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importance of and improving power curve

General engine tech -- Drag Racing to Circle Track

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randy331
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importance of and improving power curve

Post by randy331 » Tue Aug 28, 2018 1:02 pm

Below is a couple pulling truck videos of the same pull.
One in cab and one from the stands.
Second place pull with 20 trucks in our class.
Shows how important a wide power curve can be.

https://www.youtube.com/watch?v=2fAWrog5Y_s
https://www.youtube.com/watch?v=MCbvK927ceA

I built a sled simulator so we could load the truck chassis the way a pulling sled does. Studied the hitch/chassis etc, and found some deflection we didn't like. So we made some changes to the chassis to help keep the truck hooked up better at the end of the pull, and have less hitch height loss under load. This past Sat. we tested the changes. ( the above videos )
It's the hardest it's worked the engine so far this year.

I hear some truck pulling guys say all that matters is power past peak, but,.... at this pull the power around peak TQ was worth some feet for our truck.


So how do you go about improving power at 9000 rpm plus, at peak HP rpm too (7500 ish) and at peak TQ rpm ? Or add power in part of the power curve without a loss at any other part. It kinda needs to be an EMC type of power curve but 3000 or more rpm higher.


I'm planning a bigger carb ( 1250 maybe ) and some better headers over the winter. May try a different cam but that's not likely to gain everywhere, but probably a trade for gain at some rpm for loss at a different rpm.


It was a second place pull so we still need to do better, and more rpm mid track would have helped, but not if it had less around peak TQ rpm.

You should here my son describe the sounds in the cab during that pull. LOL :D


Randy

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Re: importance of and improving power curve

Post by CGT » Tue Aug 28, 2018 3:03 pm

Needs more "bowl" :lol: MOO

Seriously, sounds really damn good. That little motor just doesn't wanna give it up!
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Re: importance of and improving power curve

Post by CGT » Tue Aug 28, 2018 3:39 pm

randy331 wrote:
Tue Aug 28, 2018 1:02 pm
So how do you go about improving power at 9000 rpm plus, at peak HP rpm too (7500 ish) and at peak TQ rpm ? Or add power in part of the power curve without a loss at any other part
Cubes
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Re: importance of and improving power curve

Post by GARY C » Tue Aug 28, 2018 3:44 pm

You always say the key to making more power is to reduce flow #'s... I am thinking a 1.94 valve on a 60* seat should be a solid 30 hp/tq gain. :)
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Re: importance of and improving power curve

Post by paulzig » Tue Aug 28, 2018 4:59 pm

Yeah, your cam is wrong :)

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Re: importance of and improving power curve

Post by GARY C » Tue Aug 28, 2018 5:24 pm

Actually as good as it runs I would be afraid to change anything but I think the dyno test showed the carb to be a restriction?

Have you been able to test others and or headers?
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randy331
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Re: importance of and improving power curve

Post by randy331 » Wed Aug 29, 2018 11:19 am

So,... I have the wrong cam,.. need more cubes,.. bigger bowl with less flowZZ??? :D

Well, the cubes is probably out since Austin turned down the 474 cube big bore/short stroke sponsorship, but I've had lots of others willing to take me up on that sponsorship. LOL

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Re: importance of and improving power curve

Post by CGT » Wed Aug 29, 2018 11:30 am

randy331 wrote:
Tue Aug 28, 2018 1:02 pm
So how do you go about improving power at 9000 rpm plus, at peak HP rpm too (7500 ish) and at peak TQ rpm ? Or add power in part of the power curve without a loss at any other part. It kinda needs to be an EMC type of power curve but 3000 or more rpm higher.
I guess I'll bite, not many takers here offering input. Just some thoughts without knowing every single detail of your 421.....Compression, more lift, headers for sure, Carburetor, more vacuum, try a bit more exhaust duration maybe....just throwing some stuff out there.

