New Guy with "New Guy" questions....

[samg1730]

New Guy, New Truck, crappy Dyno #s....

Hello folks, have always love the square body GM trucks, finally can call myself an owner. Recently purchased this 85 GMC short bed with 383 stroked motor and 700R4. Guy wanted $800 with a clean title so I jumped on it. The previous owner told me that the engine had been a not-original 350 when he purchased it. He claimed to have had it bored to 355 and added a crank, pistons and cam taking it to 383.

Bolt-ons appear to be a 600 CFM Edelbrock carb, Edelbrock intake manifold, Thorley headers going to 2 mufflers that end right under the cab.

Since purchasing I have:

-08/16-
Torque Converter (reconditioned)
Transmission Governor Assy
Driveshaft rebuilt


-07/16-
Flywheel
Battery
Starter Assy
TV Cable
Shocks
Alignment
New Rotors and Calipers

-06/16-
Transmission Rebuilt (seals, mount, pump, gaskets,o-rings, filter, etc)
Transmission Cooler (aftermarket)
Wiring Harness
Speedometer Cable
Ignition Switch
Blinker switch
Spark Plugs
Valve Cover Gaskets
Valve Cover Hold-downs & studs
Timing Cover
Control Arm Bushings
Sway Arms Bushings
Upper A Arm
Tie Rods
Wheel Bearings
Air Filter

So after completing the above jobs I took it to have it Dyno'd. I pulled only 179HP and 268TQ. I will add the graph once I can find the slip.

SO WHAT GIVES? I was expecting rather low, but man! The gentleman that did the dyno said that the TQ numbers were indeed indicative of a stroked motor but that it could be breathing problems that are resulting in the low HP. Then of course he recommended I junk the carb'd engine and go straight to LS 5.3 Swap.

I am in serious need of opinions. I have about 5k -6k budget on just the engine and am hoping to reach the 400HP mark. What could possibly be giving me such low numbers?

THANKS!

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[rich weyand]

what cam did he put in it? That's the big question.

 

[samg1730]

Cam is unknown. Sorry, I have enquired quite a few times to previous owner. This is the most I got from him:

"Hey. When the engine was bored we got a new crank, cam, and pistons. That's all I know since I was the student and the guy who was helping me was the real mechanic."

So, there's that....

 

[Georgeb]

Sounds like it's time to pick a new cam and change the recipe.

 

[samg1730]

Sounds like it's time to pick a new cam and change the recipe.

Thanks for the advice! So I shouldn't view the low 176HP as a show stopper? Of course the shop tech says LS 5.3, anything else is a waste of money.

In addition to a cam, How would be best to go about recouping all that lost HP? Do I need to refresh the existing bolt-ons? Heads?

I have around $5k to spend.

 

[1987 GMC Jimmy]

Thanks for the advice! So I shouldn't view the low 176HP as a show stopper? Of course the shop tech says LS 5.3, anything else is a waste of money.

In addition to a cam, How would be best to go about recouping all that lost HP? Do I need to refresh the existing bolt-ons? Heads?

I have around $5k to spend.

Absolutely not. That motor has a lot of potential. And that guy is full of ****. I'm sorry, but going fast in a GM wasn't unheard of before 1997. I would look at the casting number on the heads and research them. There are all kinds of heads and the mating of the right cam with the right heads go a long way. There are various "boat anchor" heads that were used on carbureted vehicles, swirl port heads that came on TBI (torquey but nothing special), fuelie/double hump/camel hump heads, and Vortec heads. The fuelie heads are old school, but they can be worked to do well. The Vortec heads are the gold standard in factory cast iron heads and probably what I'd go with if I were you and what I will be going with in my Jimmy. There are also Aluminum heads out there that you can explore. There are a few ponies laying around that you can use. A tip top ignition system helps. Good components but also your timing and your spark timing curve. Your rear gears play a part. Carburetor functionality is important as is the amount of air it's taking in. There's a such thing as too much or too little. Quadrajets get it just right every time so there's food for thought. Smog pump deletion if you haven't already. Rear gearing definitely. Do you know what you have? It's gonna feel more like a slug with taller rear gears. And little things like tire pressure.

 

[Georgeb]

I would think you will want to figure out what you have for specs like
What heads, what size combustion chamber, what the bore and
stroke actually are and what type of piston is in it. List that all off or ask for help here in figuring it out. With that there will be suggestions as to what cam to run, what to use for ignition and how to set it up and how to tune your carb to work correctly. If all this is done right the next thing to happen should be a set or worn out rear tires accompanied by a big ol' grin!

Edit: yeah, what 1987 said....

 

[rich weyand]

Even with smogger heads, it's pretty easy to get 300 hp and 450 lbft out of a 383 with the right cam. Comp Cams 12-234-2 looks nice for that. 300 hp @4000, 450 ftlb @2500.

 

[samg1730]

Thanks for the advice fellas.

 

[rich weyand]

Also, and I realize I'm something of a heretic on this, there's nothing wrong with the NP203. Just put a part-time kit in it and manual locking hubs. You do need to spin the chain once in a while to put oil in the reservoir above the main output shaft bearing, because, being designed as a full-time unit, there's no oil pump. In the winter, I drive around with the hubs locked, so the chain is spun from the wheels, no problem. The rest if the year, with hubs free, I just put the NP203 in HI LOC for the first couple miles I drive it every day, then pop it out into HI while rolling. Done.

