Ok this maybe a stupid ? but why do push-rod motors make more tq. than a OHC motor, even if they are the same displacement? I'm not tring to start a flame war just wondering :smash: <--- this little guy is cool :D

 

Anybody know? :crazy:

 

What makes you think this? I've never heard this.

You would have to compare identical engines, with the only difference being the location of the cam..... otherwise, there are too many variables to be able to say it's just the OHC.... Torque is determined by the total design.....

 

Well i'm think in the terms of 5.0 vs mod. motors on the mustang. It just seems that the 5.0 makes alot more tq. than the mod. Also when i had the 99 with the supercharge it doesn't seem to have as much tq. as the ls1 has. If you took the same engine and 1 was a pushrod and the other was a OHC which would make more tq.? or would the tq. just be different in the rpm band? My thing is why is it that a 4-valve (281) v-8 doesn't make more tq. or aleast = to a ls1 even though the size is different 4 valve's flow more air than 2 valve's right?

 

How did you know I was a Ford guy at heart? The 5.0 and the Mod motor are totally different designs. You are correct that the 4 valve DOHC motor has more intake *area*, but this has more affect on horsepower and RPM capability than torque. Larger intake area reduces lowend torque...like the difference between a 351 cleveland with 2 barrel versus 4 barrel heads. My Boss 351 is pitiful on torque at the lowend because of the huge ports....a 5.0 motor will pull it off the line...but the boss will pull strong to 6200 RPM, while the stock 5.0 peaks at 4250 RPM. It's all in the overall design....

Another Ford example: The 427 is an awesome race motor...but a garden variety 428 has more torque due to the longer stroke. Oh, yea, I have a GT500 also..8-)

 

Torque is going to depend very heavily on bore and stroke etc even with the same displacement. I'm not sure comparing OHC to pushrod really would apply unless the motors were EXACTLY the same dimensions.


[Modified by yellow01, 5:36 PM 8/10/2001]

 

The Northstar Engine used in Cadillacs is 4 valve double OHC engine that produces plenty of horsepower and torque.

With an increase in size (it's 4.6 liters) and some performance upgrades it certainly could rival the LS1/6. It may do so in the EVOQ production car.





[Modified by wwashing, 5:54 PM 8/10/2001]

 

There was an article in, I think, Hot Rod Mag. not too long ago where they took a push-rod engine and dyoed it and then converted it to a OHC setup that used the same bore/stroke etc. and dynoed it. If I remember correctly the push-rod engine did have more low end and the OHC had more top end. I'm not sure, I will look at it when I get home and let you know what the #s were ;)

Jerry

 

Thanks i just want a more clearer understanding of why. I understand that a engine with more displacment will have more tq. i was just unsure why a 281 doesn't produce more than it does even being smaller, by the way i love the ls1's low end tq. :yesnod:

 

Stroke more than anything determines torque. The more stroke, the more torque. OHC engines are usually designed to rev higher, something that can't be done as easily with push rods. Short stroke is also conducive to higher revs. They compliment each other.

 

In order to take advantage of the 4 valves ability to breath they must rev higher. In order to rev higher
they must be configured in such a way that torque suffers.

 

The LT1 has more seat of the pants difference in torque. When I traded in my '97 Z28 for a '99 Z28, the '99 Z28 to me felt like it was weak... almost like turbo lag. The LT1 would pull hard right off the line, but would die out at about 3800 RPM. The LS1 would pull hard from 3800 to 6200 RPM. It took me a long time to get used to this. The problem is that most of the time I'm driving around town, I'm under 3,000 RPM. So I have to keep the gears lower to keep the RPM's up just to keep the engine in the right torque band.

The LS1 is great if you want to win races, but for regular driving around down not banging the tach to red-line, the LT1 felt like it was a lot more fun.

I raced my '97 Z28 against my friend's '98 Z28. I took him by a car length and a 1/2. By the time he got into the upper RPM's, I heard him bark the tires in 2nd gear and then he dusted me so bad... and his car was BONE STOCK! I was so pissed off. Then I traded my '97 in for the '99.

Now I'm trying to buy the Z06 and I'm guessing it's going to have the same problem. Not much fun under 3,000 RPM... but once it gets going... WATCH OUT!

 

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No actually the Z06 pulls strong at any RPM due partly to its gearing. It has lots of low-end grunt. I previously drove a Mustang Cobra and talk about a delay in power. Most DOHC engines are too peaky, but I don't know why the LS1 would be that way. I think you'll be happy with the Z06 though. IMHO, the Viper is probably one of the only new cars currently produced that has more low end torque.

 

The 2001 LS1 actually had slightly more low end torque than the LS6. The added power on the 2002 LS6 is all on the top end too, so the LS1 should have a bit more low end torque than that as well.

Chevy showed overlaid dyno charts, and you could see the difference. I don't remember the link anymore, though.

 

Okay, here's the link to the article by Hib Halverson (he's a forum member, BTW):
http://www.c5registry.com/2k2z06/page2.htm

The LS1 has a very small advantage below 3000rpms, about 5 ft-lbs, and then above 4000rpms, the LS6 starts to creep ahead, and then blows it away at higher rpms.

It was a lot closer between the 2001 LS1 and 2001 LS6.