Fishey

Learn to read and then get back to me because thats not the entire quote.

So, I have this car thats a 2.3L and spins to 6500rpm how much power does it make? 200hp? 800hp? 100hp? Maybe its 20hp...

Your Pal
-Dr F.

Chris Prack

I don't understand your question. How I am not reading your posts correctly.

Please explain to me what you are talking about then because clearly I have missed it.

It seems to me that you are running out of bull**** and now just trying to cloud your words with garbage.

In your example I cannot give you an answer because with the info you provided it's not possible.

I quoted your words, and now have done it again.

How am I reading it wrong? Maybe "determine" is where you are going but it certainly has an influance.

Fishey

1. Correct, you cannot give me an answer because RPM doesn't determine HP.
2. So when I say RPM doesn't determine HP Except in theory . I mean that in theory RPM will determine your maximum HP because the more RPM you have the more HP you will have given everything else is the same. However, in the real world it is sometimes better to change other things to get your HP then RPM and in the 944 its better to change other things to make power with RPM as a final step after you have done everything you can to make power.

Chris Prack

Ok. How is a horsepower number determined? Is horsepower measureable?

Fishey

Mass Air Flow.

Chris Prack

That is news to me. I have never heard that.

I was always under the impression that horsepower is based on torque x rpm/ 5252. So in that case rpm does in fact determine hp according to a widely accepted math formula based on rpm and torque.

Fishey

I just installed a calculator into my engine bay.. I AM GOING TO SMOKE EVERYONE...

Sure, math tells us what HP is but it doesn't tell us why it is.

Chris Prack

Now that you have edited your post to read "mass air flow" how does this affect an engine running based on speed density?

BBailey

Give it up Chris, you're arguing with a 12 yr old who isn't even thinking in the same ballpark engine wise as you, Dave, et al. He's thinking about bolt on engine performance at best. Some day he'll realize that racecar's don't survive with bolt on's at the horsepower levels necessary to be competitive.

Please keep us updated on your progress. I'm very interested in what you guys come up with in your search for an improved crank as I'd love to piggyback on your work to build a high RPM normally aspirated engine to run in GT3/4 when my new chassis is finished.

Chris Prack

TORQUE X RPM / 5252


I can't make it any clearer than that.

Fishey

Thats great Chris P. Hp and Tq are related.

So your saying a car spinning 1000rpm can't make as much HP as a car spinning 6000rpm? I don't see the point in your post.

Chris Prack

Sorry but I am going to go drink now. You won. You are right. I don't know what is wrong with me.

Brian you are also correct. I get carried away sometimes.

Fishey

Google Density for me real quick...

All cars have Mass Air Flow we just might not measure it as such. So please continue onto why TQ X RPM / 5250 has anything to do with what I said? I could say that my car makes 1,000hp at 1,000,000,000 RPM. That means that its fast right? 1,000hp. Gear much?

Waterguy

HP = torque*rpm/5252

That means that anything you can do to increase torque at 6,000 rpm is going to produce 6 times as much power as anything you can do at 1,000 rpm.

Fishey, I agree with you that in the "real world" of relatively stock motors with simple, low-cost, bolt-on upgrades (which is what most of us do with our 951s) there is little point in increasing rpm. We have an early-80s 2 valve motor tuned for mid-range torque and not top end power.

However, some people (Chris White, Chris Prack, Dave, John, SpecialTool) are prepared to do all the expensive mods that are required to modernise our engines and produce big horsepower by getting increased torque (yes, requiring increased air flow) at high rpms and producing reliable racing motors that benefit from those same high rpms. I can imagine that after you spend the $25,000 plus to build an engine with all the necessary upgrades to make power at 7500+ rpm (turbo, intercooler, throttle body intake, head, cam, headers, cross-over, lifters, pistons, rods) that you might develop nagging little problems like factory crankshafts cracking. For them a stronger crank may make ense and be (relatively) cheap.

Beats the heck out of me why a factory 2.5 L crank would crack but a 3.0 L one wouldn't, though.

fortysixandtwo

It's probably not that the 3.0 crank is any stronger, but that there are a heck of a lot more 2.5 cranks being used, stock or otherwise. In addition to that, I would guess on average, the engines using a 3.0 crank are built to a higher standard. All things being equal, the failure rate (not total) would probably be equal or higher on the 3.0 crank.