CarburetorsCarb discussion and questions. Upgrading a Third Gen carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.
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You are on the right track with the headers and the 3" exhaust. I wouldn't waste my time with an intake swap just yet. The LG4 has a weak cam but the one you have posted up there is too small to justify swapping. Find something a bit bigger. I'm about to put a Crane 2032 in my 350 (roller), and it's huge compared to that cam and it still comes with a 50-state CARB #. Look for something a bit bigger that what you posted up and you should easily get over 200 hp...
Headers and a 3" catback is worth a fair bit more than 8hp... the LG4 had a brutal exhaust system. I wouldn't call 20hp overly optomistic, it really is a pretty healthy gain.
Intake isn't necessary if you have the factory aluminum intake... it will not become a restriction untill you are getting into the 300hp range. I'd leave that alone. Changing to something else probably won't gain you much, if anything at all.
The single snorkel air cleaner they came with is another must-change. Change to either an L69 dual snorkel air cleaner (best option) or a generic parts store 14x3" open air cleaner with a dropped base. I can't really put a number on what a better air cleaner is worth, HP wise, but it would be a decent gain as well. They aren't expensive either.
Another thing that I would highly recommend is to recalibrate the CC carb to L69 specs. It had a much better jet/metering rod set in it for a performance setup. The LG4 carbs had really lean-running fuel economy jets/rods in it. There is a fair bit of mid-high RPM power to be gained this way. I think Edelbrock sells a jet/rod kit for the Quadrajet that will work, or you can buy the peices individually. Or look in the classified section for someone selling a carb from an L69 engine and use that or use it for parts.
If your engine is an '87, it will already have the high-compression L69 pistons (9.5:1 compression ratio) so that will make the engine a bit more 'responsive' to modifications than the older LG4 (the pre-85 ones had 8.2:1 if I remember right).
If you plan on upgrading the cam, the LT4 hotcam would be a GREAT choice, though pretty aggressive for a 305. The stock LT1 cam would be a pretty good one for a 305 as well, and will make a pretty good bit of power, and lots of torque.
By the way.... the 'L69' engine is the 4bbl 5.0 HO engine. Had 190hp stock.
You could even put in a ZZ4 cam, but the heads would have to be reworked first (as they would with the LT4 Hot Cam).
I wouldn't be doing a Crane Cam right now. Not with what's apparently happening with them.
As Adam hinted, you'll need more than headers - you'll need the complete '86-'90 TPI single cat application exhaust. Figure on a 10% or so jump in power.
The power gain from each part isn't the way to look at it. The power from all the parts put together is what's important.
BTW, '87 had 9.3:1 CR - slight dish with valve relief pistons dropped it from the L69 and '85-'86 LG4's 9.5:1.
getting over 200 hp from an LG4 is pretty easy
i think i had my '82 LG4 over 200 h.p. with these mods:
-headers with dynomax 3" super single,dynomax
muffler.
-mild aftermarket cam,weiand,don't remember exact
specs,was just slighty hotter than L69 cam
-removed ccc system and replaced carb and dizzy with
those from a 1976 305 pickup engine-just dropped carb
on and it worked fine as is.
-made air induction system a lot like on the x-fire '82
-83 z28s
-had to replace mechanical fuel pump with electric
because mechanical would not keep up for some
reason.
all this made for a DRAMATIC increase in hp with no
loss of low end torque or economy .
also,on your '87 i would replace those steep 2.73s
with 3.23 or 3.42s-i really like the 3.42s in my car
only turn about 2500 rpm cruising fast on the
highway.
BTW did this back in the early '90s-could do a much
better job today!
If you're keeping the Computer Command Control system installing a PROM from a L69 car should provide a small boost. They had a much better timing advance programing than the LG4 PROM.
Appreciate the great ideas! This year I'll go with headers, 3" cat & cat back; connect a second intake & hose to the air cleaner assembly; and try some "DR" secondaries. Next year I'll probably add an LT1 CAM and maybe scuff up those ports too. But I'm not sure what prom I can plug straight into my 1987 ECM and still keep the knock sensor and EGR functional. This and other threads gave me some clues but I'm unsure about what prom to use. http://www.thirdgen.org/techboard/di...ccc-q-jet.html (OLD CCC-Q-Jet stuff)
back in the late 80s/early 90s eldebrock, (i think it was
eldebrock)came up with a replacement ecm for LG4s
that had updated electronics and was meant for high
performance use-if you could find one of those that
would probably help some too.
Easy! My '85 lg4 with crappy edelbrock headers, a hooker catback, and a rebuilt l69 carb made 166hp at the wheels and thats with 100k miles on it. The exhaust is def the biggest bottle neck.
A really cheap alternative to the L69 chip is to bump up your base timing a couple of degrees at a time until you start getting pinging at part throttle loaded. Then back it off 2 degrees. That's all I've done.
What difference - earlier this evening put on a new Accel cap and rotor on as part of regular maintenance, and then set timing to the last timing mark - my LG4 slug now runs so much better that it really can't be called a slug anymore! wha hoo!
