Wanting suggestions about engine overhaul

[Rapid Roy]

Thank you to all who have expressed their opinions on this thread.

Now I want to know if anyone has known that if the heads were redone and did not do complete rebuild, if the engine started burning oil due to older piston ring oil seals? I'm still unsure just what I really should do.

[bd]

Refurbishing the heads will have zero impact on oil consumption past the piston rings.  Quite the contrary, with properly sized valve guides and new valve stem oil seals, less oil will draw past the guides into the combustion chambers.  To boot, new intake gaskets may better control oil drawing into the intake runners from the valley area.  Conceivably, oil consumption might decrease. 

For best results I recommend Viton positive-stop valve stem seals (no machining required) used in conjunction with the OEM square-cut valve stem o-rings caged between the valve stem locks (keepers) and spring retainers for both the intake and exhaust valves in lieu of the OEM umbrella seals.

[hatzie]

I agree with Bruce. 
The L31-R should still have provision for the pre 2000 transmissions.  The 305 Stewart recommended does not.

There's no replacement for displacement.  The L31-R 350 comes with Vortec heads.  The L31-R is 255hp 330ft-lb compared to 230hp and 285ft-lb on that 305 with the stock Cast Iron exhaust manifolds and intakes used in the 1990's T400 chassis.  You can eke a few more horses out with better exhaust and intake manifolds.

The L31-R cam doesn't have a fuel pump lobe and the block is not machined for one either so you will be installing an electric fuel pump to use the Vortec 350.

You can use the GMPP #14097395 Camshaft from the HT383 & 350 RamJet without otherwise changing the L31-R valvetrain for some more HP & a lot more torque.  Roughly 280hp & 400ft-lb...  This will void the engine warranty tho.

Your Cast Iron Quadrajet intake will not fit the Vortec heads.  If you want decent driveability and fuel economy without sacrificing much, if any, performance get an Edelbrock Performer Dual Plane Intake and install a properly rebuilt 4M4E Quadrajet.

You will not be sorry you moved up to that 350 and the upgrade is inexpensive.  Keep your factory engine in the barn or garage.

[Stewart G Griffin]

I agree with Bruce. 
The L31-R should still have provision for the pre 2000 transmissions.  The 305 Stewart recommended does not.

There's no replacement for displacement.  The L31-R 350 comes with Vortec heads.  The L31-R is 255hp 330ft-lb compared to 230hp and 285ft-lb on that 305 with the stock Cast Iron exhaust manifolds and intakes used in the 1990's T400 chassis.  You can eke a few more horses out with better exhaust and intake manifolds.

The L31-R cam doesn't have a fuel pump lobe and the block is not machined for one either so you will be installing an electric fuel pump to use the Vortec 350.

You can use the GMPP #14097395 Camshaft from the HT383 & 350 RamJet without otherwise changing the L31-R valvetrain for some more HP & a lot more torque.  Roughly 280hp & 400ft-lb...  This will void the engine warranty tho.

Your Cast Iron Quadrajet intake will not fit the Vortec heads.  If you want decent driveability and fuel economy without sacrificing much, if any, performance get an Edelbrock Performer Dual Plane Intake and install a properly rebuilt 4M4E Quadrajet.

You will not be sorry you moved up to that 350 and the upgrade is inexpensive.  Keep your factory engine in the barn or garage.

Really?   i thought ALL  305's will accept any of the common transmissions----th-350,400, 700 etc.?

The reason why i suggested this 305 over the more popular 350's is that Roy wanted more umph than his present engine, which i think this 305 can provide AND the mpg will not be any worse and probably a little better.      i understand and agree that for the most part 350's are superior to 305's in power, but in this case you get decent power without being too much engine, better fuel economy, less wastefulness.

[hatzie]

I agree with Bruce. 
The L31-R should still have provision for the pre 2000 transmissions.  The 305 Stewart recommended does not.

There's no replacement for displacement.  The L31-R 350 comes with Vortec heads.  The L31-R is 255hp 330ft-lb compared to 230hp and 285ft-lb on that 305 with the stock Cast Iron exhaust manifolds and intakes used in the 1990's T400 chassis.  You can eke a few more horses out with better exhaust and intake manifolds.

The L31-R cam doesn't have a fuel pump lobe and the block is not machined for one either so you will be installing an electric fuel pump to use the Vortec 350.

You can use the GMPP #14097395 Camshaft from the HT383 & 350 RamJet without otherwise changing the L31-R valvetrain for some more HP & a lot more torque.  Roughly 280hp & 400ft-lb...  This will void the engine warranty tho.

Your Cast Iron Quadrajet intake will not fit the Vortec heads.  If you want decent driveability and fuel economy without sacrificing much, if any, performance get an Edelbrock Performer Dual Plane Intake and install a properly rebuilt 4M4E Quadrajet.

You will not be sorry you moved up to that 350 and the upgrade is inexpensive.  Keep your factory engine in the barn or garage.

Really?   i thought ALL  305's will accept any of the common transmissions----th-350,400, 700 etc.?

The reason why i suggested this 305 over the more popular 350's is that Roy wanted more umph than his present engine, which i think this 305 can provide AND the mpg will not be any worse and probably a little better.      i understand and agree that for the most part 350's are superior to 305's in power, but in this case you get decent power without being too much engine, better fuel economy, less wastefulness.

Read the link you posted on that engine...  apparently the LSx and later 4.3L v6 were not the only engines that require the newer Gen III style transmissions.  Something was changed about the depth of the crank flange in relation to the bellhousing face IIRC.

Yes and no. ..  The 350 doesn't have to get significantly less MPG than the 305.  I've had a stock 1985 305 and a properly setup truck 350 get right around the same 14-15mpg highway fuel mileage and 11-12mpg in town.  The 350 had more torque on tap when I needed it but was not working real hard to make the pickup roll down the highway.  Certainly nowhere near peak torque where you use a lot of fuel.
It is a package deal...  The choice of carburetor, intake, exhaust, and cam along with tires, axle ratios, and transmission setups have a serious effect on fuel mileage.  A Carter AFB or Rochester 2G will not sip fuel like a Quadrajet on the primaries or a good TBI or MPFI system.  Using intake, cam, exhaust, and heads to increase lower RPM torque will improve MPG.  Set your tires and gearing up to take advantage of the torque/HP curve is essential too.
The L31-R is a cheap way to get very good heads and reasonable cam on a fresh motor for comparatively not much cash leaving you free to optimize the other parts of the package...

[Stewart G Griffin]

i dunno;  i think that engine should be able to accept pre 2000 transes----the L30 is the same as the L31 just 305 vs.350.   i think the link says IF you're putting it in a 2001 or newer truck, you gotta use the 2000 and after starter and trans.

Anyways, whatever;  i was just suggesting this engine because it does (at least on paper) offer more spunk than the stock LM1 350 AND  the L30 305 has roller lifters and higher compression too, so it should get better mpg than the original engine.

[Rattler12]

I'd rather (and have on 6 occasions) rebuild my own engine to my own specs than to invest in a crate motor hecho en Mejico no matter the savings on the crate motor.......cheap parts and cheap labor equal cheap engine.....you just need a competent machinist to prepare your block and heads.......chevy small block parts are readily available for reasonable prices in a varierty of combinations to make some serious HP for less than $2500 including machine work....putting a reliable performing small block together is not rocket science........ IMHO