Godspeed

Just playing around with some numbers:

Stock LS1

3.625" stroke x 3.900" bore = 346 cid
bore/stroke ratio = 1.076

382 LS1

3.625" stroke x 4.100" bore = 382 cid
bore/stroke ratio = 1.131

4.000" stroke x 3.900" bore = 382 cid
bore/stroke ratio = 0.975


422 LS1

4.000" stroke x 4.100" bore = 422 cid
bore/stroke ratio = 1.025

4.125" stroke x 4.035" bore = 422 cid
bore/stroke ratio = 0.978

427 LS1

4.000" stroke x 4.125" bore = 427 cid
bore/stroke ratio = 1.031

4.125" stroke x 4.060" bore = 427 cid
bore/stroke ratio = 0.984

432 LS1

4.125" stroke x 4.080" bore = 432 CID
bore/stroke ratio = 0.989

Anyone care to comment on the bore to stroke ratios of these different combinations? I have read that "Theoretically, the larger the Bore-Stroke ratio, the higher the engine will RPM."

[ November 27, 2001: Message edited by: Godspeed ]</p>

Colonel

I like the higher ratios for higher revving engines. There's too much side loading with a super long stroke. There is a point of diminishing returns HP wise when going up on stroke. That point gets lower and lower the higher RPM you're talking about trying to run.

(This will be asked so...) Sideloading-think of it as the rod trying to push and pull the piston into the sides of the cylinder...most evident when the crank arm is at the 3 o'clock and 9 o'clock positions. The longer the stroke the more angle the rod has at any position other than when the crank is at 12 o'clock and 6 o'clock and the more this power robbing and parts wearing sideloading takes place.

[ November 27, 2001: Message edited by: Colonel ]</p>

2quick4u

The engine with the higher bore/stroke ratio will rev higher because it has a smaller stroke. A smaller stroke = less piston speed for any given rpm. Less piston speed means less crankcase windage losses, less stress on recipricating components, and less piston ring friction which increases as the square of rpm. The engine with the larger bore/stroke ratio also has the larger bore which is good to unshroud the valves more, or you can run larger valves. You can actually destroke an engine and it will make more peak hp, even with less displacement, but you will take a big loss in low rpm torque AND you will have to rev it much higher to see the extra peak hp.

The engine with the higher bore/stroke ratio will always make more peak hp, if you want to rev it high enough. That means it makes a great race engine but not necessarily a good street engine. On the street, you will miss the low rpm torque production (throttle response) of the larger stroke engine.

In the end you just have to decide what rpm you want your peak hp and peak TQ at and then choose the best stroke to do that.

Confuscious say: 'For street car, must have balance' <img src="images/icons/wink.gif" border="0">

[ November 27, 2001: Message edited by: 2quick4u ]</p>

2quick4u

[quote]Originally posted by Crazyquik:
<strong>
Tangent - do you think the LS series of motors will ever be used in Winston Cup? Maybe in 4 or 5 years to replace the SB2? I guess the C5R block would be a good place to start if you were going to build a 358 ci Cup car motor.

J.</strong><hr></blockquote>

It's a distinct possibility, since the ASA series uses the LS1. But since Winston Cup engines are heavily modified, they will probably stick with the Gen I SBC platform to keep engine costs down. An LS1 based engine with the same type mods as the Winston Cup SB2.2 would probably cost at least twice as much.

In ASA the racers use basically a factory modded and blueprinted LS1 that is given to them by ASA and they are not allowed to modify it at all. This turns out to be cheaper than each team building their own heavily modifed V6s like they used to do. If NASCAR ever decides to use this same approach, then it would cut down the cost of racing as well as the speed of the cars.

QUASAR

iTrader: (6)

[quote]Originally posted by Crazyquik:
DZ302 - 4"x3" - 1.34 and we know how those lived at high rpms. Also take a LS1 block with a 4.10" bore and the crank from a 4.8 pickup (3.268") and you'd have a 345.2 cube LS1 with a 1.254 bore/stroke ratio.

