LS V8 or JUDD V8? Why are engines produced like the JUDD if something like the LS exists?

Hello,

Interesting topic came up between me and some colleagues on why specialty engines like the JUDD V8 is produced when you can make a LS with more power for cheaper, and especially one that does not have to be rebuilt after 1800 miles. I am not a LS guy, and I love to be versed in different technical topics, but it got me thinking. Looking at some small forums around I could see there being a limit of displacement, certain technologies, etc, but for more open classes I cant explain why you would buy something way more expensive that needs to be rebuilt frequently rather than a LS for a cheaper cost.

I myself chose to supercharge my FA20 in my FR-S for track rather than putting a turbo on it for a multitude of reasons even though it was a bit more expensive than a turbo setup, so I am used to the "unpopular route".

You're an LS guy that's use to the unpopular route? Lol 

In reply to yupididit :

Not a LS guy at all. If I was I would have went that route over supercharging the flat 4 in my car, and I would know everything about them but instead I focus myself on way more useful things like how to setup a car, how chassis work, and vintage racing ideas. Please reread and actually answer the post instead of thinking I am just some LS guy (when I am on the JUDD side of it).

Judd engines are made for racing and top speeds. Run an LS to the 9-11K that Judd motors spin to and you'll have nothing left of it.

If you look at a lot of the series that they are in there are restrictions to capacity or HP and some both. For sportscar racing, you want the wider operating range so you can run higher final ratio gearing. No one is running a Judd engine in their street car to go get groceries. 

Just to give you an idea here is the typical range that the Judd engines run by displacement:

Maximum Power:
3.0 litre – 560 bhp @ 11,000rpm (estimated)
3.4 litre – 610 bhp @ 10,250rpm
4.0 litre – 670 bhp @ 10,000 rpm
4.4 litre – 670 bhp @ 10,000 rpm

There is a Le Mans spec version of the LS engine (and the LT), though. Would that be a plausible one to use in place of a Judd?

In reply to bmw88rider :

Much better help than the other guy...thanks.

I can see how the operating ranges based on RPM and gearing could favor the Judd. Coming from a engine that revs to 7700, it makes sense that gearing can be adjusted a lot better with something that has a bigger range to run. 

I assumed displacement was one of the bigger factors into it, as the smallest LS is still bigger than any Judd V8. Same thing with power.

Forgot to mention that I am versed in something that is made to race vs something that is capable to race. The supercharger on my car was "27k" from factory (did not spend that much), but its inherent cooling and durability was designed exclusively for track scenarios rather than street (got rid of A/C). Just from a overall engine perspective and with the availibility to modify an engine rather than a supercharger just wanted to see what the answer generally is. Thanks

bergy32204 said:

In reply to yupididit :

Please reread and actually answer the post instead of thinking I am just some LS guy (when I am on the JUDD side of it).

since you're new here, Welcome to the forum!  you'll find a ton of valuable and interesting info on this forum, and a lot of interesting people as well.  you'll also note there's a lot of good-natured ribbing that goes on here, so it's best to assume the best, especially when someone says Lol, before you get too snippy.  stick around.  this place is fantastic.

In reply to Keith Tanner :

I assume price would be higher than a Judd, as I suspect there was a lot less made and the production numbers would be much smaller than for a Judd (as they would have to be for GM specific vehicles, whereas the Judd has been used in plenty of cars). If I remember correctly, when Lotus stuck the LT5 into the Elise GT1 it filled the power deficit that the TTV8 Lotus had, but it was unreliable in racing.

In reply to AngryCorvair (Forum Supporter) :

Thanks for the welcome! Might be because I am too used to the FR-S/86/BRZ (FT86) forums and FB group where there are a bunch of idiots around that have 0 clue what they are talking about haha. Also, love to see a Corvair. Looking at picking one up soon as a DD.

bergy32204 said:

In reply to AngryCorvair (Forum Supporter) :

Thanks for the welcome! Might be because I am too used to the FR-S/86/BRZ (FT86) forums and FB group where there are a bunch of idiots around that have 0 clue what they are talking about haha. Also, love to see a Corvair. Looking at picking one up soon as a DD.

signal to noise ratio here is arguably the best on the internet.  spend a little time in the builds and project cars section and you'll see insane ideas come to life.  and if you've got a question that isn't car related, the off-topic section is full of, well, off-topic discussion.

Is there a specific JUDD V8 that you're asking about?  They've made a number of them.

As with most things in life, there are a lot of design trade offs when making an engine.  Weight, lifetime, red line, maximum power, production cost, number that you're going to build -- you can improve some of these at the expense of others.  The right set of trade offs for a mass production street motor are not the same as the ones for a purpose-built racing engine.  For example, GM probably wants to use the same bare block in a 700 hp Corvette as they do in a 300 hp truck motor.  That works fine, but it means that the block in the truck motor is overbuilt and a little bit heavier than it needs to be.  It might only be 5 pounds which is trivial for a truck (and the cost savings in not having a custom block for the Corvette make it worth it), but that's a lot of weight in a purpose-built race car.

