SPOOL Stage3 dyno stats!!!

[PhyschoMP3]

hey ben how much would JE charge for rods and pistons? like forged and dropped compression

 

[big_ben]

If it's just forged rods that are the same specs as the stock, they are around $1000 alone. The pistons are about the same and they can make them to any comp. ratio you want. If you just want to go cheaper, just get the forged rods that are the same specs as stock and forged 8:1 pistons. You could easily boost to 15psi or more with those.

 

[mushin25]

i have talked to je for a piston set it was like 680 dollars, but they needed a piston from the engine to make the piston.

 

[big_ben]

That's a pretty good deal! You can probably talk to Clint(mazdamastertech) and he may be able to get you a used piston to send them. That's a good price though. The rods will be more expensive though.

 

[Keith@FP]

Whoa whoa whoa!

Big_ben, you're wrong. Totally, utterly wrong.

The only way to increase the stroke is with the crank. The rods will NOT affect the stroke.

Look at it this way. The stroke is the difference between the upper limit of the piston's motion and the lower limit. What determines this? The crank - specifically, the offset of the rod bearing journals.

Shortening the rod will move the upper and lower limits down the same amount. This will lower the compression ratio, but the stroke is unchanged.

To lengthen (or shorten) the stroke, you need to change the crank. It can be done with an offset grind on a stock crank or with a totally new crank. Ideally, you should also change the pistons and rods to move the wrist pin up higher and maintain a decent rod ratio. But the crucial element is the crank.

Sory, Ben, but TK is right here. Whether the specs are appropriate is another matter and cannot be determined without some study. We actually cut a block in half to work out our Miata stroker setup.

Keith

 

[big_ben]

How would shortening the rods not increase the displacement? It would have to. I understand that "stroking" a motor includes regrinding the crank, but I don't understand why you say that shortening the pistons will not do the same thing.

 

[mushin25]

so is the tk kit any good? also i looked on the net and could not find anything really about tk, and what i did find very few people said anything bad.

 

[Keith@FP]

Displacement is the volume of the swept area of the cylinder. In other words, it's (bore/2)^2 x stroke x pi. Stroke is defined as the distance moved by the piston. You'll notice that the total volume of the combustion chamber is not involved. Shortening the rods will NOT affect the distance moved by the piston. The only way to change the displacement is to alter the throw of the crank or to enlarge the bore.

The compression ratio of the motor is defined as the volume of the cylinder with the piston at the bottom of its stroke over the volume of the cylinder with the piston at the top of its stroke. In this case, moving the piston further down will decrease the ratio. SO a shorter rod will drop the compression ratio but not affect the displacement of the motor at all. However, simply shortening the rod affects other geometries. It's best to alter the shape of the piston itself. Which is why rods are usually available in stock sizes while pistons come in different compression ratios.

In general, long stroke engines are torquier but less happy to rev.

Keith

 

[big_ben]

I get you now. You can increase the volume that each cylinder can hold, but the goal is to displace that volume. I get it now.

Now, another question. if you did have shorter rods, couldn't you just boost the piss out of it. Like 20psi and that would kinda be like replacing it's compression. It would probably rev as fast as a motorcycle though. I see how it could greatly alter things, but why couldn't you just run really high boost to fill the added volume inside the cylinder. Would this not result in the desired gains?

 

[Keith@FP]

Shorter rods will make the rod ratio worse. The engine will be less eager to rev. A far better way to increase compression is with pistons. I'm sure I already wrote this.

Lower compression will allow you to run more boost, and make more absolute power (all else being equal). However, it will come at the expense of spoolup and off-boost response.

Keith

 

[twilightprotege]

keith, yeah you got in before me. i was going to explain what stroking an engine is.

imo, the best way to "stroke" our engine to a larger displacement is by boring the cylinders. this was the pistons are not moving as far as they would if the crank was stroked....in other words, the engine will be rev happier. the easiest way to prove this is a comparison between our engine and say a honda b16a etc. our bore is much less than stroke. the b16a is the opposite. the advantage of a larger bore is more torque, the advantage of a larger stroke is more horsepower (in a vauge manner of speaking). the optimum for bore and stroke is for them to be equal...but then again, what's optimum for me mightnt be optimum for you.

has anyone bored the cylinders out yet? i very much doubt this, but worth a shot.

keith, how have miata's handled boring???

later.

 

[PhyschoMP3]

I think linuxracer has his bored out

 

[melicha8]

Remember there are already Rods available from Pauter for 720.00. They are a company your could actually trust as opposed to Tomas Knight

 

[Keith@FP]

imo, the best way to "stroke" our engine to a larger displacement is by boring the cylinders.

It's not called "stroking" at that point. It's called "boring". It'll increase displacement, and it's a whole lot cheaper since you only need to change pistons.

Miatas deal with it well, but in that case there's not much extra room in the block. The 1600 will only go to 1680 or so (that's my engine) and the 1800 to about 1880. If you go too far, you get weak cylinder walls. I don't know what the limit of the FS would be.

Keith

 

[PinoyNinja]

Now for the quote of the day....."It's still a neon."

perfect, absolutely perfect. I was laughing for like 5 minutes

 

[Kooldino]

perfect, absolutely perfect. I was laughing for like 5 minutes

???


Anyway, now I'm confused...
Keith said a longer stroke is torquier but has less rev, and twilight seems to be saying the opposite?

 

[PinoyNinja]

Sorry about the confusion, that was abot the neon

 

[70]

I'm confused because I thought the Thomas Knight convetion was over on this board.

There are a number of people saying that his stuff is less than quality, on this board, on the other board, on a number of Probe forums. I'm surprised people actually want to try his stuff out, again.

 

[twilightprotege]

hey.

just to clarrify (i think i was in a rush whey i typed my last lil blab....i did get it around the wrong way...sorry)

a larger bore give allows the engine to rev move

a larger stroke allows the engine to make more torque

later

 

[Keith@FP]

Actually, a bit more clarification. An engine that has a larger bore than stroke (oversquare) will tend to produce more power and less torque than one that is undersquare - ie, the stroke is longer than the bore.

The FS has a bore of 83mm and a stroke of 92.

However, simply boring out the engine will not make the engine rev more easily. It'll simply give you more power and torque.

Keith