Head & cam - HP VS. TQ
12-06-2009, 04:28 PM
#1
On The Tree
Thread Starter
iTrader: (1)
Join Date: Aug 2008
Posts: 123
Likes: 0
Received 0 Likes
on
0 Posts
Head & cam - HP VS. TQ I have always wondered why head cam packages or just simply cam only swaps take the stock HP/TQ rating on our LS1s from having more torque than horsepower to having more horsepower than torque. It seams to me that a head cam package and especially a cam swap always increases the horsepower more than the torque...why is that?
I have been looking endlessly for a head cam package that increases both TQ and HP equally to keep the factory more TQ than HP ratio.
Any insight on why...and any recommendations on a possible head cam package that would fit this profile?
Thanks guys!
I have been looking endlessly for a head cam package that increases both TQ and HP equally to keep the factory more TQ than HP ratio.
Any insight on why...and any recommendations on a possible head cam package that would fit this profile?
Thanks guys!
Last edited by 35thAnniversaryPhil; 12-11-2009 at 10:48 PM.
12-06-2009, 04:53 PM
#2
Teching In
iTrader: (2)
Join Date: May 2005
Location: Near Madison, WI
Posts: 19
Likes: 0
Received 0 Likes
on
0 Posts
Most heads and cam packages or even cams alone increase the engines efficiency in the higher RPM's. Since HP is a function of Torque and RPM, then the higher the RPM can go, the more potential there is for higher HP. Here's the equation linking HP and TQ.
HP = TQ * RPM / 5252.
So HP and Torque will always be equal at 5252 RPMs. Peak torque occurs at an engines most efficient operating RPM. If you look at the equation, you should be able to see that even if you were able to keep the torque at a constant value all the way to redline, eventually the RPM portion of the equation becomes more influencial than the torque number. That's why an engines HP will continue increasing past the peak torque even though the torque is decreasing.
The reason the stock torque number is higher than the HP is simply because the stock engine loses too much efficiency in the upper RPM's.
Did I make any sense trying to explain this?
HP = TQ * RPM / 5252.
So HP and Torque will always be equal at 5252 RPMs. Peak torque occurs at an engines most efficient operating RPM. If you look at the equation, you should be able to see that even if you were able to keep the torque at a constant value all the way to redline, eventually the RPM portion of the equation becomes more influencial than the torque number. That's why an engines HP will continue increasing past the peak torque even though the torque is decreasing.
The reason the stock torque number is higher than the HP is simply because the stock engine loses too much efficiency in the upper RPM's.
Did I make any sense trying to explain this?
12-06-2009, 04:55 PM
#3
TECH Enthusiast
iTrader: (6)
Join Date: Sep 2007
Location: Mo
Posts: 546
Likes: 0
Received 0 Likes
on
0 Posts
I could be wrong but I think it has to do with the rpm that the stock numbers are acquired.
For example in order to make a comparison with a H/C build you would have to compare at the same rpm as the factory ratings.
example
310 HP @ 5200 rpm and 340 lb.-ft. Torque @ 4000 rpm
For example in order to make a comparison with a H/C build you would have to compare at the same rpm as the factory ratings.
example
310 HP @ 5200 rpm and 340 lb.-ft. Torque @ 4000 rpm
Last edited by BaddBird; 12-06-2009 at 05:05 PM.
12-06-2009, 11:07 PM
#4
TECH Fanatic
iTrader: (23)
Join Date: Feb 2008
Location: Los Angeles, CA
Posts: 1,839
Likes: 0
Received 0 Likes
on
0 Posts
Most heads and cam packages or even cams alone increase the engines efficiency in the higher RPM's. Since HP is a function of Torque and RPM, then the higher the RPM can go, the more potential there is for higher HP. Here's the equation linking HP and TQ.
HP = TQ * RPM / 5252.
So HP and Torque will always be equal at 5252 RPMs. Peak torque occurs at an engines most efficient operating RPM. If you look at the equation, you should be able to see that even if you were able to keep the torque at a constant value all the way to redline, eventually the RPM portion of the equation becomes more influencial than the torque number. That's why an engines HP will continue increasing past the peak torque even though the torque is decreasing.
The reason the stock torque number is higher than the HP is simply because the stock engine loses too much efficiency in the upper RPM's.
Did I make any sense trying to explain this?
HP = TQ * RPM / 5252.
So HP and Torque will always be equal at 5252 RPMs. Peak torque occurs at an engines most efficient operating RPM. If you look at the equation, you should be able to see that even if you were able to keep the torque at a constant value all the way to redline, eventually the RPM portion of the equation becomes more influencial than the torque number. That's why an engines HP will continue increasing past the peak torque even though the torque is decreasing.
The reason the stock torque number is higher than the HP is simply because the stock engine loses too much efficiency in the upper RPM's.
Did I make any sense trying to explain this?
12-07-2009, 12:01 AM
#5
Staging Lane
Join Date: Jul 2008
Location: north judson indiana
Posts: 73
Likes: 0
Received 0 Likes
on
0 Posts
the reason is that horsepower is a measure of torque x time and if you look at the math used you will see that 5252 number in there but if you look at a dyno graph any graph from any type of engine thr torque qnd horsepower is always the same at 5252 rpm or put another way looking at a dyno sheet the line for hp and torque will always sross at exactly that point.
12-07-2009, 12:45 AM
#6
Launching!
Join Date: Feb 2004
Posts: 260
Likes: 0
Received 0 Likes
on
0 Posts
I have always wondered why head cam packages or just simply cam only swaps take the stock HP/TQ rating from having more torque than horsepower to having more horsepower than torque. It seams to me that a head cam package and especially a cam swap always increases the horsepower more than the torque...why is that?
I have been looking endlessly for a head cam package that increases both TQ and HP equally to keep the factory more TQ than HP ratio.
Any insight on why...and any recommendations on a possible head cam package that would fit this profile?
Thanks guys!
I have been looking endlessly for a head cam package that increases both TQ and HP equally to keep the factory more TQ than HP ratio.
Any insight on why...and any recommendations on a possible head cam package that would fit this profile?
Thanks guys!
If you stay small duration with good lift you will always make more peak torque than peak hp.
The capacity of the engine is also part of the equation.
If it's for a street d/d car, ideally you look for a cam that makes the most torque as early as possible and maintains good torque for as long as possible.
Good heads will extend both the hp & tq.
If you go to this web page of dyno graphs, you can see how as you go up in cam duration on this 355cid engine the hp/tq combination slowly changes....
http://www.compcams.com/Technical/DynoSheets/
p.s. check the HR types lower down the page, as they would relate more closely.
12-09-2009, 06:20 AM
#7
TECH Resident
Generally speaking, a longer duration cam...218+ (intake) will begin moving you higher into the RPM range with more HP than torque. There are other factors besides this but it is a pretty good rule of thumb.
As for the heads, a smaller port will (generally) see greater torque benefits than a larger port. The stock 243 and 317 heads are 210cc intake and many ported/CNC heads are 220+. The AFR 205 head is an excellent choice for maximizing torque. If you can swallow the cost, they are definitely the way to go. However, (I believe) most people on here would think you were foolish to use this head and a cam that isn't at least 218+.
Just my $.02 .
As for the heads, a smaller port will (generally) see greater torque benefits than a larger port. The stock 243 and 317 heads are 210cc intake and many ported/CNC heads are 220+. The AFR 205 head is an excellent choice for maximizing torque. If you can swallow the cost, they are definitely the way to go. However, (I believe) most people on here would think you were foolish to use this head and a cam that isn't at least 218+.
Just my $.02 .
