General Question?

[Kromulous]

Design or Build question i guess. Anyway, i want to try and get an idea of how to get less torque, and more HP?

Say if one engine has 900 hp and 650 ft lbs, and another has 850 hp and 700 ft lbs.

What could be done to alter those results?

Cam, cylinder head flow, exhaust, carb?

I know someone will ask, so all aluminum SLM Engines, no restrictions other than a 4 bbl and the usual rules.

Thanks, Krom

[Kromulous]

HP is a calculation of TQ * RPM / 5252 so it would seem RPM would be a key in making more HP.

I am reading a Cam with a little more duration.

Retarding the cam a little, and tighten up on the valve lash, but i am not sure how much impact this will have.

It seems to be a contest between cylinder head flow, volumetric efficiency, and bore and stroke, but i am still studying...

[fast_crew]

More duration, more lobe separation, installed slightly retarded. Crank the rpms up.

[billetbirdcage]

HP is a calculation of TQ * RPM / 5252 so it would seem RPM would be a key in making more HP.

I am reading a Cam with a little more duration.

Retarding the cam a little, and tighten up on the valve lash, but i am not sure how much impact this will have.

It seems to be a contest between cylinder head flow, volumetric efficiency, and bore and stroke, but i am still studying...

## deleted picture as it's too big and messes up thread##

Here is prime example: blue cam has more torque in the lower RPM ranges but drops off sharper at the higher RPM, thus it doesn't create a lot of HP because the torque is dropping so bad after 5252 RPM.

Short on time right now, but I will try to explain a few options and one you listed that will not really make a lot of difference and should look elsewhere on options of what to do.

MY bad sorry about the large picture: https://st.hotrod.com/uploads/sites/...ne-224-cam.jpg <---direct link might be easier to read

[Kromulous]

So they 5252 number is an RPM? LOL i didnt know that.

So if the torque number really starts to fall off after that RPM, it will impact negatively on the HP.

That's very interesting, it seems a high torque number in the lower RPM range, say 500 to 1000 rpm lower, and falls off pretty hard has a stiff impact on HP.

[95shaw]

Because hp is a calculated number, based on the formula,

Hp = tq times 5252 divided by rpm

Hp and tq will always be the same at 5252 rpm.

Bigger carb will make engine "lazy" on the bottom end.

[Kromulous]

Lazy on the bottom end, but more to end?

Thats something i never really tinkered with, different Carbs, we have an older Stealth and just run it religiously, its a 1.42 venturi and a 1.75" base i believe, but need to check.

We have a big Braswell but have never run it, its a 1.45 venturi.

[95shaw]

I guess help on top end will be if the carb is the restriction in the system.
If the intake, or head is the restriction, you know.

All will be a compromise. No free lunch.

[billetbirdcage]

The item I mentioned as not being overly viable is the carb change, least as how you have described.

1. Obviously it's expensive to buy several carbs or just another one to try it.
2. Using a smaller carb or restrictor to reduce power in the slick, is common now a days but you said lower torque and increase HP. Most of the time doing one of these things is going to kill power mostly on the top end when it's actually cutting off air to the engine. It will reduce power, but not really like you are saying you wanted as far as top end.
3. Going larger can reduce torque down low and might add some on top, but it can/will/might make the car lazy at lower RPM's so you push on the gas a little harder to make it go, then as the RPM's climb it all of a sudden takes off and blows the tires off. Think 2 stroke engine or light switch engine.
4. Again just going of what you said you where trying to do, I don't feel there is much gain and it will be expensive to just try it unless you have access or can borrow some carbs as so you don't incur cost purchasing some.
5. If you have dyno sheets on the engine, see if there is a vacuum value on the engine at full throttle. Like .5" or 1.5" of vacuum at full throttle. If this is on the higher side, like over 1" then going to a bigger carb might gain some top end but obviously might cause drivability issues. Basically if the engine still has a fair amount of vacuum at full throttle, then the carb is sort of a restriction and on the small side.

*Again not an engine expert but do have my own dyno but stopped doing anything with engines for a while now.

