GMPP HT383E swapped into 99 Suburban K2500

Discussion in 'GM Powertrain' started by Tachyon, May 8, 2011.

  1. rileyjr16

    rileyjr16 Epic Member 5+ Years 1000 Posts

    Thats a very nice mod. I wanted to replace my old 4.3 with a big old 383 when I had my 97 but never had the money nor the time.

    Just gotta ask though, who beat up the transmission pan? :lol:
  2. Tachyon

    Tachyon Rockstar 100 Posts

    Heh, yeah it does look like it doesn't it. No it's fine. I had a new 4L80E put in when I did the engine swap. The replacement tranny's come with that pan. My guess is that some other model requires that indentation in the pan so they just put that pan on all the replacement tranny's to reduce the part numbers they have to stock.
    But every time I look under there, I think the same thing for half a second "Aww crap, what'd I hit...oh wait..."

    The dent in the factory muffler and crossover pipe on the other hand, I'd like to know the story on those. They were there when we bought the vehicle so they're a mystery.
  3. Tachyon

    Tachyon Rockstar 100 Posts


    One thing I didn't mention in the previous post is that when the exhaust system was installed, we discovered a problem with the header on the passenger's side. We think the bolts weren't torqued properly at install because two were missing! We had developed a bad exhaust leak around the header flange and it made a terrible racket and affected performance.
    I went back this last Saturday and the awesome team at Promax Performance took the header off, cleaned off the head, straightened and belt sanded the flange flat and re-installed with a new Mr. Gasket gasket and some copper seal. They also checked the driver's side and found several loose bolts there. Fortunately no gasket damage or leak was found on the driver's side. After they buttoned the whole thing back together and it's now leak free.

    I took it on it's first real road trip today on the highway and included an couple of full power on ramp merges.

    WOW!! What a difference. It's like a whole new vehicle. The engine is now silky smooth and the exhaust has a smooth, mellow bass tone that's not too loud. When you go full throttle it's a smooth bass howl. The best way I can describe the exhaust tone is that it's like Barry White calmly saying "OK baby, hang on, we're gonna go fast now, oh yeah".
    I am now super impressed with the Magnaflow system. It's a perfect match for the rest of the power-train. In fact the power-train package as a whole is complete now. It feels perfect. Smooth, powerful, integrated. It's like it came from the factory this way, but from a secret cooler factory where they all love cars and hot rod and cool jazz.

    Suddenly it feels like I have a brand new, off the assembly line truck with a hidden label somewhere that reads something like GT, or Limited Edition.

    At this point I can't possibly overstate how happy I am with this powertrain combination. The K&N Intake, the HT383E engine, the Magnaflow exhaust and the Hypertech program are now like a bad ass jazz quartet that's been playing together for years.

    Oh, and one more piece of awesome. I was heading down an on-ramp this morning, it was a two lane ramp that merged into one lane just before merging onto the highway. We were going from a stop light to the 110Km/h speed limit and there was a Navigator in the merge lane that thought he would just jump out of the light in front of me and beat me to the merge point. Man was he surprised. He was 3 truck lengths back by the time we got there. Ha, suck it Ford!
  4. phoebeisis

    phoebeisis Epic Member 5+ Years 1000 Posts

    THANKS for the extensive update!!
    So in short- you love it- it is a winner-no real downside.
    Any chance you have any HY MPG numbers?
    Yeah I'm a mpg nut-
    Little odd owning a Suburban- but mpg improvements on 1/2 tons save a lot more gas and $$ than mpg improvements on most cars.
    Do you think it get maybe 15 mpg at 60 mph-that would be pretty good-roughly stock-mpg considering all the utility of a large 4x4 tow capable 3/4 ton vehicle
    "Someday" Ill upgrade my 1/2 ton 2wd 98 Suburban-new motor-or maybe by a used 2004 when gas spikes and folks stupidly bail out of their Suburbans-like they did in 2008 and in 1979.1980.
    Yeah-thanks for the update.It is REALLY HARD to beat an OEM genuine GM engine for reliability. You can get more power for less-from the aftermarket-but it just won't be as reliable-simple as that. Reliability is worth another $1500 spread over the 10-years of its extended life.
    And the aftermarket crate motor builders-LIE about their HP torque-their claims are never checked-and usually require extensive intake and exhaust changes.
    And they break-more power-means more breakage
    Yeah-smart move
    For $15,000 you get new upgraded drivetrain-with more or less the same Suburban utility and road trip comfort(we use ours for road trips-and evacuate 2 dogs 5 cats 3 adults-4 miles W of NOLA). The only thing you are shorted on is the somewhat better mpg of the 2007 ons-maybe 3 mpg hy-2 mpg city
    but for $35,000-you can buy LOTS of gas.

