I have the stock carbed 305 and I'm wondering what are some of the best ways to increase HP without hurting fuel economy. I hoping to get it to about 250 HP compared to its 170 HP.

 

Thats going to be nearly impossible with a carbed 305. The only way I can think is maybe an LT swap or LS swap. EFI is a good way to keep your fuel economy up. A good open exhaust is a way to improve things, if you can keep your foot out of it.

 

getting rid of the three oh five will help alot! lol

 

250hp is easy for a 305 anyone who says otherwise looses all credibility.

Since you have a 86 (guessing from your name) you should have a good compression ratio already. Full exhaust from head to tail-pipe, that was made for a 350 TPI, is where you start.

Once you've done that a intake and cam swap is in order to meet your goal.

Finally you will need to tune it well. Do some research on tuning the CCC Qjet, there is some awesome information on this website. Tune the primaries with a dwell meter/auto analyzer.

If you want any more HP then that though you are going to have to pull the heads IMO.

 

I agree 100% with doom.

 

He wants to keep his fuel mileage, I was just trying to prove a realistic goal. A 305 with that much compression and a big enough cam to make 250 is not going to make anywhere near the gas mileage he is getting.

 

We have an FAQ forum for a reason, and this question is one of them:

https://www.thirdgen.org/forums/faq-...5-engines.html

Two hard-to-swallow facts:
1) An LS1 will get better fuel mileage than an LG4, while having about twice the power.
2) You can buy a lot of fuel for what an LS1 swap will cost you.

 

If the guys has a moderate goal of 250hp and keeping fuel economy why in the world would he want a LSX? (which I'm guessing what you are getting at five7kid) Now if he wanted 400hp and economy well yeah.

A tuned 86' LG4 with headers and full exhaust will get better mileage then stock. Adding a mild cam wont make much if any difference unless he's going to be sitting around idling all day.

He doesn't need some nasty loping cam to make his goal. After doing the exhaust, intake, and tune you should be around 200-220hp already.

A comp cams XE256 would be about perfect for this IMO.

 

Yea I too am a little confused by five7kid comment about the LS1 if hes suggesting a LS1 swap or against it? Regardless though I have to side with doom on this one. The lg4 was not particularly impressive when it comes to gas mileage and 250 hp is not really all that much to ask of a 305. I think doing the exhaust alone (headers/y pipe, high flow cat, and a performance cat back of your choice) would get you into the 200s without much trouble and improve gas mileage. Add a cam tame cam to that equation as the stock one is pretty terrible and I think you would be right up on your goal while maintaining good mileage. Personally ide throw on an aftermarket intake too just for good measure as again some decent gains to be had there but im not sure if you would need it to hit your 250 goal so thats a judgment call. Plus all of this could be done with street legal parts on top of it.

 

40hp-60hp from just exhaust, and intake & a tune? I find that VERY hard to swallow, as anyone reading that should.

 

Although I can see your skepticism the LG4 equipment is just that bad in some respects. Im not sure what he means when he says an exhaust if hes just referring to a cat back or a full set up headers on back but I can say this. Ive read I believe even on this site a discussion about intakes for carbed third gens where there were dynoed claims of just over 20 hp with just an intake manifold and our exhaust systems are pretty terrible especially the LG4s which only had a more restrictive exhaust manifolds and 2.5 exhaust instead of the 3 in intermediate pipe the higher end v8s came with. Im not confident he would hit 40-60 with an intake and cat back I think that is being a bit optimistic but if he was talking about a full exhaust I could definitely see it.

 

I had a brand new fresh carb'd/intake/cammed/full exhaust (LT headers to tips) L69 & I doubt I was pushing those kinda #s. So yeah...I'm skeptical about a LG4 hitting those #.

 

Perhaps I'm missing something here but wasn't the factory l69 rated at 190 hp? A l69 with those mods I dont see how it could not be in 200-220 hp range and beyond unless something was horribly wrong?

 

I agree,Ive owned several tpi 305 irocs and with just cam and headers and tuning I was always gettin 240 to 250 hp but thats also a tpi not a tbi.305's arent hard to get to 250 hp at all with some elbow grease and they will pick up fuel mileage IF you keep your foot out of it.

 

yes I was summing exhaust and headers together since I already mentioned you would need both.

If you've done what you mentioned to a 305 and can't get 220hp I don't know what to tell you other then something is wrong.

 

I was responding to the first quoted comment above.

Obviously, my "hard to swallow" statements are contradictory. As in, there's no free lunch. Ditto when it comes to getting more power out of an LG4 while maintaining the same fuel economy.

