LC3 rabbit hole

[MPRCTCL]

So, I’m down the rabbit hole on this. My buddy has an ‘06 STS-V with the same engine as my V, but…. It’s rated for more horsepower. Has anyone sorted out the story? Was it a marketing thing? Component differences? Yesterday, I spoke with a Northstar engineer, but he’d left GM before the LC3 came about and didn’t have a good idea.

Cadillac STS-V LC3 Supercharged Northstar | CaddyInfo – Cadillac Conversations Blog

 

[mickeytee]

I think I read one time it was thought the belt drive system on the xlr combined with the exhaust resulted in lower HP. I personally think the supercharger does not turn as fast on the xlr as on the sts. The bigger power steering pump pulley that was sold aftermarket a while back supposedly bumped the HP up on the xlr. I found this from the guys that made the bigger pulley so it seems that was what the found also.


'Good question. Everything internally is the same between the two vehicles. The only differences you have are fuel map, exhaust system, and intake track. The fuel map change can be attributed to the change in exhaust between the two cars. The intake is just routing.

The 26HP is coming mostly from the exhaust (i.e. exhaust manifolds and tuning). The XLR-V exhaust manifold has a wicked kink in it, whereas the STS-V is a little bit better flow wise. We have developed headers for the XLR-V application and the vehicle REALLY RESPONDED WELL!! We did the same for the STS-V and the gains were good, but not as good as the XLR-V application.


p.s. Also there is a slightly different pulley track between the two engines. The XLR-V uses a 2 row pulley system whereas the STS-V uses a 3 row with its own blower belt. Dont want to leave out any details... =)
Hope that helps'

 

[Z1.]

GM decided to detune the XLR-V's HP a little bit in the ECU calibration for some reason. Table doesn't look as aggressive in fuel to air ratios. Maybe they did this to make though the warrantee period.

 

[mickeytee]

the fuel map change was due to the exhaust manifold design and poorer flow ability than the more open sts

 

[MPRCTCL]

I think I read one time it was thought the belt drive system on the xlr combined with the exhaust resulted in lower HP. I personally think the supercharger does not turn as fast on the xlr as on the sts. The bigger power steering pump pulley that was sold aftermarket a while back supposedly bumped the HP up on the xlr. I found this from the guys that made the bigger pulley so it seems that was what the found also.


'Good question. Everything internally is the same between the two vehicles. The only differences you have are fuel map, exhaust system, and intake track. The fuel map change can be attributed to the change in exhaust between the two cars. The intake is just routing.

The 26HP is coming mostly from the exhaust (i.e. exhaust manifolds and tuning). The XLR-V exhaust manifold has a wicked kink in it, whereas the STS-V is a little bit better flow wise. We have developed headers for the XLR-V application and the vehicle REALLY RESPONDED WELL!! We did the same for the STS-V and the gains were good, but not as good as the XLR-V application.


p.s. Also there is a slightly different pulley track between the two engines. The XLR-V uses a 2 row pulley system whereas the STS-V uses a 3 row with its own blower belt. Dont want to leave out any details... =)
Hope that helps'

Thanks for the great reply. That makes complete sense. It also helps me stay grounded, I want to do some upgrades, but they are hard to acquire and if the exhaust manifold is the (literal) limiting factor, "more air in" has a very limited potential if air can't get back out.

 

[sergioeddy]

I think I read one time it was thought the belt drive system on the xlr combined with the exhaust resulted in lower HP. I personally think the supercharger does not turn as fast on the xlr as on the sts. The bigger power steering pump pulley that was sold aftermarket a while back supposedly bumped the HP up on the xlr. I found this from the guys that made the bigger pulley so it seems that was what the found also.


'Good question. Everything internally is the same between the two vehicles. The only differences you have are fuel map, exhaust system, and intake track. The fuel map change can be attributed to the change in exhaust between the two cars. The intake is just routing.

