1986 SUB C20: 350 LT9 engine improvement

[86 Belgium Sub]

Hello everybody, I'm now using my Suburban for a few years now as a second car, mainly to go with the family on camping trips and towing the RV trailer of 3500 lbs or some occasional daily (nice weather) trips.

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As I'm getting more free time now (since I'm nearly finished rebuilding our house) I'm making plans to change the Burb and improve a few things.

Although the engine came originally with 185 HP, I seem not to have them found yet. So I was wondering what can be done to improve the performance but keep the reliability of the engine/truck.

So what are we talking about ?

· TRUCK:
1986 Chevrolet Suburban C20 2WD Silverado - 1G8GC26MXGF161694

· OPTION CODES:
LT9 5.7 Liter (350 Cu. In.) 4 BBL V8
MX1 3-Speed automatic THM-400
Z82 Trailering special equipment package
VR4 - Weight distributing trailer hitch
KC4 - Engine oil cooler
V02 - Heavy Duty water & transmission oil cooler
UY7 - Heavy Duty 7-lead trailer wiring harness
F51 - Heavy-Duty front and rear shock absorbers
N41 - Power steering

· ENGINE:
LT9 - 5.7 L - 350 cui V8 16V 4BBL
SAE Net Horsepower 185 PK / 136 kW @ 4000 rpm (Certified to SAE J1349 @ crankshaft)
SAE Net Torque 285 Lb-Ft / 386 Nm @ 2400 rpm
Engine Code Stamping Number: V-0306-UPB / CGF161694
Edelbrock Carburator 1406 - 0144 / 600 CFM – (Prim Jet .098 - Sec Jet .095 - Metering Rod 75x47 - Power Piston Step up Spring Orange)
Ignition Coil: Accel Hei Super Coil 140003

· TRANSMISSION:
Original: THM400 - 3 SPEED - (2,48:1 - 1,48:1 - 1,00:1 - R2,10:1)
Has been replaced by: THM700R4 - 4 SPEED WITH OVERDRIVE & LOCK-UP CONVERTER (3,06:1 - 1,63:1 - 1,00:1 - 0,70:1 - R2,29:1)

· FINAL DRIVE:
GT5 Rear axle ratio 4.10

· WHEELS & TIRES:
285/60VR18 116V Bridgestone Dueler H/T D684 II
American Racing AX188 Ledge 8x16 ET0

I've already checked the engine compression and this is at least 90% on each of the 8 cylinders.

What has been changed ? : Spark plugs, Spark plugs cables, Ignition Rotor, Free flow exhaust new (No catalyc converter anymore), Smog/Air pump system deleted, Water Pump, Alternator, Airco Compressor, 2 Batteries (installed a second one), Additional electric cooling fan and most important, as mentioned above, The THM400 has been replaced with the THM700R4.

Briefly, the Suburban is not performing as expected. Comfortabel cruising speed is 50-55 mph in third gear. 4th gear seems not usable when going (slightly) uphill or having wind upfront. And certainly not when towing. So my "1 million dollar" question: What can be done to improve performance and keep this engine without changing to LS or Big Block ?

I contacted Summit Racing and they suggested to change te intake manifold (Edelbrock Performer EDL-2101) and the cylinder heads (Promaxx Performance PMX-2169) but they could not predict the expected improvement.

I hope I can get some good reliable information from you experienced forum members. Thanks !

PS: As I plan a few other, smaller improvements, I will share this transformation with pictures in other threads...

 

[45acp]

Kurt, Here's my two cent. I have an 1984 gmc k1500,350,700r4,373 gear ratio. I tow a Jayco Hummingbird travel trailer 2890lbs ( 1312 kg ). All these modification i have done was to improve the towing capability. 4 core champion aluminum radiator,derale dual electric fan w/pwm controller,edelbrock aluminum intake,mild shift kit and Mag-Hytec trans pan (2 extra quarts ) Hayden trans cooler,auto meter trans temp gauge. The Rochester carb was tweaked a little. All this and my sweet spot is 60-65 in overdrive ( flat land only), 55-58 in drive ( any kind of a hill or head wind). I'm in California so there is very little i can do about smog regulations,I just wish I could do what you've been able to do. I guess what I'm saying ( besides bragging about the stuff I've done to my truck ) is unless you change to a higher gear ratio of drop a big block in it ( a lot cheaper than a LS ) you got what you got! Now I think they're a lot sharper people on this forum than me so hopefully they can be more help.

 

[Raider L]

@86 Belgium Sub,

You need a RV cam. Keep the carb it'll probably be okay, and that intake they suggested. The cam is a "towing" cam. I have one in my truck as a small performance cam. It's a Lunadi "duel pattern" cam. It won't affect your gas that much at all. Also, get a set of headers on the thing. This will improve performance and horse power without hurting gas mileage, as a matter of a fact it may improve it some because you'll be pushing down on the peddle less and getting more out of the engine. I don't know much about Edelbrock carbs but those jets seem large to run without a cam to use all that extra fuel that size jet would be allowing in. I wouldn't dive off into heads until you see what changes you get with the cam, headers, and intake.

