LLT heads on an LFX short block... Doable? Worth it?

[Jason@JacFab]

I'm think that the LLT heads will bolt onto an LFX... The 10-11 LLT, and 12+ LFX both use the same head gasket, which tells me for mounting/oiling/cooling purposes, they are probably identical.

It seems the MACE cam's don't work so hot in the LFX supposedly because of it's single exhaust outlet? Not to mention you don't get the cool cam sound. The LLT engined cars just seem to sound better than the LFX cars in general.

To sum it up, potentials gains are:

Headers (more power?)
Better sound (w/ and w/o headers)
Cams available (more power? cool sound)
Maximized porting area on the ex side.

What potential losses could be suffered from this swap? I can only think of two off the top of my head...

1) The LFX got a slight compression bump over the LLT. 11.3 on the LLT vs 11.5:1 on the LFX. I am not certain if this was a result from changing the shape/size of the combustion chamber, or if it was simply just the pistons

2) The LFX has larger intake valves. 38.3 mm vs. the LLT's 36.96 mm. This should be an easy fix by just installing the LFX intake valves.

I think the only thing that might screw a guy on doing this is if the injectors, fuel rail, and HPFP are so different between the two that you had to run the LLT stuff also, which would add additional cost to the swap.

Thoughts?

(ps: I scored a set of LLT heads with a fresh valve job today...)

[Jason@JacFab]

No thoughts?

[bandier]

Go for it.

[GretchenGotGrowl]

Honestly, I never even thought about it. It would be nice to have headers. So, can you pipet the two heads and see how the volumes compare? The CR difference may be the pistons. I'll think about a while and see if I come up with some questions. I have some ported LLT heads in the shed...

[NewbieDIYer]

Ah from one project right to another. Awesome!! Here's another thread to subscribe to!

[dmginc]

Being able to run headers would be awesome...

Sent from my LG-VM696 using Tapatalk 2

[KMPrenger]

First off I just want to say that I think the simple fact that this idea was even thought up is pretty cool. One of those "why didn't I think of that?" things....but it sounds like it could work.

Worth it??

Well I don't know...I think the LFX owner would have to want headers awfully bad to take the plunge and purchase/install LLT heads just so they can have a bit more power and better sound. I guess thats why you mentioned cams, as I can see if the owner wants to also do cams, then it make more sense to get it all done at that time.

But we still haven't seen a real successful cam install on a Camaro V6 so I'd be pretty intimidated about that.

I applaud you for thinking outside the box. I still think an LLT with headers and an appropriate exhaust sounds awesome! Maybe now a few LFX owners will get to experience the same!

[Jason@JacFab]

Originally Posted by KMPrenger

First off I just want to say that I think the simple fact that this idea was even thought up is pretty cool. One of those "why didn't I think of that?" things....but it sounds like it could work.

Worth it??

Well I don't know...I think the LFX owner would have to want headers awfully bad to take the plunge and purchase/install LLT heads just so they can have a bit more power and better sound. I guess thats why you mentioned cams, as I can see if the owner wants to also do cams, then it make more sense to get it all done at that time.

But we still haven't seen a real successful cam install on a Camaro V6 so I'd be pretty intimidated about that.

I applaud you for thinking outside the box. I still think an LLT with headers and an appropriate exhaust sounds awesome! Maybe now a few LFX owners will get to experience the same!

This idea may never even make it into the car... But then again it may. I wouldn't even think about doing it if I didn't have another LFX engine sitting at home in my garage. I bought the LLT heads for a song, so I can at least bolt them on the spare engine and verify if there any issues with the cam/timing chain affair still being able to work with the LFX bottom end. If there are no issues there, and the LFX injectors, fuel rail, and HPFP look like they will work, I may end up sticking it in the car... maybe. I'd hate to do a billion engine swaps. I guess the deciding factor is what the LF3 intake manifold ports look like, if I can use the "Adaptolator" (gm part) to put the LF3 intake on the LLT heads, I may try to put it in the car (boosted of course).