There are also some unusual requirements for racing engines in purpose-built race cars.  Modern prototype and formula cars use the engine as a stressed member, part of the "frame" of the car.  It's bolted to the back of a carbon tub, with the transmission bolted to the engine, and the rear suspension attaced to the side of the transmission.  That places different loads on the engine than you would ever see in a street car.

In reply to bergy32204 :

Yeah, My 8500 rpm red line engine runs a 4.592 FD where my 7100 rpm red line engine runs a 4.021 FD. Same block and displacement.

The difference is the weight of the rotating assembly. My 8500 RPM engine is a rev happy motor and is much lighter rotating assembly. (Flywheel, Crank, and Rods) Because of this there is much higher pressure on the cylinder walls which causes higher wear on them.

I don't expect my 8500 RPM motor to run 100K+ miles where I expect the 7100 RPM red line motor will. 

The weight difference has to be a factor, and may be part of the reason behind why a race team would chose to run a car with a Judd V-8. On their site, Judd claims their current purpose-built 3.0-4.4 V-8 is 110kg-116kg dry, or about 240-255 pounds. They don't state exactly what all that includes, but it is next to a photo of a deluxe longblock. Even if it is just a longblock without ITBs, airbox, fuel rails, etc. it has to be lighter than an aluminum LS. Using the lighter engine (and possibly as a stressed member) means a lighter chassis, which means in turn means better performance and less stress and wear on brakes/tires. I could see the tradeoffs making sense even though the engine will need rebuilding sooner.

In reply to bergy32204 :

You was praising an ls but claimed to not be an ls guy. Was joking to get you some post in the thread 

Race cars, and by extension race engines are a product of rulebooks. A small cube, high dollar judd V8 isn't built because it's the best way the make power, just the best way within a certain set of rules.

In reply to ae86andkp61 (Forum Supporter) :

Here is a complete, wet, aluminum 5.3 LS with t56 right before being put in my Volvo. It makes about 400-450hp. The t56 is about 120lbs of the total, but the LS is still over 500lbs.

Made me look :) The C8.R Corvette race engine is a 5.5 liter DOHC unit with a flat plane crank. It makes 500 horsepower and 480 lb-ft of torque at 7400rpm, limited by restrictors. No word on the weight of the powerplant.

Another question, is the Judd capable of being a stressed member? Can an LS be a stressed member?

Rons said:

Another question, is the Judd capable of being a stressed member? Can an LS be a stressed member?

Which Judd?  There are about 2 dozen of them listed here:  https://en.wikipedia.org/wiki/Judd_(engine)  As a general rule of thumb, anything that was used in a pro-level formula car or prototype in the last 30-40 years was a stressed member, and for some cars it goes back even further than that (Cosworth DFV was one of the first, IIRC).

I dunno if you can use an LS that way or not.  At the very least, it's probably missing the attachment points on the front where it would bolt to the chassis.

Keith Tanner said:

Made me look :) The C8.R Corvette race engine is a 5.5 liter DOHC unit with a flat plane crank. It makes 500 horsepower and 480 lb-ft of torque at 7400rpm, limited by restrictors. No word on the weight of the powerplant.

The same basic engine is used in the C8 ZO6 and makes 670hp/460 lb-ft and weighs "just 2.2lbs more than the LT2 in the standard C8". And that standard LT2 weighs 472lbs wet (including the engine mounted dry sump oil tank).

Once you do the correct mods to make a 3 liter LS that can rev to 5 digit figures, with all of the wallet-hemhorraging learning experiences along the way, you could have bought a Judd engine, probably.  And the Judd wouldn't be so heavy.

When the valvetrain disassembles itself at 9500rpm there is usually little left of an engine.  Maybe you get to keep the valve covers.  Hopefully you get to keep the nice expensive forged short-stroke crank (billet is cheap, you need reliable) when the valvetrain failure turns the pistons into gravel and the connecting rods come apart as they beat holes in the cylinders and oil pan.  Which is a not uncommon failure mode for LS engines that see heavier use than a burp up the drag strip for a few seconds.

One of my former co-workers wanted to build a 9000rpm LS2 for his Miata.  He realized that this was a little nuts when the top end package he would need for that would cost more than the rest of the engine, and the engine swap, combined.  And the thing with valvetrain parts in pushrod V8s is they are maintenance items, so this isn't a one time expense even IF you don't turn the engine into a parts kit on the back straight.  If you have solid roller lifters, they have a very short lifespan and need to be changed on a regular basis, the rockers wear, the valve springs have a very short life no matter what you do to try to cool them....

Rons said:

Can an LS be a stressed member?

Not sure if it can in the way described above, but, I know that the LM4's (found in an early Envoy XL for example) have the front diff bolted to the oil pan.

Someone explain what a JUDD engine is?

Appleseed said:

Someone explain what a JUDD engine is?

Judd is a company that makes engines for racecars (as well as other things as well).  Iirc, they made v10s that sounded glorious a few decades ago.

In reply to Appleseed :

https://juddpower.com/our-engines/