With the speeds you're saying it cruises at you really need the power builders I mentioned so far. These changes wouldn't cost much either. Start out cheap and build up. You can also make some changes to the rear end gear ratio to. You'd be surprised how much faster and a good use of engine power a gear like maybe 3.46, 4.10 would make. But ask someone who knows more about that because there's a point where you loose your gas mileage. But those headers and a cam and intake will probably do what you want.
Good Luck

 

[Raider L]

@ 86 Belgium Sub,

That cam number, if you want to look into it is: cam number #06107 High Efficiency Cam Duration @ .050" of lift is 205 deg. intake, 215 deg. exhaust, advertised duration 255-265, gross valve lift .427" in., 453" ex., lobe seperation 112 deg. This cam offers good idle. Excellent off road and performance cam in a 350. Power range is 1000-5000 rpm. You want the lifters as well of course, #71817, and springs #73943. These are the lifters and springs that go with this cam.
This cam says it's for "off road" which I think would be the same as towing because of the drag on the engine going through dirt and whatnot. You can take a look at it and ask around for any other cam recommendations. I'm thinking about gas mileage, you know and power to. I think you'd be doing a heck of a lot better than 55 mph with this cam, headers, and intake. I think you'd be very satisfied with the increase in performance.

 

[Bextreme04]

A good towing/RV cam will make a big difference, but your biggest single power improvement will come from good heads that will kick your compression up a bit. Your stock LT9 compression is probably in the 8:1 range and is your single biggest issue. If you get some well designed heads with smaller chambers and pick a good head gasket thickness, you can really bring that motor to life. I'd try to get it closer to 9:1 if possible. That combined with long tube headers and a decent cam will make it feel like a whole new engine. You probably want to make sure you have a heck of a cooler with that 700R4 also, especially if you bump up the power and are towing regularly with it.

 

[Raider L]

I agree with Bextreme04. I overlooked at the fact it's a LT9 engine to. How in the world could that series engine only have 185 hp? I thought all those LT engines were hypo? Is there anything that can be done with the heads that the engine has on itr now. You know there is the camp that believes it's less expensive to mod your own heads rather than buy new heads. A good combustion chamber polishing and a larger set of valves with the three angle valve job, and 1.6 springs could do wonders as well. What do you think about that @Bextreme04?

 

[Bextreme04]

I agree with Bextreme04. I overlooked at the fact it's a LT9 engine to. How in the world could that series engine only have 185 hp? I thought all those LT engines were hypo? Is there anything that can be done with the heads that the engine has on itr now. You know there is the camp that believes it's less expensive to mod your own heads rather than buy new heads. A good combustion chamber polishing and a larger set of valves with the three angle valve job, and 1.6 springs could do wonders as well. What do you think about that @Bextreme04?

Its a thing... my biggest issue would be how much do you need to machine off the head to get a small enough combustion chamber to get some real compression, and can you even do it without getting into a water jacket or something else. With the dirt cheap price of good cylinder heads for a SBC, and the fact he is in Europe, makes me thing the quickest, easiest, and cheapest route would be to order a set of already good heads. By the time you get into the parts and trying to find a shop that knows how to do that kind of work with old GM heads IN BELGIUM, you likely aren't going to be ahead on cost or time.

Almost all of the old 350 truck engines are that low in stock HP. Heck, even the 350 TBI engines are only 210hp... they had better compression, but more restrictive emissions cams.

 

[idahovette]

I agree with Bextreme04. I overlooked at the fact it's a LT9 engine to. How in the world could that series engine only have 185 hp? I thought all those LT engines were hypo? Is there anything that can be done with the heads that the engine has on itr now. You know there is the camp that believes it's less expensive to mod your own heads rather than buy new heads. A good combustion chamber polishing and a larger set of valves with the three angle valve job, and 1.6 springs could do wonders as well. What do you think about that @Bextreme04?

....What are "1.6" springs?.....

 

[Rusty Nail]

I contacted Summit Racing and they suggested to change te intake manifold (Edelbrock Performer EDL-2101) and the cylinder heads (Promaxx Performance PMX-2169) but they could not predict the expected improvement.

I hope I can get some good reliable information from you experienced forum members.

All you gotta do is change the head gaskets. Run a Fel-Pro shim and make no other changes.
Verify proper spark plug heat range.

All you gotta do is change the head gaskets. It's easy!

 

[Green79Scottsdale]

Vortec heads, or any similar upgraded heads, and a matching cam. Watch the beginning of this video. They took a 190hp crate motor, which is basically what you have, and added Vortec heads and a cam.

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[Catbox]

Perhaps with the 700R4 trans in there instead of the T400 a new set of matching rear end gears would help your towing abilities.
Especially with over drive.

 

[Catbox]

Perhaps with the 700R4 trans in there instead of the T400 a new set of matching rear end gears would help your towing abilities.
Especially with over drive.

Never mind.
I see you have 4.10's in there now.
I missed that part.