FYI: How Bore & Stroke affect Cubic Inches

[Magnus]

Because of the recent bore posts, I did some math over the weekend. This info will be put up in the tech database soon.

Stock:
Bore: 3.800 (in)
Stroke: 3.400 (in)
CI: 231.4

If the stroke is kept at 3.400 and the bore is changed:
3.810 232.6
3.820 233.8 (Max safe bore)
3.830 235.0 (Pushing it)
3.840 236.3 (Fogeddaboutit)

If the bore is kept at 3.800 and the stroke is changed:
3.450 234.8
3.500 238.2
3.550 241.6
3.600 245.0
3.650 248.4
3.700 251.8
3.750 255.2
3.800 258.6

I believe 1ci increase on our motor to be worth ~1rwtq.

So you see, boring isn't worth much at all.. the $/HP ratio is just outrageous.

I'd really like to have a 3.8 stroker though!!! :eek:

[jmorgan]

you would need a custom crank to get it stroked correct? it would change the compression negatively so you would have to get longer rods no? i dont know anything about boreing and stroking anyone with info would help.

[ March 04, 2002: Message edited by: Jason Morgan ]</p>

[Magnus]

Yeup.

Stroker kits include bigger cranks (Radius is larger) and shorter piston rods.

A bored motor can usually handle more power than a stroker motor.

With a stroker motor the angles at which the piston rods connect to the piston is much greater and there is more "swing"..

This topic was discussed on ls1tech.com and they can shed a LOT more light on the subject than I can.. if you are interested in some real good tech info, I recomend searching over there.

I read ls1tech.com daily.

[jmorgan]

whats the formula to figure the ci and what is the formula to convert it to Liters like what would a 250ci engin = in liters

[HAZ-Matt]

1L = (1000cm^3)(0.3937in / 1cm)^3 = 61.02337795in^3

[jmorgan]

so 250ci would be a little over 4 L

[TurboProject]

Isn't displacement just the volume of a cylinder times the number of cylinders? The formula is v=PI*r^2*h so divide the bore by 2 which is the radius and square it and multiply by the stroke which is the the height, then multiply by PI. Just making sure if this is true.

[navyblue2000]

what kind of numbers, power wise would be involved in a boring out like that? is there a formula, or is it just based on hp/cu in?

[camaro_zach]

ya, the fomula is dont do it. =) lol, good info mangus.

[DominusEtDeusNatus]

Good job Keith! Once again you did your homework.

[navyblue2000]

<blockquote>quote:</font><hr>Originally posted by camaro_zach:
ya, the fomula is dont do it. =) lol, good info mangus.<hr></blockquote>
:rolleyes:
um...yeah...i was talking about the stroking, no doubt. seems a little more worth it than boring.

[Patrick Javert]

Boring out your engine gives you good gains everywhere in the powerband. Stroking, however, is rpm dependent. If you are looking at running a high rpm engine, short stroke and long rods are the way to go, if you want more torque down low, a stroker is better with more stroke/less rod. The 2 limiters on stroking is rod ratio and stroke length. lower rod ratio means more stress on the rod and requires beefier or titanium/forged/billet rods or running a lower rpm range engine. The longer the stroke, the more worrys you will have about piston speed. If the piston goes too fast up and down, the wrist pins will break and the piston will blow up or down the cylinder, ruining your engine. A good stroker pkg. for our cars based on 3.4 stroke, 5.750 rod length is 3.55 stroke and 5.6 rod length which keeps the rod ratio around 1.5:1 whick is good for our 6000 rpm limiter. If I knew what the piston compression height was or the deck height of the series 2 block, I could work that in too to get more stroke and less rod angularity. As for bore, If you listen to magnus and bore out .02 over, you can get larger valves in your heads to help with breathing issues.

[ March 09, 2002: Message edited by: Patrick Javert ]</p>

[bluecmaro96]

It must be slot different for the v8 when its bored. Over on the other site some guys seems to think the first .010 is good for 5 ci, go over there and read it

[Magnus]

The bigger the motor, the more a .010" bore will affect CI.

With our small V6 231 CI motors, it doesn't do much.

[Dominic]

At stock 0.82VE, +1ci = +1hp almost exactly

--PSCALC