Another plus to running the LLT heads that GretchenGotGrowl mentioned, the LLT heads are easily ported, where as the exhaust side of the LFX you can only really do so much because of the single exhaust outlet.

I have a complete LFX engine harness. If I could somehow plug another ECU in and disable the VATS and whatever else it would take to make it run I could put it on a local engine dyno..

IDK, It seems like it would be a farce to try to build some BA NA Frankenstein engine just to tear it back out and throw an FI engine in it.

*EDIT* A little more research shows that (it appears) the VVT cam actuators are the same from 2010-2013 (the online prats thing I'm looking at only goes as new as 2013), that makes one less issue of a cam/head swap. Assuming the alignment of the heads/cams, etc hasn't changed in relation to any of the other timing chain related components, I think that leaves the only potential problem of this head swap is the injectors, fuel rail, HPFP.

[JantzenOKC]

Definitely a mad scientist at work... I like it!

[PolynesianPowerhouse]

Originally Posted by Jason@JacFab

I'm think that the LLT heads will bolt onto an LFX... The 10-11 LLT, and 12+ LFX both use the same head gasket, which tells me for mounting/oiling/cooling purposes, they are probably identical.

It seems the MACE cam's don't work so hot in the LFX supposedly because of it's single exhaust outlet? Not to mention you don't get the cool cam sound. The LLT engined cars just seem to sound better than the LFX cars in general.

To sum it up, potentials gains are:

Headers (more power?)
Better sound (w/ and w/o headers)
Cams available (more power? cool sound)
Maximized porting area on the ex side.

What potential losses could be suffered from this swap? I can only think of two off the top of my head...

1) The LFX got a slight compression bump over the LLT. 11.3 on the LLT vs 11.5:1 on the LFX. I am not certain if this was a result from changing the shape/size of the combustion chamber, or if it was simply just the pistons

2) The LFX has larger intake valves. 38.3 mm vs. the LLT's 36.96 mm. This should be an easy fix by just installing the LFX intake valves.

I think the only thing that might screw a guy on doing this is if the injectors, fuel rail, and HPFP are so different between the two that you had to run the LLT stuff also, which would add additional cost to the swap.

Thoughts?

(ps: I scored a set of LLT heads with a fresh valve job today...)

anything is worth a shot especially with the correct tuning...go for it.

thoughts on it???

aren't the new single exit exhaust port heads supposed to be more efficient. chevy isn't the only company going to them. the phoenix engine of the charger/chally/300 also have the same setup.

supposed to be lighter, due to no need for bulky headers, better scavenging effect (a key determinant in exhaust performance), and afterall, the llt engine as a whole only kicks out 304-312, right? or supposed to at the crank...

the lfx has 12-19 more HP to the crank than the 10-11 LLT engines... its like swapping all the parts from the newer to older would be like playing catch up...



just my thoughts on it... the new single outlet design is supposed to be a step ahead. it would seem to be stepping back, to add weight to an engine, and have to mod the older heads just to get what the stock lfx one is already putting out.



this clip alone states that they IMPROVED air flow.... now I'm guessing they mean over the previous (LLT) engines... they speak of the intake and exhaust. with exhaust, keeping the gases as HOT as possible is how you keep efficiency, scavenging effect, and flow rates high... once exhaust exits the head and goes into headers, it starts to cool, until the cat converter, which serves as a reheat/maintain station for temps. also why we ceramic coat pistons, and headers....they act similar to lava tubes to keep lava moving fast before it hits open air and cools, which ultimately slows it down...

so if the exhaust ports integrated into the head keep the heat consolidated, and also dumps it right into the cat, with no need for headers or other tubes that can serve to let it cool, even if 100-200 degrees for a sec, then the more efficient design would be the lfx...