    If you get a chance let us know hy mpg- or just regular fill up mpg-which I would guess would be about 10-11 mpg in mixed city suburban hy driving.

  5. Tachyon

    Tachyon Rockstar 100 Posts

    The Fuel Economy Question

    Regarding your first part. Yes, I am extremely happy with the final outcome of this long powertrain journey. I also really can't point out any downside other than not having the money to do it all at once and having to spread it out over a year and a half. But like I said before, given what I've now spent on the vehicle and the results I've obtained versus buying a new vehicle and still having payments on it, it's a no brainer with a win/win outcome IMO.
    I think that taking the time to do a lot of research and finding the right people to help is what has made this go so smoothly and why I'm so happy with the outcome.

    Regarding Fuel Economy.
    I've wondered about this too. I do keep a fuel log so I have fuel economy information. I've assumed that at this point I should see some MPG improvements in normal driving and especially highway driving IF I can keep my foot out of it. At this point it's not only responsive, but it's smooth so you forget and drive it like a car, a fairly sporty one, and you don't notice you're doing it. It will be hard to do a full tank without any peppy driving.

    I fully intend to track fuel economy both with driving my normal routine, and on a highway trip. I'm also very curious to see the numbers.
    That said, I'm not going to count this first tank for two reasons.
    I) The computer is in relearn so it will be a few hundred km before I feel it's settled in.
    II) The new cats are not "broken in" yet. I think this will also take a few days.

    That said, I filled it up the night before the header repair and drove it to the shop the next day. I think it had 14km on the trip by the time they got it. I took one short 45km highway run and a run through the city to test it it out get everything up to temp etc. I now have 145km on the trip and have used an eighth of a tank so far! This is really good compared to previous fuel use. This puts me on track for 17MPG (US gallons) and 21MPG (Imperial Gallons). Not that I expect it to end up that high, but it's impressive anyway even for a rough estimate.

    I'll certainly update once I get some real numbers.
  6. rileyjr16

    rileyjr16 Epic Member 5+ Years 1000 Posts

    Did yall evac for this one?
  7. Skippy

    Skippy Member 2 Years 100 Posts

    I love the fact you've updated this post periodically. It's a great testament to the upgrades you've made.

    Well done.

  8. Tachyon

    Tachyon Rockstar 100 Posts

    Well I hate when I'm looking for someone's experiences on something and I find posts related to the topic online somewhere and they post something like "So I'm going to try it tomorrow...." and that's the last post and it's a year old.

    I know I am very careful about how I part with my hard earned money so if I can help anyone else learn from my experiences and my mistakes then I'm happy to share the info. Actually I was worried someone would be thinking "I wish he'd shut up already and stop updating this old post". ;')
    Last edited: Aug 28, 2012
  9. Skippy

    Skippy Member 2 Years 100 Posts

    HAHAHA! Me too! It's why I posted here, and stay active with my account... to periodically update my towing experience with my rig.

    I despise the "I'll update when I get them put on!" and that was listed in 2008. Yeah. Promises promises.

    It's why I took the time to thank you for your updates. Too often people come in and read and appreciate without saying anything. :)


  10. Tachyon

    Tachyon Rockstar 100 Posts


    Powertrain wise, I'm very happy with this upgrade and consider it pretty much complete. I have lots more plans for the rest of the truck, but I prioritized on the powertrain and got it done first.

    However, there is one thing I've been thinking about doing and that's to replace the Hypertech program with a custom tune. That said, I don't really have the time and experience to mess with EFI Live at this point (or the funds for that matter). Maybe down the road. If I come into some cash maybe I'll look up someone that does them locally and just pay for a pro to do it. Don't get me wrong, the Hypertech is great. But it's designed for a stock 350 and stock powertrain. At this point I feel like there are efficiencies being left on the table and I think there's power and economy that can still be wrung from the system.

    Also I'd like to dyno the system A) to satisfy my curiosity about the power output B) to find the power and torque curves so I can optimize WOT shift points.
    Last edited: Aug 28, 2012

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