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Lifelong S-10 Owner
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Discussion Starter #1
I have a 2002 ZR5 Crew Cab Sonoma that is stock. I was wondering if there is any usable power available below 4000 rpm by increasing the Y-pipe to a 2.25" size like the MagnaFlow style system and then a custom 2.5" catback with dual tailpipes out the sides. I do not hotrod the truck around at 59 years old anymore so its just highway driving, towing about 3000# trailer and errands. I don't use high rpm just lower rpm torque. The truck does have the 3.73 gears and 235/75R15 stock tires with a 1.5" lift. What are your recommendations? Thanks, John
 

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Been there Done it
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7,059 Posts
It's gotta help. Think I'd try just the Y-pipe first. That's the most restrictive part of the system.
A complete system gets spensive and I don't know if the improvement would be justified.
I have a regular 02 CC and it's a dog with 3.42's.
I'm thinking a Vortec 5.7 might help. Fuel mileage can't get any worse.
 

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254 Posts
On my '03 V6 5 speed RCSB 2wd I changed my Y pipe to 2" and added a 2.5" MagnaFlow high flow cat. This was added to a custom single inlet, dual outlet muffler exiting out the back.

Lower RPM was not noticeably hurt and it improved top end and helped smooth the revving of the engine some. I drive it from 1,000-4,500 rpm. Peak butt dyno is between 2,500-3,500 and there is still a drop off after 4,000, just not as bad as it used to feel. I have no issues cruising in 5th at 35 mph at around 1,100 rpm, and although slow, it will accelerate from that point. Realistically, it feels like the small turbo diesel engine in the SUV I rented earlier this year: no need to downshift when you would in a modern medium sized gas engine, both for hills or accelerating.

Now, there is a big weight difference between my truck and yours (mine is 3,500 w/o driver) so that will change the dynamics when using the same engine. But I wouldn't worry too much about torque if your good with how it is now. I have driven it multiple times with more than the 800 lbs. max load in the bed and it drove fine from an engine standpoint. I had to drive it a short time without a cat and it surprised me when it didn't lose the low rpm power, and that was more free flowing than my current setup.
 

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Lifelong S-10 Owner
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301 Posts
Discussion Starter #5
This is why I changed my Y pipe: 1.25" ID at the manifold

View attachment 335505



Also, manuals have a crushed crossover:

View attachment 335506 View attachment 335507 View attachment 335508
Wow. Why would they design it so small and then crush it for clearance too? No wonder these trucks can't breathe. Looks like the crossover pipe is the best place to start with an improvement in pipe size. I just don't want to hurt anything as I never get over 4000 rpm and I don't drive it hard at all.
 

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Wow. Why would they design it so small and then crush it for clearance too? No wonder these trucks can't breathe. Looks like the crossover pipe is the best place to start with an improvement in pipe size. I just don't want to hurt anything as I never get over 4000 rpm and I don't drive it hard at all.
No idea why. I don't believe the automatics have the crushed section. I'm not an automotive engineer, but there are more than a few things about these trucks that are lacking. GM had there reasons, be it testing and development results we aren't aware of, saving money, or just plain bad decisions. Personally I have taken this as a fun experiment to try and improve my vehicle cheaply. Something that is hard to do in newer cars.

I understand the hesitation. Initially I did cut the crushed section out and replace it with a round pipe. I did this with both the original and the warrantied Y pipe after the original cats went bad. Though this helped, eventually I decided to make a custom 2" Y and I don't regret it. One of the things I have always loved about my truck is that for most everyday driving, I don't have to downshift to the lowest possible gear or run through the entire rpm range in each gear to drive "spirited". I think what I'm trying to say is I don't "feel" like my engine's torque was negatively affected by the larger Y pipe.

Depending on your skills, your best bet would be to have a shop do the job for you. It was a pain to do myself since I had no equipment, and I ended up having to take it to a shop and pay to fix the leaking.
 

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LS3 Cruisin'
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1,764 Posts
The stock camshaft has no overlap, not even close... exhaust doesn't help pull intake in, no scavenging or any of that business. Piston moves up the bore, pushes exhaust gas out... even a smallish pipe isn't truly that much of a restriction. You won't gain noticeable torque down low... A few HP at the high end sure.

If you actually want a bit more power without the hassle of putting a 5.7 in... a cam swap is a good place to start.

Then the Y Pipe and cat-back start to make sense.

I mean sure, I had a Magnaflow dual cat back system and larger Y pipe on my 4.3 years ago because I wanted dual out the back and more throaty exhaust note, but I never felt it gave me any more power. Ditto with those old air raid TB spacers haha...

Adding E-fans, and using an under-drive crank pulley would free up a few ponies as well, but without changing the engine dynamics or reducing parasitic hp losses you don't gain much from just changing the exhaust system.

The stock manifolds are probably restrictive as well, as are the stock valve size and lift... so regardless of what upsizes behind them, its small gains.

Really think about it... if all it took for GM to advertise that the truck had 205hp instead of 190hp or 180hp, was upsize the exhaust diameter an inch... you don't think they'd have done that from the factory? In those days the marketing was pretty tense when the best LS engine of the day (LS6) had 405hp and most commuter vehicles were lucky to have 170... Now 300, 400, 500+ hp is a click away on Ford.ca on the F150... Anyway take it for what its worth :)
 

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Lifelong S-10 Owner
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301 Posts
Discussion Starter #8
I would definitely have a custom exhaust shop do the crossover and pipes. I've built engines, street rods and muscle cars but getting older makes it harder for me to work on them. I did the motor mounts and front seal on this S-10 along with ball-joints, axle shafts, and the lift but its just not as much fun now with bifocals, aches and pains slowing me down. I think I do more cussing than working! :LOL:
 
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