Polar Bear Suburban

[DirtyLarry]

Originally Posted by ScottsdaleK5

Hey Larry, I just finished reading through this thread and your attention to detail is immaculate..! I wish I had the patience to do the same; I'm always too eager to get it in and get it going! However, someday when things slow down I'd like to do the same.. The 'Burb looks great and you got a great deal on it! I'm quite jealous!

On to my questions, I have an '89 K5 Blazer that I plan on doing an NV4500 swap on.. It came stock with a 700r4 but after three of those I replaced it with a th350 adapted to my NP241. Now from what I understand it needs a 32 spline input shaft to work with a NV4500. I was wondering if your case already had the 32 splice shaft or if you put one in.. Is it best to find a case that has the 32 spline shaft or just buy a new one?

Thanks for the help! My Blazer will probably end up with an LQ4 for now but would really love to have an 8.1L in it.. they're just so damned expensive!

Welcome to the forums and thanks for the compliments!

Correct, you will need a 32 spline 241 or 208. 32 spline cased came behind TH400 and SM465 manual transmissions. My Burb was originally a SM465 so it already had a 32 spline 241 in it. Swapping a 32 spline input into a 241 is easy enough but finding the input will be the hard part. Might was well keep your eyes peeled for a complete 32 spline tcase and just use it.

LQ4’s are great engines but once you really start digging into researching the Gen III “LS” small block engine swaps and 8.1L swaps you’ll find there isn’t that much difference in cost. The 8.1L does not require exotic engine mounts, aftermarket accessory brackets to run A/C and the scavenger hunt Gen III swappers go on to find an inexpensive exhaust manifold that doesn’t require hacking up the frame. Mating a Gen III to a manual trans can also be another bag of worms. With the 8.1L, they bolt right in just as any old BBC or SBC and any older BBC header/manifold will fit the engine. It does require a unique flywheel but the clutch used is the typical 12" clutch GM used for eons. I see 8.1L’s pop up often for $1000 whereas Gen III’s are pulling bigger money because of their popularity. When people say LS engines are cheaper to swap I have to chuckle.

Good luck with your project!

[83GMCK2500]

Originally Posted by DirtyLarry

Welcome to the forums and thanks for the compliments!

Correct, you will need a 32 spline 241 or 208. 32 spline cased came behind TH400 and SM465 manual transmissions. My Burb was originally a SM465 so it already had a 32 spline 241 in it. Swapping a 32 spline input into a 241 is easy enough but finding the input will be the hard part. Might was well keep your eyes peeled for a complete 32 spline tcase and just use it.

LQ4’s are great engines but once you really start digging into researching the Gen III “LS” small block engine swaps and 8.1L swaps you’ll find there isn’t that much difference in cost. The 8.1L does not require exotic engine mounts, aftermarket accessory brackets to run A/C and the scavenger hunt Gen III swappers go on to find an inexpensive exhaust manifold that doesn’t require hacking up the frame. Mating a Gen III to a manual trans can also be another bag of worms. With the 8.1L, they bolt right in just as any old BBC or SBC and any older BBC header/manifold will fit the engine. It does require a unique flywheel but the clutch used is the typical 12" clutch GM used for eons. I see 8.1L’s pop up often for $1000 whereas Gen III’s are pulling bigger money because of their popularity. When people say LS engines are cheaper to swap I have to chuckle.

Good luck with your project!

Not quite hen's teeth but 32 spline is also behind the 4L80-E in '91 V-series, also nets you the electric VSS.

[Jonboy]

I ended up with a 32 spline NP241 and that's how my Jimmy project spiraled out of control. I originally was going to just flip the truck with a fresher 350 and a rebuilt TH350/NP203, but a low mile parts truck we acquired (90 3/4 ton Suburban ambulance) gave up it's transfer case and axles. A 4L80e bolts right to the case, and you might as well do an LS in front of that, so that's where I am at now. I am wanting to mimic your suspension lift for my Jimmy too.

[ERASER5]

So you are down sizing the cam? Was it a drive-ability problem or tuning issues?

[DirtyLarry]

Originally Posted by ERASER5

So you are down sizing the cam? Was it a drive-ability problem or tuning issues?

