how much mileage can the 305 handle?
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Supreme Member

Joined: May 2002
Posts: 1,333
Likes: 1
From: Texas
Car: 1991 Z28 Convertible
Engine: 350 TPI
Transmission: 700R4
Axle/Gears: 3.23 with Eaton posi
how much mileage can the 305 handle?
Stuck here....on a budget for the next year. I've got a 1991 305 with 186000 miles on it. Holds great oil pressure. Smokes at start up (alot).
I can afford to rebuild the 305, but cant afford to install a 350 yet. I need to put another 20-30k miles on this car. Frequent oil changes and regular tune-ups.
What do i need to do to get another year out of this thing? Until I have the cash flow to put in a new 350 with all the goodies plus a new trans.
I can afford to rebuild the 305, but cant afford to install a 350 yet. I need to put another 20-30k miles on this car. Frequent oil changes and regular tune-ups.
What do i need to do to get another year out of this thing? Until I have the cash flow to put in a new 350 with all the goodies plus a new trans.
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Joined: Feb 2005
Posts: 1,054
Likes: 1
From: Ajax, ON
Car: 85Z28 87GTA 91GTA 98SS
Engine: SBC, LS-x
Transmission: T-5, 700-R4, T-56
Should be ok for another year. Mine is close to 400K and still running. I'm about to replace it with one around 90K. Cheaper than rebuilding it.
My 305 had 225,000 plus when I pulled it and it still ran great, other than the mentioned cloud of smoke at startup. It also had a 120 shot of giggle gas on it for about 25,000 of those miles.
My old truck now has 413,000 on the original 350. And get this, it DOESN'T smoke on startup. Now that worries me.
Bottom line: change the oil and take care of them, they will run for a very long time. Your motor will be good for years...
I recommend the Lucas Oil Stabilizer, though. I had a lot of great success with that stuff in our fleet of trucks, and have been using it in my truck for a while now.
My old truck now has 413,000 on the original 350. And get this, it DOESN'T smoke on startup. Now that worries me.
Bottom line: change the oil and take care of them, they will run for a very long time. Your motor will be good for years...
I recommend the Lucas Oil Stabilizer, though. I had a lot of great success with that stuff in our fleet of trucks, and have been using it in my truck for a while now.
Joined: Feb 2001
Posts: 13,756
Likes: 560
From: Cincinnati, OH
Car: '90 RS
Engine: 377 LSX
Transmission: Magnum T56
You can rebuild a 350 cheaper than rebuilding a 305. You only have to swallow the cost of the core. I wouldn't waste my time with a new 305. Start up smoke sounds like bad valve seals. Get those replaced or you can slowly decrease what life is left in your motor. If everything else is in working order keep it for the time being until your 350 is ready.
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Joined: Aug 2004
Posts: 178
Likes: 0
From: Gray, GA
Car: 1986 Trans Am
Engine: 6.0L LQ4
Transmission: 4L60E
Axle/Gears: 2.73
I'm closing in on 200,000 miles with my 305 and it doesn't smoke at startup. (198,000 miles). But there is an enexplainable "Squeal" from the front of the engine. We changed the alternator, and I am changing the water pump tomorrow. (I'm pretty sure it's the water pump).
But yea, my 305 is nearing 200,000 and my grandfather's/my '88 Chevy Silverado 1500 is up to at least 260,000 on the original 350. and get this. My grandfather bought the truck knew and noone has ever changed the oil in this truck but him save one time.
So just keep the oil changed and try to stop the smoke and it should last you a year (I would think)
But yea, my 305 is nearing 200,000 and my grandfather's/my '88 Chevy Silverado 1500 is up to at least 260,000 on the original 350. and get this. My grandfather bought the truck knew and noone has ever changed the oil in this truck but him save one time.
So just keep the oil changed and try to stop the smoke and it should last you a year (I would think)
Originally posted by HalfInchWrench
Should be ok for another year. Mine is close to 400K and still running. I'm about to replace it with one around 90K. Cheaper than rebuilding it.
Should be ok for another year. Mine is close to 400K and still running. I'm about to replace it with one around 90K. Cheaper than rebuilding it.
If it were one of those "high quality" Hondas or Toyotas, you probably would have changed the engine twice already, or at least the head once.
Joined: Nov 2002
Posts: 3,466
Likes: 5
From: MA, USA
Car: 83 bird
Engine: 305/383
Transmission: WC T5
Axle/Gears: 3:42
My car has about 200,000 on the LB9. It was only raced by the previous owner, for two years! It smokes on startup and when you get on it. I'm looking for some sort of oil additive so it can last till I get the new motor in.
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Joined: Mar 2000
Posts: 43,187
Likes: 42
From: Littleton, CO USA
Car: 82 Berlinetta/57 Bel Air
Engine: L92/LQ4 (both w/4" stroke)
Transmission: 4L80E/4L80E
Axle/Gears: 12B-3.73/9"-3.89
Originally posted by aaron7
My car has about 200,000 on the LB9. It was only raced by the previous owner, for two years! It smokes on startup and when you get on it. I'm looking for some sort of oil additive so it can last till I get the new motor in.
My car has about 200,000 on the LB9. It was only raced by the previous owner, for two years! It smokes on startup and when you get on it. I'm looking for some sort of oil additive so it can last till I get the new motor in.
That goes for you, too, Matthew91-Z28.
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iTrader: (3)
Joined: May 2004
Posts: 4,345
Likes: 1
From: Brighton, CO
Car: '72 Chevy Nova
Engine: Solid roller 355
Transmission: TH350
Axle/Gears: 8.5" 10-bolt 3.73 Posi
If you're going to rebuild your 305, just grab a 350 for an extra $50 and rebuild that. Even a stock rebuild will get you more power than the 305 and you can switch over your TPI/TBI and just get bigger injectors and retune your computer.
It's a total of only a few hundred dollars for alot more power.
It's a total of only a few hundred dollars for alot more power.
Supreme Member
Joined: Aug 2004
Posts: 4,168
Likes: 3
From: Marietta, GA
Car: '91 Firebird Convertible
Engine: 305 TBI (LO3)
Transmission: 700r4, Vette Servo
Axle/Gears: 3.27 9 Bolt, PBR disks
Originally posted by urbanhunter44
It's a total of only a few hundred dollars for alot more power.
It's a total of only a few hundred dollars for alot more power.

