Limits of stock LT5 with boost?
 

Is there a known failure mode when pushing a stock LT5 engine?

In a turbocharged application, if you kept turning up the boost / power until something broke, what do you think would fail?

What sort of power or torque do you think that failure would occur?

Let's assume we are working with a correctly tuned, healthy, stock engine, and that we're using a high quality fuel.

Thanks.

Re: Limits of stock LT5 with boost?
 

My guess would be that all things being equal, a stock configuration LT5 on boost, the most likely first failure would be head gaskets.
We already know the bottom end is bullet proof as evidenced by the 415 builds out there, and also considering the success proven by FastLane's and Dave's Obsession cars.
Of stock valve train failures there only have been a few that i've heard of over the years, although i have heard of multiple camshaft failures, but those were attributed to aftermarket camshafts made from incorrectly hardened steel.
If i were to guess, I'd guess that big enough turbos could easily drive the HP well in excess of 600-700hp, but the first hiccup of any kind would pop the head gaskets with ease.

Just my $0.02

Crabs

Re: Limits of stock LT5 with boost?
 

Agree with Crabs.
Head Gaskets have been the first point of failure. The most resistant head gasket would be the Cometic MLS. Lingenfelter machined receiver grooves in the cylinder head, for the flame guard on the cylinder sleeve. The open deck design makes it more difficult to get everything just right. The head gasket has to separately seal oil return passages, coolant and cylinder pressure. The Lingenfelter approach functioned very well, allowing boost in excess of 15 psi (with lower compression pistons).

For a completely stock engine, I think 5 psi boost is about the maximum. The Tuning has to be spot on. 5lb boost is approx 1/3 atmosphere and that would approximate the incremental gain in power, i.e. for example, 390 hp normally aspirated would yield about 130 hp gain with 5 psi boost, equaling 520hp.

This amount of gain can likely be achieved normally aspirated, with cat-back exhaust, headers, porting, cams & tuning.

To get the really big power numbers, in excess of the biggest N/A LT5 engines, by turbocharging the LT5, will cost a lot.


Graham Behan would be the resident expert to discuss turbocharging the LT5.

Just my $0.02 also :-)

Re: Limits of stock LT5 with boost?
 

I appreciate it guys, thanks! If the head gaskets were resolved, anyone have an idea of what the next failure might be?

I'd like to talk to Grahm if possible, is he a member here? I met him briefly at the C4 gathering a few years ago, but it's unlikely he remembers me.

I've built several turbo / twin turbo cars; mostly LS swapped fox mustangs, the occasional gen 1/2 SBC or Windsor Ford, a handful of 4/6 cylinder import cars, a turbo Regal / Grand National or two, but never an LT5.

Most recently I built a car for myself, an LS swapped, twin turbo, 1993 Mustang. My Mustang has been a pretty great car over the last few years. Full interior, heat and AC, power windows and stuff, 22 MPG, cruises at 2500 RPM or so at freeway speed, is quiet enough inside to easily chat with a passenger or talk on the phone at 75 MPH, and has been 8.77 @ 156 in the 1/4 mile.

Anyway, the twin turbo LT5 is an itch I've always had... I'm contemplating scratching it.

I appreciate the insight, thanks everyone!

Re: Limits of stock LT5 with boost?
 

At 520chp, I would think the ?juice isn?t worth the squeeze?. 520 is pretty much achievable NA while maintaining the 5.7L displacement.

Re: Limits of stock LT5 with boost?
 

Any build for more than 5psi boost is going to mean different rods & pistons.

More displacement means a new crankshaft.

You might find it simpler to just say how much money you have to spend and how much horsepower you want. You know the game. The $/hp cost just gets greater once all the low hanging fruit is picked. Just remember, there are twice as many valves and four times as many cams in the LT5.

Re: Limits of stock LT5 with boost?
 

Actually four times as cams, Jerry.

Re: Limits of stock LT5 with boost?
 

Duh! I knew that..... just one of those senior moments :-)

Thanks for the opportunity to correct my post.

Re: Limits of stock LT5 with boost?
 

Now we have resolved the cam quantity.
A conservative turbo system nets roughly 3-4% power increase over base engine power level per pound of boost. So Jerrys performance estimate is pretty close. The main drawback with turbocharging an engine with 11- 11.25:1 compression ratio is knock limit of the fuel .

Re: Limits of stock LT5 with boost?
 

Is that an issue with ethanol based fuels; IE pump E85?


I've tuned a couple hundred turbo charged V8 applications on my dyno and have never been able to push an ethanol based fuel into knock before MBT.


I guess the LT5 is more knock prone than most engines?