Yep, the RayLar cam came out last night. Both actually, but tuning is the main issue causing less than sterling drivability habits. I give up on dealing with anymore local tuners. The rig ran like a rapped ape at WOT but the overall drivability was sucktastic. Major idle flare during shifting, hunting idle, etc. I almost decided to drive it to San Diego for a business trip back in October and have RayLar’s tuner fix it up but he was pretty certain to clean it up I would need to convert to an electronic throttle and add VSS. An automatic trans would also make the tuning easier according to several of the tuner guys. I didn’t feel like doing any of that and a brand new stock GM 8.1L cam was only $140 from work and I had the tune from the K10 copied in burnt into the Burb. The K10 runs great even in stock form so in theory, the Burb should run exactly like the K10 as they will be identical aside from the burb having headers and the K10 running manifolds.

Rob and I got the engine out yesterday and swapped the cam last night. Just need to pick up some gaskets tomorrow and get engine dropped in tomorrow night. Hope to have it all wrapped up by the time the girls get home from visiting our in-laws in Florida Thursday.

At the end of the day, I think the RayLar 202 cam would be the cats meow for something with an auto trans and electronic throttle. The benefit of the electronic throttle would be to for the tuner to play with the throttle cracker to help with idling instead of running the IAC so aggressively. I don’t like electronic throttles in 4x4’s because they’re too touchy off-road. I will miss the big power the Raylar cam gave it though. It was fun beating down unsuspecting diesel heybro dudes for a while.

[DirtyLarry]

Christmas vacation wrench-a-thon! Rob on his K5 and me on the Burb


Rob getting after the rear window gremlins

[1985-GMC]

I'm glad you're getting that sorted out.

Have you put any thought into a roof rack for the burb?

[DirtyLarry]

Originally Posted by 1985-GMC

I'm glad you're getting that sorted out.

Have you put any thought into a roof rack for the burb?

Me too! Hope this gets it sorted out once and for all.

No, no plans on doing anything on the roof of the Burb. The K10 does all the long distance trips so no real need to add roof storage on the burb as it doesn’t go out as far or for as long. Rob has a roof basket for his K5 though.

[1985-GMC]

That's what I figured. My burb is going to be my road trip/ trail rig so I'm trying to figure out a roof rack but I don't want anything bolted to the roof or drip rails.

[DirtyLarry]

Well, well, well! I was finally was able to take it on a test drive this morning and I am a completely satisfied camper! It runs identical to the K10 as I had hoped! Tons of power with Cadillac drivablity manors. No more idle flares, hunting idle, dying, jerky jerk operation…. blah, blah blah…. Ah, and having the low-end grunt to let it lug itself around is so nice. Best of both worlds. Sucks it took 6 months to get here but it was worth it in the end.

You’re all probably tired of pictures but these are the latest pictures with the final hose/harness routing and clipping. It is now DONE under the hood with respect to the 8.1L swap. Speaking of the hood, that is the last thing that needs attention….the hood needs adjusted badly! I’ll try to get some videos soon.

Engine out for the cam swap, day after Christmas


Made stand off brackets for the hydroboost hose from the pump to the booster. This is a GMT400 booster hose (those hose with the blue clamp).


Made another stand off bracket for the hose going to the pump. It has a p-clip holding to the stud to prevent the metal portion of the hose from vibrating resulting in fatigue cracks










Might have a leak at the p/s pump that I need to keep my eye on. It didn’t leak over night after I wiped it off


Final Final!



This should be the end of the engine swap reporting for a while. Next up I need to adjust the hood, driver’s door and get after the horrible driveline angles causing major highway vibrations. Aiming to take it on a long roadtrip in May to the Overland Expo

[jbclassix]

I see green drops, is that what you're talking about?

[DirtyLarry]

Originally Posted by jbclassix

I see green drops, is that what you're talking about?

Haha, the green antifreeze is overspill from topping off the radiator and burping the stubborn sumbish

....that is what I am talking about!

[jbclassix]

got a beast there for sure. I would love to have a 2001+ 8.1L burb, but since it would have to be a daily driver, I'll have to settle for the measly 6.5L.

[Dieselwrencher]

Larry, glad to hear you got it figured out and running great. I'm sure that was a huge pita dealing with.

[Duramax40]

Very nice work I like the attention to detail. I had a question on the underwood factory wiring. I have an 89 big block truck that I converted to an lq9 and I'm starting to dissect the TBI harness out. My LS harnes is already done. What wires did you end up keeping. So far Iv found the 12v and couple sensor wires but everything else is confusing with out a year specific schematic book. It doesn't look like you had to keep that many to make it work. Great build!!! Thanks for any in site

[DirtyLarry]

Originally Posted by Duramax40

Very nice work I like the attention to detail. I had a question on the underwood factory wiring. I have an 89 big block truck that I converted to an lq9 and I'm starting to dissect the TBI harness out. My LS harnes is already done. What wires did you end up keeping. So far Iv found the 12v and couple sensor wires but everything else is confusing with out a year specific schematic book. It doesn't look like you had to keep that many to make it work. Great build!!! Thanks for any in site

Thank you sir!

