I'm going to start building my 305 soon and ive been looking at some things I want. I want to know what you think my net hp will be. Mods are as follows
- eldlebrock preformer intake manifold
- holley carb, probably a 750 double pumper, will buy new jets if needed.
-MSD street fire distributor
- hooker 2460HKR headers and y pipe with high flow cat and 3" slp cat back
- electric water pump
thats all i have planned so far.

what if i added an lt1 cam or a diffrent cam(sugesstions?)
are there any better gm heads I can use or would i have to go after market? if you could give me a link to some good heads that would be nice.

would it be worth it to port and polish the stock heads?

how about boring them a little?

any and all help/suggestions are appriciated! thanks

 

no help?

 

A 750 is WAY too big for a 305. I wouldnt go bigger than a 600-650.

Exhaust will net you in the 15-25 hp range. You will feel a difference, but it wont make you a race car.

Now that you start talking about camming the engine and pulling the heads...thats when we start telling you to just swap a 350 in it. A 305 (unless REALLY worked) is a turd. Even with a cam and exhaust, a turd is still a turd. My suggestion for a 305 is to go with a carb, intake and exhaust. Anything more than that is kind of futile and you could be saving for a 350....

 

Is this really a L69 HO?

Forget changing the carb. Anything you put on other than the stock CC q-jet would be a downgrade. ANYTHING.

If you really want, put an MSD box on. But, a simple module and coil change are all the computer ignition needs to support anything that 305 can put out.

The Performer intake is okay, a little (but not much) better than the stock intake.

The electric water pump might net a few HP, but have you ever noticed no OEM uses an electric water pump? Take a hint from that, unless this will be a track-only vehicle.

The 2460 headers are better than stock manifolds, but they won't hook to your stock y-pipe, and the y-pipe Hooker makes for it is terrible. Getting a decent y-pipe fabricated will cost approximately twice what the headers cost. A better choice would be the Hooker 2055HKR headers - best off-the-shelf y-pipe out there. Use a '86-'90 TPI single cat direct-fit cat and same application cat-back, and you'll be set for exhaust.

All that will net you about 15-25 HP. You want more, a cam change is needed. Want more still, the heads need work.

Of course, all of this is documented in the 305 thread in the FAQ forum.

 

if I change the carb and dizzy then i can adjust the advance curve which could give me more horse power and possibly better fuel economy right?

what would you suggest for an intake if not the performer? honestly half the reason for it is just to make my engine look a little cleaner.

a lot of upgrades like the water pump arent oem, thats what makes them upgrades

why is the y-pipe terrible? I read somewhere that if you cut it off after the split and weld on a 3 inch pipe instead they are really good.

I already have the cat back, just have to put it on.

I may be interested in a cam eventually and ive heard the lt1 cam is a good upgrade over stock. is this true? what head work would need to be done?


trust me, im planning on doing a LT1 swap eventually, but right now im just having fun messing around with this. plus i need more experince before I tackle a job that big and i think working with the heads and putting a cam in would be good ways to get that experince.

 

the only things ii'm doing/did to my 305 are

New intake.
Headers-exhaust

and a cam swap in the spring.
https://www.thirdgen.org/forums/tech...am-choice.html

i also took some weight off of the car.

the lt1 cam IIRC wont work in the early thirdgens.

from what i hear, porting and polishing will help it breathe better. so if you plan on keeping the 305 for a while (IMO 8+ months) then why not

 

i will look at the cam help page, thank you. I may get them port and polished while they are off becuase I would like new head gaskets anyways.

You should try to find some old l69 heads for your LG4. I hear they are much better and shouldnt be to hard to find or expensive. Just a suggestion. trick flow also makes some nice heads for smaller chevy v-8s but they are expensive...

 

i think i'm going to end up getting the X678 cam? or whichever the guy suggested.


from what i've been told the heads are the same, the only difference is the air cleaner, computer, cam, and a less restrictive exhaust

 

No. No gain whatsoever in power, and certainly a reduction in fuel economy.

The Performer is fine. Just don't expect a big HP boost from installing it. It will support other upgrades, such as cam and head porting, better than the stock intake would. But, on a stock cam engine, little to no change in power.

That makes them a "change", not necessarily an "upgrade".

You didn't address whether this was a track-only car. If it isn't, don't put an electric water pump on it. While some electric water pump manufactures say "streetable", ask them how their pump would do on a 750 mile road trip through the southwest in the summer.

Because you have to cut it off after the split and weld a "Y" like a Flowmaster onto the pipes so you can weld a 3 inch mandrel bent pipe onto it instead. By the time you pay for the 2460's, pay for their y-pipe, pay for the Flowmaster "Y", pay for the 3" mandrel bent pipe at the outlet, and pay someone to do this work, you could have gotten 2055's that you could bolt on. Even if you can do the cutting and welding yourself, you'll have to do the cutting and welding. Unless you like spending money, cutting and welding, for the sake of spending money, cutting and welding, it makes more sense to get something that works out of the box.

