limits of boosted l76?

[parish8]

from what i am reading ~14psi ~800rwhp is pushing the l92 heads. around there they start deflecting and loose seal.

from what i can tell that is the first limit

if i were to bolt on a set of heads with 3/4" deck and some head studs what would the next limit be?

if the tune is spot on. plenty of octane, plenty of fuel, no knock, moderate timing. would it be crazy to try pushing the stock pistons to lets say 900rwhp? 1000rwhp?

i feel like the rods can take a ton of power if i dont try and rev it to 7000+rpm. the compresive strength of latemodel rods has to be up there doesn't it?

i am looking to avoid ther snowball effect. seems like if i was to do heads i should do pistons. if i was to do pistons it would be silly to not do rods. if i were to do rods it would be silly not to put in a bigger cam... how about just heads and more boost?

[BlownPoncho]

Late models pistons can take a good amount of boost usually I think. Most of the gtp guys push a lot of boost to their blocks and pistons and they have the same type pretty much ...I'm far from an expert though just thought

[NIevo]

I too am planning on a future boosted motor and am very curious as to this question. Also at what point would it be cheaper to just pull the motor and do a complete, turbo friendly, low compression build?

[norm8332]

Our pistons are cast aren't they? I was always led to believe cast pistons were easy to break with boost. Of course I'm going on research only

[Bonnetts02Vette]

i believe they are cast hypereutectic pistons. every motor is different as far as tolerance to stuff and its all in tuning but at some point they stock stuff will fail. one person could blow their ringlands with only 400rwhp while someone else can go over 700rwhp and be fine but be advised you are on extreme borrowed time with that power on the stock pistons.
at this point parish i would go ahead and just do the pistons and if your going for around 1000rwhp i would worry more about head lift under boost. especially anything over 20psi on aluminum block and heads. Places machine your block and heads for 1/2" head studs.

The main point is every engine is different and some can blow stock and some can take lots of power. The part of the rotating assembly that can take more power than you can make and not break is the crank, but i wouldnt trust the rods or pistons at 500+rwhp, let alone your power level parish. you do heads then you might as well do rods and pistons as well, simple enough at that point. Kill 2 birds with one stone.

anything over 1000rwhp then i would go LSx iron block and some 6 bolt heads.

just my .02

[WickedMom]

http://tapa.tk/mu/6332c3b0-7921-db24.jpg
This was in our dyno room last week :)


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[laserred]

Turbos are a little easier on parts than either PD or centrifugal blowers, since you don't have all the extra stress pulling on the crank snout. Not a whole lot, but late model hypereutectics are pretty strong, KB rates theirs for a 250 shot, and I'd say the shock on the pistons is much greater with nitrous than with a turbo which builds gradually, both on and off. And the rods should be strong enough sub-6500, like Jim said it's usually not compression loads that ruin a rod's day, it's overrevving them. That said, 635rwhp on powdered metal rods is nutz! So realistically, Jim, when you get to the point that the question of "When" becomes stronger than "IF" it goes, I'd say you're looking at a 402-404ci motor, since there's no sense in changing the rods and pistons without swapping the crank either! Now, you can add some cam for the extra 40 cubes and still maintain stock idle quality. Send your heads out for some CNC work during the downtime, and I'd bet 800rwhp at 10psi with twins is an easy goal. It only gets crazier after that....

[laserred]

Edit- now, Jess, since you posted that pic of the LSX- I'm pretty sure Magnuson dyno's their blowers off the engine- what's a 2300 take to spin it at 7000(crank)RPM with pulleys typical of a normal motor? I don't know what the typical blower shaft speeds are.

[WickedMom]

Edit- now, Jess, since you posted that pic of the LSX- I'm pretty sure Magnuson dyno's their blowers off the engine- what's a 2300 take to spin it at 7000(crank)RPM with pulleys typical of a normal motor? I don't know what the typical blower shaft speeds are.

We do test the blowers off the engine, this was just stored in the dyno room... If it made it, it will be displayed in the mothers booth at sema in a chevelle.