The best thing you can do is to go on Ebay and buy a factory GM wiring diagram manual…. Like this one that is only $10. (I’m assuming your 89 is a square body not a GMT400)

Without a good roadmap you will have a much more difficult time knowing exactly what to cut away. As far as my Suburban, it was very straight forward. All I kept was a 12v hot, 12v key on, starting and charging circuits and gauges (oil, volt & temp). On that other hand, I just did the same thing to a 91 K5 for a 5.3L swap but it was much more complicated compared to my Suburban as it has an auto trans and electric speedo plus it had many ABS wires to be pruned away.

Get a GM Wiring Diagram Manual…..don’t even bother with Chiltons, Hayes, All-Data or any aftermarket diagram. Get the real deal!

Don't let pictures like this one scare you too bad

[Billhilly]

Hey Larry,
Just had a quick question about Duratrac's. I have just finished a drawn out build on my K2500 (http://67-72chevytrucks.com/vboard/s...d.php?t=217490) and am running 285 75 16 Duratracs on it. I imported these tyres and they are only now becoming available down here so there is no real 'local knowledge' as such. I don't know anyone running these tyres, I am wondering what sort of pressure you are running in yours? I figure Polar Bear would be a similar weight to my (empty) truck. I am currently trying 55lbs. I've only done 1500 miles so far and have gone from 50lb to 55lb. Still undecided and looking for opinions!
Loving your 8.1 swaps, I think one would be fun in my truck! Oh, and a five speed swap!

[DirtyLarry]

Originally Posted by Billhilly

Hey Larry,
Just had a quick question about Duratrac's. I have just finished a drawn out build on my K2500 (http://67-72chevytrucks.com/vboard/s...d.php?t=217490) and am running 285 75 16 Duratracs on it. I imported these tyres and they are only now becoming available down here so there is no real 'local knowledge' as such. I don't know anyone running these tyres, I am wondering what sort of pressure you are running in yours? I figure Polar Bear would be a similar weight to my (empty) truck. I am currently trying 55lbs. I've only done 1500 miles so far and have gone from 50lb to 55lb. Still undecided and looking for opinions!
Loving your 8.1 swaps, I think one would be fun in my truck! Oh, and a five speed swap!

Hey Billhilly!

Yeah, I’ve been watching your build but mostly through my phone, which isn’t easy to make comments with. Also dug your pictures on the mountain. Too cool!

I tell ya, I really like these Duratracs! The set on the Polar Bear really belong on the K10 but the bear borrowed them for a while to chase a vibration issue (turned out the vibration wasn’t the tires anyway). I need to swap them back soon. Anyway, I run the air pressure at 50 psi front/rear when they are on the Burb and 50 psi front/55 psi rear when they are on the K10 due to the weight of the camper. They seem to be wearing very well. In fact, they don’t show any wear hardly at all although I only have about 7,000 to 8,000 miles on them. Maybe a little more…. I kind of lost track of the miles being I’ve swapped them back and forth from truck to burb a few times. I highly recommend them. You going to love them! I have a set of 285 Duratracs on my Silverado HD as well but those probably only have a couple thousand miles on them if that.

Thanks for the engine swap comments. They've definitely been fun to do!

[DirtyLarry]

Nah, I sure don't. That project was 10 years ago in 2006. Built it for a friend that lives in Detroit. It got an AM General 6.5L backed by a TH400. He swapped in a 4L80E and painted it when it got to Michigan.

[NastyBuzzard]

Originally Posted by DirtyLarry

Nah, I sure don't. That project was 10 years ago in 2006. Built it for a friend that lives in Detroit. It got an AM General 6.5L backed by a TH400. He swapped in a 4L80E and painted it when it got to Michigan.

Ahh I see. I am just trying to figure out how I will have to do it or what I will need. I am supposed to be picking up my NV4500 today. It has the bellhousing on it for the 6.5 which from my research should bolt up to any standard SBC bolt pattern. I think the hydraulic clutch setup is on the passenger side though or something. I see you used the AA bellhousing.

