L18 8.1L swap resource thread

[BoondocK5]

Yep, I'm reading this thinking to myself, "boy, I sure am glad I kept the engine and all its electronics bone stock."
I understand the whole VSS thing, I have enough problems, why add more?

 

[folkenheath]

Yep, I'm reading this thinking to myself, "boy, I sure am glad I kept the engine and all its electronics bone stock."
I understand the whole VSS thing, I have enough problems, why add more?

I read your comment thinking, I don't think I've ever thought I wish I left it stock.

Why add more....power? ...Torque? ...Efficiency?

I did leave my daily driver bone stock so far I guess, but I wish I bought one of those Edelbrock/Eaton Superchargers back when they had them on sale for only $4K a few years ago...now they are about double the price.

Seriously though, the aftermarket EFI makes it so easy now, there's too much potential to leave it bone stock.

If raising the idle a little bit is the biggest problem, it's a pretty minor problem to have more power available.

 

[Babaganoosh]

I read your comment thinking, I don't think I've ever thought I wish I left it stock.

Why add more....power? ...Torque? ...Efficiency?

I did leave my daily driver bone stock so far I guess, but I wish I bought one of those Edelbrock/Eaton Superchargers back when they had them on sale for only $4K a few years ago...now they are about double the price.

Seriously though, the aftermarket EFI makes it so easy now, there's too much potential to leave it bone stock.

If raising the idle a little bit is the biggest problem, it's a pretty minor problem to have more power available.

I completely agree, at first I was hesitant to go after market EFI because of all the horror story's. After watching a lot of drag and drive events I was like why can't I do a semi bone stock engine and go down the highway?

 

[ZooMad75]

While I’m all for power, the 8.1 in a heavy truck in stock form is pretty bulletproof. I have a tune that Howell set up for Larry’s first 8.1 swap and it’s lightly adjusted to deal with the mechanical throttle and elimination of the torque management bs and burst knock retard on the timing. It’s dialed. If I can keep my foot out of it the 8.1 knocks down similar mileage numbers that the 5.3 I pulled out did on the highway.

I can’t ask for any more than that. Plus I don’t trust myself doing the tuning. I have no clue what I’m doing in that realm and my little stint I did with the 5.3 proved it.

Honestly I know it sounds crazy but for my truck the 8.1 with stock setup and lightly tuned is very consistent and drives as oem-like as possible. I’m not lacking power anywhere. It’s kind of the beauty of the 8.1 in that scope.

I certainly know there is more power on the table between tuning and cam grinds. I guess it’s the adult side of me that says I don’t need to go nuts with it. I drove Larry’s burb when it had the Raylar cam in it. While it was an animal that probably made it the fastest 4x4 squarebody I’ve ever driven, it was really neutered down low. It was a rocket above 2,000 rpm but the off idle torque the 8.1 is known for was absent. The cam as Larry pointed out snowballed other issues that did push the limits of the stock pcm for tuning. Pro tuners couldn’t dial it in and he went to two of them.

I won’t deny Larry has a level of ocd that is unmatched and his dealing with UPS over calibration has pushed is ideal setup to be as smooth and oem-like as possible. The setup is turnkey. Drives better than his factory equipped 8.1 Silverado.

No changes planned for mine as far as pcm or tune that’s for sure.

 

[folkenheath]

Yeah, modified isn't for everyone, everything has tradeoffs, almost always, whether it be top end, low end, idle, cost, time, etc. Everything is a compromise/balance of what you want it to be able to do. I was just trying to let people know, don't be afraid of it is all.

I haven't had to touch anything but change the oil every year and spark plugs one time (just maintenance), and flush/replace the coolant once, in the last 13 years with my 8.0L 489. I did change the intake to try and improve it with the EZ EFI, but it surely wasn't necessary, it's been very reliable with the aftermarket EFI. I am about to go full CnP with the truck and a Terminator X, and either nitrous, twin turbos, or both.