Anyway. Blower speed... Let's see if I can remember the formula. I have it on my desk... But I'm in bed now... :)
For front driven blowers, Crank pulley size / SC pulley size X max RPM = blower speed (I think). But jack shaft blower calculations are a lot more difficult.

Eaton rated the max speed of their 2300 rotors at 18,000rpm... I've heard of blowers spinning at well over 25,000 rpm, they just don't spin as long...

So the real answer requires a spreadsheet calculation, that I can do after I get back from SEMA, if you remind me :)


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[Boostpatrol]

Parish

I cannot believe that your ring lands havent shattered on your motor yet! We sold my stock motor to an RX7 swap guy who wanted to forge it and we found that piston 7 broke a ring land with no detonation. It was probably from my trans slipping so bad, over revving and me getting off and back on the gas quick. This was done on a 500 hp boost setting. O- ring your block for the high boost stuff. My block is a livernois cast iron with oringed block. It was made for 8.0s in a 3600 lb twin turbo car.

[parish8]

we have pushed stock parts pretty hard over the years and as far as i know we have never hurt a motor with boost only. i have killed a couple with nitrous or boost+nitrous but never just boost. makes me wonder what the limit really is.

some examples.

5000lb truck ran 10.92 on a cam only 6.0. 13psi and a 75shot. engine blew up later when a nitrous noid stuck open and i tried to start the engine.
3200lb fairmont ran a 9.49 with a cam only 5.3. something like 18psi but turbo was maxed. engine is still running after several hundred runs.
3300lb mustang ran a 9.33 with a cam only 6.0. something like 15psi. engine is still running strong.

boostpatrol. if you were only at the 500rwhp level then i would bet money that at some point it did knock, it only takes a sec.

[Robert@KBXPerformance]

I'd say you're looking at a 402-404ci motor, since there's no sense in changing the rods and pistons without swapping the crank either! Now, you can add some cam for the extra 40 cubes and still maintain stock idle quality. Send your heads out for some CNC work during the downtime, and I'd bet 800rwhp at 10psi with twins is an easy goal. It only gets crazier after that....

You pretty much stated the exact combo I am currently building, except I am staying with stock L92's versus bothering with CNCing them.

[laserred]

Yeah Robert, the only thing I am waiting on is one of the tranny places to step up and prove they have a good 6L80 program so that i need not worry about a $4k pile of smoking clutch material. Maybe RPM Transmissions near Indy will get it done since they have a good 4L65 program.

[parish8]

You pretty much stated the exact combo I am currently building, except I am staying with stock L92's versus bothering with CNCing them.

seems like you are skiping the weakest link. how are you going to keep the heads down? from what i have been reading l92's are known for having one of the thinest decks for a factory head and lift around 800rwhp. even with studs.

[exesivefire]

I as well would worry about ringlands breaking before anything else ( in a perfect world situation )

I have nothing for proof with this motor, but from where I have been ( boosted ecotec 4 bangers ) ringlands were always the first to let go.

Catastrophic failure from something like a rod, usually happened from something that shouldnt have happened ( over rev, detonation etc...)


Problem is, I don't know if the answer you are looking for is really out there, I would venture to guess you are one of the few at that limit. And the question you need to ask yourself, Is how would you feel if you found the limit the hard way?

For example, it was always assumed, and known that the 300 whp mark in the ecotec world was about the limit for a stock bottom end, but there is always one guy that thinks they can go farther. So recently someone tried, and was rather "proud" of doing so. untill about a week later when he over revved on a shift and ended up with piston pieces throughout his motor, and turbo.. He is now building a new motor, and probably replacing parts he wouldn't have before...

[Bonnetts02Vette]

all LS heads will start to lift at higher boost. from places ive talked to either 1/2" studs or 6 bolt heads with LSx block is necessary if you want to make big power and want it to last

[parish8]

Yeah Robert, the only thing I am waiting on is one of the tranny places to step up and prove they have a good 6L80 program so that i need not worry about a $4k pile of smoking clutch material. Maybe RPM Transmissions near Indy will get it done since they have a good 4L65 program.

the only thing you need to do with a 4l60/4l65/4l80.... to keep from hurting them is keep the line pressure up and even on that many of the builders remove that variable by putting in vacume modlulated line pressure rather than the computer controling it. other than that you just tell it when to shift and if the tranny is strong enough it will last.

the 6l80e is completely diferent. 100's of tables that can effect how long the unit will last under power. even with a perfect tune that doen't mean the tranny will live in stock form. there are some factory updates that may be needed.

