rhosch

Hi guys, been searching the web, and sites like this, and really haven't found much info on this question. Maybe I'm not searching correctly, or maybe its just tough to answer.

Any rules of thumb (or better yet, something more than just a rule of thumb) on cylinder wall thickness for boost in aluminum blocks.

I know it has some importance, as GM moved from the LS7 to the LS3 block for the LS9, at least partially I presume because of increased wall thickness. And at a rather "tame" 600ish HP.

But that is an OEM cast block with cast in iron liners.

Say you were looking at a more aggressive target, perhaps in the 1K HP ballpark, but willing to go to aftermarket blocks like DartLS Next, RHS or maybe a modded ERL block etc, and now can fit thicker siamesed pressed in liners, nodular iron or other stronger ductile materials, etc. What max bore size would you look at? 4" or less for conservative safety factor? More? How afraid would you be running 4.165 or 4.200 with a quality sleeve in an aftermarket block?

I ask for obvious reasons. But more specifically, it seems bore size is a sort of "freebie" for power and weight, and might allow a bit less boost to reach the same power levels (opening up pump gas as a viable option for example). I know nothing is really for free, thus this question, where the tradeoff is strength/integrity of the block. Usually this is discussed, if at all, in the context of stock blocks. I know some run modest boost on the LS7, but I'd probably start from scratch with a quality aftermarket block.

Thoughts?

stevieturbo

A better question would be, for a power goal of 1k, why do you feel any need to push limits of bore sizes ?

rhosch

Maybe I don't. But ignoring for a moment the issue of cylinder wall thickness, ballooning, etc,

A larger bore could... allow a shorter stroke for the same displacement making life a bit easier at higher RPM... or give a larger displacement for the same stroke hitting HP target with lower RPM, or maybe more importantly lower boost making life easier with pump gas... or some combination of the above. Am I right?

I guess for my intended use of such an engine, I'd like to overdesign in some ways so that 1K HP isn't really stressing the engine to the max. Sure, I'd love fill up with C16 and run 1200++ HP, but I know in the long run my goal would be around the 1K mark with some semblance of reliability. So big displacement, good forged internals, biggish whipple on top, valvetrain designed to survive at high RPM -- but run at a modest boost, sane redline, and have something that isn't about to self destruct.

But I'm certainly open to other suggestions to achieve something like that. I know the 6.3L LS3 block (or aftermarket alternative) isn't a bad place to start. And I know iron would largely alleviate the tradeoff concern, but weight is just as important as power if not more so for this build (cornering, etc.)

I guess what I'm really wondering, is at modest boost levels (which I know seems a waste with a good whipple), are the benefits of the larger bore (decreased boost and/or RPM requirements) more or less important overall than the downside (thinner cylinder walls) when assessing their impact on reliability and durability of the engine?

rhosch

Oh, and I guess a simpler way of phrasing the initial question would be for quality aftermarket blocks with good pressed in liners, what bore size would you aim for in a modestly boosted build trying to hit around 1K HP?

gnx7

iTrader: (28)

What will you be using it for? What chassis is it going into?

You don't need 1000hp in a car built to corner... nor will you be able to keep it cool... or least you will be constantly battling the temps when ambient temps are high.

Most keep the bore around 4.125" on aftermarket blocks/resleeves and boost to keep as much meat as possible in the liner. For "only" 1000hp just stick with an LS2/LS3/LSA/LS9 block for cost and thick deck heads. Piston oil squirters are a nice addition to any performance build. LSA/LS9 blocks have them.

rhosch

Ultima GTR/Evolution. I know, 400hp would be wild, 700 difficult to handle, and 1000 insane. But (1) I was an engineer in a former life and there is something in the challenge and build as much as the result, and that includes something more interesting on the engine side, and (2) I will only build one and much like breast implants, I don't want to later think "wish I had gone bigger!!"

chuntington101

Might be worth having a look at the below section of Piston heads. loads of useful information about Ultimas and good support all over the world!

http://www.pistonheads.com/gassing/f...h=0&f=20&mid=0

Also might be wroth having a look at Clive's thread on Pistonheads or on here. he is building a custom chassis based off the Ultima GTR. Clive is going for a big bore short stroke turbo motor that he is hoping will deliver up to about 1500bhp. This is massively over the top but then when you see Clive's work you will understand why.

http://www.pistonheads.com/gassing/t...+Answer+is+%21

Finally, why not just get the engine from the factory? You know it will fit then, it comes with a limited warrantee and there is plenty of support. I think some forget that just building these types or cars is a job let alone building / spec'ing a monster spec engine to!

If you want to have a little google have a look for these cars:

Schwartz TT Ultima Gtr
Hefner Performance twin turbo GTR

and for giggles

Mercury Racing Ultima GTR (twin turbo 32 valve quad cam 9ltr V8).

stevieturbo

Unless you need the torque...I see no reason to push engine capacity.....and presumably a lightweight Ultima, doesnt need huge torque.

RPM's on the other hand could be useful depending on your gearing and speed needs.

1000hp is in some ways a modest goal, in others it could be perceived high, but it isnt uncommon these days.

As for pushing any limits of the block with such power....the only thing that will put you at risk is pushing too high with the CR baring in mind you're using pump fuel.

