So what are you Guys reving your 2.5L's to?

[GLHNSLHT2]

I don't think this thread is "Where the peak power is" Just where your shifting your 2.5 to get the fastest times. Peak power can be in numerous places and can be peaky or flat.

[turbovanman²]

16v...

The statement was, NO 2.5 will make power above 5000 rpm, no confusion here,

[turbovanman²]

I real don't like peaky motors they leave a lot a usable torque on the table i like very flat wide power bands I'm shooting for 6500-7000 rpm with possible over shooting in 1st to 7200rpm and I'm planning on boosting over 15 in 1st and up to 30# in all other gears I'm leaving the cam selection till last when gearing (auto / manual and final drive )is sorted out.
and there will be nitous and a hoslet turbo with a tube header to boot ,intake will be like boostgeeks http://www.turbo-mopar.com/forums/sh...ad.php?t=37923

You've driven mine, even at only 20 psi on 93 octane, it pulls like a freight train.

Simon hasn't posted #s proving his point that it makes peak HP at 7,000 rpms.

Any 2.2 turbo or not... makes power at 7,000 rpms. Just not near peak power.

I'll dig up my dyno sheets, if the dyno guy still has them. I only have 20 psi runs on that crappy 60 trim.

And for the record, just because my engine still pulls up there, doesn't mean I am shifting it up there, I shift around 6-6500 to keep it in the powerband,

[bakes]

You've driven mine, even at only 20 psi on 93 octane, it pulls like a freight train.



I'll dig up my dyno sheets, if the dyno guy still has them. I only have 20 psi runs on that crappy 60 trim.

And for the record, just because my engine still pulls up there, doesn't mean I am shifting it up there, I shift around 6-6500 to keep it in the power band,

I like to think yours is a wide power band is just starts pulling and it just keeps coming till shift point not like my 89 LS theres nothing till 4500 then someone throws a switch and its go time till 7200rpm

[puppet]

Just throwing this out there but isn't the idea of spinning higher rpm's supposed to relate to a increase in displacement? If an engine eats xxx cfm @ 6000rpm it'll .. in theory, eat 20% more A/F at 7200rpm. This can mean more HP in an N/A application ... why not in FI apps?

Steve ... you should be able to speak to this.

[mopar-tech]

Just throwing this out there but isn't the idea of spinning higher rpm's supposed to relate to a increase in displacement?

Other factors start coming into play like piston speed and intake running tuning.

Yes, even on a turbocharged engine runner size and length plays a part.

I'll give some of you a bit of advice, which took a long time to come by the hard way.

Find an engines natural hp peak and focus on making the most power at that point.

[GLHNSLHT2]

What's that mean? You want a stump pulling no rev torque monster of a 2.5 with tons of boost but falls on it's face above 5500rpms?

[2.216VTurbo]

What's that mean? You want a stump pulling no rev torque monster of a 2.5 with tons of boost but falls on it's face above 5500rpms?

Or a no torque rev happy 2l that doesn't make peak HP till 9200 RPMS, if that's where the peak is, optimize gearing/shift points aound it. I believe that is what Garry is saying I'm just running an experiment with this 2l motor, I may hate a motor that makes 200lbsft and 600WHP Won't know for a while yet, still collecting the key motor parts...

[a89mini]

This thread is nothing more than the old TQ vs HP argument!

and those in the know need not argu because torque is KING!!

+1000 on Garys(mopar-tech) posts

BTW I just ran a 14.3 in my van short shifting @ 5500 @ 20psi W/steet tires

and im thinking of reducing that to 5300 now!

in answer to Q; what are you Guys reving your 2.5L's to? w/auto anything

more than 5500-6000 is a waste of rpm! and tq!!!

[GLHNSLHT2]

Maybe with an Auto, The gearing and slip in the TC might make the torque far outweight the hp, But my 5spd 2.5 goes faster letting the thing rev out farther. I don't think a blanket statement like "anymore than 5k rpms is a waste of time" flies. Because I've found that not to be true.

[mock_glh]

Torque is not always the best thing. Some of the fastest racers have gone to smaller engines to reduce the torque enough to improve traction, while retaining the same horsepower by revving a little higher.

