Menace

If HP is calculated from TQ, I'm no expert here... But if you made 400 TQ @ 4000 RPM (peak) Wouldnt' that mean your peak HP would be at 4000 RPM too? So in that case.. Why do you get Peak TQ around 4000-4500 and Peak HP around 5500-6200?

GT John

Yeah...............what Crazy Al said.

That being the case.............and I cant believe no one has asked yet.[sm=drooldude.gif]

What is the best exhaust setup for our N/Acars for the verybest performance?[sm=chattypair.gif]

And who makes the system................I want one.[sm=happy046.gif]

Thanks Al

ford4v429

horsepower is 'work', torque is force...forceover distance = work

I thinkby definition, 1hp = 33,000 ft lb per minute, or in'reduced to automotive terms':
(HP * 5252)/RPM= ft lb
or (ft lb * RPM)/5252=hp

so (400 ft lb*4000)/5252=304 hp,
but to make same hp at 6250 redline: (304*5252)/6250= only 255 ft lb...

hope this helps

edited- shoulda read the whole thread- crazyal covered pretty much all of it - regarding the bottom end torque, I do *kinda* agree that you will feel that more than anything else in 99% of driving...I'd trade my 300hp 6000 rpm 320 ft lb at 4500 rpm stock engine for a torque monster with a 4000 rpm revlimit if I could(and no diesels- gotta sound like it does now!)...my old 429 was I think 480 ft/lb at 2800 rpm or such- that was a blast to drive- even 'normally' it was fun...I love the new mustang for sure, but it really dont start pulling till it starts getting loud- I miss the bigblock feel...horsepower is fun, but normally cant legally use it at all on the street...effortlessly slipping the tires with a quietbigblock dont make much noise, and still plants your butt in the seat- probably at least as hard as nearing30 mph in first gear in the new mustang, but without the noise- beautiful noise, yes, but police have ears too
I want a positive displacement blower so bad I cant stand it...400 ftlb would rock, and I think if the rpm was conservative, itshouldnt hurt the motor at all...the hard part would be keeping rpm down as these little suckers love to rev

CrazyAl

If you had 400 ft-lb TQ at 4000 RPM, then you'd have:

HP = 400 * (4000/5252)
HP = 400 * 0.76
HP = 304.6 (at 4000 rpm)

Have a look at the equation. At 5252 RPM HP and TQ are equal. (This is true for ANY and ALL engines). Below 5252 RPM the TQ will always be more than HP, becasue the fraction at the right side of the equation (RPM / 5252) is less than one. Above 5252 HP is always higher than TQ because that fraction is higher than one.

So, just becasue your TQ peak occurs at 4000 RPM doesn't mean that your peak HP will occur there. If your TQ drops off faster than the slope of 1/5252 then yes that would also be your peak HP. But if your TQ doesn't fall off that fast, then your peak HP will occur later.

tritonpwrd

Al,

Thanks for the response but I have 1 more question. As I said before, I just ordered an off road h-pipe with no cats and a tune from brenspeed. In the tune he shuts down the rear o2 sensors because of the catless h-pipe. Is this bad for the car in anyways to shut down those rear sensors? Or are they just there to see if the factory cats are working properly?

Also if I take a road trip and want to put the factory mid-pipe back on because of the noise will it be harmful to run the factory setup with the rear o2 sensors off because of the tune?

Thanks so much for your help, I just dont want to do something that will screw up my car.

4LITER6

CrazyAl,
I really appreciate your knowledge and writing style......................this site or any Mustang site would do well with the "Ask CrazyAl Section"........questions submitted all week answered on a weekly basis on whatever question you want elaborate on........Just Ask CrazyAl....................[sm=icon_rtfm.gif]

Anyway, great writing!!!

Cheers!!!

CrazyAl

The truly best exhaust system choice is going to depend on your application to some degree. For race use with a modded engine the ideal setup would be different than that for a stock engine. But, assuming a natually aspirated engine, with no mods or relatively minor mods, your best HP is going to come from a set of longtubes, an offroad X-pipe, and a set of straight-through type mufflers, such as the Borla Stingers, Loudmouths, and other mufflers of that same design.

The brand of longtube doesn't matter much. They are all very similar as far as performance goes, though there is a slight advantage to those that are made of stainless or that are coated.

An X-pipe will have a slight HP advantage over an H-pipe, and also a broader powerband. Highflow cats are not as good for flow as an offroad pipe. But you may want to deviate from the ideal setup based on your sound preferances (H vs. X), or potential smog hassles (Cats vs. no cats).

The majority of your power is coming from (in order)

1) The scavenging ability of the longtubes
2) Removing the pressure drop (backpressure) across the OEM cats
3) Reducing the backpressure caused by friction in the OEM manifolds and the midpipe (and a tiny bit in the mufflers).

In a cost-no-object situationthere is something else you can do to squeeze a little extra power out of the setup: Get all your engine specs to a company like Burns Stainless who has the sophisticated computer modeling in order to design a set of megaphones & reverse cones for you. (Thisrequires filling out a very complex form) Cut the factory collectors off your headers and have them make you a new set of hand-polished merge collectors with the megaphones & reverse cones attachedand install that. Redo the X-pipe using a new "X" crossover with a specially calculated middle diameter. This will broaden the reasonance peak of your headers, which makes them work over a larger powerband, and would also improve flow slightly. Your peak HP would probably go up by 5-10 HP or so beyond the normal LTs and you could also expect a widening of the powerband. However, that would cost you about $1500 in addition to the cost of your headers, plus the labor to have these parts welded in...and you'd need that done by a real pro, not the local muffler shop.

CrazyAl

The FRONT O2 sensors are used by the ECU for adjusting fuel delivery to the engine. The REAR O2 sensors are only used to make sure the cats are working properly. Disabling them is technically illegal, but it will not harm your car at all. It won't be harmful at all to swap the OEM midpipe back in if you want to.

BigDave

Ford4v429, my screw blower makes my car feel almost exactly the same as the mildly built 460 that was in my 70 Torino. It really wakes these cars up...

blueherd02gt

I thought the best gains are in headers..(long tube) and not the midpipe....