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8.1L dyno test today.

Nah, I can give you a quick rundown of it though. Im not a full bore member here so I cant post pics. I have a video of it on the dyno on my telly, and a few pics of it all painted up and sitting on the stand.

XR270 cam, biggest one Comp offers for it at the moment.
Beehive valvesprings, Comp roller rockers, hardened pushrods, rings, bearings, oil pump, lightened the crank, ported the heads and milled them down for more compression, ported the intake, Gibson headers, cold air intake.

And here soon, as soon as I can get around to it, as I need to make 2 driveshafts for mine, fix the actual 8.1L owners other truck. It will be getting most likely a Walbro pump, a 03 8.1L regulator and returned to the dyno fella and re done. I am really hoping it doesnt need injectors as they are most likely hella spensive.

All that being said, its a completely different animal now. It pulls all the way up to 6k like a train. It knocks down 15mpg going 65 on the highway, it will roast the 33in tires off till they fall off the rims, and with that nanny torque management (read no burnouts basically) off, it burns the tires from a standstill and chirps third depending on the road and temp outside. Speaking of all that, he raced a tuned Furd F250 with the newer than the 6.0 coal burner. Cant remember its displacement. But, anyways, dead even till the Furd hit the speed cutoff, and since the 8.1 doesnt have a top speed block anymore, it kept pulling. Its pretty legit now I will say, he will probably wipe it out being a nitwit, but the joys of being 26 with no kids and a great job knows no bounds. Me, on the other hand, having kids and all that, I cant have that sorta fun anymore. The lady isnt a fan of me sleeping in the driveway and all that comes with the 26 yr old lifestyle. I have tried convincing her that its fun, but she doesnt approve. :haha:
 
If I actually get the truck bought (there is a lot of time between now and Friday when I can go look at it), it will remain stock with the exception of the cat back it currently has.

I turned off all the torque management on my old mans 01 8.1 last year and it did seem to run harder. The plan on his was to leave the exhaust but remove the cats so the cat overtemp can be turned off hoping to gain mpg.

I may actually be tuning my truck on the dyno then copying parts of it to my dads current mild tune. I plan on going in stock and tuning a little at a time so we can see the improvement. My buddy does custom tuning for a living so I am getting him to guide me. It will be tuned for 89 octane (yep e10) I am a farmer so you have to use what you produce.
I need to keep my head about me. If we start throwing parts at this I will have another project. The current plan is bad weather driver, tow rig, farm rig. It needs to stay that. This will allow me to trailer my K30 to the black hills, CO or Moab etc. I have enough one use toys.
 
454Sub said:
I would recommend headers, I know they are expensive and all that. But, the factory manifolds are crap, plain and simple. GM had to recall the trucks and put heat shields on the motor mounts because so much heat was backing up in there it was melting the rubber and the motor would vibrate it apart. The 8.1 mounts are completely different than a regular old BB/SB mount, and its not near as mechanically attached as the old mounts, the 8.1 I did would jump up and down inches. Plus, the manifolds suck and you will get MOAR POWER. Not to mention the motor mounts are a GM only thing and cost 110$ a piece.
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WHAT!? Where does this stuff come from? None of that is true. The L18 8.1L manifolds are not crap, they are well-built of stainless steel, not known for cracking or anything although they may not flow as well as headers… a no brainer there.

And the “Recall” you are talking about never happened. There was never a recall on engine mounts to add heat shields. Heat shields were added to the beloved LS small block truck engines (not L18 8.1Ls) for the reasons you mentioned, and certainly not under any kind of recall.

The engine mounts with heat shields were added as part of a new model year product enhancement around 2007. GM also added the shield to service part mounts around that same time. The old small block engine mounts without the shields have been superseded to the newer part number which now includes shield. Even if you have an old 1999 GMT800 truck with a 5.3L and ordered a new engine mount for a 99, the new ones come with shields. Interestingly enough, the L18 engine mounts in the GMT800 trucks and G-Vans included heat shields from day one even though they never had any of the isolator heat derogation issues like the small block suffered.

Also, only the 8.1L engine mounts in the GMT800 trucks are different than the old SB/BB mounts because of the piss poor frame design of that truck platform. The same generation of G-Vans, medium duty and Workhorse with L18s all used the same ole BB engine mounts that have been around for decades and none of those had engine mount issues either.