The 26HP is coming mostly from the exhaust (i.e. exhaust manifolds and tuning). The XLR-V exhaust manifold has a wicked kink in it, whereas the STS-V is a little bit better flow wise. We have developed headers for the XLR-V application and the vehicle REALLY RESPONDED WELL!! We did the same for the STS-V and the gains were good, but not as good as the XLR-V application.


p.s. Also there is a slightly different pulley track between the two engines. The XLR-V uses a 2 row pulley system whereas the STS-V uses a 3 row with its own blower belt. Dont want to leave out any details... =)
Hope that helps'

Hello @mickeytee I am interested in purchasing a set of these headers. Any chance they are still available?

Thanks,

Eddy-

 

[mickeytee]

Sorry no. That was a quote about what dc3 did on the engne. Funny thing they claim they made more than 50 header sets yet ive looked at 100 cars at least and spoke with more owners than that and never seen a set on a car. So somewhere there has to be a bunch of them sitting on a shelf.
Id love to see someone with a set.

 

[sergioeddy]

Sorry no. That was a quote about what dc3 did on the engne. Funny thing they claim they made more than 50 header sets yet ive looked at 100 cars at least and spoke with more owners than that and never seen a set on a car. So somewhere there has to be a bunch of them sitting on a shelf.
Id love to see someone with a set.

No worries, I figured it was a long shot. Thanks for your reply!

 

[MPRCTCL]

I recently learned that the difference between the STS-V LC-3 and the XLR-V is the XLR has a shorter intake manifold for hood clearance. That accounts for the difference in horsepower, not the exhaust. That’s from Dave Leon’s lips to my ear… Not disagreeing with anyone, just sharing what I learned.

 

[mickeytee]

They use the same superchargers and the intake manifold is part of the supercharger so not sure

 

[MPRCTCL]

I’m just saying what Leone said when I asked him what the horsepower difference was between them.

 

[mickeytee]

Haha, well it does not matter to me but recently i looked at a new oem long block. Part number showed xlr and sts. It came with block ,heads and supercharger . no front assesories or exhaust manifolds. So the basic engine was the same for both cars. Same camshafts etc. Dc3 said they thought because of the exhaust on the xlr they had some different tuning and the intake pipes are different so it may make some difference.

 

[mickeytee]

I spoke with a guy from the caddy tuner. They said on the dyno the xhaust was a manor choke on power. Opening up the intake tubes did not help as air in air out and out was restrictive. When they added. Long tube headers they ooened tge air box and got more hp. So when the guy says the intake he must have beenn talking the pladtic v inlet as tge side tubes and everything else is the same as sts. Sts uses a bigger intake pipe but it has several bends that would restrict airflow so the xkr is more direct. Thats why the fresh air intake on the base does a better hp increase than the v due to restrictive exhaust.

 

[justdennis]

That all sounds logical, thanks for the clarification.
Does anyone make headers for the V and can you eliminate the cat's, and would you want to?

 

[mickeytee]

Ive never seen a set in person but there was a photo once with 20-30 sets side by side. I still wonder whete are they. I think one member in virginia has all the d3 modifications on his car.

 

[LC3]

Hi Mickeytee Hope you may be able to help. I have an LC3 engine and trans that is basically new, and I'm in Melbourne Australia and we have NO info on these Caddy engines other than what I can find on the internet and bits of info I follow on Northstar on Facebook. I am putting this engine in a 53 Chev Pickup that we are hotrodding. I didnt want to use a LS as everyone else does but I'm finding a few problems. I have to get a complete new loom end ECM made for it and also a new control for the trans. Are you aware of any one there in the US that makes/has made stand alone engine looms for the LC3 please??? I also have a private email that you could reply to orourkekevin53@gmail.com Really hope that you can find the time to drop me a reply , even if you cant help with any info or advice on these - we have nothing here in Melbourne, Victoria , Australia - we never had Cadillacs...even.....

 

[mickeytee]

That looks like a great conversjon and will be different than an ls for sure. Looks like you bave a lot of the wiring and all not sure what all you might need. I sent you a privatemessave to help