[billetbirdcage]

Maybe this might make things clearer on the torque/HP/RPM:

Lets say you want 800HP at 8000 RPM, regardless of what the engine makes for peak torque or how the torque curve is shaped on the graph it has to make 525.2# at 8000RPM. To make 900HP at 8000 RPM it has to have 590.9# at that 8000RPM.

Torque is always lower then HP over 5252 RPM and always the same at 5252 and higher under the 5252.

So to make more HP you need the torque to stay higher (not drop as bad after torque peak) or move the torque curve up in RPM's.

While impossible, if you have a engine that made 300# of torque and stayed at that 300# no matter what the RPM was then this would happen:

5000 RPM = 285HP
8000 RPM = 457
12000 RPM = 685
20000 RPM = 1142
30000 RPM = 1713

Hope that helps

[LRtireCHANGER]

Billet is dead on. Look at the dyno report on an indy car engine, it makes insane hp at 18000 rpm, but they never quote the torque numbers, because they are likely under 300 ft. pounds at that insane engine speed.

[Kromulous]

Were going to try that Braswell, with the 1.45 venturi's we already own it. We can also play with the lash a little, and just see how it feels. just maybe .004 / .006 either way.

How about carb spacers, thicker, thinner etc?

[billetbirdcage]

Were going to try that Braswell, with the 1.45 venturi's we already own it. We can also play with the lash a little, and just see how it feels. just maybe .004 / .006 either way.

How about carb spacers, thicker, thinner etc?

Lash: I would talk to the cam manufacturer, depending on the curve of the ramp during opening and closing so you have an idea how far is safe to go. This is mostly on loosing it to make the cam smaller and tighter will make that lobe act larger. Going too loose on lash can cause the valve to slam into the seat do to not using enough of the closing ramp and slow the valve down before it hits the seat.

They can also tell you what the safe range is and roughly how much duration so many thousandths will make. It's common to adjust either intake or exhaust lash while dyno'ing to give you an idea if the engine likes more or less duration on that lobe so you have an idea on where to go with the cam if you want to get a new one. Typically most lobes will allow .004 to .006 looser and be safe and you can tighten them about to zero, but again caution doing so without talking to cam manufacture. Don't talk to the phone flunky's that answer general tech stuff, they will give you a generic answer will might be wrong and cause damage.

Carb spacers are really engine specific as you can have one that picks up a ton with a 2" open and on another it kills some. But on a general statement or on average, a thicker spacer that adds more plenum volume will usually take away a little down low and add some on top but can add everywhere or take away everywhere also. A 4 hole or 4 hole tapered spacers will usually add low end or not lose it over the open spacer and still have some gain on top end. Again it varies so much it's hard to say but that is the more typical happenings.

Cam install centerline: Again it varies, but typically retarding will remove bottom end and add top end. However you might be surprised at times it does very little. Example, I got a external belt drive so it was easy to adjust cam timing while I was dynoing my engine. Retarding the cam 4 degree's (thinking like what you want - remove low end and add top end for when track was slick) killed power almost everywhere. It was down 30 foot pound all the way threw the RPM and so down on power everywhere including the top end. However removing 3 degree's of ignition timing killed the same low end 30# of torque but the engine made about the same HP on top as the timing normal. It only killed the off corner RPM torque and HP and was within 8HP of it's normal power on top end. Again every engine is gonna be different but the ignition timing was a much better and easier way then the cam timing was on this engine.

[Kromulous]

Thanks for all the great info Billet and others, once i tear into it and rebuild it, were gonna dyno it again and then i will have a multitude of things to try and shape it. Maybe even another cam to try. Its a great engine for working stiffs like us, low budget team, but i think you should always try to do better with what you got.

I think the intent will be to flatten the torque curve, and raise its peak a little, so that carrys over to the big end and makes a little better power. If i could trade 40 lbs at for 30hp at the top end that would be ideal.

[Kromulous]

Sidebar question, i see all / most of the big boys run Fords, why is that?

My only experience with Fords are really not racing related, but high performance engines. They always seemed to be softer on the low end, and pull for days on the top end. Which in retrospect thats kinds what were after.