And Penny just keeps on changing...

[Vegas69]

Definitely over square...been through this whole analysis.

[Steve1968LS2]

Originally Posted by Vegas69

Definitely over square...been through this whole analysis.

Over square is where the bore is larger than the stroke

An engine is described as oversquare or short-stroke if its cylinders have a greater bore diameter than its stroke length - giving a ratio value of greater than 1:1.

For example an engine which has 100 millimetres (3.94 in) bore, and 80 millimetres (3.15 in) stroke has a bore/stroke value of:

100 mm / 80 mm = 1.25:1

Since my bore is 4.165 and my stroke is 4.250 the engine is really Under Square.

An engine is described as undersquare or long-stroke if its cylinders have a smaller bore (width, diameter) than its stroke (length of piston travel) - giving a ratio value of less than 1:1.

For example an engine which has 90 millimetres (3.54 in) bore, and 120 millimetres (4.72 in) stroke has a bore/stroke value of:

90 mm / 120 mm = 0.75:1

That's from Wikipedia.. but I double checked a few places. it's under square.

But these days that's pretty common. Take the Tall Deck RHS block. The max bore is still 4.165 but you can go 4.600 on the stroke and that's WAY under square.

I'm comfortable with the .977 ratio of my bore/stroke ..

Will be interesting to see how the two builds play out and how they compare to the 1.00 square 440 I just finished.

And keep in mind.. I'm NOT and engine building expert.. I just know lots of smart people to brain pick.

[DFRESH]

Steve, not to hijack the thread, how is the trackrat project coming along? If you keep "borrowing" the parts from it to "try" out on BP we may never see the thing

You've convinced me that if you are going to buck up for a radiator, that going the AutoRad setup is the way to go--I can't believe the amount of surface area available is so large for the radiator---they are spendy, but worth it now in my opinion.

Doug

[Vegas69]

Sorry Steve, it's late and I've had a few drinks. I meant under square. It's unusual to see an undersquare engine. Very few factory engines were built this way. The slant 6 is one bullet proof instance. I'm interested to see how it works out for you.

[Steve1968LS2]

Originally Posted by DFRESH

Steve, not to hijack the thread, how is the trackrat project coming along? If you keep "borrowing" the parts from it to "try" out on BP we may never see the thing

You've convinced me that if you are going to buck up for a radiator, that going the AutoRad setup is the way to go--I can't believe the amount of surface area available is so large for the radiator---they are spendy, but worth it now in my opinion.

Doug

What happened to Track Rat is that BOS had it ready for paint and then I went and had the panels stretched.. now it needs to be readied for paint AGAIN.. BOS is swampped right now so we are putting off that body work until after the Del Mar show. Then we will dive back in. Should go fast since we have the drivetrain, suspension, and brakes all ready to go.

I just borrowed the CF panels. The radiator was taken from the TR project for Penny since it's a bit more expensive and more fitting BP than TR whis is SUPPOSED to be a lower $$$ project.

As for the AutoRad deal.. Yea, it's a bit more $$ but that's because of the core support. The radiator itself is priced pretty good. I had a friend get one because if figured the core support was cheaper than having hours spent making a stock one look good (welding up holes, smoothing out).

The bodywork on TR has taken a lot longer than expected.. but that's what happens and I don't want to just slap the car together.

[Steve1968LS2]

Originally Posted by Vegas69

Sorry Steve, it's late and I've had a few drinks. I meant under square. It's unusual to see an undersquare engine. Very few factory engines were built this way. The slant 6 is one bullet proof instance. I'm interested to see how it works out for you.

Hey, send a few drinks over here! lol

I always mix up high and low impedence in regards to injectors..

Under Square is becomming more common, especially in LS applications where crazy long strokes are. Hell, Lunati just came out with a 4.625 stroke crank.. Obviously that's going to be WAY bigger than any possible bore size.

So I have three engines going now.. an Over Square (1.017).. and Under Square (0.977) and a Square 1.00 -- should be interesting to compare.

On the one for Penny I feel the ratio of .977 is close enough to true square as not to be an issue.

[GregWeld]

Not to jack the thread -- but in 140 characters or less.... what is the advantage in a motor that is over sq vs under??

I once read an article where they built two motors to do this comparo... big bore short stroke - and same disp with longer stroke. If I remember right - they made the same power = just at different RPMS... and the conclusion was inconclusive.

[ohcbird]

Greg-
It will depend on the breathing characteristics of the engine. The better the heads / chamber / cam are, the easier it is to go under-square.

The easy answer is that that fast acceleration & decelration (for a given RPM) of the piston will help produce more power across the band. The hard part is getting the combo right...but LS engines are almost too easy now.

Todd- Like Steve said, there are lots of US engines being produce now, especially inline engines. I know it sounds counterintuitive, but they are actually easier to produce and balance as well.

Back to your regularly scheduled Penny update...

[Vegas69]

Normally it's more low end torque and slightly less high end horsepower.

[GregWeld]

Nowhere in Steve's math did he mention ROD RATIO.... and I always thought that this was important. I've actually been thinking of de-stroking the 427 because it has such "bad" rod ratio (4.125 bore - 4.00 stroke - 6" rod)

Is this no longer an issue with the taller decks of the LSx ?

Steve --- LOVE the updates -- like Eric said - it's fun to live vicariously.