924Board.org

[Dave]

I just talked to Web cams about a cam for my car. They said with the mods that I have the cam that they think would be best for me would make my car have alot of mid and high end power. They also said If I get my heads ported and polished that that would also helo mid and high end power. SO I ask you guys how Do I improve low end power and keep the outstanding mid and High end power I would get with these mods. Do I increase compression???

[AppleBit]

Hey Dave,

well, yes- the stage 1 cam will not loose any low-end power and it will give you more upper end power and YES! you should port & polish your head to get even more power--

I also am going to recommend a Franco cam gear to more people in the future after I get some better information on ignition recurving specs. The Franco cam gear made my car have so much low-end torque that I have no problems at an autocross event to get back up to speed in 2nd gear around a tight bend (see my Auto-X video on my website to understand what I am talking about)

You could just change your timing (have it only 5 degrees advanced instead of 10) to get some more lower-end torque (I think it's 5 - 10 - !!someone verify!!) but then you sacrifice upper end ignition

or you could be like me- spend countless thousands trying to get the most HP when for all the money you could have had a used Boxster paid for by now...

:-}

But 924's are better

- Jon


_________________
Classic British Sports Car Restoration v6 + v8 Engine Conversion Swaps

Porsche 924 Wide Body LS1 Corvette 500 Horsepower Engine

[larso]

in order to do that you have to fluck around with the exhaust, lengths diameters and stuff.

The porsche 928 5 litre engine has a supercharge effect in the high 2000 low 3000 rpms because of pipe tuning, and then of course once you get to the high rpms you keep getting power.

Time consuming and a lot of testing needed to be done to get the effect, but that's the only way you can install a high duration cam and get low end.

Oh you can get the variable cam thing but that wont do as much as exhaust and intake tuning. Oh yah, also you can get these things from NOLOGY that control the back pressure, you stick it on your tail pipe, but its not just a bolt on to get any real difference (they claim it is) you would have to piddle around with piep lengths and stuff.

[Dave]

So If I run long headers that should help with low end power? They guy at Web cams said to raise my compression to help low end power. How would that help??

[larso]

yeah raising the comp always helps when you do flow improvements and the advantage of upping the compression is it helps both low and high end, as long as match up the octane accordingly and the flow, otherwise it won't do anything. Maybe try some of that Octane booster crap in a bottle, if you up your compression enough to need it, i think it may be a hoax but I predict it will work on high comp engines.

I just bought a g-tech, and i'm gonna try all this crap in the store and actually see if anything helps on a number of cars, 924s, hondas, etc.

The long skinny headers help your low end, but any long header is better, wether fat or skinny, the longer the better, except for weight.

Running 4 carbs on the car and a specially tuned exhaust (long hours of testing) is the easiest way to the supercharge effect, unless you wanna get someone to design you an intake manifold ( i would like to see how much the 928 five litre manifold costs, 8000 dollars maybe? just the manifold itself on that car probably shaves one half a second off the 0-60), it's always "the money" that limits us...and it IS very possible to get low end power, along with high end, BUT HEY, WHO IS A MILLIONAiRE HERE.

Check out the exhaust back pressure variable thing at nology though, i think its http://www.nology.com ,...it's overpriced, and it may not gonna work unless you piddle around with the exhaust a little, but it's a thought.

Remember Peter gave us those autospeed URLS that showed us how length of exhaust and intake made the cars increase HP a lot?

Well the 928 5 litre engine has this Blurp in the torque curve at 2700 RPM, i should scan the torque curve that shows supercharge affect. It's caused by specially tuned intake manifold/exhaust, you could do this to your 944 or any car, but it takes lotsa money. Long sinny headers aren't gonna do this for you instantly, and this is exactly why some people see negative effects when they put a cherry bomb muffler on, or when they put a 3000 dollar exhaust on, or even a K and N. If you changed the exhaust on the 928, and the intake, you would totally F up the whole car...

Anyway
The longer the headers, the better, though...because that keeps the pulsations in the exhaust separate from each other for longer, there is no advantage of mixing the exhaust at all, the only reason the y put single pipes on the cars and collectors is because of weight, money, If you want power all around any rpm, the best system would be to have four straight pipes out each cylinder, four carbs, but lots of time and practice done on the lengths, I stress, it takes money, time, facilities.
The 928 engineers managed to do it with fuel injection, it's hard as hell to do that cuz you've got all the pulsations on the intake side mixing, it's much easier to have four carbs, keeping the pulsations seperate from each other. I now realize why the 928 costs so much money, that car did have some wacky effects on it. The 5 litre did, anyway.

and always remember about crank rotation too, each intake pipe should actaully be different lengths, they sholdn't all be the same, same with the exhaust, and if you MUST combine the exhaust together, 1-4 go together, and 2-3 go together, because of the spark 1-3-4-2 see how 1 and 4 have some time between each other, so the pulsations won't affect each other...

