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This is regarding the 1990 K1500 383 stroker FAST EZ efi 2.0…

This is regarding the 1990...
This is regarding the 1990 K1500 383 stroker FAST EZ efi 2.0 project. I need a recommendation for high flow catalytic converters. I am running dual 3" exhaust with balance tube down the R side. I currently have 2 Magnaflow catalytic converters. One was starting to rattle before I started the project. They are 3" high flow, hollow in the center. I don't think that they are much more than just straight pipe. I have pulled the catalytic converters off a vehicle before and it ran good, but the exhaust stunk. Getting my truck through emissions might be a consideration once I am finished with it. I need them to be 3", high flow, and have clean exhaust. Reasonably priced as well. Thank you.
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Answered in 1 minute by:
8/17/2017
K. Wiggins
K. Wiggins, ASE Certified Technician
Category: Chevy
Satisfied Customers: 3,236
Experience: ASE Certified Technician, Associates Degree in Automotive Technology, 15+ years in the trade
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Hello, just letting you know I'm reviewing your question and will be back in a few minutes.

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Thanks for your patience. I've had good luck with the flowmaster 223 series. About 40 cheaper than the magnaflows and to me they seem to do a better job of getting rid of the smell. Some people have complained of them breaking apart inside but honestly I've not ran into that and my exhaust guy says he's seen two out of maybe 500 do it. If you're in California let me know and we can possibly find something different for emissions that's CARB compliant.

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Customer reply replied 6 months ago
I'm actually in Florida, but will be moving to California in the next 1-2 months. I'm getting as much of it done now as possible, but will ultimately be finishing it there. So I will need something that is CARB compliant. I'm not going to run the oe air pump or egr etc, but that shouldn't matter as long as the exhaust is clean. It currently has Magnaflow mufflers on it now.

OK, here's what we have for CARB compliant

Flowmaster

Magna flow (there's cheaper ones on amazon but no listing of inlet/outlet size)

Walker

If it wouldn't be out of budget I'd go flowmaster. For budget the Walker shouldn't disappoint. I've installed tons of walker converters and muffler over the past 17 years or so and never had an issue.

The thing about the walker and flowmaster are the warranties. I believe both are 50k/5yr emissions and structure. Only 1yr on magnaflow.

You may also be able to google the part #'s and find them a little cheaper somewhere.

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Customer reply replied 6 months ago
Will the Magnaflow mufflers that I have now work for the CARB compliance. I think I got them from Jegs for approx $45.00 each. If not, please recommend some mufflers. If they are good, any issues using the Flowmaster catalytic converters with the mufflers that I have now? Any difference in performance between Flowmaster and Magnaflow? If not, I'm going with the Flowmasters. Please recommend Flowmaster mufflers that are CARB compliant, if I need them. Are the Flowmaster catalytic converters that you recommended high flow or will they flow good for the 3" dual exhaust? Thank you.

So as far as mufflers go out in California they do not have to meet a carb compliance. What they look for is 95 decibel max for vehicles under 6000lbs GVRW. So unless they are super loud your current ones should work. HERE is a link to the law on it.

The flowmaster cats will work with your set up and due to the extra catalyst in them vs 49 state converters (still high flow compared to stock) it should quiet down your note out the tail pipe. They also only measure the sound at a % of max rpm listed for the vehicle and since the "stock" max rpm for your truck was like 4500RPM that will help as well.

If you do find the magnaflows are too loud I would go with the 50 series flowmaster or the 40 series delta flow. Here is a clip with sound and dba level. I run delta flow 40's on my 383 s10 and find them to not raise eyebrows with law enforcement unless you get on it hard in low gear. I've also had the 40 series non delta flows and they were around 102 decibel when checked with a smart phone app, delta flow 40's on my truck are around 85-88dba on the same app.

K. Wiggins
K. Wiggins, ASE Certified Technician
Category: Chevy
Satisfied Customers: 3,236
Experience: ASE Certified Technician, Associates Degree in Automotive Technology, 15+ years in the trade
Verified
K. Wiggins and 87 other Chevy Specialists are ready to help you
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Customer reply replied 6 months ago
That Flowmaster catalytic converter part # that you listed is discontinued. Go with the Walker, or is there a Magnaflow part #, or alternate Flowmaster available. I don't want to save money now, only to have to replace it in a year because the engine burnt them up. The engine is capable of 6500+ rpm. I don't mind spending extra on the right parts. They need to be CARB compliant and high flow. Thank you.

I apologize for that. It looks like Flowmaster discontinued the 3" version of those. You can still get it HERE as new old stock. Walker would be my next pick due to it have the same warranty as the flowmaster.

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Customer reply replied 6 months ago
I tried to order them 2x, from Jegs, and the eBay link that you just went. Both emailed back that the part is discontinued.

OK, It's going to take me a couple of hours but I want to do some research on the walker flow ratings and see if there's any other options for you here.

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Customer reply replied 6 months ago
Great. Thank you.

You're welcome, I'll be back asap.

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Thanks for your patience. I talked with reps from both magnaflow and walker. Also did some comparisons. Both reps admitted the flow on the cali cats are similar. Biggest difference between the two below is the magnaflow is 3" in the pipe and case while the walker is necked down a 1/4-1/2" " at the case from the pipe.

The magnaflow is also full stainles while the walker is just stainless case and aluminized steel pipes. Both DO carry the same warranty.

Walker

Magnaflow

Those comply to the carb eo number for your truck.

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I was unable to find dyno runs from either of these which is something I was really looking for.

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Customer reply replied 6 months ago
I'm running a 160 degree high flow thermostat. Do I need to run a higher temp thermostat to keep emissions down, or will the FAST system automatically adjust?

I would suggest running a 195 for the emissions testing. Most of the guys I work with in California tune it one way for testing and then have a "normal" set up.

195 stat

Close to factory timing is what I'd suggest for the testing.

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Customer reply replied 6 months ago
That's a little far out, just need to know. I am going to run the 160 for initial startup, break in. After the 500 mile mark, I will go to the 195 for testing then, back to the 160. The system is self-tuning. Is there a way to setup 2 different tunes with this system?

I need to research if there's any manual tables that could be loaded. I know the self tune part is fairly quick. Biggest reason for the 195 is to get up temps so it will run leaner and output less hydrocarbons on the smog test.

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Customer reply replied 6 months ago
Will there be a noticeable difference in performance between the Magnaflow carb compliant and the Flowmaster 223 catalytic converters? If so would it be worth switching them out after testing?

Based on what I've read and input from people I've helped in california the difference would be around 5-15hp and 5-20ft lb of torque. Although I can't endorse or suggest changing from the compliant ones to non I can tell you many people I know there do just that.

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