Port velocity is what limits the efficiency of any particular size engine. Increasing the cross section of the ports and runners, along with valve size, etc.,will raise the efficent RPM range of any engine, as will increasing the length of time the valves stay open.

I launch my 2.5 (5 speed) at 6500 RPM and shift at 6500. My trick is a well ported intake and a 280 degree cam.

[WickedShelby88]

I did notice that during the time that engine size and boost were limited in the Indy car series they made the cars rev higher to get more speed out of them and probably moved the point at which peak power was made through number of changes.

[mopar-tech]

Port velocity is what limits the efficiency of any particular size engine. Increasing the cross section of the ports and runners, along with valve size, etc.,will raise the efficent RPM range of any engine, as will increasing the length of time the valves stay open.

You are ignoring piston speed and rod angles.

Try reving a 440 up to 8000 rpm and see how that works out.

[t3rse]

Like I said before, ford stroker guys (lima) with piss poor rod angles and ratios rev to 9k. The motor might not like it, but it will most assuredly do it if you can keep it together, and make power.

[mopar-tech]

Like I said before, ford stroker guys (lima) with piss poor rod angles and ratios rev to 9k. The motor might not like it, but it will most assuredly do it if you can keep it together, and make power.

The ability to do something doesn't automatically make it worthwhile.

I see my point is still missed- Find the engines natural HP peak and make the most of it there, you WILL go faster.

[Shadow]

The ability to do something doesn't automatically make it worthwhile.

I see my point is still missed- Find the engines natural HP peak and make the most of it there, you WILL go faster.

Agreed!

[Directconnection]

The ability to do something doesn't automatically make it worthwhile.

I see my point is still missed- Find the engines natural HP peak and make the most of it there, you WILL go faster.

To comment on a previous post: HP is an acceleration force, and not torque. Therefore.... torque is not king and only beneficial to stump pulling competitions.

Gary, to prove our points better: take 2 engines of exact specifications like a 2.2 and a 2.5. Use the exact same hardware (ie: head, manifolds, turbo, rods, etc...) and only differ with the pistons and crank. Now, let's see which one revs higher and makes MORE hp.

We build a small block Mopar for a local out of our shop. Car was a National NHRA record holder and runs low 9's. It is NA and only 381ci at 730hp! My claim to fame is that I resized his rods, pistons and crank along with a pedestal modification on his Indy heads (and intake)

Anyhow.... make cubes with BORE.... not stroke for more hp. Can't have BIG hp #s without the revs, and that's why bad geometries limit the hp production of the 2.5.

[GLHNSLHT2]

heh, my 2.2 liked to be shifted at 5200 rpms. I took the 2.2 shortblock out, put a 2.5 shortblock under everything that was on the 2.2 and it liked to be shifted at 5700 rpms.

[johnl]

Doesn't piston speed have something to do with it, too?

If you can get it to breathe (16v), and if you can get the rings to seal and the piston to hold together at high piston speeds , then I do not understand just how stroke defines the engine speed at which peak power is made.....?

Really, help me out here.

[Kevin]

Doesn't piston speed have something to do with it, too?

If you can get it to breathe (16v), and if you can get the rings to seal and the piston to hold together at high piston speeds , then I do not understand just how stroke defines the engine speed at which peak power is made.....?

Really, help me out here.

The harmonics (think natural frequency) of the engine is what will dictate where an engine does or does not make power.

What many people fail to realize is that there are pulses in and out of the intake/exhaust while an engine is running and these pulses change as an engine moves through the rpm band. Change these pulsations to produce constructive interference and it's possible to create an NA engine with a volumetric efficiency over 100% Meaning the actual amount of air entering the cylinder is more than theoretically possible.

Stroke is a piece of the puzzle that creates these harmonics.

There is also something to be said about the angle that the connecting rod is acting on the crank shaft. An engine with a relatively longer stroke will move through a larger maximum angle acting on the crankshaft than the same engine with a shorter stroke. As this angle increases so do losses associated with transmitting the energy from combustion into crankshaft rotation. These losses increase exponentially as engine speed goes up.


Simply put, this discussion is far more complicated than anyone is making it sound.