SouthernSon

History- LS6 with 40k miles about 7-8K on the roadcourse. No problems, ran strong. I then install heads/cam and tune up to air/fuel ratio of 13.0. Dyno showed 440HP. Lasted 2 hrs at VIR and dropped number 7 cylinder.

Inspection showed #5 had comp. of 170#, #7 cylinder - 0, leaking into crankcase, not through the valves.

Questions: Am I to accept that LS6 engine is simply inherently lean on #7 and should therefore go back to stock engine? Should I go with a good forged short block and, if so, what about fuel delivery A/F ratio?

I am feeling a little pain here after throwing about $6K at a perfectly good LS6 and turning it into a pile of junk!

ERND IT

OUCH!!! really sorry to hear this...

stairman

Arte
I hate to hear this happened to you.
The LS6 is a great motor and I would go back to it. I would not tune it to a 13.0 afr just to close for comfort. I personally like to keep them at about 12.3 to 12.5 just to be safe and knowing that the rear cylinders are usually leaner. I would also recomend getting flow sheets on your injectors and putting the fatter ones in the rear. I know what it feels like, I have popped #7 in the first few minutes of dyno tuning it before. If you have any questions just let me know.

Good luck with the next one.

Mike

96CollectorSport

The best bang for the buck engine is a LS6 crate motor from GM, Scoggin Dickey had a few of them in stock and they were shipping them out for somewhere around $3500. They have the CTS-V pan but it's an easy swap, you'll also need the Corvette pilot bearing.
I would do that over heads and cam, take a look at what a T1 car can do. Just me but I'd rather take the reliability over the hp.

KY-Traveler

You could buy a LS6 crate engine

You may want to call Gene at GMPARTSHOUSE.COM

Here's the link.

http://www.gmpartshouseusa.com/partl...layCatalogid=0

If you just need the block, here's a link to GM Performance

https://store.gmperformanceparts.com...umber=12561166

waddisme

Hate to hear that. It brings back some painful memories. Here is what my #7 looked like after letting go on the backstretch of VIR:

[IMG][/IMG]

Also, #5 was on its way there also. It was a long 3 hr drive home on 6 cylinders but it made it. It was also supercharged at the time. Now I have a fully forged 402 with a very conservative tune. It doesn't have as much hp, but is faster at the track. I started to do the LS6 crate, but decided to put few $$s more and do fully forged. However, I am still using 42# injectors from old motor, but can't find anyone locally to flow match them. I wouldn't mind getting that done.

Did you have an Accusump on yours? I have one, just haven't had time to install yet. Just curious if that would make a difference with the #7 issue. Good luck with your new motor project.

rbl

Do you think the issue is also cooling related or just fuel AFR?

I would "think" a shop could come up with a fat injector for #7 and #5 pretty easy if it is just fuel and then you could run the tune you want. I run at 12.5-12.7:1 and don't dare cut it back to 13:1 or more.

Not sure, but even some bad gas could come into play and the Sunoco racing 100 fuel is 9% ethanol and ALL of the fuel at VIR has Ethanol. I finally got them to placard the pumps late last year.

davidfarmer

I think it likely the engine was getting close to the end of it's track life, and the upgrades were not responsible. Remember, pro racing engines have to be freshened every 40-50hrs

kwhiteside

To answer your question about #7, it is a known problem.

I posted this pic up to the tuner guys at EFILive Forums and they quickly responded that #7 is a problem. These are out of my LS6, in the order you look at the engine from the drivers side. #7 is firewall drivers side they tell me.

As far as 13.0 AFR in your PE table. I believe 12.8 is stock. I run 12.6, but 12.5 in the low torque range as that is where the knock usually kicks in. I really don't think a Dyno is going to simulate coming out of a turn doing 80-110 at part or no throttle, then easing into full throttle. It's not a drag strip out there. As you come out of that turn, you are running on your BE table for a moment (if under 4k rpm), then the MAF, then when you nail the throttle you cross over into the PE mode. They don't tune that stuff at the Dyno (unless you have a buddy), I promise you. Those transistions sometimes lead to lean spikes and engine knock.

I also hear about some guys doing 150mph in 4'th because the set the limiter to 7200rpm

drivinhard

153.46 on a 25.3" tire

waddisme

From what I got from the forum when mine let go, it was really cooling related, ie - pre-ignition vs pre-detonation. I might have to dig that thread up for detailed explanation of difference as I forgot now.

For me, my rev limiter is set at 6750 I think and with 19" PS2s (26") I have been at 151 at VIR but not on rev limiter (yet).

AU N EGL

#7 ? Oiling issue ?

wallyman424

Yeah, and I've been doing it for 3 years on a 5 year old motor.

AlwaysInBoost

I don't think an accusump would have helped in his case. if we were talking about a spun bearing then maybe, but a cracked piston is usually from too much cylinder pressure.

13.0 is way lean for a motor running near redline for 20-30minute. for reference my forged 346ci is around 11.3:1 @ peak TQ and leans out a little bit more as the RPM increase. the only time I see 12:1 is @ part throttle. was this on regular pump gas?? ON hot days or at track that have long straigts I will usuall spike my tank with some 100oct unleaded for added safety. Last weekend they were selling it for $4.00/gallon @ NJMP.

varkwso

Sorry to hear it Arte. If it makes you feel any better both of my C5s are down with engine ills and you know they were hardly ever driven.

LS6 crate....I may buy 2 soon

wallyman424

Couple things that might be nice to add here:

1. as everyone above said 13.0 is way high for road racing, shoot for mid-low 12's.
2. Get your injectors flow tested and put the fattest one in cylinder 7, so you know its getting the most fuel.
3. If you want to make 440whp in a road racing motor, you might be better served upping the displacement rather than going with a big head/cam.

sothpaw2

1. What table is it in the program that I should be looking at?
2. Recommend a place that tests them? I assume this is not something a regular mechanic would do for you?

wallyman424

1. I assume youre talking about a table to check the AFR? You can't accurately see the AFR from the cars computer, you need a wideband hooked up to the exhaust. The car's stock O2 sensors are not used in open loop fueling (WOT and such) and are not accurate enough to tune by. You can either buy a wideband and hook it into the exhaust or get a dyno tune w/ a wideband stuck in the tailpipe.

2. I know a bunch of guys that use deatschwerks (google them) to bench test injectors. I really wouldnt bother with a stock motor, but if youre going to run it ragged with a head/cam its worth the effort.

SouthernSon

Ouch! ole buddy! Reckon we need that forged LS2 from Tx. Spd for less than $4K? My AFR heads should be fine but I might change that G5X3 camshaft since it comes in after 4K rpm. I am waiting on a mechanic guru friend from McCluskey to weigh in on the idea.

SDPC had the LS6's for $3500 recently. You need the long blocks?

kwhiteside

{B3618} handles your afr

{B3616} handles the percent throttle/rpm that pe kicks in.

When not in pe you'll be running on either the main ve {b0101} or the maf {b5001}, both of which try to get you to 14.63 stoich, then you cross into Pe which is a very simple table.

The guys at the dyno have the luxory of hitting full throttle and using this table and spark for tuning. At the track, you are in and out of pe mode.

There are a lot of different guys with different goals and pocket books and opinions.

I don't understand risking the engine for a little more pop on the straights when to me, there is much more time to be gained from the turns. But I'm starting to understand how TT's work and its all about that one lap, maybe a track record is worth the risk of the engine. But if you're just a middle of the pack driver, or even worse like me, surely seattime is more important than eeking out a second on a straight.