Boring, stroking and more.

[Metapharstic]

Also that last part is going to be deleted b/c it's very frowned upon if you have yet to discover that

Which part? The question w/ compression of a 5.0L V8 vs a 2.0/2.4 420A? Or w/ the power steering?

Right... stroker kits mean the piston is moving a greater distance per engine revolution. When you break that down, it means each piston is moving significantly faster than in a non-stroked engine. That increased piston speed prevents you from revving really high, because the pistons would just be moving too fast. That's another reason I stayed away from stroker kits... like I said before, I think top end power is really important for a FWD car, and a stroker kit bascially limits how much power you can make up there. I'd rather take top end power over bottom end power any day.

Ahh, alright. I understand. Basically, increasing engine displacement lowers your powerband? Or, well, dosen't lower it, but sacrifices power you're making in the top of your powerband to make more power on the bottom?

So, stroke kits increase low end power, but takes away from high end power? Would that be the same if you swaped for a 2.4 cloud block? How much would an extra half liter of displacement actually effect your top end power? Also, if our governer/rev limiter kicks in at like 7200RPM stock, what would limit you from still taking it up to 7200RPM with a stroke kit/bigger block?

Also, I understand the higher you are in your powerband, the more power you're making, but if we're running with boost, wouldn't you want more power in your low-end. At least, like, considering turbo-lag and the limited amount of torque our engines make unmodified?

And about the compression... most people use low compression (8.8:1 or so) for turbocharged cars. It all has to do with avoiding knock. High compression ratios (even up to 10.5:1) provide more power, and the can be used with boosted cars, but you're going to need to run something like methanol or water injection to prevent knock when you're under boost. Beyond that, you'll have to rely on good tuning...

I thought all "knock" was, was your rod bearings/bolt going out, or that "knocks" usually develop where the rods/crankshaft meet. Wouldn't you be fine as long as you paid attention/strengthened/replaced the rod bearings/bolts? Or is the idea not to have to touch the bottom of the block? Wouldnt it be super easy to work on the bottom of the block just by removing the oil pan?

Brian (DR1665) always says every point of compression ratio (i.e. 8.5:1 to 9.5:1) is worth 4% of horsepower. When choosing your compression ratio, decide whether or not just 4% worth of horsepower is worth having to constantly struggle with knock.

So whats the most you can tweak your compression? 7.5:1 to 11.5:1? Whats the :1 mean? If something has a compression ratio of 8.5:1 does that mean that when/before the gas/air combusts inside the piston, its 8.5 times more compressed then it would be naturally?

 

[ninjai_ruken]

I cant read all of this I have to get to work, so if this has been said before im sorry but Superchargers take HP to make Hp. Having a Turbo set up is free HP gains...gotta go laters guys

 

[Locke]

knock (as we refer to it) is generally the sound of piston slap or counterforce caused by detonation.

increasing displacement isnt the issue, rather the fact that stroking a motor increases the throw on the crank. longer throw = more leverage = more torque. stroke is the total travel of the piston, from BDC to TDC, and is throw*2. longer throw also = higher piston speed = lower limit.

if you did the 2.4 swap, you will still cut at 7200 with the stock ecu. you would have to just not bring it up that high.. with MS and such you can adjust the limiter. the only thing that would limit you to revving it to 7200 would be the weight and strength of the rods/pistons/pins/bolts.

the colon ) is the comparator in a ratio, and is read as "to", "eight and a half to one". you basically got it though. 8.5:1 will pack the air/fuel charge down to 8.5 times as small as it was when it was drawn in. like crushing a can to an eighth its size.

It would be well to get your physics book out, as other than metallurgy, engine building is pretty much physics.

 

[delta448]

Ahh, alright. I understand. Basically, increasing engine displacement lowers your powerband? Or, well, dosen't lower it, but sacrifices power you're making in the top of your powerband to make more power on the bottom?

Increasing stroke lowers the safe rev limit, which is not the same as your powerband. The speed of the pistons and the forces that are now loaded more to the sides of the cylinder will decrease engine longevity when you push your engine hard. However, a stroker crank gives more torque throughout the rev range because there is an increased lever advantage. Like the difference using a cheater pipe on a ratchet handle makes.

So, stroke kits increase low end power, but takes away from high end power?