[83GMCK2500]

Hi Larry, I've read through this thread, the NV4500 swap thread, and the 8.1 install thread for the K10 and I have some questions for you. I'm looking for big block exhaust recommendations/advice and your threads were the first that came to mind. I am past due for exhaust on my '96 and after reading through your threads I recognize you've got a lot of big block experience. If you have the time or inclination to impart any exhaust wisdom upon me, I would appreciate it. If you would like to reply back to me in my thread on my '96 instead of cluttering your thread that works for me.

I've got just under 290k miles on my truck and for the last 20k or so I've had something rattling in the muffler, I assume a weld has broken internally. It's obnoxious and I find it embarrassing.

Ultimately, when this is no longer my daily driver, I'd like to freshen up the engine, rebuild the heads, and put a more aggressive cam in it, injectors, 0411 ECM swap and tune. I would like to replace everything from the manifolds back and I'm considering a dual in/out muffler (unless otherwise recommended), at this time I'm looking at the oval 5x11 Magnaflow mufflers. Unless absolutely recommended I wasn't going to do headers at this time. When the time comes for those, this shop is local to me. I'm open to not replacing the cats, I'm prepared to have it tuned for that (now) or dummy O2 sensors.

The questions I haven't been able to find the answers for: what size exhaust to run on a big block, what kind of backpressure/velocity/flow characteristics are ideal? Do I use two separate mufflers but incorporate an x-/h-pipe before them or is the Mf 5x11 with internal x sufficient? I'm shooting for "not obnoxious at highway speeds" but sounds good if I get on it. I would think that my wheelbase (will take exhaust to behind duals with stock appearance) will help quiet it. With my gearing I'm running ~2,500RPM +/- 100-150 on the highway, depending on speed limit. The muffler is available in/out: 2.5/2.5, 3/2.5, or 3/3. What size do you think is appropriate? In my research to try and find what size exhaust you used on your vehicles I came across your L18 swap resource thread on CK5 and I read about the redesigned cat. converters on the '06+ vehicles. Should I try and source a pair of the new ones? Lastly, I'll be using mandrel bent tubing for the bends.

[DirtyLarry]

Originally Posted by NastyBuzzard

Ahh I see. I am just trying to figure out how I will have to do it or what I will need. I am supposed to be picking up my NV4500 today. It has the bellhousing on it for the 6.5 which from my research should bolt up to any standard SBC bolt pattern. I think the hydraulic clutch setup is on the passenger side though or something. I see you used the AA bellhousing.

Correct, the 6.5L bell is no different than any other SBC or BBC. You didn’t mention if your ’88 crew cab already has a manual trans or not. If so, you already have the hydro pedals but the master cylinder for the square bodies is not compatible with the slave that would be on the passenger’s side on a factory NV4500 bellhousing. That is the exact reason why I use the AA bells on my K10 and Burb….so I can use the square body specific driver’s side mount slave cylinder and off the shelf factory GM square body hydro hose. AA has two bell housings as well, one for the 1 gen NV4500 and another for the second gen (trans to bell mounting holes are different). If you go the route of the AA bell you’ll need to determine what year your NV4500 is. Pretty much it comes down to if the NV4500 has the deep granny gear and the shift lever that push and twists on you have the 1st gen. If the shift tower is held on by 4 bolts and the lever itself screws on to the tower then you have the second, which would be the same that I have in both of mine. Personally, I would not use a factory GMT400 bellhousing on a square body due to the slave location and the way the hydro hose is connected (square bodies have screw in fittings and GMT400 have push in). Outside of creating a custom hose, there is no a hydro hose with a screw in fitting on the m/c side and push in on the slave side.

Originally Posted by 83GMCK2500

Hi Larry, I've read through this thread, the NV4500 swap thread, and the 8.1 install thread for the K10 and I have some questions for you. I'm looking for big block exhaust recommendations/advice and your threads were the first that came to mind. I am past due for exhaust on my '96 and after reading through your threads I recognize you've got a lot of big block experience. If you have the time or inclination to impart any exhaust wisdom upon me, I would appreciate it. If you would like to reply back to me in my thread on my '96 instead of cluttering your thread that works for me.

I've got just under 290k miles on my truck and for the last 20k or so I've had something rattling in the muffler, I assume a weld has broken internally. It's obnoxious and I find it embarrassing.

Ultimately, when this is no longer my daily driver, I'd like to freshen up the engine, rebuild the heads, and put a more aggressive cam in it, injectors, 0411 ECM swap and tune. I would like to replace everything from the manifolds back and I'm considering a dual in/out muffler (unless otherwise recommended), at this time I'm looking at the oval 5x11 Magnaflow mufflers. Unless absolutely recommended I wasn't going to do headers at this time. When the time comes for those, this shop is local to me. I'm open to not replacing the cats, I'm prepared to have it tuned for that (now) or dummy O2 sensors.

