Bore vs stroke

I did a search and didn't see anything. What's better big bore short stroke or the opposite? Why?

Big bore short stroke === rpm

Long stroke small bore === bottom end power

I love my big bore short stroke combos just my driving style  ( I love to rpm a engine )

Big bore + big stroke is more better......

Forgot to mention its for twin turbos.

It's a relative and depends on the goal and what parts you have to use.

This is where you get in a lot of arguments with people. The 526 hemi guys run 4.5" stroke and run over 10,000 rpm all day. Most BBF engines can't rpm like that and make the valve train live.

In the twin turbo world, I'm going to to go out on a limb and possibly upset some people but... It doesn't really matter. I like bigger bore due to getting the biggest darn valve I can get in an engine. Lol

whatbumper wrote:This is where you get in a lot of arguments with people.  The 526 hemi guys run 4.5" stroke and run over 10,000 rpm all day.  Most BBF engines can't rpm like that and make the valve train live.

In the twin turbo world, I'm going to to go out on a limb and possibly upset some people but...  It doesn't really matter.  I like bigger bore due to getting the biggest darn valve I can get in an engine. Lol

When dealing with twin turbos, wouldn't the bore/stroke combination basically just determine what rpm it will need to turn to max out the turbos?

Hardy wrote:

whatbumper wrote:This is where you get in a lot of arguments with people.  The 526 hemi guys run 4.5" stroke and run over 10,000 rpm all day.  Most BBF engines can't rpm like that and make the valve train live.

In the twin turbo world, I'm going to to go out on a limb and possibly upset some people but...  It doesn't really matter.  I like bigger bore due to getting the biggest darn valve I can get in an engine. Lol

When dealing with twin turbos, wouldn't the bore/stroke combination basically just determine what rpm it will need to turn to max out the turbos?

Yes and no. You can basically determine that through camshaft and turbo choices.

i thought I read somewhere with a big bore the flame travel is to long and it has a better chance of melting Pistons.

The spark plug's location in the chamber would matter a lot.

On a boosted application, the larger bore REALLY helps to un-shroud the valve and get air in the cylinder.
A long stroke crank is not necessarily needed,....as the turbo(s) will do the work to make the torque.

Naturally aspirated I would agree with the valve unshrouding theory but with boost who cares. You are feeding more in the than it'll take most likely anyway.

Keep plenty between the cylinders, plenty of meat between the valves. Run the best piston you can get, with the best crank you can afford. Rod length doesn't matter much either on this application except to make everything fit. Head flow is huge on the exhaust and makes some difference on the intake. The cam is crucial. Most people put waaaay too much duration in these motors with too narrow of centerline and way under lifted. And most are under compressioned. Even on gas. Keep a lot of quench in the motors too and it'll help with burn rate and keeping the cylinders alive.

whatbumper wrote:

Hardy wrote:

whatbumper wrote:This is where you get in a lot of arguments with people.  The 526 hemi guys run 4.5" stroke and run over 10,000 rpm all day.  Most BBF engines can't rpm like that and make the valve train live.

In the twin turbo world, I'm going to to go out on a limb and possibly upset some people but...  It doesn't really matter.  I like bigger bore due to getting the biggest darn valve I can get in an engine. Lol

When dealing with twin turbos, wouldn't the bore/stroke combination basically just determine what rpm it will need to turn to max out the turbos?

Yes and no.  You can basically determine that through camshaft and turbo choices.

Displacement is everything, camshafts and turbos are secondary.

Great info guys! Thanks! I'm planning on a premium block, Bryant crank,Oliver rods. Not sure on the heads compression or even what cubic inch to make it. I would like to make around 2,000 hp.

What type of fuel do you plan on running this combo on? Gas, Alcohol, Methanol, ?

jason wrote:Great info guys! Thanks! I'm planning on a premium block, Bryant crank,Oliver rods. Not sure on the heads compression or even what cubic inch to make it. I would like to make around 2,000 hp.

With good parts, you can make 2000 at 460 inches!!

I have a 4.5 stroke, 4.600 bore. 598". I have no problems running over 9000 rpm at 30+ #'s of boost, with twin 88's. My valve train took some time to get right, but now it's all good.

Chappy

I dont mean to highjack the thread, but I am getting ready to build a new engine for my '91 F350. I am thinking of using a Turbo and going small bore long stroke. Now this is a every day truck. It sees alot of High Way use. I want the duel milage to be close to or around 20mpg. My cruise rpm is around 2K. It needs to make is power there or it would be a waste of effort and money. For eveyday use what would be max compression ratio, also what size turbo should be used.?

JR Performance Motorsport wrote:I dont mean to highjack the thread, but I am getting ready to build a new engine for my '91 F350. I am thinking of using a Turbo and going small bore long stroke. Now this is a every day truck. It sees alot of High Way use. I want the duel milage to be close to or around 20mpg. My cruise rpm is around 2K. It needs to make is power there or it would be a waste of effort and money. For eveyday use what would be max compression ratio, also what size turbo should be used.?

making a gas engine operating like a diesel. Like to see how that turns out.

garys gt wrote:

JR Performance Motorsport wrote:I dont mean to highjack the thread, but I am getting ready to build a new engine for my '91 F350. I am thinking of using a Turbo and going small bore long stroke. Now this is a every day truck. It sees alot of High Way use. I want the fuel milage to be close to or around 20mpg. My cruise rpm is around 2K. It needs to make is power there or it would be a waste of effort and money. For eveyday use what would be max compression ratio, also what size turbo should be used.?

making a gas engine operating like a diesel. Like to see how that turns out.

The funny thing is it has been for a very long time, it runs @1900 around 70mph. That poor old dog has a lil over a million miles on it now. It just needs more power and efficiancy, well thats what i want.