'Specs' on L48 ('71) ?

[pgtr]

Can anyone share or know where I can look up 'original' specs and details on a '71 base L48 270hp engine?

Things like:
* stock cam profile specs (& P#)
* head CCs and valve sizes
* distributor advance curves
* piston type
etc

thanks,

 

[SG4206]

My info shows cam .390-.410 lift, 195 - 202 duration at .050
64 cc heads, casting #487 with 1.94 and 1.5 valves.
dished pistons
cast iron Q-jet intake casting #469
That's all I have. I use NHRA and NCCC tear down specs.

 

[tomtom72]

Hi pgtr, I had a set of original shop Manuals from GM that the first owner of my 72 gave me with the car. The book that had the motor overhaul & trouble shooting & tune up specs had all that info in table form. These are still available from GM at their restoration site, they are not cheap. If I remember right about $90.00 for a reprint of the originals. The heads were 76cc chambers with 1.94 intake/ 1.58(?) exhaust; the pistons were flat top cast aluminium w/4 valve reliefs. I never knew the numbers on the cam and the specs on the distributor as I had an LT-1. According to NCRS judging book 2004, 3973487 is head casting #; the distributor # is 1112050. Maybe a call toone of the cam Companys might get you the specs on the cam. I can't find the P/N for the cam in the judging manual, I guess they can't see it so it's not in the book. I'm sure someone else with more info will come along shortly, I hope this gives a little help. tt72 I type too slow and SG4206 has the info you need so I stand corrected.

 

[Vettehead Mikey]

FWIW, I don't believe the base engines were called L-48 prior to '73 but stand to be corrected.

At least I know they weren't called Targa tops! :L

 

[pgtr]

I noticed the 487 heads were used on both the L48 and LT1 in 71. So those are 64cc heads according to the racing folks huh? I'm surprised the LT1 had the smaller valved same heads that year.

Thanks also for the dished pistons and cam info - (if anybody has a part# on the cam let me know)

===========

Tom I have the '71 CSM and did not see this info there in either the Engine section of the Specifications but may have missed it. SG4206 posted a different cc for the 487 heads. However I did some further digging and found some info that also suggests the 487s were 76cc...

I think the '71 CSM is a lot cheaper ($40-$50?) thru mail order outfits if it helps any else.

===========

Mikey they were not 'commonly' called or 'marketed' as L48s prior to 73 but the base 350/270 was the L48 in '71 AFAIK. The L48 came out around 69 or 70 I believe. I personally call it generically the 'base 350/300' out of habit but HP ratings dropped to 270 in '71 and were later recalculated at roughly ~200 net from 72 on. Obviously L48s varied somewhat from year to year in other ways so the year of L48 in question is important.


Thanks

 

[SG4206]

The '71 LT-1 had a flat top piston. My source says the # 487 head in the LT-1 had 69 cc chambers with 2.02 and 1.6 valves....... Go figure------

 

[pgtr]

Gotcha. So the '71 LT1 ran a flat to to the '71 L48s dished piston. In fact it looks like the base L48s pretty much always ran the same heads HP 350s.

I just got thru thumbing my Lingenfelter SB book and he talks about the "487X" head which I'm certain is the same thing - he lists them at: 1.94/1.50 76CCs like Tom said.

Other than being a bit heavy he said these were pretty good and very durable cast iron heads and part of the 993/487/441/442 'family'. The 487 has a fairly large intake port area but they all flowed similarly.

Do you know if those are fully dished or partially dished factory pistons in the '71 L48?

thanks,

 

[curtis]

If you have some 487X heads for sale I would be interested.

 

[tomtom72]

LT-1 pistons

Hi guys, I beg to differ with the LT-1 pistons. 70 LT-1 used the "fuelie heads", or camel hump heads(the casting mark on front of head). They were small chamber heads, 64 CC combustion chamber volume. They flowed just fine for the time period on both sides. The 71 & 72 LT-1s used the larger, 76(?)/78CC heads of basically same flow traits. Larger chambers = lower compression & compatability with future unleaded fuels was the idea. The LT-1s, 70-72, all had the same basic internal parts inside a 390010 & 3970014 4-bolt blocks. All LT-1s used TRW forged alum. domed pistons with two valve reliefs in the dome, the L48s used the flat top ones. The pistons remained the sme for all three years, the head CC droped to drop the squash and the HP & torque #s to yield motors that would run on the revised octane ratings of the fuels used by I think 1974: and then the unleaded stuff that came with Cats. The only small problem is that the LT-1s were not set up to use unleaded prem. from the factory. I guess they were not looking that far ahead or didn't care about the exhaust seats & valves. If you drive a 72 L48 vs an LT-1 you notice the torque difference due to the pistons & the higher squash #s. tt72

 

[Tom73]

In fact it looks like the base L48s pretty much always ran the same heads HP 350s.

