[Eldi Z]

There is a lot of information floating around about how vulnerable the LT1's are when boost is increased above 7.5 - 8.0 PSI max. when running on pump gas (even 93 on the LT4 fuel system: Low side, High side pumps and injectors).
This, due to the 11.5 CR, tight ring gaps and pistons not being forged.

On the other hand,
Little is being mentioned about the LT4's ring gaps and vulnerability under significant boost levels over stock (stock being ~11.5 peak PSI).

LT1 Static CR = 11.5:1

LT4 Static CR = 10.0:1

When performing CR Vs. Boost calculations, finding the effect of boost increase/ decrease on the resulting effective CR, I found that for instance LT1 under a boost load of 8 PSI, results in a 17.8:1 effective CR (with zero altitude corrections).
When performing the same calculation on the LT4, this effective CR (17.8:1) is achieved at a boost level of ~ 11.5 PSI (~ LT4's stock peak boost level).

Why is it then, that LT4 engines can up their boost (I.E. smaller size upper and/or larger size lower pulleys) to ~ 15 PSI, which brings up the effective CR to over 20:1 and not worry about their rings to butt running pump gas 93?

I know that the LT4 pistons are "Forged" and LT1 pistons are Hypereutectic (cast), but what about the rings? Are the gaps that much wider around the LT4 pistons, that they can withstand so much more of a higher effective CR?

I think that the expansion of the forged material is less than that of the
Hypereutectic, but could this difference be really that significant in practice?

Thanks for educating me

[Eldi Z]

Quick correction!
I meant to say that the Expansion of the Forged material is greater than that of the Hypereutectic/ Cast....

[95 imp]

I have felt the reason that the LT1 goes boom is more related to lack of octane than ring bind. All the pics of the tear downs thus far have not shown that the rings are binding in the cylinders.

It wouldn't surprise me that the meth kits are another reason. The manifold was designed to be "dry" and making it "wet" causes distribution problems (i.e. lean cylinders).

And yes, forged pistons do expand/contract more than hypereutectic pistons.
This one of the reasons OEM's use them. Less gap = less emissions and better MPG.

[KingLT1]

LT4's have a wider ring gap and the piston is more tolerant of heat. The LT1 has very tight ring gaps so you have to keep the cylinder cool to mitigate ring expansion. The best way to do that is run a fuel that burns cool such as E85. Even then you are only going to go so far. As the piston heats up the rings expand...if there isn't enough gap then the rings will butt and that will crack the side of the piston. Notice most failures are chunked on the side. I don't like pump gas / Meth setups on a SBE LT1 because there is very little room for error and distribution issues are a thing. Unless you read plugs and tune for the lean cylinder, then it's real easy to burn a LT1 up on meth. LT4's are much more forgiving in that regard.

[Eldi Z]

Thanks for the insight 95imp and King.

So lets look into the Octane issue further:
In its NA, stock format, the LT1 combusts 93 pump gas, even lower octane 91 and I dare say, 87 without damage. Timing retard comes into effect, in order to mitigate detonation. What about heating of the rings/pistons? There should be a protection mechanism in place for this as well I guess? Your average person does not mix Meth or additional "E" into his fuel and the motor lives on happy.

Why would the same not hold true on a boosted application (I.E. TVS 1760 unit on an LT1 motor), as long as boost levels are kept at ?PSI and Timing Advance is kept at ? Deg. and Injectors PW is kept at ?mS for pure-straight 93 gas off your average Chevron/Exxon/Shell/Texaco pump?
Talking about a "good / responsible-safe" tune.

What is your take on this King? Can't it be done? Driving an LT1 motor with ZL1-like R-WHP levels, using LT4 fuel parts to support (Inj., HPFP, LPFP) reliably without blowing the engine.
There are even quite a few CA people with such setup (LT4 blower on LT1 engine), who daily drive at a lower 91 Octane without mixing "additional" substances in their fuel. For many good miles so far....

[95 imp]

Originally Posted by Eldi Z

Thanks for the insight 95imp and King.

So lets look into the Octane issue further:
In its NA, stock format, the LT1 combusts 93 pump gas, even lower octane 91 and I dare say, 87 without damage.

The PCM can only yank so much timing. You can't run an 11.5/1 motor on heptane and expect it to last long thru the magic of electronics.

