86LG4Bird

iTrader: (1)

Taking the advice of several people on this board, I swapped in a set of DR rods and a G hanger for the stock pieces on my daughter's 86 LG4 a few weeks ago. I could tell immediately just by driving the car that it helped; I could actually feel a power increase when the secondaries opened, whereas before all it did was make noise!
The car had previously run a best ever NA of 15.40 @ 87.5 mph. Tonight at test n tune, without the good air it had for its previous best, it went multiple passes of 15.1x @ 89.x with a best of 15.11 @ 89.9. With the weight of the car at 3475 with me in it, I'd have to chalk up at least a 20 hp gain, possibly 25 when the air is considered. It's substantial when you're starting with LG4 power.....lol!
Mods on the car are: 3.73's, TPI manifolds/exhaust system, S-10 TC.
60's on the street tires were 2.02 to 2.06.
Hmmmm.....I'm thinking maybe now those previous runs with the 100 shot of 13.0 @ 104 might just translate into some 12.9's

1badeagle

iTrader: (2)

Why not buy my headers lol. Seriously though, Headers and a better intake would have to help. Even port out your heads at home like I did on my dads 350 tpi to get it down the road faster.

86LG4Bird

iTrader: (1)

I'm not putting any work into this engine. Valve seals have been replaced, that's all! There's a ZZ4/Vortec 350 and an Edge 2800 TC sitting in the garage if I get ambitious this winter
What kind of headers do you have? I was thinking just trying the manifolds first with the 350, but..........if it doesn't run a 12.9 naturally aspirated, headers would be the next step.
Better intake.......seriously? I didn't think the GM intake manifold with the CC carb is holding this mighty 150 hp motor back.....lol!
If you mean BEFORE the carb, I'm running a taller filter with a flat lid so it doesn't have to breather through the soda-straw stock filter housing snout.

1badeagle

iTrader: (2)

Yep, better intake. I had a el camino with the lg4 in it. I replaced the stock one with a torker 2 intake and a small Holley and it ran a ton better. Then with headers instead of manifolds it ran a hell of a lot better. I have a set of new in the box hooker long tubes for a 3rd gen. Nice big 1 3/4" primaries for when you step up to that zz4

86LG4Bird

iTrader: (1)

I don't see ever doing longtubes on this car. Trying to adapt an exhaust to them that fits under the car looks like a nightmare. I've thought about the shorties/midlengths that still accomodate the factory y-pipe/exhaust routing.

sofakingdom

iTrader: (1)

That's basically preposterous....

If that tiny little tweeeeeeeeek gave you THAT MUCH of a difference, then SOMETHING ELSE is WAY off.

What was the air valve tension set to before, and what's it set to now?

naf

iTrader: (7)

Intake manifold, no. Keep in mind that the only real difference between the 140 hp LG4 and the 190 hp L69 was the cam, larger exhaust and air cleaner (along with the better rods/hanger to match the rest of the combo). Earlier years the LG4 had no KS and less compression but by 85 that changed.

86LG4Bird

iTrader: (1)

Preposterous? .......... is 20 hp really unheard of if it in fact it was ridiculously lean?
I'm all ears..... maybe something else IS off???
But for the way the car runs and the mileage it makes, I've had little reason to suspect so. My only gripe had been the basically worthless secondaries. I had played with the airvalve tension several times before, and no matter how tight I made it (I didn't get ridiculous to the point of damaging the spring), rolling into the throttle always made it bog until the trans downshifted and the added rpms allowed it to recover. From a dead stop, flooring the throttle resulted in no bog; I guess the pump shot in the primaries gave it the fuel it needed??
I made no change to the airvalve with this rod/hanger change. It's still tighter than the 1 turn recommended.
I forgot to add, I also cut some 1/8" radius half moon slots at the front edge of the airvalve blades.
Oh....and there was no bog before in 1/4 mile runs. As I said, smacking the throttle from a stop wasn't an issue, and the rpms were still high enough after each gear change to prevent it.

sofakingdom

iTrader: (1)

Precisely...

If not the air valve tension, then the fuel bowl level, the fuel delivery system, etc. etc. etc. Rods & hangers by themselves should make relatively little difference.

Sounds like the rods & hangers took it out of surging piston-burning lean, and now it's just stumbling struggling lean. Your track times pretty much bear that out.

For a 305, the AV spring should be around 7/8 turn; ¾ turn minimum. Some 305s will like as much as a full turn but for most that's a bit too much. It'll start to bind at around 1¼ turn.