My car has been Holley EFI for 6 years now, runs like a top. I did have the IAC valve literally fall out, its a 7500 RPM big block with solid motor plates, but some loctite and a new one fixed that issue. Runs awesome.

I like the EFI too much to go back to a carb, whether it be factory or aftermarket EFI.

 

[Stephen]

Are you running a factory ECU?

U4 cars and convertible are factory ECUs. Actually everything we have is using a factory ECU other than my K5 that has the old edelbrock proflo.

With the Holley ECU you can tune the IAC hold position, ramp down RPM, decay rates, etc. This allows you to open the IAC more under load and ramp it down slower.

I suspect part of the problem is reaction times for the IAC or throttle body trying to "catch" the engine. It sounds like Holley is giving you some options to do stuff that I suspect the VSS triggers in the factory ECU. Or maybe a better way to put it is they're working on the same problems with a different set of tools.

However, a larger camshaft does indeed need to idle a little higher because of the overlap, are you positive this is not a case where it just needed a higher idle to run properly in the first place? Also, are you running hydro power brakes or vacuum?

Idle on the convertible was pretty nice somewhere between 750 and 800 for just idling, but it couldn't always decel to that point reliably. I forget where the racer ended up but it's a little higher than necessary. Convertible is hydroboost and U4 car is manual brakes. Both have a similar higher stall torque convertor but there are so many variables with convertors (especially when you start talking about an application like racing a rock crawler) that it's hard to say what's happening with the trans to engine connection on decel. Both trannies have full manual VBs with compression braking so there's another variable too. They don't push through the brakes so they're not super tight but they're also fairly smooth in the rocks and don't have to wrap up a lot to get into the action.

I don't recall anywhere in the regular software where it changes IAC position based on vehicle speed, but I don't tune the factory ECUs, just speaking of aftermarket like Holley, Edelbrock, FAST, BS3, etc. Holley does offer "advanced tuning tables" where you can offset the IAC position based on other factors like gear or speed, this could be used to do what you speak of.

What about your torque converter? If you have a performance cam but have a tight torque converter for engine braking or rock crawling it may cause other issues that are just a side affect of what you need. When you increased the idle, how far, what RPM was it? Was it enough it was hard to hold the vehicle stopped at idle, or not nearly that much?

I am not saying any of these are your case Stephen, just throwing out possibilities and potential solutions.

No problem, I just threw out the idea that maybe this input could help with some of the tuning issues that pop up with modified stuff. It doesn't surprise me at all that guys are happy with a stock 8.1 as they're going to have the ability to overcome some potential problems with sheer inertia. One thing that seems to be emerging here is that using the VSS input is likely only an option with a factory computer and so far nobody really knows how it interacts. I'm sure guys know, just nobody that has popped in here. So, in the end, having a good handle on how to tune the aftermarket computers for driveability is huge since that's the direction a lot of the swap world is going now, whether it's an 8.1 or anything else.

 

[folkenheath]

One thing that seems to be emerging here is that using the VSS input is likely only an option with a factory computer and so far nobody really knows how it interacts.

I have no idea how the factory computer handles that, no experience tuning that.

Though using a VSS is surely an option with an aftermarket ECU.

It sounds like your idle is somewhat normal assuming the cam is what I would expect, which doesn't surprise me, you obviously know what you are doing.

I would think HP Tuners or EFI live would be able to tune the position of the IAC valve with the factory computer, but I don't know that. I know the aftermarket can, and I know the Holley can also change it based on vehicle speed (VSS signal) as well with the advanced table, if that is what you want to do.

It should not be an issue of the IAC valve not being "quick enough" because the computer should open it when you open the throttle. Then when you let off, it's already open, and it just "ramps" back down at a rate you specify. I suspect that when your engine was tuned with the new cam and upgrades with the factory ECU, they changed the idle, but didn't change the throttle open position of the IAC in the software? So it idles higher, but doesn't open the IAC further at load to compensate. It may also need to ramp down slower, to "catch" the engine on the way down. If it ramps down too quick, the engine may stall.

