[Ambitious67Mustang]

Sorry this is an ls question but I do own a mustang and wanted to post anyway. I’m starting a build on an ls 5.3 and wanted to boost but am a beginner. My engine has
9.9:1. It makes 310hp at flywheel stock. I want to run pump 91 but also want 500whp from a stock engine. How much boost and should I switch out the pistons, which are flat tops right now, to something else to lower the compression a bit. Thanks for any help

 

[zray]

It depends how much boost.

the stock HiPo engine has 10.0 or 10.5 CR and that is no problem with the vintage Paxton ball drive supercharger . It has 6 psi of boost. Low by modern standards.

However I did lower the total ignition advance from the the stock specification of 40 degrees BTDC to 35 degrees BTDC when using the Paxton.

If you are planning a boost number in double digits, then yes, a CR of under 9.0 would be advisable.
For comparison, my factory supercharged 2002 Jaguar XKR has 11.9 psi boost with the stock pulleys and 16.5 - 21 psi boost with aftermarket pulleys.

The compression ratio is 9.1

Z

PS. anything higher than 400 HP and you will be needing more than just a piston change. The lower end will need some attention as well.

 

[wicked93gs]

The rule of thumb is that you don't want to go more than 10psi if you are are at 10:1 compression. A higher compression ratio will gain you more power per psi of boost...but it will also detonate that much easier. A properly set up turbocharged(supercharged is not as efficient in many ways) engine can make 20HP per psi of boost....but neither psi or HP/psi is that easy to nail down. For instance 1psi of boost is a lot more air on a TDO6 compressor than it is on a TDO4 compressor. Air is a fluid...pressure is not all that matters, volume plays a huge role in the amount of power per PSI produced, as does intercooler efficiency, etc.

The more important question than boost is why in the world are you using a LS engine? Sure, they make a lot of power, no one is arguing that...but you are talking about swapping one into a classic mustang. Aside from the hate you will get from many people(I couldn't care less), while its a fairly easy swap as far as swaps go, its STILL an engine swap...all engine swaps are expensive(relatively speaking) and come with many challenges. If your goal is 500HP from a stock engine, you are far better off grabbing a stock long-block 351W and turbocharging it. It fits with minimal work and will have no trouble handling the power.

But the most important question is...why do you want 500HP? What is the goal? 500HP is just silly to have if you aren't building a race car of some sort. The problem with building high power, high strung engines is that they generally have bad fuel mileage and are unreliable....all so you can drive around on the street and never use it? I speak from experience here...been there, done that, it was a stupid waste of money, ESPECIALLY when it comes to vintage cars. These cars are NOT competitive in any type of racing without fairly significant modifications. If you want a 500HP LS engine in a racecar I can think of half a dozen cars better suited to it depending on the type of race car. No...you are far better off building something reasonable(mid 300s in HP) without the complications boost ads and spend the majority of your money upgrading other things on the car.

 

[Israel]

Why 500, can the car handle that?

 

[mike306]

Look up Engine Masters - I think you can still find episodes on you tube. They have two episodes where they take a bone stock junk yard 5.3 and 6.0 and boost the crap out of it. Stock bottom end, the only thing they did was open up ring gap.

 

[wicked93gs]

Look up Engine Masters - I think you can still find episodes on you tube. They have two episodes where they take a bone stock junk yard 5.3 and 6.0 and boost the crap out of it. Stock bottom end, the only thing they did was open up ring gap.

Just because someone got away with it does not make it a good idea, especially if you want a reliable engine. In the end, if you are removing the pistons to open the ring gap, then you might as well replace them with something lower compression anyway. I mean, if I am going to remove the pistons and rods, you can be sure I am going to replace them with something better able to handle high boost because even if you open up the ring gap, your upper limit of boost is still limited before you start getting detonation. Some people push 15psi through 10:1 motors...but those motors don't last very long, all it takes is one injector to start flowing a little less than it should and boom. THAT is the main difference between a high compression turbo engine and a low compression one...a low compression engine is much more forgiving of an imperfect air/fuel ratio.

That being said, that just factors into reliability again. What do you want? A 500HP engine that might break down at any time so you can brag that you have 500HP, or a reliable 350HP engine that you are not afraid to drive anywhere? That doesn't even take into consideration the fact that the rest of the car is not set up to handle 500HP to begin with.

 

[Atti]

LS1Tech might be a better forum to check out. They have a lot of great info there on all sorts of LS builds, and the 5.3L turbo is popular.

You're going to need to find out exactly what engine you have. Is it a Gen III or IV? If you decide to lower the compression, an easier way might be to trade heads with someone looking to raise their compression. There are several options out there for the combustion chamber volume and a set of stock GM heads will likely support your goals with a turbo. Also, if you have a Gen IV engine, be aware if it is equipped with Active Fuel Management (AFM) or Variable Valve Timing (VVT) as you may want to get new lifters and/or disable the VVT system. There's a few other things you'll need to think about too, like opening the piston ring gap, changes to the ECM, and upgrades to the fuel system.