This is the engine mount shield you have your wires crossed on. This is small block LS engine mount. The L18 always had a large tin shield from the first day they went into production. This mount came out of my '05 Silverado HD with a 6.0L small block. The latest and greatest engine mount with the heat shield is on the right


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You know the LS engine mounts are burnt out when your air induction pipe rubs the fan shroud like this..... Again, L18s did not have this problem....only the small block LS engines

3358196407_a3b98c76e7_z.jpg



Now for the kicker..... the heatshields GM Powertrain added to the LS truck engine mounts doesn't work! As it turns out the heat shield holds more heat in than it reflects causing the isolator to degrogate that much faster meanwhile I have never seen a L18 mount fail in a GMT800 truck, G-van, medium duty or Workhorse period.
 
The manifolds on the 04 I have sitting in my garage are not stainless. The are regular cast iron. Junk, plain and simple. And unless the counter guy at my local GM center is a complete moron, which is completely possible, and his info on the recall could be wrong. The recall didnt effect the header choice, it was logic and the cam required a header install as the manifolds cant flow enough for the cam. They want 40$ for 2 sets of heat shields, and 110$ a piece for the mounts. The shield is a completely different piece that mounts separately from the mount itself. But who knows, doesnt really matter either way. When you order a L18 mount from GM, it does not come with a heat shield. They give you the option of buying them separate.

The 04s I have seen did not have a factory heat shield. It was offered later down the road as a bandaid for the factory piss poor 03 04 manifolds. Maybe the later models got a stainless decent manifold, but the 04 did not have a stainless manifold.

I may still have the factory mounts and I can get some pics. The metal tang that goes through the slot is bent, and nearly cut in half on both mounts. We managed to pull the motor out without unbolting either mount via some crafty crowbar massaging.
 
So is there an aftermarket or a different application motor mount that is more robust? Less prone to be effected by heat? You know us guys can't leave well enough alone!

Gary
 
Napa usually carries such odd objects and that doesn't surprise me. Our Advanced and Autozone did not. Plus with GM being close, meh, worked and was easy enough.

And its not the design that's terrible, imo, its the manifolds that create the heat that causes the melt that breaks the bond. Now, people can believe whatever the choose, but I have not 1 but 2 that the rubber is melted and trickling down like a candle, and the mechanical "locking device" is about sheared off.

Plus, while the headers are pricey. 425$ but came with all gaskets and hardware. They bolt right up to your factory exhaust no problem. Would be a breeze to install, and nothing wrong with more hp. Plus, I got quite a bit of under hood heat reduction, never a bad thing.
 
454Sub said:
The manifolds on the 04 I have sitting in my garage are not stainless. The are regular cast iron. Junk, plain and simple. And unless the counter guy at my local GM center is a complete moron, which is completely possible, and his info on the recall could be wrong. The recall didnt effect the header choice, it was logic and the cam required a header install as the manifolds cant flow enough for the cam. They want 40$ for 2 sets of heat shields, and 110$ a piece for the mounts. The shield is a completely different piece that mounts separately from the mount itself. But who knows, doesnt really matter either way. When you order a L18 mount from GM, it does not come with a heat shield. They give you the option of buying them separate.
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By junk, I still don’t get it unless you are just talking about hotrod flow. They are not plain cast iron although they look like it. They have stainless in them but I cannot find the exact content in the L18 Application Manuals. Now, the older big block manifolds were junk, those cracked and broke all the time. In fact, the old 454 manifolds I have on the 8.1L in my K10 are more of the junk variety but the factory L18 manifolds won’t fit old trucks without major frame hacking so I couldn’t use them (I am not much of a header kind of guy. Run manifolds for reliability and durability on all my trucks).



454Sub said:
The 04s I have seen did not have a factory heat shield. It was offered later down the road as a bandaid for the factory piss poor 03 04 manifolds. Maybe the later models got a stainless decent manifold, but the 04 did not have a stainless manifold.
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I don’t believe that is true, as I have never seen a L18 in any GMT800 truck that didn’t have heat shields around the mounts even as late as the 2007 classics, which were the old body style. And again, there is not thing wrong with any of the L18 manifolds. If there is anything to blame for the exhaust damaging the engine mounts on these trucks (small block LS engines) it is due to the less than sterling frame design to accommodate IFS.

That is correct in that the GMT800 L18 engine mount has a separate tin heat shield that is not part of the actual mount assembly. It has its own part number, which is not easy to find in the GM parts catalog. If yours is missing, I suspect someone removed it somewhere along the way or they vibrated off. :dunno:

This is as virgin as any factory L18 GMT800 truck can get, right down to the factory engine mount heat shields. I bought this truck brand new in 2001 and it only has 56,000 miles on her today.