If the ramp rate is too slow, you lose the throttle response at low load, because it will idle down slowly. If its too fast, the engine stalls when coming from higher RPM back down faster.

With the hold position and ramp rates at low load, and increased opening and slower ramp rates at speed, you could get the best of both like you speak of with the Holley. With the factory ECU, someone else would have to answer that, I don't know.

 

[Lp1985]

They just find me . The engine in the background is a L96 6.0L

Don’t forget, ANY GM BBC manifold or header will fit the 8.1L. That certainly makes it easier to find manifolds for them. I have 80’s 454 manifolds on my K10 and 67-91 BBC Sanderson shortly headers on my Suburban. Brand new manifolds from Napa are under $100

If anybody can share some pics of there exhaust routing from below that would be awesome.

8.1/4l80/208 is the combination I'm using.
1975 k10 is the application.

I have my old headers that are pretty tight to a few things and I also bought a set of manifolds for an 85. I do not really like where the flange on the driver's side manifold is. So I would like to see what others have done to help my decision.

 

[Dragracer_Art]

Any suggestions on what drive-by-wire 102mm 4-bolt throttle body would be (if possible) a plug-n-play swap for my existing drive-by-wire 3-bolt, 78mm throttle body ???
Im looking at swapping on Raylar's new intake.
This is a 2007 marine application... so all bets are off. lol

 

[folkenheath]

There are different connector types on the DBW throttle bodies. So you'll have to find one that matches both the wiring type and the bolt pattern to work correctly. I just searched my suppliers and couldn't find one.

I believe Granatelli and Nick Williams both make what you need.

 

[chrisgt]

I searched the entire thread for oil cooler information and all I can find is how to delete the thing, I don't want to do that!

I was thinking about just getting a generic oil cooler with 1/2" NPT inlet/outlet fittings and mounting it up in front of the radiator. To connect this cooler to the engine, I have come up with two options:
1. The GMC Kodiak has adapters (DORMAN 800710) that go from the radiator end of the lines to 1/2" NPT, from there run hydraulic lines to the cooler.
2. Remove the oil line fittings from the engine block and simply thread in 1/2" NPT hydraulic lines from the block and run straight up to the cooler.

I kind of like option 2 since it's more simple and my 1983 K30 has basically infinite amount of space to play with under the engine, just wanted to see what others think about this.

 

[Wes Harden]

I like option 2. unless you get a custom radiator or make a factory 8.1 rad fit, the stock cooler lines will be a pain to adapt.

 

[BoondocK5]

I don't remember where I found the I found the info about the oil cooler.
I remember I yanked the bypass out of the block. Then, used some 1/2" pipe threaded plugs, with some industrial sealant.
Do same at your own risk. Because I have no bypass now. If my filter clogs, 8.1 is ****ed!

 

[chrisgt]

I don't remember where I found the I found the info about the oil cooler.
I remember I yanked the bypass out of the block. Then, used some 1/2" pipe threaded plugs, with some industrial sealant.
Do same at your own risk. Because I have no bypass now. If my filter clogs, 8.1 is ****ed!

There is abundant information in this thread about that and it isn't what i'm trying to do; i want to KEEP my oil cooler.

 

[Bent77]

Did anyone ever answer if the 12” clutch fits?

I was pretty sure the 11” did, but I haven’t assembled one
Is the flywheel the same as the other LS flywheels?

 

[BoondocK5]

There is abundant information in this thread about that and it isn't what i'm trying to do; i want to KEEP my oil cooler.

Ok, so have some hoses built and run them to an oil cooler.

 

[ZooMad75]

Yep, that is the right flywheel part number guaranteed. What I posted is definitely correct

12582964 Flywheel
12563485 Flywheel bolts

Not sure where the confusion is at? I see this is an 8.1L specific flywheel (internally balanced) that also fits the internally balanced 427 and 572 GM Performance Parts big blocks. It is not common with 454’s because they are externally balanced.