[laserred]

Jim, wouldn't the "old school" way of cutting grooves and using a copper ring take care of this? I mean, I know it would only be good so far, but remember the golden rule of turbos:

If a 300HP engine has 14.7psi of boost, it should make roughly 600HP.
Now, make that engine make 450HP, and it only takes 7PSI to hit 600HP.

If you make the 800HP motor make 550HP before the turbos, you will have relatively low boost pressure to hit the 800HP, instead of taking a 360HP motor and boosting it with 15-18lbs of boost and having crazy cylinder pressures.

However, I will admit: I'm not 100% sure that the 550HP engine will put less stress on the head gaskets than the 360HP engine would, but it seems to make sense. And, I did stay at a Holiday Inn Express last night. :)

Maybe Kenny Duttweiler would know.

[parish8]

Jim, wouldn't the "old school" way of cutting grooves and using a copper ring take care of this? I mean, I know it would only be good so far, but remember the golden rule of turbos:

If a 300HP engine has 14.7psi of boost, it should make roughly 600HP.
Now, make that engine make 450HP, and it only takes 7PSI to hit 600HP.

If you make the 800HP motor make 550HP before the turbos, you will have relatively low boost pressure to hit the 800HP, instead of taking a 360HP motor and boosting it with 15-18lbs of boost and having crazy cylinder pressures.

However, I will admit: I'm not 100% sure that the 550HP engine will put less stress on the head gaskets than the 360HP engine would, but it seems to make sense. And, I did stay at a Holiday Inn Express last night. :)

Maybe Kenny Duttweiler would know.

you bring up a good point and it would be a good discusion. i am not sure of anything but i have some ideas.


i dont think boost pressure has much to do with the limit of the head gaskets. now 13psi is 700rwhp, good heads it may only take 11psi to get to 700rwhp. either way i think it is the same amount of work for the head gaskets.

when it comes to lifting heads i think it has more to do with peek tq than anything else. with that in mind swaping to a larger cam that keeps the same peek tq but pushing it up into a higher rpm range might be a good way to maximize power without working the head gaskets any harder.

it would be nice to hear some other theories on this.

[laserred]

SO you're working with the "pile of beans" theory with power- keep the same amount of torque, but just push the pile over to the right side of the graph and watch the HP skyrocket! I think I agree, as long as you keep the peak BMEP under control, it should help. But the big thing about boost is that the higher you go, "effective" compression starts to take on a paraboloid shape, and the difference between "uh-oh" and "oh-shit" is a very small distance on the x-axis. So, keep the boost pressure down and the peak BMEP and I think you could theoretically make as much HP you want as long as you don't pull the big end of the rod apart or pull the wristpin out of the piston or small end. Simple really, no? LOL

[parish8]

another question i have always had.

if you were to lower timing but up boost wouldn't that lower peek cylinder pressure but at the same time increase average cylinder pressure on the power stroke? right now i am at 14deg of timing and at most 13psi. if i were to drop that to 10deg and then turn up the boost until i was at the same hp would my peek cylinder pressure be less? i bet it would. next question is how far can you go with this idea? what timing would give you the most average cylinder pressure with the least peek cylinder pressure. there would be a little more too this like what is the pressure at diferent crank angles.

it seems like there would be a way to measure cylinder pressure and chart it compared to crank angle and maximise tq on the crank with the least cylinder pressure.

[Robert@KBXPerformance]

seems like you are skiping the weakest link. how are you going to keep the heads down? from what i have been reading l92's are known for having one of the thinest decks for a factory head and lift around 800rwhp. even with studs.

Not at all. I don't plan to go past 800rwhp, if even that. Just make whatever power/torque I do make on lower boost and have a mean street setup.