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Now, they may have stainless mixed in them, but they are not stainless as say a Gibson stainless header for example. If, and thats a if, they do mix some small bit of stainless in them, its a lower grade than what Gibson or Hooker or whoever your choice brand of header would be. I used to know every type of stainless and what it was used for as its part of my job. And there is over a dozen types of stainless and several classes which they fit in. Some rust, some dont, some are used for boiler walls to take intense heat, some can not. ect. So its not impossible the L18 manifolds are not stainless, but they rust, so its not a huge dash of stainless, and its a grade capable of rusting. Possibly a 200 series stainless, as 300 series does not rust and is used in jewelry, surgical instruments, and for certain saltwater applications.

The 04 I worked on did not have the heat shields. Another 03 I worked on did not as well. But, GM in all its wisdom could have cut certain corners for certain vehicles. Who knows, either way, the 2 I have done did not have them. Both had bad motor mounts, I didnt put the 03s in, but I did do the 04 along with the motor itself.

And, its been awhile since I did the mounts, but I thought the tin shield was sandwiched by the bolt head and the motor mount. I could be wrong though. Like I said its been awhile.

And on the durability/dependability thing, I can understand that to a point. I always use a soft gasket (which came with it) and copper grade rtv. I have only ever had to tighten my flange and collector bolts 2 times after initial tightening. Once after its first heat cycle, and once after about an hr of run time. After that, never had problems with any headers if they werent el cheapo 1/4in flange wallmart headers.
 
my bet is the Cat converter over temperature has more to do with the motor mounts than the manifolds
 
This truck has no cats. Only Borla mufflers. Having no worries on emissions the cats are usually torn off just about everything and scrapped for beer money. :woot:

And, the original owner was a older guy, maybe in his mid to late 50s, who didnt abuse or use the truck in a way that is common in 20 yr old drivers. Every oil change and maintenance receipt. Had 80k ish on the ticker when the 2nd/current owner got it. Now its just ticked over 101,000 or so I believe. Either way, its no big deal on them. The mounts are new, shields are on, so, its ok. Plus, it runs like a dream, and gets better gas mileage than its ever gotten. Plus, the HP/TQ difference is pretty substantial. I drove an 03 8.1L with cat backs, and while it runs good, it doesnt hold a candle to this 04 now.
 
Meh, the 6.2 has a nitch the 8.1 can not fill. Its stupid simple to work on, and while its not a fire breathing monster, it is reliable. I personally do not like diesels, just not my thing. I passed up several trucks because of the 6.2. I always been a fan of 454s and such. But, I can not argue with a 6.2s simplicity and ability to truck on through without a worry on an electrical system or anything.

But, a good ol warmed over 350 in the 6.2s place does pique my curiosity. I always enjoyed building motors. Good times, plus the SB is pretty easy to make decent power. Thats what I am going to build next, a Vortec roller block and heads with a new cam and blah blah with a TBI on top for a 76 3/4ton mud truck.
 
Well I got my new pile. So far the first tank was 11 mpg. The speedo is off about 3 mpg at 65 so the odometer is off and that is what I was using for the calculations. Pulled home a blazer last night and it rolled right down the highway at 65 never shifting never struggling. I ordered a thermostat, some 285s and I am planning on a tune coming up. I will mess with the speedo on my HP tuners but I want a unmodified baseline.
 
When you get it tuned, they can adjust your speedo for you. Im sure you already know that, but something to keep in mind. Depending on your year you got, the 03s and down have an adjustable vacuum F/P regulator that I hear you can crank up a touch stock and help it out quite a bit. The 04s and up the regulator is in the tank, which is beyond stupid, but luckily the fuel rails are the same as the 03s.

Something else, the tuner fella I used wanted the truck to have a fresh filter, new fuel filter (which I couldnt do as its in tank as well :confused:), new plugs and fresh gas of whichever octane your wanting to run (we went with 91 for max HP). Im sure you know that as well, but just another thought.
 
I own the tuning program. I will be adjusting my own speedo (so I can get it perfect). We are actually using my computer to tune it. HP tuners was actually cheap when you know it is also a scan tool and comes with a cable. The tuner is one of my best buddies and I am going to watch so I understand better the ins and out of tuning.
 
Learn as much as you can, its pretty neat how much you can mess with in the various programs. You will be impressed on how much better it will run all said and done. I would still recommend the plugs and such, as they cant hurt. I know that nowadays they "say" they last till 100k, but that really is a stretch I think. But, congrats on it, hope you enjoy it. And good luck with the tune, wish I knew and had the stuff to do my TBI gen IV 454. Above my paygrade I guess.
 
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