__________________ Time to add a little more HP...
Not really. Ported stock heads with 1.94" intake valves, more cam than the 262 they used, good headers and exhaust, a 305 will easily put out more than one HP/cubic inch. You just need to get the powerband above 5300 RPMs or so.
But, you don't want to go nuts with RPMs, or you'll ventilate the block when a rod bolt breaks. Other famous magazine articles (400 HP stock block 305) proved that.
Not really. Ported stock heads with 1.94" intake valves, more cam than the 262 they used, good headers and exhaust, a 305 will easily put out more than one HP/cubic inch. You just need to get the powerband above 5300 RPMs or so.
But, you don't want to go nuts with RPMs, or you'll ventilate the block when a rod bolt breaks. Other famous magazine articles (400 HP stock block 305) proved that.
From what I have read, vortecs would bolt right on my '87 305 block (that sounds really nice!), but keeping the stock heads (with some work) vice bolting on some vortecs is going to provide plenty strong response for the 3,000 to 4,500 rpm range?
I have an LT1 CAM, better air flter intake, and 3" exhaust/cat/cat back planned, but honestly, this car will never hit the track and will just run in town/highway.
Either one would be fine. The only issue with the Vortecs is the lower compression ratio with their larger chambers. But, it will run better than unported stock heads.
It will seem like a different car. I think you'll be pleased.
ok, then if vortecs will just bolt straight onto my 87 LG4, then I'll keep an eye out for a set of vortec heads. BTW, are there any vortecs that won't work well, fit without modification, or otherwise steer away from?
__________________ Time to add a little more HP...
I don't see anything in those threads about Vortec valves not working on an LG4.
Don't get me wrong, the 081 heads are fine with a little work. But, even with lower compression, Vortecs are still an overall improvement over stock 081's.
Bottom line - if 200 HP is your goal, stock 081's will be fine. Cam and exhaust is all it will take to get there.
K&N is an expensive way to let more dirt into your engine. You don't need a K&N, a quality paper filter is fine. Personally, I prefer the AMSOIL Ea filters.
Well so far, new cap, rotor, and coil from Hypertech, SLP Headers (1 3/4"), 3" cat to 2.50 catback, (don't know if i should just go 3" all the way) new msd spark plug wires, ngk shorties, l69 intake, the dreaded k&n filter , hypertech fan switch on at 200 off at 180, 180 thermostat, and that's about it so far. now your guesstimate would be appreciated.
been reading about cams on here, so was thinking on going with the one that came on the 1987 l98 engine. seems like a decent swap with new springs, lifters, etc.
L69 intake? '86-earlier bolt pattern, which you had to modify to fit your '87 heads? If so, a shame, because the L69 and LG4 intakes were the same parts.
You're probably in the 175-180 range now. 3" would be better eventually, but you're probably okay with 2.5" for the time being.
The L98 cam is better than the LG4 cam, but the LT1 is even better. Pretty easy to pick them up from eBay as take-outs (there's one that ends in 6 hours that includes the lifters and dog bones, current price $10.99).
Been reading on other posts that a L69 Dual snorkle intake, increases horsepower by adding 20 HP. Now, that seems too much for an air cleaner. I am guessing five HP maybe 7.
I haven't seen quantified test results. I do know that on my stock LG4, going to an open element picked up a couple of tenths over the single snorkel air cleaner. And, with other modifications, it will have an even more significant effect.
I got my L69 dual snorkel after putting in the 350. It was getting cold outside before the dual snorkel arrived, and I was having problems with a really bad dead spot off-idle as the engine was warming up with the open element. So, I put the stock single snorkel back on, and while that warming-up dead spot went away, the effect on power was very noticeable, even on the street.
I haven't done back-to-back comparisons on the track between the L69 and open element, but on the '57, the cooler air was worth a tenth in the quarter mile, most of it gained in 60'.
Long answer to a short question, but the single snorkel is significantly restrictive, even on a stock LG4.
Dynoed my car at my cousin's friends shop and got 202 h.p. with the mods I have on my car. I made sure I properly wraped the intake hoses so they would not take in hot air. Now mind you, I am going to a different shop and get a new run just to be sure. My cousin's buddy may be off a we bit. So before I start jumping for joy and throw on the 3" cat back, new cam, rebuild the carb with better rods, etc...gonna get a second opinion.
in, what else could I do to get to 200 hp? Motor needs to stay emissions legal in case I move to the DC area 
Appreciate the great ideas! This year I'll go with headers, 3" cat & cat back; connect a second intake & hose to the air cleaner assembly; and try some "DR" secondaries. Next year I'll probably add an LT1 CAM and maybe scuff up those ports too. But I'm not sure what prom I can plug straight into my 1987 ECM and still keep the knock sensor and EGR functional. This and other threads gave me some clues but I'm unsure about what prom to use. 
, hypertech fan switch on at 200 off at 180, 180 thermostat, and that's about it so far. now your guesstimate would be appreciated.
