L31 Rookie

[May-39]

Hey EFI folks.
And FAST355!! lol

Anyway, I wanted to create a weekend two tracking/fishing camping rig. Needed 4 doors (dogs). I also STRONGLY prefer manual transmissions.
My buddy and I have seemed to have created a cottage industry converting VWs to 5 speed diesels..This requires a TCU delete and conversion/repin of ecu. Then of course recoding to manual trans.
This fall, I saw an 96 obs Silverado with a 5 speed my mind started racing. I spent the weekend on google and discovered this swap didn't require a lot of fab and what seems to be (I can't believe it) fairly little wiring correction.

I scooped up a lower miles 99 obs 4x4/5.7 off an older gent. Pretty rust free, a rarity up here in the north. Good price cause the front end is GONE. still factory BJs complete with death wobble over 55 mph.

I have found a donor 98 Silverado...
I will have all kinds of tuning gremlins to work out I'm sure.

I found fast355s build and am very interested in a similar build...no headers, upgraded manifolds, cam and I'm researching the heck out of these marine intake swaps. I'm sure a 411 swap will be done once the tranny swap is done and suspension straightened out.
Fast I left you a pm..lol

[1project2many]

Welcome to GM land. Until recent years GM made vehicles very similar, likely with the idea that making vehicles as generic as possible would require the fewest configuration specific changes to the engineering and manufacturing processes. Those of us who grew up with GM are always amazed at the mount of effort a seeming simple change can require with other vehicle makes. We've been spoiled for a long time, and unfortunately I believe GM no longer builds vehicles in a way that makes swaps and configuration changes easy.

Sorry to be confused about what you're up to... You're putting the manual trans into the Suburban? A minimal effort swap would leave the extra transmission wires tied in a bundle outside the trans. Folks wanting to make the swap cleaner would remove unneeded wiring completely. Which 5 speed trans? Do you have a target for power or torque, or are you just planning for a few mild upgrades and letting power end up where it ends up?

You should face a minimum of tuning issues as the 5.7 was available with both manual and automic transmissions. You're likely to find little difference between most truck and Suburban calibrations as long as you stick with the same basic GVW / family (1500/2500/3500).

What's with the thumbs down? Just because you're a rookie doesn't mean you lose points around here.

[May-39]

I have no idea who put the thumbs down up there wasn't me. Maybe I upset someone?

Helping pal with a 350 conversion in his cj7 is what got me thinking about gm platform..Parts were easy to find and reasonable.

I am planning on 3550 trans..I have a donor 98 Silverado with manual trans..So I should have what I need.
I don't think an NV4500 is required..I'm not hammering this trans or pulling much weight etc.
My power goals are more efficiency goals. I want 17 mpg at 70mph if possible while making more power. So lt1 (not hot) cam or crane 4x4 cam, some better manifolds (not headers, don't want to deal with leaks, cracks or noise), 2500 midpipes, possible marine intake swap. Probably a 411 swap. Will install a rough country 3" lift with some factory width 285 all terrains. This is going to be a camping/fishing rig that I can drive 4-8 hours to the places I want to go. Then idle down logging roads, back down banks to launch, climb washed out two tracks in steep country etc.

I would love to get what fast355 had posted before he installed the headers.. That seemed awfully respectable.

[1project2many]

Thumbs down fixed. Looks like it got added accidentally.

17 mpg may be possible if you don't tow. I get 20 mpg in my 99 Suburban. Tuning is ongoing. 302 SBC, Marine / Ramjet cam, shorty headers, duals using stock front pipes, through a 4L60E. Raising the truck generally decreases fuel economy so the job will get tougher but not impossible. Just curious, are you using a true 3550 Jeep trans or a GM version 3500?

I do not often see the truck style Marine intakes that were popular several years ago. I still seen the converted single plane carburetor style and the tunnel ram style from time to time. The tunnel ram style will work in the -98 pickups.

