USMCFieldMP

iTrader: (1)

LOL...

RooTBeeR

iTrader: (4)

Just a higher c/r will give you 5hp tops acording to that calc^^^

InfinityzeN

I think it is pretty close actually. Seems if I went from stock to 12:1 (and I could keep my car from blowing up... HEH!), I would go from about 251whp to 266whp. Normally the calculations are 2.5~3% for every 1 CR of change. The higher you go, the closer to 2.5 you get. Only time you'll see 3%+ is when your working with very low compression ratios, such as found in old cars. You ever see what happens when an old flathead is bumped to 9.8:1 CR? Beautiful. Averaged ~4.5% per CR.

bridfi

whoever made that up is a retard. i tried 155 at 10:1 and then at 12:1 it said ill have 165.

yeah f***in right.

i sure hope not. spending the $500 on taller pistons is going to get me 10 hp?

id rather stick with full bolt ons

Witt

I changed my static ratio in my LSJ only because the new cams brought effective compression down a bit so I wanted to make up for it. Thats the only time I ever increased static on any car.

InfinityzeN

Sorry bro, but it's the truth. Should have researched it. You would have seen that a 0.5 CR increase will only net you about a 1% power increase.

However, you might as well get the higher CR if you are getting custom made rods and pistons to allow you to hit higher rpms. The higher rpms will net you more power with the breathing work and cams.

And since you would need custom pistons to go with the longer rods, anything you would gain from the higher CR would basically be free power, since you needed to buy the custom pistons anyway.

bridfi

well at least i found out before i bought the parts.

i thought an increase in cr would make that hp jump. guess not.

true... so basically all the power ill be getting from the build is from the built top end, not the higher CR.

****, might as well go with a small turbo build....

Hahn RaceCraft

I'll add a few cents:

Shorter stroke engines are favored for high-RPM durability due to the reduced strain on rotating and reciprocating assemblies (cranks, rods, pistons). Yes, they produce less torque than their longer-stroke brethren, but the additional power cycles created by the higher RPM capability more than make up for it.

All else being equal, a given engine that has its stroke reduced will then receive longer connecting rods. Increase the stroke, and the rods get shorter, but something else also happens that increases stress...

When we increase stroke and use a shorter rod, the mean rod angle is increased. This is not a good thing, for this significantly increases wrist pin and piston skirt loading, and it magnifies strain on the rods themselves too. As such, rod angles are a big factor when designing an engine combination.

With any of these aspects, there are practical and physical limitations as well, so far as wrist pin diameter, piston ring packaging, internal engine block clearance for stroke and con rod changes...it's quite a set of factors, and this is why it's all best left up to professional designers and engine builders.

You want to build a good hi HP normally aspirated Ecotec? Destroke it to 2.0 liters and rev that puppy! The parts exist, and it's a proven combo.

I could not have said it better! Turbo engines are easy and affordable to build, especially when compared against high-strung, high-RPM normally aspirated engines with big cams, valves, porting, etc.

bridfi

yeah, i really didnt like the idea of increasing stroke and shortening rods, due to the rod angles being so harsh on cylinder walls and wrist pins. i might just keep stroke and rod length factory and throw on a small turbo with low cr pistons. or go taller pistons.

thanks guys

bridfi

i like the idea of better atomization and sweet sounding BOV, anyway...

RooTBeeR

iTrader: (4)

nice, another turbo 2.2 in SCE!

InfinityzeN

For street, yea I would say F/I is the way to go. A finicky high reving engine is fun at the track, but not something you want in a daily driven car.

My old Flathead is bored/stroked to 313cid, 10.1:1 CR, Edelbrock heads, full valve train w/ bigger valves, much more aggressive cams (They actually make power to 5.5k rpms! ), and a **** load of other minor tweaks. Specially on the oil and water pump. Of course, everything but the minor tweaks only cost me ~$3k in parts. Things are cheap for the flathead.

IonNinja

man this thread was ******* confusing...

first people are saying rod length doesn't effect stroke at all...how so? I'm still not picturing how two different rod lengths give a piston the same amount of travel???

then on page 3, a guy comes in saying to get longer rods, shorter piston height...nothing about the crank and nobody says ****. lol

I need some clarification here...

RooTBeeR

iTrader: (4)

Ok, rod length doesn't effect your stroke except for where it sits in the cylinder.
i.e. longer rod will make the piston sit higher in the cylinder, shorter rods will make the piston lower in the cylinder.

Where as if you were to make the crank arms longer that would make the distance that the piston has to travel longer, hence a longer stroke.

http://auto.howstuffworks.com/engine1.htm

Witt

The first part about rod length is correct, you can't change stroke by changing rod length. Its purely a function of the crank as others said.

What the guy was saying about the longer rods was to safely increase engine speed limits is to get longer rods and/or a shorter stroke, not the con rods are what actually are changing stroke. The shorter stroke will slow down piston speed and the longer rods will decrease the harsh angle at which they operate. He stated by changing rod length and piston pin height only, it will allow a higher engine speed as the angle of the con rod is different. This alone doesn't change stroke, but destroking also allows a higher engine speed which is why they go hand in hand.

tru2nrtt777

iTrader: (1)

I am no pro either but I have built a few engines in my time and you are exactly correct my good sir.
Correct, these are the effects of changing sizes from stock:
Crank= stroke/rod angle/compression ratio
Piston= compression ratio
Rods= compression ratio/where along the cylinder walls the piston will move
Haha, we all gotta start somewhere bro.
You wont spend $500 for 10hp but you will spend $3000 for 50? What kind of sence does that make? Also the calculator is assuming everything else stays stock. If you have been dyno'd with everything else making 230 hp then it will be more like a 20 hp change when you up the CR.
You may need this too grasshopper:
http://www.wallaceracing.com/max-rpm2.php

bridfi

how about this: im going to buy a SS/TC for another 10000 for that extra 110 hp.

and a turbo wouldnt give me 50, id shoot for 100.

RooTBeeR

iTrader: (4)

Even better, DO IT!

TVS_SS

now we just need to throw in, valvetrain stability, flame speed, location of peak pressure, Pressure differentials across valves, and how cylinder head flow bench numbers at 28" dont really mean anything..

then we'll start to have a good conversation!

Changing one thing on an engine doesnt "increase power significantly" Proper engine design requires more tradeoffs than i care to discuss..

InfinityzeN

All very important points, but most likely beyond most people here.

tru2nrtt777

iTrader: (1)

^^^ I have to agree there. Most experienced engine builders I know(redneck backyard mechanics who run drags and dirt track) dont even understand a sentence in TVS_SS's post.

bridfi

cool

but it was just a simple question. and i got my answer.

so /thread

ss/tc here i come

InfinityzeN

Hey bro, come on. If we end up having a discussion on the effects of varies changes to an engine, at the least it will proof informative to people who read it.

USMCFieldMP

iTrader: (1)

Why not just buy MY car... and beat the SS/TC? AND save $8000.

Or go one step further... buy my car AND the Hahn 20g kit/TVS/ZZP Twincharge and beat EVERYTHING... Muhahahaha... (well, not EVERYTHING...)

https://www.cobaltss.net/forums/complete-cars-101/fs-usmcfieldmps-vic-red-ss-sc-110757/