Howdy Bay Area!
Joined: Mar 2000
Posts: 43,187
Likes: 42
From: Littleton, CO USA
Car: 82 Berlinetta/57 Bel Air
Engine: L92/LQ4 (both w/4" stroke)
Transmission: 4L80E/4L80E
Axle/Gears: 12B-3.73/9"-3.89
I agree about not rebuilding a 305.
I'm just recommending a simple gaskets and seals replacement job. That's all that's needed to fix the reported problem.
Oil additives aren't going to do it.
I'm just recommending a simple gaskets and seals replacement job. That's all that's needed to fix the reported problem.
Oil additives aren't going to do it.
Senior Member
Joined: Jan 2003
Posts: 801
Likes: 1
From: st. Petersburg, Fla
Car: 83 Z28
Engine: vortec 305 for now
Transmission: 5 speed
I'm with 57. throw some vlave seals on it to get by and let it eat. It's a small block, if you really feel bad throw a timing chain at it. See you in 30,000 miles.
Joined: Nov 2002
Posts: 3,466
Likes: 5
From: MA, USA
Car: 83 bird
Engine: 305/383
Transmission: WC T5
Axle/Gears: 3:42
I'm not putting any more money into this motor, unless it was a cheap additive. I'll live with the smoke for another month!
Thread Starter
Supreme Member

Joined: May 2002
Posts: 1,333
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From: Texas
Car: 1991 Z28 Convertible
Engine: 350 TPI
Transmission: 700R4
Axle/Gears: 3.23 with Eaton posi
geez thanks for all the input. I checked into doing a rebuilt 350 but what was prohibitive (budget wise) was the cost of 22lb injectors (cant find cheaper than $35 per injector), and some of the other items totaled together (afpr, chip, etc.) And the 350 was $300 more than the 305 due to mismatched core.
I may just do valve stem seals and call it a day until I have enough scraped together to get a 350 and build it the way i want with cam/heads/intake.
thanks all
I may just do valve stem seals and call it a day until I have enough scraped together to get a 350 and build it the way i want with cam/heads/intake.
thanks all
Joined: Apr 2003
Posts: 1,230
Likes: 2
From: Madison, WI
Car: 1986 Camaro Z28
Engine: 400
Transmission: T5
Axle/Gears: 10 bolt Posi 3.73
I've got a buddy with 230k on an LG4 in a 84 berlinetta. My uncles F150 with the 4.6 trition has about 240k. Take care of it and change the oil, it'll last a lifetime... (well prolly not that long)
Senior Member
Joined: Mar 2003
Posts: 966
Likes: 2
From: NE Ohio
Car: 83 Z28
Engine: 305 (LG4)
Transmission: THM700R4
Axle/Gears: 10 bolt, 3.23 non-LS
Originally posted by ShiftyCapone
Start up smoke sounds like bad valve seals. Get those replaced or you can slowly decrease what life is left in your motor.
Start up smoke sounds like bad valve seals. Get those replaced or you can slowly decrease what life is left in your motor.
Supreme Member

Joined: Jul 1999
Posts: 1,556
Likes: 28
From: Adrian, Mi, USA
Car: 1988 Pontiac Firebird Formula
Engine: 5.7 TPI
Transmission: 700R4
Originally posted by phess11
How will bad valve seal decrease the life of your motor?
How will bad valve seal decrease the life of your motor?
No show stoppers, just annoyances. Changing valve seals is actually a rather simple, if time consuming process, and will eliminate most of your oil consumption problems at startup. I did mine, and now my 190,000 mile 350 does not use ANY oil between changes. Spark plugs look much better, and reduced spark knock on hard acceleration. Parts are less than 30 dollars.
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