Scott had asked about horsepower and torque. I sent him alog to one of my
friends who works with this stuff alot, he builds fuel delvery systems and
emmission systems for a living.
anyway, here was what he had to say
Thought some other gear heads on the list may be interested
Nick
>Horsepower = (Torque * RPM)/5252
>
>
>
>Torque is the actual force that an engine produces. Horsepower is only a
>value calculated from torque and rpm using the formula above. Basically hp
>is the rate at which torque is being produced and because of their
>mathematical relationship the 2 curves will always cross at 5252 rpm. I
>wouldn't say it's impossible for an engine to reach it's hp & torque peaks
>at the same rpm, but it certainly is unlikely and undesirable in a street
>engine. Some high rpm engines have hp and torque peaks that are quite close
>but that usually means they have a very narrow power band. A very wide,
>flat torque curve like the he described below is what is needed in a street
>car. If you build an engine to make torque, the hp will follow hand in
>hand. An engine will not run out of steam after it's torque peak. It will
>always pull to the hp peak (or a little after).
>
>I've used desktp dyno quite a lot and I have a few tips. First, it's hp &
>torque numbers are usually a little optimistic. I've found somewhere in the
>neigborhood of 10%. Second, be sure you are putting the cam specs in
>properly. You really need to have the cam spec card to do it properly (you
>can get them off the net for some companies others you'll need to call).
>Guessing things like the intake centerline and lobe separation angle will
>have a significant affect on the shape of the curves. Personally I ignore
>the absolute hp & torque values it spits out and pay more attention to the
>shape of the curves to compare cams.
>
>
>
>Some other things I forgot to mention. When thinking of engines and
>torque try to think in terms of cylinder pressures instead of hp. It's this
>pressure on the piston face that directly translates to torque. This is
>referred to as "Brake Mean Effective Pressure" or BMEP. Next time you run
>an engine on desktop dyno print out the complete results which include BMEP
>and volumetric efficiency [a pecentage value equal to: (volume of air
>actually entering the cylinder/volume of the cylinder)*100]. You will note
>that the peaks of these 2 numbers will coincide directly with the torque
>peak. Basically what this translates to is that there is a particular rpm
>where every engine is most efficient at filling the cylinder with air and
>it is that point where the most air & fuel fills the cylinders and the
>highest bmep is achieved. Before or after that point the engine is not as
>volumetrically efficient. How quickly this efficiency drops off as you move
>away from that point is a function of the cam/head combo. After passing
>that point each cylinder will fill with less and less air on each succesive
>stroke until the point is reached where the cam and heads cannot flow
>enough air to support the engine speed. You may ask how does it produce
>more hp if the bmep is lower? Simply because it is turning faster, so it is
>producing less torque each stroke but there are more strokes in the same
>time period. Remember hp is a function of rpm. This whole thermodynamic
>concept of bmep is the basis for the way a pc dyno calculates it's results.
>
>When choosing a cam for torque you want a cam with the highest possible
>lift for a given duration that will place peak torque at the rpm you
>choose. Most cams out there for mopars are chevy grinds adapted to mopar
>engines. This means they don't take advantage of the mopar's larger lifter
>diameter. The larger lifter diameter allows more agressive lobe ramp
>angles. This means more lift and more power with the same duration. Hughes
>engines is one place that grinds mopar specific cams. Check them out, they
>also have all their cam specs available right online for you to plug into
>desktop dyno. (www.hughesengines.com)
>Note how their cams have comparatively high lift numbers next to other
>manufacturer's cams with equivalent duration.
>
>Also pay attention to lobe separation angle. A wider lobe separation angle
>(112 and greater) means a wider torque curve but softer throttle response
>with less peak hp. A tight lsa (110 & lower) means better midrange throttle
>response and higher peak hp, but at the expense of a rougher idle and a
>narrower powerband.
>
>Happy cam hunting!!
>----- Forwarded by Joseph Bouboulis/ETG/ENGELHARD on 12/26/00 02:22 PM
>-----
>
> Joseph
> Bouboulis To: "Sperduto, Nick"
><SperdutoN@xxxxxxx>
> cc:
> 12/26/00 12:33 Subject: Re: FW: [FWDLK]
>Horespower vs torque(Document link: Joseph
> PM Bouboulis)
>
>
>
>
>
>
> "Sperduto,
> Nick" To:
>Joseph_Bouboulis@xxxxxxxxxxxxx
> <SperdutoN@DN cc:
> B.com> Subject: FW: [FWDLK]
>Horespower vs torque
>
> 12/26/00
> 09:12 AM
>
>
>
>
>
>
>Joe, I thought you might be able to explain this.
>This is from my friend Scott, he's the guy from East Brunswick that's
>building the 56 Dodge.
>You can email him at kneedrager@xxxxxxxxxxx
>
>
>Nick
>----- Original Message -----
>From: Scott H <kneedrager@xxxxxxxxxxx>
>To: <L-FORWARDLOOK@xxxxxxxxxxxxx>
>Sent: Saturday, December 23, 2000 12:02 AM
>Subject: [FWDLK] Horespower vs torque
>
>
> > I just got a neat Desktop Dyno program that allows to assemble an engine
>on
> > your computer using any block, bore, stroke, cam, intake, exhaust etc.
>then
> > run a dyno test and even simulate dragstrip runs.
> > I have been playing with a lot of different cam specs and am looking for
> > someone to help me understand the results.
> > I know these programs have their own set of problems but It gives me
> > something to do and the results do reflect reality even if the numbers
>may
> > not be 100% accurate
> > The engine is a 4" stroke 360 bored .030 over resulting in 408 CID.
> > I have been running both small block and big block cam profiles using
>flow
> > rated for mildly ported Edelbrock Aluminum Heads.
> > My favorite combination gives me massive torque values, a nearly flat
> > horizontal line of 484 lb ft from 2000 RPM to a max of 495 at 3500 rpm.
>It
> > begins to taper down between 4000 and 5500 RPM (from 483 to 348 lb ft)
>and
> > down from there.
> > The HP curve rises nicely from 185 hp at 2000 to a peak of 385 at 5500
>RPM
> > and then begins to taper down.
> > MY QUESTION IS, can someone help me understand, or point me to a web
>site,
> > how the relationship between the torque and HP values works. I know
>that
> > more peak torque is better than peak HP especially in a heavier car, but
>I
> > would think that an optimum curve would have the HP and torque peak at
>about
> > the same rpm. In my models the hp always peaks later than the peak
>torque.
> > What is the relationship between the 2 in terms of performance? Will the
> > engine run out of steam at torque peak of 3500 RPM OR contunue to pull
>to
> > 5500 RPM the HP peak.
> >
> > Thanks,
> > Scott
> >
> >
> >
> >
> > _________________________________________________________________
> > Get your FREE download of MSN Explorer at http://explorer.msn.com
>
>
>
>
>
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