The questions I haven't been able to find the answers for: what size exhaust to run on a big block, what kind of backpressure/velocity/flow characteristics are ideal? Do I use two separate mufflers but incorporate an x-/h-pipe before them or is the Mf 5x11 with internal x sufficient? I'm shooting for "not obnoxious at highway speeds" but sounds good if I get on it. I would think that my wheelbase (will take exhaust to behind duals with stock appearance) will help quiet it. With my gearing I'm running ~2,500RPM +/- 100-150 on the highway, depending on speed limit. The muffler is available in/out: 2.5/2.5, 3/2.5, or 3/3. What size do you think is appropriate? In my research to try and find what size exhaust you used on your vehicles I came across your L18 swap resource thread on CK5 and I read about the redesigned cat. converters on the '06+ vehicles. Should I try and source a pair of the new ones? Lastly, I'll be using mandrel bent tubing for the bends.

Hey Devin,

Cool! Sounds like a fun project. Yeah, the guts probably came loose on your muffler. I had a 2005 Silverado HD that did the same thing…..very annoying. Regarding the cats, if you can get away with replacing the cats with a “test” pipe like I have on my Suburban (wink, wink) you could have whoever is doing the ECM tuning just tune out the rear sensors instead of dummy sensors.

Regarding exhaust pipe size for a BBC, it seems the preferred size is 2.5” where claims of 3” or bigger takes too much back pressure way equaling loss of low end torque and anything smaller is too restrictive. I couldn’t really tell you on velocity/flow characteristics as that seems to be what appeals to each person’s ear but I can tell you that an older BBC, like the Vortec 454 you’re working on, requires a completely different muffler/exhaust configuration than an LS engine or even an 8.1L due to the different firing orders of the newer engines (1-8-7-2-6-5-4-3) compared to the older engines (1-8-4-3-6-5-7-2). The newer firing order engines absoluty need an H, X or x-muffler to sound right, otherwise they wound sounding like two poorly running 4 bangers having a shootout while the older engines like yours sound darn good with true duals, with two individual mufflers. I personally have never had an H or X pipe in an older firing order engine as I always thought they sounded good just plumbed the old school way (twice pipes with two mufflers).

My K10 has true duals, H-pipe and two individual Thrush mufflers (Cheap $30 Flowmaster knock offs). This same exhaust was on the truck when it had a 454 and sounded great but once I swapped in the 8.1L with the different firing order it sounded horrible. Added the H-pipe and now it sounds like a mix between a 60’s muscle car at WOT, cackle of a medium duty truck at low RPM and a Ferrari at cruise. Very weird, but it sounds awesome to my ear. Meanwhile, the Burb’s 8.1L is running a dual inlet/dual outlet Magnaflow X-muffler (can’t remember the exact name and I’m not home to look up the part number) but it sounds great with zero drone found with the typical dual inlet/outlet mufflers. Really quiet idle and cruise but it has a set of LUNGS at WOT almost like there is an exhaust cut out welded in somewhere. The videos posted of my Suburban are not the new Magnaflow exhaust but the old out 2” Flowmaster that sounded great with a 350 but a 50 caliber machine gun spinning at 50,000 RPM’s with an 8.1L. It was horrible. If it were me with an L29 454, I would go with cat “test” pipes and 2 individual Flowmasters or Thrush Flowmaster knock-offs (not a dual inlet/dual outlet muffler). Dual inlet/dual outlet on a 1-8-4-3-6-5-7-2 engine makes way too much interior drone for my liking. Dealt with that on my old ’98 Z71. Not sure if that helps you or adds more to the confusion but that I my offering to your question. I’m sure the heck no exhaust expert. My wife says I'm deaf anyway so my trucks may sound like crap to other people but they sound good to me now

Oh, I almost forgot....I have a Flowmaster dual in/out Big Block Muffler on a '93 C1500 with a 454 and it drones like mad. Sounds good, but the drone at throttle tip in is pretty sucktastic. It sound great on the outside though

[NastyBuzzard]

I apologize I did not specify. Unfortunately my 88 crew cab originally had a 350TBI/TH400 and is 2wd.

I do know that I have the 1st gen of the NV4500, it is from a 94 and has the 6.34 first gear. The shifter is bolted differently than yours. I just picked it up yesterday.

