Exhaust system for an automatic 1989 K5 Blazer 4WD

[clutch2k3]

I want to replace the entire exhaust system from the cylinder heads back since the driver's side manifold has a leak and I really don't like my stock exhaust sound. I'm looking for a mild exhaust tone with no droning at highway speeds but getting loud above ~2500 RPM is ok (truck is for family roadtrips and cruises ~1800 RPM). Here are my questions:

• Any header recommendations? Top priority is fitment, regular steel is ok.
• Since I'm leaving the 350 SBC TBI stock, should I just stick with manifolds? Maybe these?
• Any recommendations for an exhaust kit? Maybe a Dynomax 89007, Dynomax 89004 or Heartthrob Exhaust 8148050 would fit? Regular (aluminized) steel and a pipe diameter of 2" or more is ok.

I'm thinking Flowmaster 70 series mufflers (high dollar option) or Jones Full Boar mufflers (cheaper option).

Any help is appreciated

 

[dyeager535]

First, my personal preference, stay away from dual exhaust. It's more components to buy, more to fail, and it tends to be in the way if you need to be working under the truck. I had both, the single 3" is far better IMO. That heartthrob setup actually seems interesting but it looks to be a generic image unfortunately. I don't see there is one for a K5, I'm guessing that is due to no converter provisions as they list them for earlier trucks, and the other images show different designs on different trucks. The hangers for the other two are garbage. Exhaust doesn't need to withstand just gravity, vehicles move and sway, the exhaust hangers need to resist that, there is significant leverage on the manifolds if the entire length of the exhaust is incapable of resisting movement on all axis. The heartthrob image I see has much better hangers. Just an FYI when looking at this stuff. Yes, I've had plumbers strapping hangers, they didn't last and the exhaust moved around freely. With 3" pipe exiting in a stock location there isn't much room for exhaust, if it's free to move it will rub on things. You need some dampening via rubber, but it still needs to be kept from much movement.

Headers seem to do ok on the TBI trucks as the sole modification without needing to bother with tuning. I expect you are probably not able to extract all the power without tuning, but it probably won't cause issues. You'll need to have an O2 bung welded in if you go any route other than a properly equipped manifold.

Here's my post with recommended Hedman's: https://ck5.com/forums/threads/hedman-street-headers-69230.340453/#post-4088131

This is those Hedmans, into single 3", and what I believe is a Flowmaster 10 series out of a 350. https://ck5.com/forums/threads/new-exhaust-thoughts-and-possible-smog-delete.348681/post-4322849 I hate it in general, the truck has enough other noise without that exhaust lol. I'd definitely not recommend it based on what you are looking for, but there are enough variables that what sounds one way on one truck, sounds differently on another. But I doubt you'll not end up with some sort of drone on most "performance" mufflers. The one test I saw that compared stock type mufflers to a significant number of aftermarket choices, even so-called "quiet" mufflers, showed a significant increase in noise over stock. I am certain the stock designs are more restrictive, intentionally quieter, but for me, it's worth the trade off. It's not like you are losing 50hp because the mufflers are quiet.

 

[clutch2k3]

First, my personal preference, stay away from dual exhaust. It's more components to buy, more to fail, and it tends to be in the way if you need to be working under the truck. I had both, the single 3" is far better IMO. That heartthrob setup actually seems interesting but it looks to be a generic image unfortunately. I don't see there is one for a K5, I'm guessing that is due to no converter provisions as they list them for earlier trucks, and the other images show different designs on different trucks. The hangers for the other two are garbage. Exhaust doesn't need to withstand just gravity, vehicles move and sway, the exhaust hangers need to resist that, there is significant leverage on the manifolds if the entire length of the exhaust is incapable of resisting movement on all axis. The heartthrob image I see has much better hangers. Just an FYI when looking at this stuff. Yes, I've had plumbers strapping hangers, they didn't last and the exhaust moved around freely. With 3" pipe exiting in a stock location there isn't much room for exhaust, if it's free to move it will rub on things. You need some dampening via rubber, but it still needs to be kept from much movement.

Headers seem to do ok on the TBI trucks as the sole modification without needing to bother with tuning. I expect you are probably not able to extract all the power without tuning, but it probably won't cause issues. You'll need to have an O2 bung welded in if you go any route other than a properly equipped manifold.

Here's my post with recommended Hedman's: https://ck5.com/forums/threads/hedman-street-headers-69230.340453/#post-4088131

This is those Hedmans, into single 3", and what I believe is a Flowmaster 10 series out of a 350. https://ck5.com/forums/threads/new-exhaust-thoughts-and-possible-smog-delete.348681/post-4322849 I hate it in general, the truck has enough other noise without that exhaust lol. I'd definitely not recommend it based on what you are looking for, but there are enough variables that what sounds one way on one truck, sounds differently on another. But I doubt you'll not end up with some sort of drone on most "performance" mufflers. The one test I saw that compared stock type mufflers to a significant number of aftermarket choices, even so-called "quiet" mufflers, showed a significant increase in noise over stock. I am certain the stock designs are more restrictive, intentionally quieter, but for me, it's worth the trade off. It's not like you are losing 50hp because the mufflers are quiet.

Great points about dual vs single and I'm ok with single. Would y'all just buy a stock Y pipe?

Any specific recommendations for a kit (make/model/part number) or would y'all just get some 3" tube and fab it?

If I go with a kit, I plan on buying my own hangers and not using the ones included .

I'll weld the O2 bung myself, I've done it before.

