dizwiz24

How high do you guys rev these things? (boosted lt1, stock bottom end, 11 psi boost).

I boosted a stock bottom end 93 corvette lt1 6speed. Meth/water injection.

I made a max of 485 rwhp (dynojet) at 5400 rpm. I did not rev it higher than 5400 rpm because its a stock bottom end.

The complete mod list is in this thread, and the thread that is linked in this thread.

new dyno results: stock bottom end lt1, p600b, AFR 195 comp elim & LE cam added - Corvette Forum

96capricemgr

The self imposed rpm limit is really low I would think that cam wants to peak over 6100rpm probably higher.

RPM is hard on a motor mostly when the rod has to stop the piston from going up and then pull it back down, it puts tremendous stress on the rods/rod bolts/bearings. The boost doesn't make that any harder, if anything a slight argument could be made that it makes it easier since there is boost instead of vacuum above the piston. Not that I think it is a meaningful difference in stress.

The only reason to be disappointed with what you have there is unrealistic expectations. Let it turn a little more rpm and the number will continue to climb.

IMO though your hope of 530 is a pipedream even with the STD correction.

I don't know where you got the idea that heads and cam the size of those would risk lowend. With the pcm's 7000ish hard limit we are hard pressed to really run a cam that will hurt lowend a lot it has been done but with such a low rpm range potential it should not be normal.

Orr89rocz

You will hit your goals if you rev to 6000+. You could try leaning on it hard with pure meth injection and giving it timing but that is more risky on the stock bottom end....any hint of detonation could spell disaster But it will greatly increase hp

CALL911

My 02 cents;

I think with the others that if a higher number on a piece of paper is the goal you are after, spin the RPMs higher. It's boost in general what is damaging to a stock bottom end. They came from the factory with non forged internals and a high CR. Exactly opposite the combo you want for FI. Can you boost a bottom end motor? Sure, with low boost, safe fuel system, intercooling, meth injection and a safe tune it will run for a while. I don't care what anyone tells you, it will still grenade the motor well before the motor would go if you kept it NA. Honestly, I think you are already pushing it on the unsafe side with your setup as it is. But again, I think you already are a gambling man, so I say push those RPMs higher for your number goal.

If you really want to make the big power like you do safely, the only way to do it is to drop the big money and forge that bottom end and drop the CR. if you already planned this for when the motor goes, I say you might as well keep pushing it to have some fun before it goes.

dizwiz24

I did drop the compression ratio, with the 61cc heads I put on there.

CR is now 9.6ish:1 . I also spray meth/water injection.

The combo runs fine. I have wideband AFR display in my line-of-sight and have datalogged it to ensure leanout doesnt occur.

The worst that can happen is I crack a ring land (from a detonation event) and drive it home. Drop the pan, pull a head and throw a new piston / rod in there.

There are so many people with LSx stock bottom end motors than run crazy power with high compression ratios. Why is that engine different.

I dont believe stock bottom end longetivity is a function of what boost do you run, but other factors, such as tune, intercooling (or meth/injection), fuel pump capacity etc.

Look at all the modern cars w/ forced induction that dont employ forged pistons anymore. (Cadillac CTS-V, mazdaspeed3, subaru wrx). They do this because they have good controls over the engine.

I am willing to agree that there is a mechanical limit to stock rods and pistons. Hence why I think someone cant rev a stock bottom end to the moon.

Leanout and detonation are the scientific conditions that we are trying to avoid here. If those can be avoided. The sky's the limit.

96capricemgr

Basically forged pistons survive lean or detonation conditions better but that if everything is just right you should not hurt a hypereutetic piston with power.

Kevin Blown 95 TA

One problem is that the blower cars with water/meth inj need to be run rather lean to make the best power. Most people run them way too rich and retarded and lose power because of it - by that I mean lose more power than if they didn't have the water/meth injection in the first place. Yeah it is safer, but doesn't make any sense to flood your engine like that under boost and leave all that power on the table. It really needs to be tuned to about 12.5 without the water/meth, then add the water/meth under boost, then timing brought back in, then back out more of the fuel, then back out a little of the water/meth if you can - that's how you tune them for power.
If you are running stock pistons, one thing you can do would be to tell the PCM to pull more timing if it senses knock, although it might happen too fast to make a difference if you get bad gas or the water/meth injection fails. I think the stock pistons crack too easily and the stock ring gaps are too tight for the heat they might see (if you are making any power). Over the years, I haven't met or read about too many people putting a blower on their car and at some point saying, "I want less boost" - at least before it starts breaking. Then, it's more like, "Smoke is puffing out of my valve covers. What does that mean?"

dizwiz24

Im with you 100%

I do suspect that I could go up on my timing. Example. Last month on the dyno, I gained 20 rwTQ by increasing spark advance from 22 to 24 degrees in the 4000 to 4500 rpm range (app. 7.5 to 8 psi boost). 20 rwTQ is huge.

I didnt add any more timing, but I wonder if I added 1 or 2 more degrees there if Id pick up power.

That said, when I tried to increase spark advance from 22 to 24 degrees from 4500 to 5000 rpm, I got 8 degrees of knock retard. However, it was a 98 degree day at the time I was running. Ive also heard people say to back down 1 or 2 degrees around torque peak (4800 rpm) and then add that back in once beyond that.

Funny you speak about meth/water malfunctions.

I had that nightmare happen (got lucky) last summer. I was coming out of a tollboth full throttle, got into 3rd, and felt a huge drop in power. Heard a couple pops, and saw black smoke in the rear view mirror. Luckily, I was datalogging it. At 5000 RPM, I had a major knock retard event pulling 13 degrees of timing. Also AFR's spiked up to 12.5:1 (due to no meth being sprayed). My meth/water system controller got water-damaged and didnt work. Now, I have a 'fail-safe' rigged into my fuel injectors that will stumble them if the car tries to go into boost with meth/water system malfunctionoing.

I ran compression check and all was fine. Also had the heads off the winter. I got real lucky.

z28ke

To answer your question about how high others turn it, I run my stock bottom end to 6200rpm at about 7.5 psi. I would suggest a larger pulley to bring the boost down and turn it higher. Uncorrected mine made 528rwhp with stock heads, and I feel comfortable with that hp level, not knowing where a boosted stock bottom end will fail power wise.

dizwiz24

OK. I got things figured out at the dyno. I had another dyno session.

I picked up a bunch of power down low by actually reducing my timing. I was running in the 28 to 31 degree range from 2600 to 3200 rpm. Reducing timing 2 to 3 degrees picked up 15 rwTQ and made the car more fun to drive.

I know this contradicts my previous post, but I also reduced timing to 20 degrees from 4500 rpm to redline because higher timing didnt seem to help anything at this dyno session.

I think I saw an improvement (at high rpm) on my first dyno session because I was comparing the first dyno pull (low power pull, spark plugs cleaning themselves off, etc.)to a later dyno pull where I added some timing.


93lt1 blower. 510 rwhp. less spark advance made more power, esp. down low - Corvette Forum

Kevin Blown 95 TA

510 rwhp is good - no doubt about it; however, I don't agree with any of your deductions about less timing unless something is majorly not right in there. Now, if you weren't injecting meth/h2o or it just wasn't working the way you think, all that you said would make perfect sense...

musict

IMO your numbers look good.... running similar numbers in my combo.... would like to see bigger numbers but I'm a realist and acknowledge the P600 is maxed at 10*..... I'm spinning the hell out of it to see the boost I'm getting!!!