I could be wrong, but I'm a DIY type, so I'm willing to see what ya can do... I was kinda taken aback about lack of actual exhaust ports.... especially since I sit here with a half used standard abrassives kit, I still have from the jbody heads I originally learned on to the charger heads I recently sold.... :(

[12WhiteLS]

I think the whole turn to single exit exhaust is geared towards fuel economy and cheaper production. This isn't revolutionary, economy cars from the 50s and 60s had this kind of setup. If you made the improvements to the LLT heads, like the larger valves in the LFX heads, with full headers I think you would see an improvement. I don't know how economical it would be.... Maybe in a few years when you see more LLT salvaged engines. If anything you're car would sound better, LLTs with headers sound 100x better than LFXs with HFC.

[Jason@JacFab]

GM estimates the LLT weight at 361lbs, and the LFX at 348... Only a 13 lb difference

Without weighing the LLT heads w/ manfolds/headers etc, vs the LFX head it's tough to confirm, but I have personally weighed the LFX intake manifold (both pieces) @ 7.5 lbs, and the LLT intake w/ plenum cover @ 18.75lbs... That's an 11.25lb difference, leaving the diff between the LLT head w/ manifold and LFX head with built in exh only 1.75lbs...

So this tells me either GM is way off on their estimated engine weights, or the LFX head is heavier than we think it "should be".

In addition to the compression bump, and larger valves, I forgot to mention that the LFX cams supposedly have more duration than the LLT cams. Probably helps with that extra hp gain on the LFX. We don't know if it was the intake cam, exh, or both that got the increased duration... Perhaps it's just the exhaust side to help out the short comings of the single hole exh port?

Hard to say whether or not the LFX head really performs better, I'd say it was probably done more to cut costs than anything. If you look at GM list price for the LLT head vs LFX head, they sell the LFX heads for roughly $30ea more than an LLT head... The LFX heads must cost a little more to make I'm sure... The GM list cost for the LLT exhaust manifolds, and heat shields are about $304 for both sides. Obviously they don't pay that much for them, but let's just say they pay 50% of that, then mark it up to sell to Joe Public... This is real rough math here, but figure 85,000 cars sold per year, about 50% of that being v6 cars, so GM saves $152 per engine by not having to get exhaust manifolds X 42500 cars = 6.46 MILLION DOLLARS saved... List cost on the LFX heads is about $30ea more, so it probably costs them $15 ea x 2 heads =$30 X 42500 = a cost of $ 1.28 Million more to build LFX heads, which gives manufacturing the LFX heads a total savings of 5.18 MILLION dollars less than making the same amount of LLT heads with the exh manifolds.

Of course that's totally useless info, and just speculation based on GM list prices of certain components.

That said, I received my LLT heads yesterday. The exhaust ports look pretty puny, but they can surely be opened up. Once I pull a head off of the LFX engine I will flow the two and see how they compare. I imagine flowing the exh valves of a single cyl through the bigger hole the LFX will be better, but when you're spinning 7k rpms and everything is fighting to get out the same hole, I can't imagine it's better, but there's really no good way to test that.

Random thoughts.

[DSX_Camaro]

Well, using the basic equation for horsepower...
LLT
@ 6400rpm, 312hp 256 ftlbs
@ 5200rpm, 275hp 278 ftlbs

LFX
@ 6800rpm, 323hp 250 ftlbs
@ 4800rpm, 254hp 278 ftlbs

High rpm being maximum HP, lower rpm being maximum torque, and obviously with an enormous amount of room in between, the engines definitely behave similarly, as would be blatantly expected... I agree that an LFX with it's superior valves and cams with the header capability of an LLT would be a theoretical best (it would obviously sound the best).

Though the current set up with downpipes is just so convenient for turbocharging...

[Jason@JacFab]

Here's something interesting to look at... The GM SAE Certified dyno graphs for an LLT and LFX laid over the top of each other. (keep in mind, not entirely accurate, but probably pretty close)

(I couldn't find the 2011 Camaro 312hp graph so had to use the 2010 304 graph... I also couldn't find the 2012 Camaro LFX 323 hp, so used the 2012 Caddy with 321 hp) Close enough...

Looking at this, I would much rather have the LLT than an LFX.