My friend had mentioned I swap to the internal slave type or get a universal slave that I can put lines out the drivers side. I am not sure if that is really an option.

I am just trying to do this on a reasonable budget, my current scope is to keep this as a work horse or tow pig type build and not let it snowball into another expensive project.

I know since I will be going diesel I will have to swap to hydroboost. My 78 crew cab 4x4 that donated its dana 60 had hydroboost so there is a start or at least a core. Unfortunately it was a 350/th350 combo. I never thought I would be lucky enough to find a NV4500 at a price I could pay.

Thank you for your advice on this and knowledge. I really appreciate it.

[y5mgisi]

Just for fun I would like to add in my planned exhaust on my crew cab. It will be a 396 with a nearly stock cam. I don't know why but I am insanely excited about the exhaust I'm going to give it! It will have factory exhaust manifolds, dual 2.5" pipe, an 18" glass pack/resonator on each side where the cats would normally be, an H pipe, and big dynomax turbo mufflers. I think it should sounds very quite at idle, should be totally drone free, but should still provide a slight rumble and a decent pop at wot. Can't wait!

[83GMCK2500]

Originally Posted by DirtyLarry

Hey Devin,

Cool! Sounds like a fun project. Yeah, the guts probably came loose on your muffler. I had a 2005 Silverado HD that did the same thing…..very annoying. Regarding the cats, if you can get away with replacing the cats with a “test” pipe like I have on my Suburban (wink, wink) you could have whoever is doing the ECM tuning just tune out the rear sensors instead of dummy sensors.

Regarding exhaust pipe size for a BBC, it seems the preferred size is 2.5” where claims of 3” or bigger takes too much back pressure way equaling loss of low end torque and anything smaller is too restrictive. I couldn’t really tell you on velocity/flow characteristics as that seems to be what appeals to each person’s ear but I can tell you that an older BBC, like the Vortec 454 you’re working on, requires a completely different muffler/exhaust configuration than an LS engine or even an 8.1L due to the different firing orders of the newer engines (1-8-7-2-6-5-4-3) compared to the older engines (1-8-4-3-6-5-7-2). The newer firing order engines absoluty need an H, X or x-muffler to sound right, otherwise they wound sounding like two poorly running 4 bangers having a shootout while the older engines like yours sound darn good with true duals, with two individual mufflers. I personally have never had an H or X pipe in an older firing order engine as I always thought they sounded good just plumbed the old school way (twice pipes with two mufflers).

My K10 has true duals, H-pipe and two individual Thrush mufflers (Cheap $30 Flowmaster knock offs). This same exhaust was on the truck when it had a 454 and sounded great but once I swapped in the 8.1L with the different firing order it sounded horrible. Added the H-pipe and now it sounds like a mix between a 60’s muscle car at WOT, cackle of a medium duty truck at low RPM and a Ferrari at cruise. Very weird, but it sounds awesome to my ear. Meanwhile, the Burb’s 8.1L is running a dual inlet/dual outlet Magnaflow X-muffler (can’t remember the exact name and I’m not home to look up the part number) but it sounds great with zero drone found with the typical dual inlet/outlet mufflers. Really quiet idle and cruise but it has a set of LUNGS at WOT almost like there is an exhaust cut out welded in somewhere. The videos posted of my Suburban are not the new Magnaflow exhaust but the old out 2” Flowmaster that sounded great with a 350 but a 50 caliber machine gun spinning at 50,000 RPM’s with an 8.1L. It was horrible. If it were me with an L29 454, I would go with cat “test” pipes and 2 individual Flowmasters or Thrush Flowmaster knock-offs (not a dual inlet/dual outlet muffler). Dual inlet/dual outlet on a 1-8-4-3-6-5-7-2 engine makes way too much interior drone for my liking. Dealt with that on my old ’98 Z71. Not sure if that helps you or adds more to the confusion but that I my offering to your question. I’m sure the heck no exhaust expert. My wife says I'm deaf anyway so my trucks may sound like crap to other people but they sound good to me now

Oh, I almost forgot....I have a Flowmaster dual in/out Big Block Muffler on a '93 C1500 with a 454 and it drones like mad. Sounds good, but the drone at throttle tip in is pretty sucktastic. It sound great on the outside though

Fantastic information, thank you very much. I had a feeling I came to the right forum and the right thread. Experience is invaluable, thank you for sharing yours. I will take your muffler suggestion under advisement as well, will probably be listening to a lot of youtube videos and/or soundclips.