Grant Borman

Right now im in the planning stage for a hillclimb build utilizing a ls1-9 block.

Due to my drivetrain/tire constraints im trying to keep max torque between 850-800ft lbs of torque that will taper off to keep the horsepower around 1200hp. This will be a turbo motor along with some old indy car 4 valve heads (420cfm estimated) that will run all day at 11,000 rpm so valvetrain won't be my limit.

Due to do all of this im looking at building a 4.125in bore x 3in stroke motor. Im thinking a custom Bryant flat plane crank will be my best bet. One of my concerns is bearing life. I know people make this kind of torque all the time with larger stroke motors but i haven't seen to many short stroke motors making alot of torque. Any input on bearing life and high torque is welcome.

Thanks,
Grant

Old SStroker

Which "Indy car" 4 valve heads fit the LS block?

Why a flat crank?


Just curious.

Jon

Grant Borman

You can cut and weld to make most any heads fit, the Nissan/infiniti heads are what im using.

A flat plane crank is not mandatory but i feel the pro's out weight the cons. A few of them are....
-I already have flat plane cams, the cost of having a billet flat plane crank made would be less than getting a custom billet cross plane crank plus 4 cros plane cams.
-180 degree headers are an option to tackle exhaust tuning but due to space constraints in the engine bay i'd rather not go this route. I could also flip the heads around so the exhaust collects in the middle of the motor but this would cause issues with the intake manifolds and tire interference. Even exhaust pulses will be important farther on down the road with the turbo's/turbine i plan on running.

I realize there are alot of challenges to building a motor outside the box like this but i feel its doable by approaching each issue and trying to solve it. Right now the bearing load question seems to be a potential limiter.

Thanks

Old SStroker

Yeah, a lot of challenges is grossly understating it, IMO.

Just curious again: How many successful 3.75 hp/cubic inch engines have you designed and built? Pics would be nice.

I would be interested in seeing your bearing load calculations, especially if you are planning to spin it into 5-digit rpm. You might also look at the vibration intensity at those rpm with the 3 inch 180° crank vs. 90° crank.

As they say in Las Vegas, "You are trying to make your point the hard way."

Bob was right.


Jon

Grant Borman

Jon i think there might be a misunderstanding what i am trying to do most likely due to my inability to put my thoughts into words in a way that everyone else can understand.

Right now im looking for first hand information specifically pertaining to engine bearing load on shorter stroke engines making 8-900 ft lbs of torque.

Thanks

3.4camaro

iTrader: (1)

I'm confused as to why you believe a short stroke is somehow putting a larger force onto the main bearings, because I don't believe it is.

Also, after all of your rather outrageous engine requirements, you seem to be hung up on simple bearing calculations? As John said, why can you design/build these 3.75hp/ci motors and be asking an internet board for guidance?

Also, you're mating Nissan heads to an LSX block? Do you or your machinist have experience in alchemy?

Old SStroker

I understood your question. Perhaps you didn't understand where I was going.

I think you might be more concerned about compressive loads in the rod half of the bearing due to power rather than tension loads on the rod which load the cap half of the bearing. You will need a fairly heavy piston with all the boost you'll be using, and of course a strong (read: not light) rod, and you probably plan to twist it near 5 figures (10,000) so the inertia loads at TDC on the exhaust stroke will exceed the loads due to power. The stroke does not matter here.

Additionally those high inertia loads distort the cap half of the bearing more than the power loads distort the rod half. If you are going to have bearing failure it will most likely not be due to power.

You probably have already calculated that a good ProStock engine makes nearly 1500 hp in the high 9000s with crank pin diameters probably smaller than you plan to use so their bearings are loaded more than yours will be. The stroke on a PS engine isn't a lot more than you plan to use.

Tell us more about getting the strength back in the cut and welded heads. What is your plan there?

Jon

Hans Grüber

iTrader: (2)

The Nissan V8 engines have a bore spacing of 112mm, the early Infinity V8 Indy engines had the same bore spacing. The LSx bore spacing is 111.76 mm, so this may work if the water jackets and oil passages are similar.

I really don't see the point though. Even if the heads did bolt right up and the passages all lined up; you still need to adapt the cam drive to the LSx block, get a very expensive custom billet crank made (the crank will easily cost $5000 at least!).

This seems like a very bad idea and makes no sense at all. Why not just buy a used Nissan Titan V8 and work from there?

Grant Borman

You are correct the bore spacing is 1/4 of a millimeter off and that means the outer most cylinders will be roughly 0.375 mm offset. The head stud bores will have to be re drilled possibly removed and new ones welded in. Water jackets will need to be touched up with a rotary burr but nothing to extreme. Oil drain back will need some attention along with feed.

I did some testing for Gates belts and i did plenty of adapting of their belts to applications that were previously chain drive. I don't foresee an issue that i can't solve converting this combination over to belt drive.

I have looked into a fair number of motors and there really is no replacement for the SBC specifically the LS1-9.

You are correct i am probably incorrect to be worrying about compressive forces on the rod bearing shell over the integrity of the rod cap. Im use to some of the issues of the smaller 2.0l motors making alot of power and punishing rod bearings. A turbo motor with a 4-4.125 bore won't have a light weight piston/pin so i see how the rod cap and fasteners could be highly stressed unless they are beefy enough.

I have actually been looking at the cup car motors as a starting point since they have to for prolonged periods of time at higher rpm's. They obviously have different power requirements but i figure as long as i keep most of the speed's and loadings below what they run i should have a good starting point.


The PS motors are pretty impressive, but some of their features scare me for a motor that will have to run for 10 minutes. I will have to look into them though to see what kind of challenges they have versus the cup motors.

Thanks for the insight Jon.

Hans Grüber

iTrader: (2)

What is the point of using the LSx block for this? This makes no sense at all to me.

mwg2600

Thats what im wondering, There has got to be a better way.

And whats the point of spending 3 times what a Nealson turbo motor costs just so you can rev to 11,000rpm?