natural horsepower

[jackerman]

hey i remember reading something about a motors natural peak power. the question is does it change with size of pistons or just stroke. and what is the natural peak power of a 2.2 and 2.5. i have both and wanted to know.

[shackwrrr]

Peak power comes from where the engine has the highest volumetric efficiency. Volumetric efficiency can come from many things including the camshaft, head, and intake design. Depending on certain things these can push the peak power up or down in the rpm. Stroke and bore are used in a ratio indicating the engine as undersquare, oversquare, or square. Oversqare is when the stroke is shorter than the bore diameter. Undersqare is the opposite. This doesn't affect where the the peak power falls as much as the head, cam, ect. The "squareness" of the engine shows where the engine likes to rev, usually due to crankshaft stress, bore friction, and valve size restrictions. An oversqare engine usually likes higher RPMs and opposite foe an undersqare engine.

[Shadow]

I could not move my peak power past 5900 rpm until I did a cam swap. Now with the F4 it peaks around 6500rpm and makes power right to 7400.

[BadAssPerformance]

I could not move my peak power past 5900 rpm until I did a cam swap. Now with the F4 it peaks around 6500rpm and makes power right to 7400.

I think he is asking about displacement based HP, nothing to do with the head, etc.


Jeeze, I gotta ask, do you get paid every time you say "F4"? LOL... BTW, taking the thread further off topic, what cam were you running before that and how was it degree'd? as you know that will limit power as well...

Oh, and somehow when I had the 2.2L 8V in the Z my little FM475 cam revved to 7200 all day long, never tried higher RPM...

[Shadow]

Jeeze, I gotta ask, do you get paid every time you say "F4"? LOL... BTW, taking the thread further off topic, what cam were you running before that and how was it degree'd? as you know that will limit power as well...

Oh, and somehow when I had the 2.2L 8V in the Z my little FM475 cam revved to 7200 all day long, never tried higher RPM...

For a matter of fact I DO! JK

I had always run the 88 turbo roller, never tried any other cam.

I had the stocker degreed at 115 and I left the F4 in the same location, but haven't checked with a wheel to see where it's really at.

I could rev right to 7400 rpm (my limiter) on the stock cam No problem, but on the dyno, my peak power was at 5900 rpm.

[Juggy]

FWD F4 is similar to my taft S3 camshaft

the difference is night and day compared to stock cams......well if you have the rest of the setup to benefit from the cam swap...

[BadAssPerformance]

For a matter of fact I DO! JK

I had always run the 88 turbo roller, never tried any other cam.

I had the stocker degreed at 115 and I left the F4 in the same location, but haven't checked with a wheel to see where it's really at.

I could rev right to 7400 rpm (my limiter) on the stock cam No problem, but on the dyno, my peak power was at 5900 rpm.

Got any new stickers on the car?

Well, thats different than rev-ability and DUUUH no poo a taller cam will change the power band

EDIT: back on topic, I think how it works is the rod ratio comes into play for rev-ability then the displacement at peak RPM calculated max theoretical N/A HP ... for our turbo engines a lot of this theory goes out the window

[Shadow]

Well, thats different than rev-ability and DUUUH no poo a taller cam will change the power band

I'm only aware of documented proof that the F4 and Taft S3 work very well in these mtrs (+2-3mph). You can't just slap a grind together and be garanteed it's going to make you more power.

I also know that a # of other grinds out there do Not make significant power over the stockers.

It would obviously be more benificial to the community as a whole, if more ppl would document stuff like this. Although, having said that, if their whole set-up isn't working right in the first place (a real problem with builds I've seen) then you get fudged data like gaining 150WHP from changing your cam timing!

[Shadow]

Got any new stickers on the car?

Na, still got the flaming skulls that are half peeling off from the abuse of seeing 140mph Too often!

Really been meaning to take those off and get the "Turbo Intercooler" decals I had made on there. Maybe by SDAC.

[BadAssPerformance]

I'm only aware of documented proof that the F4 and Taft S3 work very well in these mtrs (+2-3mph). You can't just slap a grind together and be garanteed it's going to make you more power.