No. They increase power everywhere, but you can't safely rev them as high.

Would that be the same if you swaped for a 2.4 cloud block? How much would an extra half liter of displacement actually effect your top end power? Also, if our governer/rev limiter kicks in at like 7200RPM stock, what would limit you from still taking it up to 7200RPM with a stroke kit/bigger block?

Not sure what you mean by "cloud" block, but expect a 2.4 to spool a similar sized turbo 250-500 rpms quicker than a 2.0, and have a decent amount more power overall, both on and off of boost. A 2.4 can be rev'd to 7200, but I wouldn't make it a daily occurance.

Also, I understand the higher you are in your powerband, the more power you're making, but if we're running with boost, wouldn't you want more power in your low-end. At least, like, considering turbo-lag and the limited amount of torque our engines make unmodified?

That is one of the good things about bigger displacement (and also with a little higher compression), you'll have much better power at lower rpms.

I thought all "knock" was, was your rod bearings/bolt going out, or that "knocks" usually develop where the rods/crankshaft meet. Wouldn't you be fine as long as you paid attention/strengthened/replaced the rod bearings/bolts? Or is the idea not to have to touch the bottom of the block? Wouldnt it be super easy to work on the bottom of the block just by removing the oil pan?

Knock is detonation / pre-ignition or basically any type of irregular charge burning. If the charge ignites before the sparkplug fires, the result is an explosion and not a burning of the charge. In simpler terms, knock breaks shit.

So whats the most you can tweak your compression? 7.5:1 to 11.5:1? Whats the :1 mean? If something has a compression ratio of 8.5:1 does that mean that when/before the gas/air combusts inside the piston, its 8.5 times more compressed then it would be naturally?

Yes, you've got it right, basically 8.5:1 means 8.5 units of volume are compressed into the space usually occupied by 1 unit of volume. It is expressed as a ratio, hence the colon. I've seen as much as 10:1 compression on a 30+ psi boosted engine, built by a professional racer. I could never imagine attempting to tune that. I wouldn't go any higher than about 9.2:1, and even that could be challenging for an inexperienced tuner. Simply speaking, there is a safe limit to the heat level of the fuel/air charge. If you increase CR, you need to decrease boost level to avoid detonation, higher charge pressures = more heat.

 

[Locke]

im not sure if this has been pointed out or not yet (can't read all this again!) and im not sure if you know already.

if you break a rod/bolt/pin whatever, the results are usually catastrophic, and if your lucky you can snap a picture of the fresh new window in the side of your block. then there is the drivetrain shock.

i love it when internals end up on the ground. the best way to blow an engine. my buddies stock sebring knocked a good 5x5" chuck out the side of his engine, while doing 85 on the highway. the resulting shock obliterated one of his axles and the side of his differential. he said it happened like this "tick, tick, knock, POP"

anyways, not to scare you, but this is why knock is bad. extremely high piston speeds can lead to the same thing.

(BTW this is worst case)

so be smart with your goals. 11.5:1 compression and 30lbs of boost, on a stroked engine running pump gas and spinning at 7200rpm probably isnt a good idea, even with forged internals. though it would be fun to see... from a distance

 

[VelocitàPaola]

That is one of the good things about bigger displacement (and also with a little higher compression), you'll have much better power at lower rpms.

Be careful what you say in these forums... your car is AWD, ours aren't. What I've been saying all along is that increased torque in the bottom end isn't always the best idea for FWD cars since traction is an issue. Obviously, you wouldn't have to worry about that.

 

[delta448]

Be careful what you say in these forums... your car is AWD, our aren't. What I've been saying all along is that increased torque in the bottom end isn't always the best idea for FWD cars since traction is an issue. Obviously, you wouldn't have the worry about that.

Very true. Thanks Paul. I apologize if I misled anyone.

 

[bullettdsm]

Ah...so much nicer of a read. Excellent info also.

MB

 

[evilredGS]

I used to work with a guy that drove an automatic talon TSI pushing 30lbs of boost that had a laminated track slip with 10.9 for the quarter-mile.

I'm glad there is hope for my automatic GS =)

 

[fullmoon]

You can get approx 200 whp w/o a turbo but you will not have any top end and it will cost you $14,000!
You'll get the hole shot but down the end of he track you'll cry, I know a guy who did it and he wishes he didf not wast his money.