It's so complicated that it should all be in a book somewhere.

but anyway it's too much money for ya right Dave? I mean how far do you wanna go? I say that the nology gimmick looking thing for a high price is worth a shot if you could find one on ebay, or make a home made one.

[ This Message was edited by: larso on 2001-09-14 16:48 ]

[larso]

http://www.nology.com/trex.html

That is a real sales pitch going there at nology, and I wouldn't buy that trex thing unless I was able to test it on a car first...but...it's a good idea.

[cs]

i read a test on a motorcyle in the 80s (yamaha i think) that used controlled back pressure. it gave it a real flat torque curve, but of course my dad said that most people removed them if they were going to race the bike or anything, but racers don't drive in stop and go traffic.

[Dave]

YA It sounds like lots of money to do that tuned intake and exhaust stuff. I think I will just get the cam, play with a long,fat pair of headers. An mybe if I can afford it later I will up the compression. Why dont they just make a cam that improves power threw out the RPM range.

[AppleBit]

Dave,

Cams work to allow flow at a designed RPM level that the person (or OEM) thinks is best used in that certain application.

You can make a cam give you tons of low end torque, but high end will suffer

or you can make a cam that gives you WOT wicked results, but you have to rev the engine to 3000 and slip the clutch to get started.

The camshaft just allows the engine to breath at different RPM ranges.

The Franco cam gear allows that breathing to be more used because it times when the breathing should work for that certain RPM band.


Yes- if you raise compression with higher compression pistons you will see much more low-end torque. Think of sucking in a breath of air for one second. You have some air filled up in your lungs. Now, when you push that air out of your lungs, that is air being released.

Now think of gasping in air for 2 seconds. You have much more air in your lungs and when you push that out you can see you have more air in there.

Now, fuel can burn properly when it is mixed with air (14.7 parts are to 1 part fuel). Since you have more air that was filled in your lungs, you can add that much more fuel to make a bigger fire.

U.S. has 8.5:1 pistons in most 924's. The Euro pistons are 9.3:1 - the higher the number the more air it will take in. It means that it will compress the first figure down to the second figure (9.3 compresses down to 1) which results in a bigger bang and the piston thrusts down faster because of this.

- Jon


_________________
Classic British Sports Car Restoration v6 + v8 Engine Conversion Swaps

Porsche 924 Wide Body LS1 Corvette 500 Horsepower Engine

[924_fan]

Jon,
I don't think that 9.3:1 compression pistons take in more air/fuel mixture than 8.5:1 pistons. Rather, the higher compression pistons compress the same initial amount of mixture into a smaller area.

If you want to take in more mixture you can increase the displacement of the engine; or, force feed it with a positive pressure induction system; i.e. turbocharging or supercharging; or, improve the efficiency of the induction and exhaust systems; i.e porting, polishing, bigger valves ...



_________________
Skip Denton
'79 924 Sebring

[ This Message was edited by: 924_fan on 2001-09-17 00:25 ]

[AppleBit]

When you have higher compression you do need to richen the mixture. Don't and you have the possibility of burning out a piston.

- Jon


_________________
Classic British Sports Car Restoration v6 + v8 Engine Conversion Swaps

Porsche 924 Wide Body LS1 Corvette 500 Horsepower Engine

[larso]

Higher compression pistons and shaved heads/blocks also decrease your engine displacement. Somethign to think about.
But higher comp pistons can also help not just through compression, but by their shape, the flatter the better, (more force on a smaller surface area)

Compression is usually more effective than the displacement that you lose, but anyway, just remember that you should also up your octane and update your flow whenever u do compression. Remember that upping the octane level actually makes you lose performance if you do it too much, because the gas is not as reactive with mroe octane, rather it can stand higher temperatures and compressions so that you don't get pre-ignition, it does NOT help you get more explosion...it is similar to water injection...you lose some, and you have to gain by upping the boost. So don't go putting 115 octane in your 8.0 compression non-turbo car.

i think 931 pistons must suck eh, cuz they have that dish in them, they are no where near flat.

but the turbo makes up for it, blah, turbos.

[ricomartinez]

Displacement has nothing to do with compression ratio or combustion chamber volume. It is solely a function of bore and stroke. A 500cc single-cylinder engine is still a 500cc single-cylinder engine whether it has a 10-to-1 compression ratio or a 5-to-1 compression ratio.

[larso]

that's the on paper displacement

the REAL displacement is anything that is enclosed in the system.

[1987924S]

Displacement is figured out from bore x stroke based on a the stock pistons. As soon as you change out the pistons the only real way to measure the legitimant displacment is by measuring how much stuff is getting displaced in each combustion chamber x the number of chamber you've got.