I do not want Flowmaster 10 series mufflers. I do plan on clamping the muffler and testing it out before welding it in to make sure it sounds ok in the cabin.

 

[dyeager535]

If you can get away with manifolds, invariably they will be less hassle. I could tune the PROM, so I figured why not run headers.

Check Walker. I think they are the ones that list "OEM" exhaust parts, and as I recall the later trucks were 3", so that should be an option. I'm not too sure 3" is necessary with manifolds, but if GM did so, there must have been a reason. They did get rid of EFE when they went to TBI, so perhaps that freed up enough that they say worthwhile improvement going to 3" pipe.

If you can weld then it might make sense for you to fab it up yourself. A lot of people seem to dislike how factory exhaust is routed, so that could give you more options. But if stock gets it done for you, Walker is probably going to be hard to beat for a near-bolt in solution.

 

[clutch2k3]

@dyeager535 You can tune EPROMs? A few months ago I got WinALD working with my k5. Trick for me was setting the BAUD rate lower than the instructions said.

Do you have a tune for long tube headers that I could flash onto my ECM? I haven't got into tuning yet, just data logging so far (that's how I know its cruise RPM). But besides possibly flashing a tune for headers, I want to set the idle RPM higher when the engine's at temp.

 

[dyeager535]

Well, you can tune the 512 chips that the tuners had been using. I don't know where those are now, last I checked the sf512 (think that's right chip number) had been discontinued and the only ones being sold outside of a very few reputable vendors, were counterfeit. Moates.net was my go-to location for that sort of stuff, I presume they are still around but this obd1 stuff is very long in the tooth at this point, and there are generally far better options than PROM tuning.

Unfortunately I'm nowhere near my burning equipment. I recommended dynamic efi's embedded lockers in another thread for tuning, a bit pricey, but I think you are getting what you pay for. It would certainly leave the door open for future tuning if that was in the cards.

 

[Weird Beard]

I had a simple exhaust done on my 68 K10 with SBC and NV4500. Used Hedman coated headers, 2.5 in pipe run back to a dual, 2.5in, into single 3 in out flowmaster 70. Sounds great at all speeds.

 

[clutch2k3]

I had a simple exhaust done on my 68 K10 with SBC and NV4500. Used Hedman coated headers, 2.5 in pipe run back to a dual, 2.5in, into single 3 in out flowmaster 70. Sounds great at all speeds.

What did you do for the y pipe? Bought it pre made, a shop bent it, ...?

 

[Weird Beard]

My local exhaust shop ran pipe from each header. He pulled the passenger side past the t-case and tied both into the dual inlet muffler. No y pipe needed.

 

[Wes Harden]

My local exhaust shop ran pipe from each header. He pulled the passenger side past the t-case and tied both into the dual inlet muffler. No y pipe needed.

This is my plan. Past t cast over to driver side into dual inlet series 70

 

[clutch2k3]

Thanks for the help so far.

My goal is to create a parts list of stuff to buy for this project. Let's say I want to have a single exhaust with these manifolds that have a 2.5" outlet and this muffler that has dual 2.25" ID inlets.

Here are my questions:
- Would this exhaust pipe to manifold gasket (GM P/N 15592451) work with those manifolds?
- What should the inlet OD be for the ball flanges that connect to the manifolds (2.5", 2.75", 3", ...)?
- Should I use pipe reducers to go from the ball flange tubes, which I'm guessing will be 2.5", to the muffler inlets which are 2.25"? Or maybe just cut slits in the pipe and clamp it?

 

[Weird Beard]

Looks like they come with all gaskets and hardware. I would find a local exhaust shop to fit all the bits together. They will have all the hangers and assorted gaskets if needed. My exhaust guy just "made" my 2.5 in inlet and outlet flowmasters into 3in and 3 out.

 

[Wes Harden]

yes that gm flange doughnut works




Pictured pipe is 2.25" outlet, 3" outlet fits better. Don't have a picture of that one atm. The pipe flange lines up with stud holes in manifold.

 

[Wes Harden]

Looks like they come with all gaskets and hardware. I would find a local exhaust shop to fit all the bits together. They will have all the hangers and assorted gaskets if needed. My exhaust guy just "made" my 2.5 in inlet and outlet flowmasters into 3in and 3 out.

Yes they do and it's a nice thick flange. I think it would get for a street car that may not see any frame flex. For our needs I think the doughnut and belled head pipe are better.

 

[clutch2k3]

yes that gm flange doughnut works
View attachment 489000

View attachment 489001

Pictured pipe is 2.25" outlet, 3" outlet fits better. Don't have a picture of that one atm. The pipe flange lines up with stud holes in manifold.

Thanks Wes! So the 41725 ball flange works good enough, that's good because it matches that mufflers inlets (2.25").

So then you're going to fab 2.25" pipes from the manifolds to the muffler, right?

 

[Wes Harden]

Yes sir, going to cross over under the t case out put in 2.25 or 2.5. I'll decide when I get there I do have the 3" inlet 2.5 outlet vers of the 41725, I can use either one.

 

[clutch2k3]

If you use the 2.5" version, how will you connect to the 2.25" muffler inlets? Reducers?

 

[Wes Harden]

I am pretty sure my muffler is 2.5 inlet, I may run 2.25 along the pass side by the tcase, so yeah a reducer from 2.5 to 2.25 then back. I have the walker pass side intermediate pipe which is no bigger than 2.25' maybe 2", is the factory replacement piece. I may just copy it in 2.25 or 2.5 depending on clearance.