Originally Posted by Eldi Z

Timing retard comes into effect, in order to mitigate detonation. What about heating of the rings/pistons? There should be a protection mechanism in place for this as well I guess?

That is usually controlled by the A/F mixture and adding a water and/or alcohol spray.

Originally Posted by Eldi Z

Your average person does not mix Meth or additional "E" into his fuel and the motor lives on happy.

And your average person also ends up with an expensive paper weight too when they boost and do not fuel the motor properly...

[KingLT1]

Originally Posted by Eldi Z

Thanks for the insight 95imp and King.

So lets look into the Octane issue further:
In its NA, stock format, the LT1 combusts 93 pump gas, even lower octane 91 and I dare say, 87 without damage. Timing retard comes into effect, in order to mitigate detonation. What about heating of the rings/pistons? There should be a protection mechanism in place for this as well I guess? Your average person does not mix Meth or additional "E" into his fuel and the motor lives on happy.

Why would the same not hold true on a boosted application (I.E. TVS 1760 unit on an LT1 motor), as long as boost levels are kept at ?PSI and Timing Advance is kept at ? Deg. and Injectors PW is kept at ?mS for pure-straight 93 gas off your average Chevron/Exxon/Shell/Texaco pump?
Talking about a "good / responsible-safe" tune.

What is your take on this King? Can't it be done? Driving an LT1 motor with ZL1-like R-WHP levels, using LT4 fuel parts to support (Inj., HPFP, LPFP) reliably without blowing the engine.
There are even quite a few CA people with such setup (LT4 blower on LT1 engine), who daily drive at a lower 91 Octane without mixing "additional" substances in their fuel. For many good miles so far....

You can't compare NA to Boost. NA doesn't generate near the cylinder pressure or temp as a boosted engine does.

Of course you can run 91, you just have to pull a lot of timing to do it. Your limited to 10-12 degrees of timing with 7psi average boost. A stock LT4 runs 22-23 degrees of timing @ 9psi for reference.

There is 80-100ft lb of torque difference between 10 degrees of timing and 20 degrees in the stock Virtual Torque Tables. So you are missing out on a lot of performance by being timing limited due to octane.

[Eldi Z]

OK, thanks for the inputs.
So, what are people doing when they do apply boost to their 11.5:1 CR LT1 engines?
It has been done by many people, who still drive their cars after many miles and years.

What are the true limits for reasonable longevity / reliability (for your average person who drives his car daily and "steps on it" now and again) of the LT1 when adding an LT4 PD blower setup (ZL1, CTS-V style?) feeding 93 Pump gas through a LT4 fuel system?
Given that the tune has been done correctly, I.E. by an experienced tuner who knows and adheres to the limits of such setup...

[Eldi Z]

And your average person also ends up with an expensive paper weight too when they boost and do not fuel the motor properly...[/QUOTE]

So what in your opinion would be "proper fueling" on a boosted LT1 engine?

[Joshinator99]

Originally Posted by Eldi Z

OK, thanks for the inputs.
So, what are people doing when they do apply boost to their 11.5:1 CR LT1 engines?
It has been done by many people, who still drive their cars after many miles and years.

What are the true limits for reasonable longevity / reliability (for your average person who drives his car daily and "steps on it" now and again) of the LT1 when adding an LT4 PD blower setup (ZL1, CTS-V style?) feeding 93 Pump gas through a LT4 fuel system?
Given that the tune has been done correctly, I.E. by an experienced tuner who knows and adheres to the limits of such setup...

Originally Posted by Eldi Z

And your average person also ends up with an expensive paper weight too when they boost and do not fuel the motor properly...

If you’re worried about longevity on the stock LT1 shortblock, you can keep boost reasonable, say 7-9 psi. Upgrade the fuel system to run at least some E (E30-E50 is a big help) to help pull heat from the chamber like King described. If you only have 93 to work with you’ll want to keep boost about 7 psi with the 11.5:1 compression. The stock LT1 shortblock simply will not tolerate very high boost on 93 octane only for long.

[95 imp]

Originally Posted by Eldi Z

And your average person also ends up with an expensive paper weight too when they boost and do not fuel the motor properly...

So what in your opinion would be "proper fueling" on a boosted LT1 engine?[/QUOTE]

Higher octane fuel. What octane? Depends....

Weather, CR, boost PSI (really volume), intercooler efficiency, cylinder temps, amount of carbon in the chamber. It will vary from motor to motor.

