mlanglin2007

Guys - I need some help. I'm rebuilding a '73 convertible Vintage road-racer. This car was raced sporadically with a 454 that was never particularly reliable, so I'm looking to use a 350 instead, and make it a vintage-legal SCCA B-Production car. The B/P rules state that the correct engine was an L-46. Using an LT1 would push the car into A/Prod and I'd have to run against 427s & 454s.

Can you tell me the differences between the two 350s? The spec sheets in the SCCA rule book show 2.02 valve heads for both, but i'm thinking the difference must be hydraulic vs. solid lifter motor.

As you can tell, I'm not real well versed in "C3 Corvette", so your help is appreciated. Thanks.

mikem350

The LT1 was not avail after 72. The base motor in 73 was same as regular 4 bbl chevy Impala, etc, hydraulic smog motor. The L82 was the higher output option in vettes.

Others will chime in and help u bend the rules...lol!

mlanglin2007

Thanks - and I should have clarified, the SCCA Rules book (which is pretty good at specs, but not infallible by any means) showed the L46 as a base engine for 69-71. Were both that and the LT1 available during those years?

With regard to "bending the rules", yeah, there's always some of that, but really, the key point is whether an L46 had a hydraulic cam vs. solid lifter, which I think the LT1 had. The SCCA rules are such that you have to keep stock valve sizes, and are supposed to keep stock head castings, block castings, type of cam, crank and rods. I'll most likely change to forged steel crank and rods, and use a 4-bolt block.

Pretty much every other internal part of the engine is free, and cam-lift is whatever you want. One limiting factor is that for B/P, you are supposed to use the Quadrajet carb. A lot of Q-jet manifolds I've seen are cast iron. Did Chebby make an aluminum version of this manifold?

Gordonm

The L 46 was never the base engine. The L48 was. The LT1 was only available in 70-72.

Don Rickles

73=rpo l48
70-72=rpo zq 3

530planeman

Lt1' were solid lifter and had an aluminum intake and all used a holly carb

Calo69

L46 69, 70 only 4 spd.

Brcmpbl

The base engine in 1973 was the L48, which was a 2-bolt main lower compression motor, with cast crank, hydraulic cam, cast intake with quadrajet, etc.

The optional small block in 1973 was the L82, which was a 4-bolt main higher compression (9.0:1) motor with forged crank, hydraulic cam, cast intake with quadrajet, etc.

The L46 was an optional motor offered only in 1969 and 1970, on 4-speed cars. It had 11.0:1 compression, 4-bolt mains, forged insides, hydraulic cam, cast intake with quadrajet, etc.

The LT1 was available from 1970-1972. In 1970, it was essentially the same motor as the high compression L46, with the exception of the addition of an aluminum intake with Holley carburetor, and most importantly a solid lifter cam. Both had 2.02 heads. 1971 and 1972 LT1s had lower compression ratios (9.0:1) than the 1970 LT1s and L46s.

The LT1s and L46s are great motors. The L82 was, in some ways, a lower compression version of the L46, with a much, much different factory quadrajet, among other things.

mlanglin2007

A
So, the L46 had a cast iron Q-jet intake? Otherwise, thanks for the info. Very helpful!

Brcmpbl

So, the L46 had a cast iron Q-jet intake?

Yes, it did. The LT1's was aluminum with a Holley. That is the primary distinction between the L46 and LT1, aside from the LT1's special solid lifter cam.

Easy Mike

Keep in mind the LT-1 was C3 Corvette. The LT1 is a different animal and C4.

Tom73

Look here http://www.73spot.com/index_stats_files/s_compair.htm on the 73Spot. It lists the specs for the two small blocks that were available in 73, the L48 & L82. The L82 is basically the old 350ci/350hp engine with a q-jet in place of the holly and with a lower rise manifold and lower compression. It has the forged goodies that you may want.

[Edit] sorry, but apparently wrong on the 350/350 having a Holly, apparently it was also a q-jet engine. Tom...

Alan 71

Hi Tom,
I didn't think the 350/350 had a Holley…. I thought it always had the Q-Jet.
I thought during 68-72 just some bb engines and the 70-72 LT-! had a Holley carb.
Regards,
Alan

69monzacpe

If I recall, the LT-1 also used a high volume oil pump vs the standard pump in the L-46.

Brcmpbl

The L82 is basically the old 350ci/350hp engine with a q-jet in place of the holly and with a lower rise manifold and lower compression. It has the forged goodies that you may want.[/QUOTE]

Part of this is inaccurate. The 350ci/350hp is the L46, which came from the factory with a cast iron intake and a quadrajet. That quadrajet, however, was a serious one, and very different in performance capabilities from the factory than the quadrajets that came on other engines in the line-up.

694speed350

Part of this is inaccurate. The 350ci/350hp is the L46, which came from the factory with a cast iron intake and a quadrajet. That quadrajet, however, was a serious one, and very different in performance capabilities from the factory than the quadrajets that came on other engines in the line-up.[/QUOTE]

from what I see the only difference in carbs was a larger secondary jets and different rods from the base engine. I have a 350/350 carb on my on my '69 base 350 engine.

Brcmpbl

from what I see the only difference in carbs was a larger secondary jets and different rods from the base engine. I have a 350/350 carb on my on my '69 base 350 engine.[/QUOTE]

That's enough to create significantly better performance capabilities from the factory.

fishslayer143

the 1970 LT1 also had 11:1 compression dome pistons

Iceaxe

Ditto for the L46.

C2Racer

To the original vintage racing question you really need to speak with the organization you plan on racing with on how they interpret the 72 book. In CVAR here in Texas the difference is just putting a Holley on the 350 motor moves you up to AP. In SVRA a Holley leaves you in BP. No serious racers run hydraulic lifters. You will at a minimum want to run roller rockers and a stud girdle which is legal everywhere except Monterey or Sonoma. SVRA allows roller cams too. You will need over 500 hp to be competitive in a C3 with SVRA.

The carb question is a little tricky to find in the club rule books but the rest is pretty clear. Most clubs have their spin on the 72 book posted on their website so reading is your friend. CVAR will have a problem with a 73 front bumper and it would have to be converted back to a 72. SVRA is going that way too so that is something to consider before you go too far. Good luck!

Steve