4 Bolt 305? - Off-Road Forums & Discussion Groups
GM Standard SFA Trucks & SUV's All discussion of full sized Solid Front Axle Trucks, SUV's to include Suburban

LinkBack Thread Tools Display Modes
post #1 of (permalink) Old 12-15-2002, 12:03 PM Thread Starter
Join Date: Jun 2001
Posts: 1,595
Thanks: 0
Thanked 0 Times in 0 Posts
4 Bolt 305?

I just did some work on an 85 chevy 1/2 ton he says its the original 305, I didn't know they came with 4 bolts! It is starting to burn oil (rings) and he will eventually buy my 350 for some and the 305. What could I do to build this 305 to be comparable or better than a stock 350? I want to get by as cheap as possible but bore is not out of the question. Thanks in advance and also has anyone done business with Northern Auto Parts?
MIJeepBoy is offline  
Sponsored Links
post #2 of (permalink) Old 12-15-2002, 12:57 PM
Carpal \'Tunnel
wrath's Avatar
Join Date: Nov 2001
Location: Waukesha, WI
Posts: 3,323
Thanks: 0
Thanked 1 Time in 1 Post
Re: 4 Bolt 305?

The only 4 bolt 305 in existence was in some Canadian heavy trucks. And they were modified to 4 bolts, they didn't come that way.

The eighth digit of the VIN will be H if it has a 305 in it.

If you can get a casting number that will tell us what motor it is. It is very unlikely (.0000000000001%) that it is a 4 bolt 305.

I've been researching this lately. I actually plan on rebuilding my old 305 and putting it in place of my 350. Then I'll rebuild my 350 and put it back in place of the 305. It's a good thing motor swaps only take 6 or 7 hours.

Anyway here's what I'd do and the order I'd do them. #5 has two parts because you can choose one or another.

1. Tune your carburetor. Get some DR rods for the secondaries. Play with the hangers, Somewhere between K and P should be good.
2. Edelbrock 2101 intake. Good for ten horses or so unless you've got a crappy equalized dual plane intake then it's worth more.
3. Headers. Good for just about ten horses. Find 1.5" primaries if you can because otherwise you'll sacrifice some low end torque.
4. 2" open spacer under the carburetor. This slowly generates horsepower but it doesn't break the 5hp mark until 3500 rpm. If you've got room, stick it in there. It's only $20. Worst case scenario is that you'll lose some bottom end torque and you'll have a $20 piece of phenolic plastic that would go great on that 400SBC powered Camaro you've been dreaming about.
5a. Find some 58cc heads if you don't already have them (I've never heard of them not being in a truck or blazer). Get them machined for 1.94 intake valves instead of stock 1.84. Don't forget a good set of undercut valves. This should bring your compression ratio up above 9.2:1. If you can, find a set that you can mill some material off so you can get the compression up a little higher yet without toying with new pistons.
5b. Camshaft. It seems that 108 works the best. I don't know anything more than that--I'm still researching.
6. Complete rebuild. Stick some higher compression pistons in it. Port the heads.

After both #5s and a rebuild you're supposed to be able to squeak [email protected],000rpm with a properly tuned carburetor.

Most 305s had between 7.5:1 and 9.2:1 compression ratios. You can get more ponies out of it by bumping up the compression to 10:1. You usually see a 2-3% horsepower increase for 1 point compression ratio increase.
wrath is offline  
Sponsored Links

Quick Reply

Register Now

In order to be able to post messages on the Off-Road Forums & Discussion Groups forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page
Display Modes
Linear Mode Linear Mode

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

For the best viewing experience please update your browser to Google Chrome