactly are you looking for as far as compartive? Yes, the displacements are the same, but no they do not have the same HP or TQ. The 575 has less tq relative to HP then that of the LS6.


575: DOHC 48V V12
5748 cc / 334 cubes
515hp @ 7250r
434tq @ 5250r


LS6/Z06
OHV 16v V-8
5665 cc / 345 cubes
405hp @ 6000r
400tq @ 4800r

 

Size demensions etc. Since the common agreement is that cams work well for low displacement, I would like to compare equal larger displacement engines and see if cams are better or worse.

 

I think your displacements are off a little.
Based on these numbers alone it appears as though the engines have similar output until about 5000 RPM where the DOHC heads and 12 cyls of the ferrari make themselves known.

 

Displacements for the 575 are off of FNA.com
Displacements for the LS6 I know by heart

Also, different stroke can make up for lack of bore in the displacement dept.

I'll be getting the dimesions in just smidge.

 

In general you are right, Cam In BLOCK engines can have a lower center of gravity.

However, the 360 engine uses a dry sump, this lowers the engine some 5" compared to the wet sump used in the LS6. Then the 360 block is so short that the cams in the 360 engine are at/below the cams in the wet sump LS6, since the cams in the 360 are above the heads, but the cam in the LS6 is below the heads; the 360 engine has a lower CoG then the LS6. Notice the sister engine to the 360, the F355 engine, has an engine bonnet lower than the hood of the C5 vette!

If the 360 used a wet sump of the same height as the LS6 then the LS6 would indeed have a lower CoG then the F360.

 

So, in effect, you are PENALIZING the 575 for reving higher? With that kind of (de)rating, we would all be driving diesels!

Any engine that revs to 8500 RPMs will have about a 1.5 ratio between HP and TQ (ala 360).
Any engine that revs to 7500 RPMs will have about a 1.25 ratio between HP and TQ (ala 575).
Any engine that revs to 6500 RPMs will have about a 1.0 ratio between TQ and HP (ala LS6).
Any engine that revs to 5500 RPMs will have about a 0.8 ratio between TQ and HP (ala LT1)
Motorcycle engines that rev to 13,000 have a 2.0 ratio between HP and TQ.
This all falls into the "so what" catagory of useful comparisons.

Displacement for displacement, the 575 engine produces more TQ than the LS6.

 

Everything looks good except the 575M is almost exactly 350 cubes.

Here's the dimensions (bore x stroke inches):
Corvette: 3.90 X 3.62 x 8 =
575M: 3.46 X 2.95

The 575 is slightly more oversquare than the Corvette which will provide it a slight advantage on the top end at the expense of a small amount of torque.

 

Does anyone have a dyno sheet of what they 575s and LS6s power band looks like? I think it would be interesting to compare the two.I believe the 575s HP would make a jump once it gets spinning up, while the LS6 would start to slowly plateau.

575M:
Bore: 88m / 3.5 in
Stroke:77 mm / 3.03 in
89.58 bhp per liter
Top Speed 202mph
Redline 7500

LS6/Z06:
Bore: 99mm / 3.9 in
Stroke: Stroke 92 mm / 3.62 in
71.49 bhp per liter
Top Speed 171mph
Redline 6500:

 

On ************* they have the 575 c.i.d. as 350.8 as you would be pointing out, however SC.net makes a lot mistakes on many cars. Ive seen their stats on the 355 for example as 380hp @ 6000, and 268tq @ 6000. So what I did is just go to FNA to get my stats, and I would think theirs would be a lot more factual.

 

Please explain to me how the Ferrari engine is bigger in metric units, but smaller in imperial.

 

Now that you have compared the engine HP of the Z06 to the 575
How about gas mileage, Ya gas mileage!!!!!!

 

Imperial? I thought the UK used metric?

Well, going over my data I supplied it seems I made a mistake on numbers and grabbed the bore and stroke from SC.net instead of FNA,and I listed 88mm when I should have listed 89. Sorry about the confusion.

