I plan on boosting the caprice very soon (stock motor). I measured the nose of the car and will easily be able to fit the 33" X 12" X 4" intercooler from vsracing. Along with some meth/h20 my iats should be reasonably cool. Even close to ambient as long as I’m not loading the car up or doing highway runs. Now here is the real question......

If the iats are kept as low as possible, and the tune is conservative, and the pcv system is done well, plenty of fuel etc what causes the hypereutectic pistons to take a poo? Any little detonation? Is it the heat from the increased backpressure in the exhaust?

How do i keep the ring lands intact?

I want to make boosting the stock motor as safe as possible. Hopeing i can get her to live at 5 lbs around town and 8-9 lbs when racing.

Any other sugestions?

 

I have read on a stock lt1 4psi is max to play it safe but i have seen other say 6 to 7 psi but the more boost the more short lived the lt1 becomes.

good luck

 

I was running 9Psi just fine until one cold night I got a 11Psi spike. Bye bye ring lands on three pistons

Many have ran 6-7Psi for years. Some have ran as high as 12Psi for a long time. There is no telling how they drove them though.

Back when I was running 9Psi on my Stock engine we had no tuning tools. I was running nothing more then a MAF Translator and a FMU

When I was running 14Psi I just added 36Lph injectors.

My how things have changed!

I could see alot more then I was running then today very safely. A nice safe tune with lots of extra fuel under boost.

 

So for a good "tune up" I would imagine ngk tr6's or autolite 103's gapped at 0.035". Would an even colder plug help prevent detonation more?

What sort of a/f ratio am I looking at to be "safe" 11.1:1-11.7:1 ?
What sort of timing should I start at when under boost? What should the timing peak at (basically what sounds like too much timing at x rpm)? Should I back off 8-10 degrees across the board in the boosted section then add degree by degree till I start getting knock retard? Or should i pull 8-10 degrees for 1-6 psi then 10-18 degress for 6-12 psi? Do the timing curves "ramp" the same way? I was thinking timing should peak a little after peak tq then be pulled 1 degree for every 500rpm

I’m trying to understand what the order of operations on tuning the setup is. Offset stock tables for 2 bar -> remove 10 degrees of timing in boost -> set boost level -> dial in a/f ratio -> bump timing slowly till the slightest amount of knock retard is apparent? Then back off 2 degrees?

This is gonna be a lot of fun!!!

 

the only way i would everf run more than 7psi on a stock motor is with race gas. And i mean c16 or 110 octane. The hyper POS pistons do not tolerate anything so when you said consertative tune i hope you mean just that.
The h20/meth and fmic are going to be whats saving you. But that isnt going to do much without very good tuning. Which i think will be what determines the life of your stock shortblock.
If you have any money that could be put towards heads you would make your situation a thousand times better. A set of out of the box tfs's would put your stock motor around 9.3.1-9.5.1 i think? But whatever it is its going to be much better than the stock 10.4.1. good luck your going down a risky road

 

I would prefer not to pull the heads. If im pulling the heads off the whole motor is going to be done from the bottom up.

I guess you could say.... what is a conservative tune?

Are those plugs mentioned above appropriate or should i go colder? is 11.1:1-11.7:1 where i want to be? What kind of numbers am i looking at for timing(to be safe).

 

Well you asked, so I will give you my take on your situation;

You follow many others that want to "boost" a stock motor. The absolute safest way to do it is to run race gas with a big intercooler and not much boost. 4-6#'s would be the max I would ever run on a stock motor. Bare minimum, you'll need methanol if you can't run race gas on every tank. Even then, you'll also need the other supporting mods such as ignition, fuel upgrades like injectors, fuel pump, dyno tune, ect. ect., this is all to say nothing about the actual head unit (blower) you decide to run. All and all I never understood the logic, because as it sits to make it "as safe as possible boosting a stock bottom end", you're gonna be out probably around $7,000 and for what? 4-6#'s of boost ain't gonna give you much extra power. Not the kind thats gonna throw you back in your seat like never before. And even then, over time, you will put more wear on the engine than if you were to stay N/A, and its only a matter of time before even 6#'s takes something out on the stock non-forged internals.

It's much more cost effective to just stay N/A and go with a killer heads/cam/intake combo. It will cost you a fraction of the price going boosted would, and you'd probably end up with the same if not more power.