Good luck with your build. I put an LS in my Camaro last year a have been very impressed with it. Mine is n/a though, so I'm not a lot of help with the boost stuff.

 

[Scott 65Coupe]

Great advise so far - in addition, I think you should give up the idea of running 91 octane, whichever way you go. It could be the reason you don't blow up, when the stars align WRONG for you!

 

[22GT]

Why 500, can the car handle that?

With many modifications, the car can handle it. Very few drivers can. I've seen the results of cars exceeding the capability of the driver. Can be very ugly.

For street use in these cars, most drivers should stick to maybe 325 hp. That's enough to fry the rear tires, earn moving violations, and initiate divorce proceedings.

I've also seen the results of getting 500 hp out of these small engines, and it isn't pretty, either.

 

[Israel]

Agreed, my question was regarding His specific car.

 

[DrStang]

Stock 302's, 5.0's will split down the lifter valley at high HP applications but you have a great starting point with the LS. Much stronger amazing engine. 10 lbs of boost should get you to 500hp and no intercooler wouild be needed. Premium gas might still get you by, as suggested pulling some timing out will help that.

 

[Ambitious67Mustang]

Thanks all for the help. I did ask on ls1 and no answer. I plan to just throw the short block in without any other work accept springs and cam. The engine already had upgraded internals stock. I want to go boost because i already built a 300hp motor and want to try boost. Not sure what car yet. So everyone that runs boost can’t use pump gas primarily at all? Why do people say lowering compression to use more boost isn’t the only factor

 

[Scott 65Coupe]

High octane burns slower, so there is a greater chance you will NOT detonate. If you detonate while under boost, you may toss a piston through the wall.

Pulling timing helps also in a similar respect. So if you have a tune that pulls timing as boost increases that is a good thing.

Also, don't tune it in 90 degree weather for ever bit of HP - then turn around and go to the track at 45 degrees. More Oxygen - more HP.

 

[HoosierBuddy]

As a "car guy" I don't understand the project.

The only possible place I would even consider an LS engine in a Mustang would be at the drag strip if that's what it took to win.

IMHO...You are simply taking a cool car and making it that much less cool by doing the swap you are contemplating. I would tell someone with a vintage chevy that was looking at putting in a coyote motor exactly the same thing. If you save $1000 vs doing this with a ford engine, you'll give up $2000 if you ever try to resell it.

You can literally buy a brand new engine from Ford that makes 500 HP and will look right under your hood.

But...your car. So crack on.

Phil

 

[Ambitious67Mustang]

As a "car guy" I don't understand the project.

The only possible place I would even consider an LS engine in a Mustang would be at the drag strip if that's what it took to win.

IMHO...You are simply taking a cool car and making it that much less cool by doing the swap you are contemplating. I would tell someone with a vintage chevy that was looking at putting in a coyote motor exactly the same thing. If you save $1000 vs doing this with a ford engine, you'll give up $2000 if you ever try to resell it.

You can literally buy a brand new engine from Ford that makes 500 HP and will look right under your hood.

But...your car. So crack on.

Phil

I never said I’m putting it in a mustang. My 67 already has a new 351w. LS engines pulled my interest and I wanted one. I posted here because y’all reply quickly and have good input. It will go in a 280z probably if I find one

 

[Scott 65Coupe]

280Z - nice

 

[Israel]

Yes, old school Scarab for 2021, very cool!

 

[Atti]

If this is your first LS engine you might try putting it in the car n/a to start with. That'll give you the chance to solve any issues with mounting the engine, the transmission, figuring out which intake will fit under the hood, oil pan, get the fuel system straight, figure out the accessories, the wiring, and get familiar with all that you need to do with the computer (assuming you'll stay fuel injected). For me at least, it was a lot just to get to that point. Then, once you get all those bugs worked out, you could move on to adding the turbo and all that goes with that.

 

[Ambitious67Mustang]

If this is your first LS engine you might try putting it in the car n/a to start with. That'll give you the chance to solve any issues with mounting the engine, the transmission, figuring out which intake will fit under the hood, oil pan, get the fuel system straight, figure out the accessories, the wiring, and get familiar with all that you need to do with the computer (assuming you'll stay fuel injected). For me at least, it was a lot just to get to that point. Then, once you get all those bugs worked out, you could move on to adding the turbo and all that goes with that.

That’s what I think I’d have to do anyway. I will be going with a turbo cam while n/a for a bit though.

 

[Ambitious67Mustang]

High octane burns slower, so there is a greater chance you will NOT detonate. If you detonate while under boost, you may toss a piston through the wall.

Pulling timing helps also in a similar respect. So if you have a tune that pulls timing as boost increases that is a good thing.

Also, don't tune it in 90 degree weather for ever bit of HP - then turn around and go to the track at 45 degrees. More Oxygen - more HP.

Do you have any experience with the holly terminator x? I’m fine with buying whatever computer I need since I don’t have the stock one