<hr></blockquote>

Interesting. What kinds of RPM's would that be "safely" capable of? (with the proper valvetrain of course). Whatever the RPM's that would make a awsome high revving powerplant for a road course race car.

<img src="images/icons/smile.gif" border="0">

[ November 27, 2001: Message edited by: RED QUASAR ]</p>

2quick4u

[quote]Originally posted by Crazyquik:
<strong>DZ302 - 4"x3" - 1.34 and we know how those lived at high rpms. Also take a LS1 block with a 4.10" bore and the crank from a 4.8 pickup (3.268") and you'd have a 345.2 cube LS1 with a 1.254 bore/stroke ratio.

</strong><hr></blockquote>

Speaking of engines with high bore/stroke ratios, an old big block comes to mind. Ironically enough, it's the MkI 409 Chevy. A 4.3125" bore x 3.5" stroke gives a b/s ratio of 1.23. Another high b/s ratio big block was the Chevy Can Am series 430 cid engine. It had a 4.44" bore x 3.47" stroke which gave a 1.28 b/s ratio. Smokey Yunick liked to use the 3.47" cranks in his 427 NASCAR engines.

A destroked 502 with a 409 size 3.5" stroke would make a killer 445 cid racing engine IMO. 4.5" bore/3.5" stroke gives a b/s ratio of 1.29.

[ November 27, 2001: Message edited by: 2quick4u ]</p>

Crazyquik

Those old 409s didn't have heads to support it though (or did they). Weren't the first 409s based on truck engines with a W shape valve layout?

Offset grinding the stock 4.8 crank and putting it in a 4.10 bore would give you 355, 4.105 with the 4.8 crank would give an even 346

Godspeed

[quote]DZ302 - 4"x3" - 1.34 and we know how those lived at high rpms. Also take a LS1 block with a 4.10" bore and the crank from a 4.8 pickup (3.268") and you'd have a 345.2 cube LS1 with a 1.254 bore/stroke ratio. <hr></blockquote>

Actually someone has built a destroked 5.0l/302 LS1 built with a 4.000" bore and 3.000" stroke.

http://www.camaroz28.com/articles/302camaro/index.shtml

I have speculated in the past that a low compression version of that motor would be the ultimate high boost LS1/LS6 setup.


-Jeremy

Crazyquik

[quote]Originally posted by RED QUASAR:
What kinds of RPM's would that be "safely" capable of? (with the proper valvetrain of course).<hr></blockquote>

No clue, but you'd need a sheetmetal intake or a heavily worked over cast alum intake to make it work. You'd kill your torque building this motor, which is sometimes an advantage in road racing. Back in the early 90s the IMSA Oldmobiles used big blocks, had to baby the car out of the turns. With the Aurora V8 they ran the rev limiter up to 10k, had almost the same hp, less torque and could come off the corners full bore, lap times fell <img src="images/icons/smile.gif" border="0">

Crazyquik

Yeah I think Westec built that motor, solid roller, made like 37X rwhp? PSJ has driven it.

2quick4u

[quote]Originally posted by Crazyquik:
<strong>Those old 409s didn't have heads to support it though (or did they). Weren't the first 409s based on truck engines with a W shape valve layout?</strong><hr></blockquote>

Yeah those old MkI 409s with the 'W' heads didn't have enough head to take good advantage of the good b/s ratio unfortunately. That's why Chevy came out with the MkII Mystery Engine that ran at Daytona in '63 and later evolved into the MkIV Chevy bigblock after some design changes to make the engine easier and less costly to manufacture.

The original 348 cid 'W' engines were designed for both cars and trucks and were used in both cars and trucks. Back in '56, due to the available casting technology of the time, GM engineers thought that the small block couldn't go any bigger than 300 cubes and they knew they were going to need more displacement than this for the new line of much heavier Chevys coming in '58 and '59.