I also know that a # of other grinds out there do Not make significant power over the stockers.

It would obviously be more benificial to the community as a whole, if more ppl would document stuff like this. Although, having said that, if their whole set-up isn't working right in the first place (a real problem with builds I've seen) then you get fudged data like gaining 150WHP from changing your cam timing!

Wow, where did this come from? The sticker comment?

Yes there are many cams that dont help over stockers and some that hurt. With that tho, what one cam does for one engine it may not do for another, for example a 2.2L might like a cam better than a 2.5L does.

So if you have actual data from all the cams you've tried (in your particular setup) hell yeah, post it up in a new thread man.

[BadAssPerformance]

Na, still got the flaming skulls that are half peeling off from the abuse of seeing 140mph Too often!

Really been meaning to take those off and get the "Turbo Intercooler" decals I had made on there. Maybe by SDAC.

LOL, need better sticker glue...

OK back on topic, what do you think about the OP's question?

[Shadow]

Wow, where did this come from? The sticker comment?

Just my way of dodging what you were really asking. Sides, I got the response I was looking for!

OK back on topic, what do you think about the OP's question?

I think piston size is going to be negligable, stroke most deff will make a difference.

Don't have to look too far to see, the stock 2.2 is what, 500-600rpm higher peak than the 2.5 stock to stock?

[Vigo]

This is one of those almost-rhetorical questions that is going to go nowhere in the end.

BUT, i will respond to shadow's last post by saying that i think the change in displacement, not the stroke, is what makes a stock 2.5 peak lower than a 2.2. All things being equal, if you take the same top-end (head, manifolds, cams, basically AIRFLOW) and then put a larger displacement motor under it, you are going to move the powerband to the left. That would happen whether the displacement change came from bore, or stroke.

[Shadow]

This is one of those almost-rhetorical questions that is going to go nowhere in the end.

BUT, i will respond to shadow's last post by saying that i think the change in displacement, not the stroke, is what makes a stock 2.5 peak lower than a 2.2. All things being equal, if you take the same top-end (head, manifolds, cams, basically AIRFLOW) and then put a larger displacement motor under it, you are going to move the powerband to the left. That would happen whether the displacement change came from bore, or stroke.

Correct me if I'm wrong here, but isn't THE difference between a 2.2 and 2.5 (CB anyway) THE STROKE of the 2.5 crank? Don't they share the same bore?

[audiomaninc]

Correct me if I'm wrong here, but isn't THE difference between a 2.2 and 2.5 (CB anyway) THE STROKE of the 2.5 crank? Don't they share the same bore?

bingo! Meaning that in this case, the stroke is the reason for the increased displacement...therefore the stroke increases the displacement increases the torque and moves the powerband to the left?

[Vigo]

Umm nope, at least not the point im trying to make.

Instead of thinking of things in terms of bore/stroke, just think in terms of displacement.

For the purposes of the argument, think of a stock 2.2 as having 100% volumetric efficiency at 5500 rpm. Any higher rpm and the VE is dropping.

Now imagine that instead of pulling 2.2L of air through that top-end at 5500 rpm, you are trying to pull 2.5L through it. This would be the same amount of air that the 2.2 would pull if you revved it higher. Therefore, the VE of the 2.5 @5500 might be 85%. But, if you lower the rpm of the 2.5 so that it is pumping the same amount of air that the 2.2@5500 is, you could get the 100% VE back, just at a lower speed.

And VE is really what determines your powerband.

So regardless of whether it is done with bigger bore or bigger stroke, increasing the displacement of a given engine, while NOT changing the airflow of the top end in any way, is going to mean it will have peak power at a lower rpm.

[jackerman]

i found the thread, it was mopar tech wrote that you should build to the natural peak. i was thinking peak power came from crank and rods. so i figured you would build the car to max power at those levels.

[jackerman]

currently i have fm 475 on my 2.2 and it loves being of 7000rpm. not sure if its faster and never had it dynoed yet. someday soon.