I have always watched my logs and adjusted octane based on the knock sensors.

If they are pulling timing, raise the octane until they stop.

The engine can only handle knock for so long before things physically break and the PCM can only pull so much timing to try to stop it.

It's amazing these motors can run on 91/93 as it is. A L-88 or L-79, for example, would need 100+ octane NA to survive.

[jtengr87]

I've been contemplating this too. It seems there are more variables in the boosted lt1 longevity equation then we would like to admit. I'd like to push the conversation further.

I've seen a few more (in facebook groups) procharged lt1s with ringland failures then PD. Has anyone else seen this?

[KingLT1]

Originally Posted by Eldi Z

OK, thanks for the inputs.
So, what are people doing when they do apply boost to their 11.5:1 CR LT1 engines?
It has been done by many people, who still drive their cars after many miles and years.

What are the true limits for reasonable longevity / reliability (for your average person who drives his car daily and "steps on it" now and again) of the LT1 when adding an LT4 PD blower setup (ZL1, CTS-V style?) feeding 93 Pump gas through a LT4 fuel system?
Given that the tune has been done correctly, I.E. by an experienced tuner who knows and adheres to the limits of such setup...

I have had my Whipple installed since Jan of 2019. I started with 8psi(currently @ 10psi), upgraded fuel system, running on E. I have logged over 10k miles on the Whipple setup...the car has just under 16k miles total. Not a ton of miles but this is a Weekend car that has probably seen well over 100 0-60, 1/8th mi, and 1/4mi pulls with the Whipple and probably double that since I bought. When I get it out the Accelerator pedal goes to the floor at least once or twice. So I run it hard but I also take care of it. I always check fluids, filter, keep the oil changed...

Here are some key things that I consider important if you want to boost a SBE LT1.

- Colder Spark plug. Imo run a 7 heat range...you will get more cold start misfires and they are easier to foul but this imo is a must.

-Proper crankcase ventilation. Catch can with a Metco valve cover breather or Mighty mouse system. You don't want to pressurize the crank case

-LT4 fuel system minimum. I posted this in another thread:

"One thing to keep in mind. A LT1 with about 7psi makes similar power to a stock LT4 which makes 9-10 psi. The higher compression of the LT1 allows it to make similar power at less boost. The LT4 comes from the factory with a better fuel system. Ideally you will need to run the LT1 a touch richer for cooling on pump 93 due to the increased compression which further increases fuel demand. So that means a 7psi setup really needs the LT4 fuel system hence why I always suggest it as a minimum."

-Correct AFR and Conservative timing. .82 Lambda and 10-13degrees of timing depending on quality of pump gas.

I see canned tunes targeting stock AFR and trying to run 15+ degrees of timing. Then they don't even trigger PE mode until at the top of the gear. This will blow a engine up fast. The only logical reason they do this is for some reason it squeaks by at the altitude where they tested the tune and to stretch out the stock fuel system.

One variable that is very seldom brought up is weather change and how it effects performance and fueling....especially on a boosted car. Most cars seem to be dyno'd in 70+ degree weather and often times hotter. In those conditions you might have enough fuel system. If you live in areas of the country that have 4 true seasons like I do, then you have to consider the coolest temps you plan on running your car and make sure to log data at those temps. A boosted car is going to make a lot more power at 50 degrees vs 80+ degrees and that requires more fuel. A lot of that is due to making more boost and PD / Centri setups control boost with Pulleys. We don't have electronic boost controllers to bleed boost off if it goes above a target.

So as you can see there is a lot more to boosting one of these cars in order to do it correctly. It's not bolt-on 150hp in 6-8hrs, flash tune, and go live happily ever after like some of these companies claim.

Imho, the average enthusiast would be much better off buying a ZL1 or just sticking with a Bolt-on's for the SS.

[cjperformance]

Originally Posted by KingLT1

Imho, the average enthusiast would be much better off buying a ZL1 or just sticking with a Bolt-on's for the SS.

Not that you need my 2-cents , but I can vouch for everything you said. I am really hoping that in my ignorance I haven't done any serious damage. That said.... not that I WANT to spend money on replacing the shortblock, I have the money to do it if I blow up something.... but yeah... it's not straightforward. My other thread... I'm trying to put together a comprehensive blog-style list of all the boneheaded stupid things I've been doing and how to correct them.