Yes, it is better than stock. But, it is a roller lifter cam, and an '84 305 isn't set up for roller lifters. A simple Comp XE268 cam & lifter kit would be a much better choice. You will need new valve springs.

If you're going to do an LT1 swap eventually, then don't waste your money on things that won't benefit that swap. The headers will work on either engine, so that's fine. The intake and cam won't work with an LT1, so you'll have to justify them in your mind for what you'll get out of them until the LT1 goes in. The carb and distributor don't make sense either short term or long term.

 

What you heard was wrong. LG4's and L69 both used 416 castings. Same heads, same valves, same ports, same chambers, same valve springs. The LG4 and L69 intake manifolds were the same as well (except LG4's exported to Canada, which had cast iron intake manifolds).

The difference in compression was the pistons (LG4 had dished until 1985 - after that, LG4 and L69 had the same compression); the difference in power was cam and exhaust (and compression until 1985), with a little contribution from tuning (in the computer, and secondary rods/hanger).

 

I agree, only do mods that will be compatible with your future engine swap

 

why wouldnt a new carb work better? perhaps if you explained instead of just saying "no, no, no" I would understand. I might just go with a rebuilt quadrajet if you convince me.

I will get the peformer most likely

thanks for the cam suggestion, any particular brand of springs you would recommend?

I think you are making the y-pipe way to complicated. cut it, weld it. your done. 20 bucks plus the price of the y-pipe.

I'm not concerned with compatability. i will be keeping all the parts on this engine and be putting it in something else most likely.

oh yes, you are right. it was the pistions. my mistake. i appologize. thanks for the help guys. I would be nowhere without this website. lol.

 

Sorry, discussed all the time on the Carburetor forum.

At 100% efficiency, an engine can use CFM = RPMs x CID / 3456. Assuming 5500 RPMs max, 5500 x 305 / 3456 = 485 CFM. A q-jet is capable of flowing 750 CFM wide open, but the secondary air valve will keep the carb from being "too big", unlike a double pumper. The small primaries of the q-jet keep primary flow velocity up, improving the throttle response over a square bore 750.

In addition, the feedback system of the L69 works very well to adjust the mixture as needed (non-WOT), keeping fuel efficiency as good as possible (with a carb). Also, if you go non-CC, you'll lose the knock sensor function.

You're over-simplifying it. You have to get around the bend after the "Y", unless you bend two pipes to get it pointed in the right direction and then do the "Y" - which won't leave room for the cat. If you don't do mandrel bends, you'll reduce flow capacity (although they would have to be crimped quite a bit to hurt a 305). However you slice it, it's more complicated than simply cutting and welding.

 

ok, thank you very much for explaining. I'm sure you have had to do it a million times with people who arent extremely familiar with engines (like me) and that makes much more sense now. I suppose I would have better luck with my stock carb if it was tuned properly. I just dont want to mess with it for fear of messing it up worse and then my engine not running at all. part of the problem its that i tried to adjust the secondaries and i warped the spring so now they open too early at WOT and it bogs.(part of why I don't want to mess with it anymore) another problem is I think its running really rich. I just changed my spark plugs a few months ago and I havent even driven it 10 miles and they are black but its not oil. I did just adjust the timing 2 days ago and it was advanced by about 13 degrees Id say so that may have had something to do with it. I retarded it to about the 8-6 range so hopefully that helps out. If you could help me out with learning to tune my carb that would be great but I know its kind of difficult through the internet lol.

 

would these comp cam beehive springs be a good choice?
http://www.jegs.com/i/Comp+Cams/249/26981-16/10002/-1

 

oh, I also plan on getting an aluminum drive shaft, light weight fly wheel and a stornger clutch.

Would these make a noticable diffrence?

 

The aluminum driveshaft might give you a little smoother ride at highway speeds, as they tend to be a little better balanced than a factory steel piece. Otherwise, none of those will make any noticeble difference unless something is wrong with what you have now.

What I suggest doing, is getting a good set of headers (Hooker 2055 or Hedman 68470, with matching Y-pipe) and a 3" catback of your choice. They all flow about the same, but sound different - just find a sound you like. The headers/exhaust will make the most noticeable difference and give you the biggest bang for the buck.

What air cleaner is currently on the motor? Is it a dual snorkel unit that the HO motor came with?

 

ok thanks. Ill just stick with what I have for now then. I will deffenatly get some exhaust though.

yup, still have the stock air cleaner. I love how they look. puts those honda tin foil wrapped CAIs to shame I repainted mine and took off the thermac things and rivited block off platess on.
heres what it looks like now

https://www.thirdgen.org/forums/tech...l-snorkle.html

 

You would need new retainers as well.