Damon

It's not really the peak HP gain so much as the response when the pedal first goes down plus a nice little bump in torque.

Also, a stock cc-QJet doesn't allow the secondary air valves open their full ~85-90*. Which means it doesn't get the rods down onto their power tip in some cases. The combination of the higher hanger and the more aggressive taper on the DR rods equals a slightly richer mixture overall. And many engines like that richer mixture.

Might also want to consider filing down the secondary air valve stop to allow them to get open at least 80* (vs. ~70* on a factory-stock cc_QJet). A full 90* isn't absolutely necessary and will often bind the tension spring on the later air valve arm design, but there is room for improvement if you want to try it.

Agreed with above, better exhaust helps A LOT on the LG4 engines. No need to go nuts, but a set of shorties, y-pipe and matching cat-back system can do wonders. DO NOT buy a system for an LG4. They have a smaller y-pipe and everything rearward to accomodate the original (undersized) 2-1/4" cat and pipes. You want a system designed for a same year L69 or TPI engine- that gets you the full sized 3" y-pipe and cat-back.

Yes, everything must go, from the manifolds to the tailpipes on an LG4 car.

Hooker makes a nice set of shorties and matching y-pipe (available with air tubes if you want to stay totally emissions legal). I like Dynomax cat-back systems for bang-for-the-buck and they sound good, too, without being obnoxious. Any old 3" aftermarket monolithic cat will work fine between the two. Of course, there are about a bezillion different systems and manufacturers to choose from if those choices don't suit you.

Exhaust upgrade gets you more than an intake swap does at this level.

paul_huryk

You missed the fact that GM retarded the LG4 timing compared to the L69 to pull hp out of it also.

Apeiron

Moreso that the L69 had a knock sensor while the LG4 didn't, so it could run closer to the edge.

86LG4Bird

iTrader: (1)

I see a couple of misconceptions/oversights in some of the posts above, so here's a little more info on the car.

1. It's an '86 LG4, and yes it does have a knock sensor.

2. All I can tell you about timing is that it's set at 12 deg BTDC static (ECM connector disconnected). That's the limit of what it will tolerate at operating temp with 87 octane fuel.

3. As mentioned, it already has a junkyard TPI exhaust on it (manifolds to tailpipes).

4. As mentioned, it has a taller filter element with a flat lid so it doesn't have to wheeze through the tiny snorkle. Also has a Formula (cowl induction) hood, so it might even get a little bit of "cold air" benefit.

5. E-fan and 180 deg tstat that keeps it about 180-190 deg. Was about 160-170 for the runs at the strip.

6. From 3rd Gen links to specs I've looked at, this engine was factory rated at 155 hp @ 4200 rpm.

Calculating hp from the 3475 weight and 89.9 mph shows about 205 at the crank or 168 at the wheels. I'm sure the TPI exhaust system is responsible for the biggest part of that.
This calculator is the best one I've found that nearly matches SAE dyno numbers I have from my other vehicles: http://turbo400.com/cherry/HP_Calcul...alculator.html

I wonder if anyone has ever tested a bone stock LG4 car at the strip?? The calculator shows 82 mph for that weight and 155 hp; which is probably a low 16 sec ET at best.

paul_huryk

86LG4Bird:

In terms of timing, the total timing was retarded on the LG4 vs. the L69 - Edelbrock Microplus was the item to get to get the timing back into the LG4.

While a TPI exhaust is much better than the LG4 one, the manifolds and y-pipe are still a restriction, even on a 305 - probably 10hp vs. headers. Cat back is also a restriction since the pipe is not mandrel bent and the muffler is not high flow.

An open element air filter may let in more air, but it is doubtful to get any cold air from your hood unless it is sealed to the hood correctly.

I've noticed that LG4 motors (L69 and my 350 transplant as well) run better at 200 to 210 degrees on the coolant side and the air flowing into the motor at outside ambient. Picked up 20hp from changing the coolant temp from 170 to 210 on my 350 LG4.

Maybe with a 5 speed you might get an LG4 into the 16's, my 84 automatic ran 17.3 at 80mph stock and 15.1 at 92mph with bolt ons: banks y-pipe, 3" TPI cat, banks cat back, tpi dual fans, UD pulley, Micro-plus, performer manifold, and l69 air cleaner. This was back in 1991 when I had no idea about tuning with rods & hangars, thinking another 15 to 20hp because it ran very lean. I could have picked up 10 more hp with headers vs. stock LG4 manifolds too.

