I have an 86 305 Carb Iroc-Z that is currently stock with 102,000 miles on it. I would like to keep the car as stock as possible so I want to rebuild the 305, but give it some horsepower. I would like to be able to keep the car the same as it is now with the computer and cc carb and all that jazz. I know it would require a specially programed PROM for the computer for any changes I make to the cam and so on. I want to keep her as a daily driver with decent gas mileage 17-20mpg, be able to step on the pedal and get out of my own way, be conservative on the cost index. I am a dad with 2 kids, my Iroc is my hobby not my money pit. What can I do as far as a cam and lifters, specific pistons, special head work and so forth. I think you guys see the picture. If you have a built a 305 please tell me what worked well for you or what did not. Thanks guys.
Tony

 

This is what i would do: Pull the current block and set it aside so that you will have the original #'s matching motor. Then find a 350 block and rebuild that. All your current parts will bolt up. It will be slightly cheaper to rebuild and you will get the exact same if not better gas mileage, with lots more power potential.

 

I have quite a few suggestion...but first if it's carbed then why would you need a new PROM? I just need to know your setup for sure and I can definately help you. Email me with any questions.

 

In responce to Leigh's comment. You have a point but you need to realize that some people don't want to pull a motor completely out (and with 102,000 you don't need to). And also some people like the 305. I personally like it better as a daily driver as the 350. Just my worth.

 

You said you were going to rebuild it. Its kinda hard to rebuild it while its still in the car, actually its impossible.

 

It's actually not impossible....but not easy. I've done it before. I definately don't recommend it though.

 

Charman - I thought it would need a new chip that had the specifics of the new cam and any head adjustments that may have been done. As for the specifics: It is a 305, computer controlled Q-Jet, 700R4 Automatic, 2.73 gears in a single wheel burner rear end. I am currently looking for a posi, rear disc brake unit to change over to. Hopefully by engine PULL and rebuild time that will already be in place. I do plan to extricate the engine from the car for a rebuild. Please shoot me some ideas for setups. I am staying with the 305 for the rebuild to. Thanks for your time immesely.
Tony

 

Getting a more friendly cam from Summit (look at the Comp Cams XE line of cams, they're more gas efficient, bigger power band, everything improves with it)

As for having the motor rebuilt. I dont think I would do that unless it's got lower oil pressure than you like, or you plan to rev it to the moon with some mods.


I understand you wanting your car to remain very streetable daily driverish, and be budget friendly. I'm going for the same thing in my ride.

Things you can do for performance, that would still give you better gas mileage (assuming you kept your foot out of the loud pedal ) go in this order....

Exhaust : EVERYTHING from the manifolds to the tail pipes need replaced, go with a 3" exhaust, you can get some budget headers, but the more expensive ones will be more installation friendly, and more performance gains, which can also add to more gas mileage.

Quadrajet Carb: Rebuild your current carb. Lots of times all that these LG4's need to regain their gas mileage is a carb rebuild!

Cam: Look up the Comp Cam's XE (Extreme Energy) line of Camshafts. They give for very streetable idle quality, a much flatter torque curve, and better fuel efficiency.

Heads: Buy a set of 416 casting number heads (From an LG4) and port them yourself. Look up "Sitting Bull" in the General Tech/Data forum and you'll find his post on how to do this yourself!


But just an exhaust and carb rebuild / tweaking (check the tech articles for how to tweek your carb) will give you MUCH more performance and gas mileage.

edit: this was a given, but your single snorkle air cleaner will choke your system as well, if you get a dual snorkle from the H.O. motor ( about 150 dollars) , or an open element intake (like 15 dollars) you will no longer have this bottleneck, and it might gain you some gas mileage

 

I don't know how you can bore a block with it still in the car. But then again i'm 3/4 stupid and 9/16 stupid.

 

Leigh...you don't always have to bore a block when rebuilding, in my case I didn't need to.

For the most part I agree with 'sellmanb'. The exhaust is a must...huge difference (and not too expensive). Also the cam, carb and intake. Though personally I am an Edelbrock power package fan. There Performer series cam, intake, and carb would be a great combo, and coupled with the exhaust would probably be all you needed. 'Sellmanb' suggested keeping your q-jet...I would get as far away from that one as possible if it were me. And as he also said...unless there is a need for it theres no need for a rebuile...you will end up spending more money than you would like.

 

A basic but reasonably strong carb'ed 305 rebuild? Not a big deal.

Get a basic rebuild kit with flattop pistons (30-over since you'll probably be punching the block 30-over when you get it machined), which will bring the compression in at about 9.5:1 with your stock 58cc 305 heads.

Cam: $79 Summit 1103 cam and lifter kit (214*/224* duration on 112* LSA). Get a set of Crane 99848 valve springs for your heads, too (they are drop-in performance replacement springs for your stock units- DON'T reuse your stock springs with any performance cam)

Might consider upgrading to an Edlebrock Performer EPS intake over your stock unit, if you have the funds.

Also might consider upgrading your exhaust with some headers (Hooker Super Comp shorties are cheap and easy to install), y-pipe, high flow cat and high-flow cat-back. You can always do this "piecemeal" at a later point as funds permit, but it really will make a noticable difference in performance.

If you can swing the extra funds and have your stock heads pocket-ported while they're being freshed up and having the upgraded springs installed, it's money well spent.

Other than these few areas of upgrading for performance reasons a basic rebuild from your local machine/engine shop will be all you need. You can still run it with the stock chip, carb, distributor, etc. And you won't have any headache with a lot of different aftermarket stuff not working together- it's a very simple combo to assemble and install.

 

V6 3.42 axle $100-200, instant power. I like the MTC-1 cam in non roller 305's but the suggestion Damon made would make more power. MTC-1 $70. The rest of the good stuff is listed in the post above.

 

I suggested keeping the Q-jet because he already has the carb, and he wanted to keep this all budget friendly (wife and kids to take care of) and a rebuild kit is like 35 dollars, rods and hangars are like 10 dollars at most. Free mod to make it a 750CFM carb, and for 45 dollars you have a carb with great gas mileage, computer controlled (so you dont need a new dizzy), and tons of power on-demand (thus is the Q-Jet).

If I were building a hot rod or something I would get myself a Holley. Q-jets arent the prettiest things... but they work just as well, if not better than a Holley if you learn to tune them

 

I agree, I bought a 84' T/A that had a pretty new 305 in it that leaked coolant from the rear. With the engine in the car I could never figure out where so I pulled the motor and found a defective freeze plug in the rear of the block. I decided to go 350 but when I tore the 305 down it didnt need a rebuild and was already .040 over from the last rebuild in 95' so I decided to keep it. After carefull inspection of the internal engine I ended up just using Edelbrocks cam and intake power package as well as new headgasket, oil pump, and all new seals and feeze plugs. I pretty happy, it's not a 10sec car but the cam and intake gave it way more ***** than it had before. I also reused the CCC q-jet carb, however, I did buy a new one to replace the old. I also bought a set of headers and a new Dynomax Super Turbo exhaust w/no cat and removed every bit of emmisions garbage since I dont have to worry about it here. All total including all the little things I spent around 600.00 bucks.

I have found that with any project, there is only one thing thats in your way and that it MONEY and MONEY can get you out of any jam. I also own 2 other cars and this isnt my dd.

 

Great suggestions everyone and I will take all these into consideration to come up with the build plan. I will post to this topic when I think I have a solid plan for everyones reveiw and comments.
Tony