[May-39]

Nice!
What intake setup is that? I'm still researching intake options. My plan in reasonably priced efficiency upgrades.
I plan on using the "GM" 3550 or GM NV4500....The mpg is why I don't slap the SAS or a Cepeck 6" lift I have access to. That and big tires are expensive and it's harder to load coolers and dog boxes into truck. And the factory brake set up is on the light side as is.

[1project2many]

That intake was used from around 94 or so to maybe 96 or 96. The system is called "Mag MPI" or "Magnum MPI." There's also a Scorpion system used in ski boats which appears to be designed for a higher peak power rpm.

You may be able to get larger rear brakes from a "heavy half" or "light 3/4" ton vehicle. These trucks used six lug wheels and a 9.5" semi-floating rear axle. I believe you'll need to install 8 lug parts to go larger in the front.

[May-39]

Interesting will start poking around marine salvage places. Did the MPI system provide obvious improvement? My rpm range will be below 4000 90+% of the time.
If I can, I would like to score the complete heavy half axle AND brakes.
I had read posts about hydro boost conversions but could not determine if it would work with my abs, I don't want an ABS light or no abs

[Fast355]

Interesting will start poking around marine salvage places. Did the MPI system provide obvious improvement? My rpm range will be below 4000 90+% of the time.
If I can, I would like to score the complete heavy half axle AND brakes.
I had read posts about hydro boost conversions but could not determine if it would work with my abs, I don't want an ABS light or no abs

Hydro boost works with factory ABS on my 1997 Express. Even used the larger diameter 1-ton master.

As for the intake, stock intake will work below 380-400 hp however you will see noticeable gains above 4,500 even with the stock cam using a different intake.

Cam or intake doesn't much matter if you are craming the exhaust into any kind of cast iron exhaust manifolds. Headers worked so much better than even LT1 manifolds for me. My brothers 99 Suburban was also night and day difference with long tubes. The headers made a bigger difference than the cam.

[1project2many]

The MPI system was an upgrade from the previousl generation TBI. Marine multiport intakes were available in several different "flavors." The truck style manifold appeared to be sold with marine engines made by GM. Mercury Marine used a few different manifolds including a dual plane carb style:


The large plenum tunnel ram style previously pictured:


And the Scorpion manifold which utilized the same base as the tunnel ram but a different plenum and throttle body:

[May-39]

Thanks for header input. Will consider, I'm sure they perform better but I had leaks and cracks. This rig will spend much time on rutty/uneven terrain just not Baja speeds.
That's a good looking mani set up. thanks ALOT for the reference pics.
Do either of you think the manifold will show significant improvement under 4k rpms? I'm camming it either way, just not a real aggressive cam??
Thank you both again...I'm trying to spend the money right the first time.

[1project2many]

The stock manifold is not horrible. It has long runners to help enhance torque. It can provide enough fuel for 300-350 hp at the crank. And it's already on the engine and part of the tuning.

Generally, marine manifold conversions are good for engines expected to produce significantly higher horsepower than stock. They allow the builder to select injectors appropriate to the power expected. That is the primary reason for most people to switch. In my case the reasoning was different. I bought a tunnel ram style manifold for my '67 Chevelle back when GM was still promising the all-new Ramjet to the public. At that time most manifolds for Vortec heads were carbureted or TBI equipped. The OE L31 manifold was still fairly new and not much was known about it. And there weren't any affordable pfi options. I bought "everything" from a Mercruiser engine including fuel lines, filter, pump, wiring harness, and ecm for $600. It was a steal even then. The dual plane intake pictured above was partial payment for some custom work. I've had it for years. I hope to install it on my Suburban as the shorter runners should eliminate a flat spot that develops around 70 mph with the factory truck intake on the short stroke engine.

[Hog]

Here are 2 options for the truck style/crossram marine intakes. 3 bolt t-body for the stock 1996-2000 Vortec 305/350 trucks/SUV's, 4 bolt t-body if you want to use ETC.

Brand new complete 3 bolt t-body upper plenum intakes for $1479.
http://www.michiganmotorz.com/cast-i...ent-p-486.html
Brand new complete 4 bolt t-body upper plenum intakes for $1199
http://www.michiganmotorz.com/mercru...nt-p-4576.html


peace
Hog