 

Although I get what your saying here I have to disagree. Although Im sure i dont have to explain it to you for others that are reading this there are 2 basic ways to build performance. One is increase the volume and the second is increase the efficiency. This is why the LS1 is such a great motor it is not any bigger that a classic 350 but it is much more efficient allowing it to make more power and get better gas mileage. This applies to the LG4 as well. A lot has changed since the LG4 was introduced many technical advancements have been made. A great example of this would be to bolt a TPI manifold on it you would get a bump in power, torque, and fuel economy because its allows the motor to work more efficiently. Headers another great example of a mod that will yield more hp while improving gas mileage again because it allows the motor to work more efficiently. Cold air intakes on and on and on. Fact is the lg4 in its original form, although a respectable motor considering the times and what it was designed to do, is no pinnacle of automotive technology and its efficiency can be much improved with some modifications that use more modern technology than was available in the 80s. Yes these modifications cost money so you could argue that some mods will never pay for themselves in gas savings but thats not really the point the point is to get more power while still maintaining comparable gas mileage or better and this is possable.

 

1) Installing TPI on a stock LG4 may increase economy, but it will not increase power. The OP wanted to increase power without decreasing economy.

2) Headers allow more air to flow through the engine. This primarily increases power, but usually only with other mods, and can actually decrease economy.

3) Cold air will probably increase power, but the factory heats the air with the stock air cleaner for good reasons - primarily emissions, but also drive-ability and economy. Besides, the factory already does "cold air".

4) If increased power with similar economy is the goal, and not an eventual break-even, then forget modifying the LG4 - go LSx (a lower-cost option for LSx is the 5.3l LM7).

 

1. There should be no question on this a TPI intake will improve hp, torque and fuel economy. At the time of its introduction the simple addition of a TPI manifold was tested and proven to yield 20-30% gains in fuel economy, hp, and torque. Not to mention it was specifically designed for the 305. I really dont see how this can possibly argued in this case.

2. It takes energy to exhaust exhaust gasses. Headers allow the engine to waist less energy doing this. Although yes it is possible it would will allow the engine to take in more fuel as the result of being better able to exhaust the burn gasses but you need to take into account the throttle. To cruise at a constant speed you only need to produce so much HP. The amount of hp produced will be related to the amount of fuel air mixture taken in and its efficiency. So the addition of headers will increase the efficiency due to less lost energy in exhausting gasses so less air fuel mixture is required to produce the same amount of hp. Further more no more fuel will be taken in because you need less fuel air mixture to produce the same amount of hp so you will use less throttle too produce the same amount of hp as before without headers. If you did not use less throttle you would be accelerating.

3. Cold air intakes again increase economy. Yes there are cases where the factory heats up the incoming air to improve drive ability like the thermac valves on old carbed motors but thats only done while cold. This is at least in part why no one uses open element air cleaners anymore they all have a factory version of a cold air intake including ours which you mentioned. This is true even today when gas mileage is of great concern they wouldn't do it if it hurt gas mileage. Furthermore just like you mentioned the factory already does a cold air set up but it can be improved.

 

My brother-in-law has it now...Just under 2000 miles on it. I never dyno'd it, maybe he will, but I doubt it. But I'll ask him how it feels, when it gets on thhe road (1951 Chevy truck now).

 

TPI on a carb'd engine with no other changes will not increase power over the carb that came on it.

 

Actually it would. Granted there are mods that would would allow the LG4 to make better use of the intake but it still would be an improvement.

"The first production TUNED PORT INJECTION (TPI) appeared on General Motors vehicles in 1985. The GM vehicles built with these systems were Corvette, Pontiac Firebird & Trans AM, and the Chevrolet Camaro. These systems according to the manufacturer rendered up to 30 % improvement in Horsepower, torque and economy over carbureted systems, Independent labratories conducted numerous test on the TPI systems and indicated these claims were conservative and that increases of up to 35% in these three areas are attainable.

The 350/5.7L engines from the factory went from 205 HP (1984 Corvette/ crossfire injection) to 245 HP with the addition of TPI. The only differences were the addition of the TPI (1985) and improvements in the valve train (1987). Note that this is a 20% improvement over another proven form of fuel injection."

http://www.fuelinjection.com/portinj.html

 

 

My LG4 didn't really come to life until I got the carb tuned properly. It has hedman headers w/ heated O2, 3in mandrel bent exhaust, performer RPM intake, and an open element.

Owning it and another low mileage camaro with the same factory rated HP as it came with I can tell you that my LG4 is much more powerful then stock.

I don't have any hard evidence my self other then personal butt dyno. Though wasn't there an article floating about where they took a early low compression LG4 and done a few mods at a time and dyno'd in between? If memory serves (disclaimer!! ) they got 200+ HP out of the 8.5 compression LG4 using the mods I listed. It started as 145hp I believe.

 

Hey Doom have you ever taken your car to the track? And did you feel quite a bit of an increase in power from installing headers?