Dont be afraid of boost, be afraid of cylinder pressure. The two are not the same. If you must use pump fuel only, keep the CR to sane levels, and let the boost take you where you need as far as power goes

LSA/9 with oil squirters would make a good base, standard stroke crank and CR around 9.0:1 and as long as you have decent charge cooling, you should have zero issues.

rhosch

chuntington101,

Yeah, pistonheads is great. I read every Ultima subforum thread with an interesting topic and/or 10 or greater posts. Took a long, long time! That's where I started to really think I'd prefer supercharged vs turbo or NA. I've seen plenty of your posts there, thanks for the info (and here again)!

rhosch

stevieturbo,

Thanks for the info and advice. You're right, adding more torque isn't the goal and would be difficult to leverage in the lightweight Ultima, though depending on how the final engine performs I may consider changing the final drive ratio to help. I'm not aiming for a torque monster loafing around at 5000 rpm... I want one loafing around at 7000 rpm!

My thoughts on increasing bore size were really more to (1) decrease stroke to stretch the RPM range not caring so much about torque and/or (2) decrease boost requirements for the target.

If you're saying don't be afraid of boost, then it's really just a matter of whether I think aiming for say 7500 rpm vs 7000 rpm is worth the increased cost and reliability/durability concerns. I'll certainly look at LS9/LSA blocks as an option. I don't think I'll mind the extra cost up front in using an aftermarket block for peace of mind, or other benefits like better oiling schemes etc., but I don't want to just waste money if it really isn't necessary to reach my goals either. And I suppose staying around 4.125 sounds like plenty of bore in either case.

JoeNova

5.3 aluminum block, 4.8 rotating assembly, pair of 6262s.
1000 HP capable, less stress on the block, 8000 RPM screamer.

Yes, you might have to run more boost. I honestly don't see most people's determination to make more power on less boost. The only downside to running increased boost is the heat generated.

rhosch

Oh, and chris, yeah I'll definitely consider the American Speed offerings as possibilities. They accomplish pretty much what I'm looking for with the LS9 block and I think whipple charger. But being in the southeast US, just down the road from Talladega, smaller road tracks and dirt tracks on every corner, and a million "engine shops" not to mention big guys like Comp Cams and such not far of a drive away, I'll also consider a more locally sourced option. I'm not going to assemble myself.

rhosch

Not really opposed to running more boost, but with a Whipple I would have to make a choice up front between pump and race gas. For convenience, pump would be easier and I think what I would target, perhaps with changing pulleys for any drag or mile runs or serious track days an option I suppose.

1000hp 8K screamer would be fun and the Ultima would probably love and benefit from that combo. I worry about durability of the valvetrain at that speed. I'm prepared to pay for reasonably good and possibly overspecced parts like titanium valves and shaft mounted rockers, but I'd still be worried about how long it would last!? I guess I'd rather build capable of 8K and limit to 7.5 or something like that. But I'm all ears... other than swapping turbos for supercharger, what CR and boost combo at 8K would I be looking at, and would that require a higher octane fuel?

stevieturbo

If you're using a Whipple, then the last thing you need is huge engine capacity !

And increasing the bore does not decrease the stroke. Decreasing the stoke....decreases the stroke lol
You very much could do a 5.3 screamer, it would be alloy, the 5.3 blocks are well proven to be robust with boost and with the money saved on some bottom end parts you could put it into good valvetrain to allow you to rev the ***** out of it.

rhosch

I'll certainly look more seriously at a smaller displacement higher revving option. I did always think that would be Ida for the weight of an ultima, but figured the cost in valvettain durability would be too high. But I'll do some more research.

And obviously I meant increasing bore could allow decreased stroke for a given diaplacement, lol. And since stroke drops out of a Max HP analysis, leaving bore as a primary driver, that is where I was doing some more investigation.

stevieturbo

Really any engine size will be able to see your 1k goal without getting into mega expensive parts.

But if you are using a Whipple, the low rpm torque it could generate has to be factored in too, as that will be harder on things than something that produces the power/torque at higher rpms

chuntington101

Why not speak to some of the engine builder around you and see what they think? After all it probably best to go with what they recommend. Just remember to get engine build for the intended purpose.

427 motorsport (Kurt) and several others have done 427 based engines with whipple blower that will easily put out 1000bhp.

Regarding low end power you could look to use a wastegate to bleed off some of the low end boost.

chuntington101

Also some have done the Centri supercharger in an Ultima. Its another option and 1) allows easier boost control, 2) opens up lots of options for intercooling & 3) will give you a torque band better matched to the Ultima(??)

stevieturbo

I'd say a centri would be better suited to the car, but presumably space up front of the engine is tighter in these cars ?

JoeNova

The biggest problem with aluminum blocks is the meat between cylinders and the effect of side loading causing stress on the block.

4.8/5.3 blocks have massive amounts of material between the cylinders. Also, the 4.8 has a shorter stroke, and uses a longer rod on top of that. The rod/stroke ratio is excellent, and the piston spends more time near TDC than the other setups. All of this equates to less side-loading and twisting force on the block. If you want the benefits of the shorter stroke/longer rods, you can run the 4.8 rotating assembly in a 6.0 aluminum block with 6.0 pistons. It will put you back near 5.3L of displacement. I would also recommend a centri blower if you can mount it. Less power to spin it, more efficiency, and a better torque curve for such a light car.

Valvetrain upgrades for 8k don't have to be overly complicated.