86LG4Bird

iTrader: (1)

That's preposterous! (....lol! - see sofa's comment above )

This car definitely likes the lower coolant temp. It loses both ET and mph when hot lapping it.

Damon

Sorry, I missed the part about having upgraded the exhaust. Maybe you could try an intake at this point if you want- they're not expensive or difficult to change out. I tend to doubt it would help much, but you never know until you try.

I'd see if you can get an L69 chip in it. Mostly the difference is the timing curve- not just the initial and total. I've done the bumps in base timing like you have still using the LG4 chip (8-10* was as far as my motors liked- but that's still a lot of advance over the stock 0* setting!). But the best mine ran were with the L69 chip and about 10* initial timing (vs. a stock factory setting of 6* on the L69).

But they never made an L69 in the 86 F-body. Just the LG4 and the TPI motors, if I recall correctly. Not sure if an earlier 85 L69 chip would work or not. Might be worth some research.

Also, maybe some of the aftermarket performance chips are still around for these old carbureted motors. Although some of them were real JUNK programming, I should warn you.

And then there's the cam..... it's pretty much the only hardware difference between an LG4 and an L69 in that vintage (other than the exhaust which you've already taken care of). Maybe an L69 re-pop cam or better yet, a base model Edelbrock Performer cam (also sold as Summit house brand cam K1102). I've found they work real good as upgrades to the stock LG4 "peanut cam." Neither is a fire-breather but you're talking about 25 DEGREES MORE DURATION @ .050 on the intake side than the "peanut cam." Yes, the LG4 cam is THAT SMALL!

Fast355

iTrader: (2)

Stock 350 cam works very well in a 305 as well, especially with 1.6:1 roller rockers. That is what came in my 83 G20s 305 from the factory and it made 181 RWHP/268 RWTQ with the CCC Q-Jet and stock chip.

Apeiron

86 was the last year for the L69. They were rare, and IIRC all manuals.

86LG4Bird

iTrader: (1)

Update:
The previous owner gave me a box of "spare" ECM's. I may have stumbled onto that L69 chip that Damon mentioned above. Service No. 1226455. References I found for it say 1984, L69.
FYI, the stock ECM in this car was Serv No 1227169.
Anyway, I swapped in the 1226455 ECM last week, and it sure made the car snappier, probably that better spark curve mentioned above. (Still OK on 87 octane with 12 deg initial).
I took it to the track tonight and went a new best: 14.97 @ 90.2 on a 2.02 60' (just very slight spin on street tires). Air was slightly better, so I won't chalk up the .14 sec gain entirely to the ECM. But regardless........ Stock LG4 engine in the 14's - yeah Baby !!

Fast355

iTrader: (2)

Sounds like you hit an L69 chip alright, however at 12* timing, you are likely pushing 40* total timing advance at higher rpms. I would back off to 8* and see if the car picks up MPH. What I found with spark/fuel duty % maps is that the fullsize truck/van chips actually had a more performance oriented map. They did not use quite as much lower rpm timing in the maps and it is possible to dial in more initial advance. 14* total advance would give you 30* at idle, 35* at high rpm, and 22* at WOT and low engine rpm.


Spark Maps...The only LG4 map I found was an 83 Bonneville LG4





The L69 map was an 85 Monte SS





1983 G20 Van...LE9 305

86LG4Bird

iTrader: (1)

Fast, Thanks for posting those tables. I've been studying them.
I understand what you're saying that the van/truck map could be a better "performance-oriented" map for some applications. However, for this car, it really seems to like that aggessive timing provided by the L69 map in the midrange (2000 rpm being midrange for this tractor engine....lol!). It's spark knock limited only at very low rpm (1000-1200) when lugging it on a hot engine with the TCC engaged.
I don't see a big difference in the LG4 versus the truck/van timing maps, so I may try playing around with different static timing with the LG4 chip again.

Damon

Fast- what's up with that crazy looking "lip" at 95 kPa on the L69 chip? It's showing MORE timing advance at 95 than it does at 90. None of the other timing maps have that characteristic.

No only does it stand out because it's "different" but also because it doesn't follow the usual rule of less vaccum/less advance.

Apeiron

Emissions reduction on closed-throttle decelleration.

86LG4Bird

iTrader: (1)

at 95 kPa ??

Apeiron

Yeah, nevermind. That's absolute, not vacuum.

87WS6TA

Very nice runs for a LG4 even with bolt ons...wonder if a 87/88 LG4/L69 ECM with a ZZ4 PROM (or tuned similarly) would improve it even further, or if that's too much for a LG4.