Everything I need to know about tuning a 305

[DmcL]

Ok first don't say swap it out lol

I want more power from my 305 HO. Currently it's got a Holley carb (650cfm I believe) and some rare-ish 70's camaro intake manifold that's supposedly one of the best flowing stock dual planes. Its also got an HEI distributor and full exhaust system with an H pipe. It runs nice and pulls fine but it's not exactly fast... My Subaru with about 270bhp and 320lbft would run rings around the Monte Carlo.

Anyway I want to know options for getting around 300hp if not more from the 305 HO.

My first question is how high can these engines be revved on stock internals and stock valve springs? Want to know where my window for power/tq is currently as I'm thinking I may be able to see close to that target with a cam and a couple other tweaks.

I'm also wanting to know about EFI setups both stock and aftermarket.. I have a background tuning my Subaru as well as older bmw's so I'm more familiar with fuel maps and ignition maps than vacuum advance, distributor weights and carb jetting. EFI wise I may look into TPI retrofitting or some aftermarket system like Holley terminator or something.. What all is out there and which ones are easiest to install on a carbed car?

What about Boost.. Can I boost on stock internals and if so how much? A small set of twins would certainly liven the car up without it needing to rev super high.

And last but not least.. What's the easiest way to get to about 300hp on a 305 HO? Assuming naturally aspirated what sort of cam would I be looking for and what supporting mods (valve springs etc) would I need?

I got the handy dandy tuner goodies like a wideband meter with logging capability and sensor inputs so even if I stay carbed I don't need to burn plugs to check my a/f.

 

[autonaut]

Swap it out.. For an LS engine. Really.

You already know everything about tuning the 305 with ignition, exhaust and intake, yet feel it is not enough to power it. So swap it out.

Adding FI or forced induction would end up running the same as an ls swap, and you'd still be stuvk with a poor choice of engine.

Unless one wants to cruise around and occasinally haul light loads, all with the sound of a V8, the 305 wont ever make any sense. It will never be a performer unless you spend big bucks which would be foolish on that small bore!

 

[DmcL]

Swapping isn't a realistic option at present. I'm not in the US so gm v8's don't grow on trees here. Since it's a 305 HO and people put these heads on the 350 then I figure I can do what everyone does on a 350 just on a smaller scale.

The main issue with the 305 is valve size limitations from what I hear.

So what's the options for more power from the 305? Seems like a cam is the logical next step.

 

[pontiacgp]

I don't know where you live but I would leave it like it is and wait till a 350 shows up. The people who use the 305 heads on 350's think they are going to increase the compression but it doesn't work well. Even if you get the 305 up to 300 hp you still will be missing the torque of a 350. ....and when you do get it to 300 hp a 350 will show up...

 

[t01blaze]

Anyway I want to know options for getting around 300hp if not more from the 305 HO.

My first question is how high can these engines be revved on stock internals and stock valve springs? Want to know where my window for power/tq is currently as I'm thinking I may be able to see close to that target with a cam and a couple other tweaks.

I'm also wanting to know about EFI setups both stock and aftermarket.. I have a background tuning my Subaru as well as older bmw's so I'm more familiar with fuel maps and ignition maps than vacuum advance, distributor weights and carb jetting. EFI wise I may look into TPI retrofitting or some aftermarket system like Holley terminator or something.. What all is out there and which ones are easiest to install on a carbed car?

What about Boost.. Can I boost on stock internals and if so how much? A small set of twins would certainly liven the car up without it needing to rev super high.

And last but not least.. What's the easiest way to get to about 300hp on a 305 HO? Assuming naturally aspirated what sort of cam would I be looking for and what supporting mods (valve springs etc) would I need?

I got the handy dandy tuner goodies like a wideband meter with logging capability and sensor inputs so even if I stay carbed I don't need to burn plugs to check my a/f.

Stock the engine stops making power at about 4700 rpm. You can run the quarter mile faster short shifting than revving to redline.

I'd grab a 3rd gen F body TPI setup if you want fuel injection.

In the end, I think nitrous is your answer.

 

[DmcL]

Yea I know more displacementwill give more torque but I'm not looking to make a drag monster. 300ish hp from the 305 will be fine and compared to the norm for domestic and j* imports here the 305 will still make plenty of torque.

Later on I may look at building an engine up or an lsx swap or something but for the foreseeable future the 305 will stay.

So given the current setup with high flowing stock gm dual plane and full exhaust and holley 650cfm carb what sort of ballpark hp/tq would I see with a cam and what sort of duration/lift should I be looking for?

 

[autonaut]

I'd seriously advice you to get a 350 and start byuing parts for it until you stumble upon a decent block.

I have had several 305's including one with a roller cam.

The 305 i did everything "normal" to such as performer intake, fine tuned carb, perfectly set up HEI, true duals with h pipe and longtube headers, removal of AC. The engine became lively up til 4500 rpm and so, but never really became a performer.

2 months ago i gave a stock 75' L48 the exact same treatment, but with performer rpm heads a hydr.flat tappet 1500-5500 lunati cam.. This engine runs circles around that 305.

So

 

[DRIVEN]

It may be tough to get an honest 300hp without some outside help (power adder). The 305 was never intended to be a performance engine. It was designed to make enough torque to get heavy cars moving and meet mandated mpg and emissions standards. What the 305 does okay is make torque. If you like the TPI injection and can use a more modern controller, you'll improve your torque output. The downside is that it'll make it's power up to about 4500 then fall off. Not a big deal since that's probably about where your heads run out of breath. I'd contact a major cam suppliers' techline and run your combo by them. Remember, stock 305 TPIs were only rated just over 200hp but were close to 300tq right out of the box.
Shoot for torque, not HP, when dealing with 305s. It's more rewarding.

 

[darbysan]

I installed TPI on an '87 L69 305. I also changed the cam to a roller cam (LT1 cam). '87 block is already prepped for roller cam- don't know what year you are working with. I added headers and free flow cat. I could definitely feel the difference, but probably short of 250-260 hp. Overall cost to install the TPI was about $2K. Lots of stuff to change ( fuel delivery, sensors, injectors, electric fans, wiring , programming). More info for TPI on my website with spreadsheets, etc.

Here are some articles on getting HP out of a 305. Maybe you will see something there that interests you.
http://www.hioutput.com/tech/343hp/343hp.html
http://www.hioutput.com/tech/290hp/290hp.html
http://chevythunder.com/ ( TPI Swap)


Bottom line is that trying to beat a lighter weight import with 300hp is probably not going to be possible with a heavy american car with a 305. But you can sound better!!

 

[DmcL]

Nah it's not about beating things.. If I want to do that I'd bring out my 06 wrx which is roughly 270bhp/320lbft which I can patch launch control and flat foot shift on in about 5 mins with my laptop lol it runs high 13's on stock turbo and stock cats. Only have a handful of mods and remapping by me.

I want ideally about 300bhp from the 305. You guys are likely thinking in whp. Probably about 250whp I'd like to see from it. Basically enough for it to move decently and spin wheels/do some donuts once I fit a posi or something. Eventually I might want to make some decent power but for now anyway I just want to make the 305 a bit more fun.

I got a pic of what I think must be the part number of the intake manifold. Anyone know of this manifold and would I need to look at something aftermarket for the sort of hp I'm after?