Don't forget you will need to remove the dowel pins from the flywheel (not sure I ever even mentioned they need to be removed actually ). Then you can use any ole GM truck 10 spline clutch on it.

This what I have on mine. Though I think I'm running an 11" clutch. Get the right clutch and it won't lack clamping power despite the smaller diameter. Centerforce is worth the dough. I've never had it slip. However I think the hydro clutch provides more leverage without making the pedal effort high either.

 

[chrisgt]

Did anyone ever answer if the 12” clutch fits?

I was pretty sure the 11” did, but I haven’t assembled one
Is the flywheel the same as the other LS flywheels?

So from what i've been reading (which is a lot since this was a boring week at work), there are three sm465 bellhousings: the iron bellhousing, an aluminum bellhousing for 153T flywheels, and the aluminum bellhousing for 168T flywheels. The bellhousing I have is the aluminum 168T version, I can tell because it looks like it and because my 350 has a starter with offset bolts.
Apparently the bulge in the bottom of the 168T bellhousing means it is designed to accomodate a 12" clutch/pressure plate.

It looks like I can buy the flywheel/bolts designed for the 8.1, a clutch kit for any old 12" SM465 (or nv4500) and simply open up the holes a bit to fit the larger metric pressure plate bolts.

The old body style 2001 trucks came with an 8.1 and NV4500, not sure I feel like trying to be the experiment here, but it should be possibly to simply order the flywheel and clutch kit from one of those. The NV4500 has the same 10-spline count as the SM465 (or am I wrong there) and the clutch kit should go together without any modification of the bolt holes or dowel pins.

 

[ZooMad75]

So from what i've been reading (which is a lot since this was a boring week at work), there are three sm465 bellhousings: the iron bellhousing, an aluminum bellhousing for 153T flywheels, and the aluminum bellhousing for 168T flywheels. The bellhousing I have is the aluminum 168T version, I can tell because it looks like it and because my 350 has a starter with offset bolts.
Apparently the bulge in the bottom of the 168T bellhousing means it is designed to accomodate a 12" clutch/pressure plate.

It looks like I can buy the flywheel/bolts designed for the 8.1, a clutch kit for any old 12" SM465 (or nv4500) and simply open up the holes a bit to fit the larger metric pressure plate bolts.

The old body style 2001 trucks came with an 8.1 and NV4500, not sure I feel like trying to be the experiment here, but it should be possibly to simply order the flywheel and clutch kit from one of those. The NV4500 has the same 10-spline count as the SM465 (or am I wrong there) and the clutch kit should go together without any modification of the bolt holes or dowel pins.

The 4500 and 465 share the same input spline count and size. Reference my quote from Larry above.

You are right the 3500hd trucks were the only ones to get the 8.1/4500 combo from the factory and yet it’s the same flywheel used as the 800 trucks that had the ZF6 behind the 8.1.

The flywheel will accommodate the 12” clutch as long as you pull the dowel pins. Though fitting the 12” clutch is more a question of the bellhousing having the right shape to fit it. 11” clutches work fine, clear everything and were what came on the trucks.

Personal opinion here, I’d get a quality 11” unit over a cheap 12” version.

The big key is matching the clutch to the type of release bearing you intend to run. Early 4500’s with a external slave and conventional release bearing take one clutch and the later (‘96 and up) using the integrated slave/release bearing take another.

 

[chrisgt]

Ohhh I didn't realize the pressure plate was different for hydro clutches! I've worked on other vehicles where it wasn't.
Sounds like even though a 12" clutch would fit, 11" is the best bet, especially since it doesn't require removing dowel pins, which i really wouldn't want to do. Thanks for steering me in the right direction, i'll just order a decent 11" clutch kit for a mechanical sm465.

I use the truck at least once a month to haul a race car (which my SUV can do as well if it has to), so my hope is to start the day after a race and have the whole swap done relatively quickly, that can only happen if i do a good job getting all the right stuff.