And remember "Area is your friend", "put some more bowl in it", "can't make any power with the valves closed" and "get the air column moving early"
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Re: importance of and improving power curve

Post by steve cowan » Wed Aug 29, 2018 5:38 pm

Randy,
i see you welded the pinch and opened it to 2.6'' 240 cc approx 320 cfm approx with a 2.08'' valve?
do you think the head is maxed out for the 2.08'' valve ?
i ran a sim on yours with engine pro ( which i know you have as well) with your parameters you are 20 lbs/ft and 20 hp approx above and your cam parameters are close to what you have.
i am thinking 2.88 MCSA and around 260cc runner but i think you will need 2.10 valve and i read earlier you dont have the room.
what do you think helps carry the power way past peak and holds it there with ease by the sound of all the runs you have put up on line.
i have to be careful here as i dont want to dig a hole for myself and you bury me in dirt from my inexperience but just trying to learn a little.
steve c

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Re: importance of and improving power curve

Post by Keith Morganstein » Wed Aug 29, 2018 9:12 pm

randy331 wrote:
Tue Aug 28, 2018 1:02 pm
Below is a couple pulling truck videos of the same pull.
One in cab and one from the stands.
Second place pull with 20 trucks in our class.
Shows how important a wide power curve can be.

https://www.youtube.com/watch?v=2fAWrog5Y_s
https://www.youtube.com/watch?v=MCbvK927ceA

I built a sled simulator so we could load the truck chassis the way a pulling sled does. Studied the hitch/chassis etc, and found some deflection we didn't like. So we made some changes to the chassis to help keep the truck hooked up better at the end of the pull, and have less hitch height loss under load. This past Sat. we tested the changes. ( the above videos )
It's the hardest it's worked the engine so far this year.

I hear some truck pulling guys say all that matters is power past peak, but,.... at this pull the power around peak TQ was worth some feet for our truck.


So how do you go about improving power at 9000 rpm plus, at peak HP rpm too (7500 ish) and at peak TQ rpm ? Or add power in part of the power curve without a loss at any other part. It kinda needs to be an EMC type of power curve but 3000 or more rpm higher.


I'm planning a bigger carb ( 1250 maybe ) and some better headers over the winter. May try a different cam but that's not likely to gain everywhere, but probably a trade for gain at some rpm for loss at a different rpm.


It was a second place pull so we still need to do better, and more rpm mid track would have helped, but not if it had less around peak TQ rpm.

You should here my son describe the sounds in the cab during that pull. LOL :D


Randy
I’m not so sure you have a “power” problem. The engine does most of the pull at 9000, then only at the very end, it pulls down to peak torque before spinning out. It seems as the truck needs a little more speed and the engine has enough power to do that.
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paulzig
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Re: importance of and improving power curve

Post by paulzig » Thu Aug 30, 2018 2:27 am

CGT wrote:
Wed Aug 29, 2018 11:30 am
try a bit more exhaust duration maybe....just throwing some stuff out there.
\

A touch less IN duration, more EX duration widen LSA out a bit... ??

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Re: importance of and improving power curve

Post by Bighauss » Thu Aug 30, 2018 9:45 am

[/quote]

I’m not so sure you have a “power” problem. The engine does most of the pull at 9000, then only at the very end, it pulls down to peak torque before spinning out. It seems as the truck needs a little more speed and the engine has enough power to do that.
[/quote]



Fully agree with this statement

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Re: importance of and improving power curve

Post by NormS » Thu Aug 30, 2018 3:21 pm

If the engine is making peak HP at 7500, running it 1500 rpm past that is like pissing into the wind. The engine probably makes more Hp at 8000 than it does at 9000, so I would say to gear the truck to run about 8000-8200 early in the run,and that should improve sled speed in that part of the pull. This assumes you don't have a Mile Per Hour limit in your class.
By getting more sled speed early, that should get you further down the track before the sled load starts to drag you down. I know that in many pulling classes,mid range torque at the end of the pull is more important than top end horse power. I would concentrate on trying to make more torque with the engine... compression, cam , headers, cubes...
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Re: importance of and improving power curve

Post by n2xlr8n » Fri Aug 31, 2018 8:36 am

That is one of the finest sounds in the world.

Nice job. Your son has to be thrilled with the family results.
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randy331
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Re: importance of and improving power curve

Post by randy331 » Sat Sep 01, 2018 12:34 am

NormS wrote:
Thu Aug 30, 2018 3:21 pm
If the engine is making peak HP at 7500, running it 1500 rpm past that is like pissing into the wind. The engine probably makes more Hp at 8000 than it does at 9000, so I would say to gear the truck to run about 8000-8200 early in the run,and that should improve sled speed in that part of the pull.
We currently run a 27.06 final drive, to get the same wheel speed at 8000 rpm that it currently has at 9000 rpm it would need a 24.05 final. That would give it very similar axle tq to last years 355, and that set up gutted out at the end at every pull.

You think the 421 would stay on line at the end with a 24.05 final ?

Tire speed/sled speed comes much easier with rpm than gear.

Randy

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