 

[Handy Andy]

Yup, need to know what heads your workin with, and most likely a cam upgrade would be needed. The cam that Rich listed is actually what I'm going with in my 400 build. the cam quest program says with all that I am doing for my 400 build I should be around the 420hp/ 530lbft area. I'm only going to be about $2600 into it, and that includes buying an old 400 to rebuild and about $600 worth of machine work. You should have absolutely no problem getting 400 hp out of you 383 with the budget you have.

 

[Rusty Nail]

Uhh...let's get real, you don't HAVE a 383...not trying to be an ass, but I'm real.. Are you sure it's not a 305? Casting number please. You can tell the P.O. that I'm callin ********. I think your dyno tech was trying to be nice and let you down easy?

You aren't the first guy that bought not a "383", don't feel bad, but let's move past that.

If you really WANT a 383, pony up some good dough for clearance work. They cost a lot more than $800 to build... 400s are cheaper to build and make better power, IMO.
I don't think the camshaft choice is near as crucial as other factors.
LIKE ; cylinder heads and gear ratio., IMO.
You can certainly think and make it FEEL like 400 rwhp given the proper gear ratio. Good time to settle on a wheel and tire size. I think your current wheels are great, FYI.
If it's me and I had 5 grand to spend wanting to go fast, the engine is sort of an afterthought?
Put 4.10s or 4.56s and an Auburn in the back and call me. There's 1G.

Nitrous kits are plenty cheap but one could easy spend a grand on a super powershot. Torque convertor, blue fuel pump+ 3 port regulator, the kit...there's 1G and that's all you get without changing pistons. I think you can reach your 400hp goal without doing that and only using a super powershot (+125hp)

The faster one is able to GO is directly proportional to how fast one MUST BE able to STOP. Consider upgrading the brakes initially. Rear discs will run $500.

Electric fan + radiator will result in handsome dividends both protecting your investment AND providing horsepower returns.

$2500 to make up 100 horsepower? Easy. Lots of fun!

An investment. That is truly what any vehicle is -and most people's second biggest, following a HOUSE.
Should one follow and agree with that line of thinking, there are many,many places to put 5 grand.

The suggestion I make is to "think outside of the engine bay". There are other things worthy of consideration, albeit not as fun.

You have a great chance to make your $800 investment pay back a significant return! You couple triple or quadruple your initial $800 for a lot less than $5,000!!!! Plus it's white. Scrolling up I forgot about the transmission rebuild...You've done some great stuff so far-keep it up! You've already got some good dough invested.

I know right? Totally not cool post.
P.S. you'll make more horsepower with tailpipes.

 

[Georgeb]

Uhh...let's get real, you don't HAVE a 383...not trying to be an ass, but I'm real.. Are you sure it's not a 305? Casting number please.

You aren't the first guy that bought not a "383", don't feel bad, but let's move past that.

If you really WANT a 383, pony up some good dough for clearance work. They cost a lot more than $800 to build... 400s are cheaper to build and make better power, IMO.
I don't think the camshaft choice is near as crucial as other factors.
LIKE ; cylinder heads and gear ratio., IMO.
You can certainly think and make it FEEL like 500 rwhp given the proper gear ratio. Good time to settle on a wheel and tire size. I think your current wheels are great, FYI.
If it's me and I had 5 grand to spend wanting to go fast, the engine is sort if an afterthought?
Put 4.10s or 4.56s and an Auburn in the back and call me.

Nitrous kits are plenty cheap but one could easy spend a grand on a super powershot. Torque convertor,fuel pump+regulator, the kit...there's 1G and that's all you get without changing pistons.

The faster one is able to GO is directly proportional to how fast one MUST BE able to STOP. Consider upgrading the brakes initially.

Electric fan + radiator will result in handsome dividends both protecting your investment AND providing horsepower returns.
An investment. That is truly what any vehicle is -and most people's second biggest, following a HOUSE.
Should one follow and agree with that line of thinking, there are many,many places to put 5 grand.

The suggestion I make is to "think outside of the engine bay". I like the way Jesse thinks. ^

You gave a great chance to make your $800 investment pay back a significant return! You couple triple or quadruple your initial $800 for a lot less than $5,000!!!! Plus it's white. You've done some great stuff so far-keep it up!

I know right? Totally not cool.

Well, untill the OP takes it apart you don't know any more
About that motor than anybody else......

 

[rich weyand]

Popping a head and miking the bore and stroke would help a lot.

That and the casting number of the engine and the head and it's pretty easy to figure from there.

 

[samg1730]

Hello again folks, thanks for all the input. I know the only true way to know the engine size is the methods that are mentioned above. With the low Dyno #s, Im starting to think maybe just a different engine would be best. Ride this one until I decide to go 5.3 or similar. Is it worth paying to have someone pull the oilpan just to say yes its a 305, or yes it's a slow 350, or yes its a realllly slow (and possibly put together wrong) 383 stroker motor. I mean, at the end of the day, no matter what size it has some very poor numbers.

Like you guys say, this very well may be a dressed up 305, that's why I waited to work on the engine last and focused on transmission, suspension, driveshaft, etc.

Anyway, I looked as best I could and I found this set of numbers on the engine behind/below the alternator: 1M0912 7VP

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