FNA says that the bore is 3.46in, while the stroke is 2.95in, but the c.i.d. is still 334cubes, and 5.45ltrs

Using the numbers I supplied from SC.net which are 3.5 for the bore, and 3.03 for the stroke its 350 cubes like you stated, and 5.73ltrs

BUT using metric milimeter in order to determine the displacement, 89mm for the bore 77mm(which the Italians would since metric is used in Europe/Italy) the c.i.d. is 351cubes, and 5.75ltrs hence the 575 DESignation

You also might want to take into consideration that some of the numbers are rounded which throws off the values as you will see here.
89mm is equal to 3.504in, while 3.5in was used in SC.net which is equal to 88.9mm
77mm is equal to 3.031in, while 3.03in was uesd on SC.net its equal to 76.96mm

Sure the rounded off values can change the outcome, but I dont think the values I supplied earlier didnt helped at all, my apologies.

Oh for gas, the LS6 trumps the V12.

 

I should have said "swamp-jumping redneck american" units I suppose.
The conversions are going to throw some things off, however the total displacement, as you were getting at is not the say-all end-all anyway.

The corvette is designed around a totally different principle than the much more expensive ferrari, and their respective engine designs are going to reflect that. The 575 sacrifices some of practical advantages for more performance and a "racier" powerband. Fiat could have just bought lingenfelter-tuned small-blocks for the 575M and achieved the exact same performance for less money, but it wouldn't have felt/sounded/driven like a Ferrari.
I mean - let's face it, there are turbocharged civics out there than blow the doors off of the 575M in a drag race, so why are we getting all wrapped up in small performance variations between a $50,000 chevy and a $220,000 Fcar?

As far the pushrod vs DOHC discussion, let's look at what happened when the mustang went from 215 HP 4.9 pushrod to a 215 HP 4.6 SOHC in 1996. (These numbers are from MSN, please tell me if they are wrong as I remember slightly different ratings on the 4.9).

1995 Mustang GT (5.0):
17 / 25 mpg
215 @ 4200 RPM
288 @ 3300 RPM
bore X stroke: 4.00 X 3.00

1996 Mustang GT (4.6):
18 / 27 mpg
215 @ 4500 RPM
290 @ 3250 RPM
bore X stroke: 3.60 X 3.60

Torque is a wash. Fuel economy increased.
Note that the powerband shifted up slightly in 1996 even though ford switched to a square design from the 1995 shorter stroke dimension.
If you can imagine a 5.0 with a 1996 SOHC head (play along) you're going to see definate losses in torque and a higher-strung powerband with more horsepower at the top end.
Feel free to argue, but it looks like that's what OHC does for the powerband of an engine.

 

How is torque a wash? The data you posted shows to me that it made max torque at a lower rpm (2 more at 50 less), and max hp at a higher rpm.

As for the 550, it still looks to be that for near equal displacement, the 12 makes more torque and more hp progressivly then the V8, and thus more useable. Not to mention the actuall values for each are noteable higher, but that can be a question of compression, etc.

 

Okay, you're technically right, but the data I posted is too close to be conclusive in any way. Two identical engines pulled off the assembly line back to back often have larger differences than 2 lbft and 50 rpm between torque peaks.

 

Okay, from what I've read, if you want a less expensive engine that performs well, get the ZO6's LS6 (with not quite 80% of the hp and 93.5% of the torque of the 575 Ferrari); but if you need the best power producer and money is no object, get the ohc and not the ohv engine. As for an American ohc engine that does better the ZO6's LS6 (71.49 hp per liter & 70.6 tq per liter), it is the Cobra R's 5.4 modular engine: 2000 Ford SVT Mustang Cobra R (with 72.1 hp per liter & 71.17 tq per liter).
As for the Viper at Le Mans, yes, before it was legislated out of competition it won its class, but it never won the race.
------------------------------------------------------------------------
Technical Specifications:
Engine
Type: V8
Displacement cu in (cc): 330 (5409)
Power bhp (kW) at RPM: 390(287) / 6250
Torque lb-ft (Nm) at RPM: 385(522) / 4250
Redline at RPM: 6600
These figures a only slightly better hp & tq per cubic inch than the ZO6's LS6:
Engine
Type…
V-8, aluminum block and heads
Bore…
99.0 mm
3.90 in
Displacement…
5665 cm3
346 in3
10.5:1
405 bhp@6000 RPM
400 lb-ft@4800 RPM
6500 RPM