If you wanted more power, and don't mind risking the stock motor, and don't want the cost of being boosted, you could always buy a nitrous kit. This would at least be cheeper, and will do the same damage boost would to the stock internals with high CR.

If you are dead set on going boosted, why not just do it right? The only way you know you will be 100% safe is if you take the stock motor out, and build it for boost with a lower CR, and forged internals. You'll still need all the supporting mods you'd need before, but now by having the engine that can withstand safely 18+#'s of boost you can have a reliable monster.

It's by no means cheep to do. You can save some money by buying the cheeper parts like "Summit" or "Eagle", or you can get the bulletproof stuff like "Lunati" and "Oliver" like I did. Even if you went with the cheeper parts, all said and done with all the supporting mods, engine work, tune, you're gonna be in the $17,000+ range. This is all to say nothing that the added power will require a stronger tranny or clutch, better driveshaft, rear end, and if you want to be able to use the power, suspension.

It's not cheep to be boosted and have it done right, thats why you don't see every other modded LT1 with a blower on them. Thats why many people such as yourself try to go the "cheep route" by boosting the stock motor. IMO, its just not a good idea, as you will be out thousands, and it will no longer be reliable unless you run next to no boost, and then with what little extra power it will actually give you for the money invested, whats the point?

If you don't care about the engine, and just want cheep un-reliable power, then run more than 6#'s. You might be lucky like some and make it 25,000 miles before a rebuild is in your future, or you might not make it to 2500 miles before something goes "BOOM". But then you will have a fast car for cheep (just not for long).

 

The car is already setup 60# mototron injectors, aeromotive fuel system, built tranny, built rear.

I understand were i am going, Ive always wanted a turbo. I will eventually build the motor.

I UNDERSTAND ALL THE RISKS!!! Everyone just seems deadset on trying to talk me out of it. The piping is already done. all i need to know is

WHAT a/f ratio, what plugs, and what kind of timing am i looking at

 

None of what we do here is cheap. Even with the very best parts and tunes there are failures

Hell I made 602RWHP and 780Tq with only seven cylinders. . .

 

Well if you didn't want that info, you probably should not have named your thread "Stock motor vs iat vs #boost". If you would have named it "what a/f ratio, plugs and timing to run" then you may have gotten more specifically what you were looking for.

We are not trying to talk anyone out of being boosted. We are mearly making sure that people who think about going boosted with the stock engine know all the risks (because there are plenty). That way when they do go boosted on the stock motor, and fry a piston before their next oil change at least they knew what they were getting into.

 

I blew up my stock motor after about 8 months with a powerdyne 4.5 psi kit. I had all the supporting mods and a dyno tune. Finally a head gasket went and the coolant slowly filled my oil pan. With the new motor and same boost set up I'm pulling around 110 degree Fahrenheit IATs on a 75 degree day at WOT.

NGK TR55s would be a good plug for that heat range. They come gapped to .35 which is a good start for a boosted motor. Timing and A/F I would have done on the dyno, because I wouldn't trust myself doing that. Hope this helps.

-Pete-

 

i would try to find a baseline tune arond here or on www.forcedinductions.com or maybe even at ls1tech.com. The plugs should be okay and gapped a .035 to start. As for the a/f, same deal ask around or find someone who has already done it. 11.5.1 i would think would be a good starting point. They will be able to speak from experience, which i cannot.
Mainly and above all you need to get the car on a dyno. You need to know whats exactly going on to make sure its going to last 20 min being boosted. Otherwise you could end up like many who only made it a thousand miles before their rebuild. I think after everybody being all over you about you initial boost levels you ll bring them down to start. Than once you have it tuned properly and have an extra shortbock you can push it to 8, 10psi. good luck

 

Anyone have any suggestions for how much timeing i should pull? And were i should pull it?

 

It's not about how much you pull, but how much timing you're running. I'm going to start at 16 with my built motor to get my AFR right. Probably only go up a couple degrees from there, I want to keep mine really safe on the streets.

 

cause4panic:
My boost is quite mild. I'm planning to limit my advance at high rpm & map to the mid or low 20s. I think people are reluctant to give specific answers because the serious players have lots of dyno time and money invested in getting it right. ISTR reading some suggestions of pulling at least 2 degrees of advance for every pound of boost above an NA motor at the upper end.