The unique design of a 74 deg. deck and having the combustion chambers in the block instead of the head was actually copied from a '50s Mercedes Benz 6 cylinder engine.

SIR

How about the 377!!! That thing is a screamer!!!
4.155 x 3.48!! b/s 1.19!!!
Or how about the ole 327 ...b/s 1.23 on a 4.0 x 3.25!!!

a few ways to get close to 377 on a ls1.... 4.08 x 3.625 = 379 and b/s 1.12

Crazyquik

[quote]Originally posted by 2quick4u:
<strong>

That's why Chevy came out with the MkII Mystery Engine that ran at Daytona in '63 and later evolved into the MkIV Chevy bigblock after some design changes to make the engine easier and less costly to manufacture.

</strong><hr></blockquote>

What was the MkIII, was there one? What about the 377 dual plug that ran in the Gulstrand Corvettes? That was a big block based engine wasn't it?

Chris Spiess

Opinions on how much stroke is too much.

2quick4u

[quote]Originally posted by Crazyquik:
<strong>

What was the MkIII, was there one? What about the 377 dual plug that ran in the Gulstrand Corvettes? That was a big block based engine wasn't it?</strong><hr></blockquote>

No, the 377 engine for the '63 Grand Sport Corvettes was to be a tricked out all aluminum version of the small block (I think it was supposed to use a 4.0" bore and a 3.75" stroke, 327 block with 400 size stroker crank). Zora was against putting big blocks in the 'vette at that time because the effect the extra weight would have on the handling capabilities of the car. When GM pulled the plug on factory racing in '63 and killed the GS program, the engine became a lot less exotic. No special two plug heads and standard rochester FI unit or 4 weber carbs on a cross ram intake was used. I think TRACO may have been contracted to make the engines. These engines were also run in the ill-fated '64 Bill Thomas Cheetah.


The MkIII big block was never produced. It was a very large bore Packard design bought by GM when Packard went out of business.

[ November 27, 2001: Message edited by: 2quick4u ]</p>

2quick4u

[quote]Originally posted by spiesscj:
<strong>Opinions on how much stroke is too much.</strong><hr></blockquote>

Depends on where you want your torque and hp peaks and what you want your max useable rpm to be.

I personally wouldn't feel comfortable running anything less than 1:1 b/s ratio on a street/strip car though.

[ November 27, 2001: Message edited by: 2quick4u ]</p>

kewlbrz

[quote]Originally posted by SIR:
<strong>How about the 377!!! That thing is a screamer!!!
4.155 x 3.48!! b/s 1.19!!!
Or how about the ole 327 ...b/s 1.23 on a 4.0 x 3.25!!!

a few ways to get close to 377 on a ls1.... 4.08 x 3.625 = 379 and b/s 1.12</strong><hr></blockquote>

Hell Yes <img src="images/icons/smile.gif" border="0"> I run this motor in my 79 vette with 4speed and 4.10:1 gears. Its a beast.

I beleive Zora ran the 377 4.115 x 3.48 in the CERV II in the early 60's. That sucker was all wheel drive and ran 2.6 or so 0-60 times.

Terry Burger

iTrader: (4)

What's a 4.125" stroke with a 4.125" bore?

2quick4u

One that you left out that I am sure Tony would like to show is:

382 'all-bore' (4.1"x3.62") = 1.13 b/s ratio <img src="images/icons/smile.gif" border="0">

382 'stroker' (3.9"x4.00") = .975 b/s ratio

Gen I/II SBC 350 (4.0"x3.48") = 1.15 b/s ratio

Gen I/II SBC 383 (4.030"x3.75") = 1.075 b/s ratio

[ November 27, 2001: Message edited by: 2quick4u ]</p>

2quick4u

[quote]Originally posted by Terry Burger:
<strong>What's a 4.125" stroke with a 4.125" bore?</strong><hr></blockquote>

A 441 cid big *** motor.