Usualy used the same head casting numbers but the valves were different sizes (the small 1.94/1.50 valves for the L48 and the 2.02/1.60 valves for the LT1s and L82s)

tom...

 

[SG4206]

Gotcha. So the '71 LT1 ran a flat to to the '71 L48s dished piston. In fact it looks like the base L48s pretty much always ran the same heads HP 350s.

I just got thru thumbing my Lingenfelter SB book and he talks about the "487X" head which I'm certain is the same thing - he lists them at: 1.94/1.50 76CCs like Tom said.

Other than being a bit heavy he said these were pretty good and very durable cast iron heads and part of the 993/487/441/442 'family'. The 487 has a fairly large intake port area but they all flowed similarly.

Do you know if those are fully dished or partially dished factory pistons in the '71 L48?

thanks,

NHRA works very close with GM on these engine specs. I have to believe what ever they say will pretty well be gospel.
They show a .096 deep dish , the ccs ( 12 ) will indicate size. 12 cc is a full dish.

The head casting numbers listed are all heads they allow for class; not necessarily the original casting # for the year.

They list the minimum ccs a head can be; from a casting number for a given year and engine size. Same for the pistons.
Go to NHRA.com , click on tech , click engine blueprint. You'll see a world of information on chevy engines , you didn't know about.

I use the NCCC rule book for original casting #s.

 

[Vettehead Mikey]

Mikey they were not 'commonly' called or 'marketed' as L48s prior to 73 but the base 350/270 was the L48 in '71 AFAIK. The L48 came out around 69 or 70 I believe. I personally call it generically the 'base 350/300' out of habit but HP ratings dropped to 270 in '71 and were later recalculated at roughly ~200 net from 72 on. Obviously L48s varied somewhat from year to year in other ways so the year of L48 in question is important.


Thanks

Curiosity got the better of me and I followed up on the L48 name by asking on the NCRS board. Base engine in 1969 was called L30, and 1970,71,72 was called ZQ3. L48 in name (or RPO) did not appear until 1973.

 

[pgtr]

Sorry - no 487s for sale!

---

Curiosity got the better of me and I followed up on the L48 name by asking on the NCRS board. Base engine in 1969 was called L30, and 1970,71,72 was called ZQ3. L48 in name (or RPO) did not appear until 1973.

Mike, from an NCRS perspective no explanation on my part will probably do because numbers and codes are of such great importance. However AFAIK the ZQ3 factory build code engine IS the L48 RPO engine! Just a thought but perhaps a better question for you to have asked is precisely what is the technical difference(s) between the factory code ZQ3 and RPO L48 engines in 71?

The L48 goes back to AT LEAST 1968 for Chevrolet and possibly earlier when Corvettes were still runnign 327s. I've always referred to as it as the 350/300 however the 300hp rating is an approximation and changed when SAE ratings were introduced.

The L48 engine NEVER existed as an RPO in any Corvettes because it was already the base engine. However the L48 engine did exist as an optional engine in other models and thus the 'L' RPO code. And St. Louis started designating in their build codes the L48 designation in 73 or so.

In certain years (70-72?) there was a slight variance(I think maybe an add'l vacuum port...?) between the L48 for 'base' Corvettes vs those for L48s as optional engines for other Chevrolets. When such a variance occured they introduced an (obscure?) factory code like ZQ3 to make the distinction since one of the engines (Corvette in this case) was a base engine and didn't need an 'L' RPO code. This allowed Flint to differentiate which L48s were sent to other Chevrolet factories who installed them as optional engines and thus needed the 'L' code. In St. Louis wether the base engine started w/ an L or Z was incidental. However when Chevrolet could eliminate even the smallest differences across it's various production lines it did so and by '73 the subtle difference between the Corvette base engine and the L48 were eliminated such that they didn't need the ZQ3 code anymore. They simply used the RPO code for in house factory build codes in St. Louis and whether it was a Z or L it served the same purpose. All of this is to the best of my knowledge.

I think saying that a 71 ZQ3 is NOT a 71 L48 is splitting an awfully awfully fine hair for a non NCRSer - but if you have some specifics that make this distinction worth consider please do share them!

---

?s still remain - '71 L48 (or ZQ3 if you prefer) - what is the original cam part# or cast# (and any add'l cam specs) as well as further details on the original dished pistons... As well as anything else special, unique or of interest re 71 L48s...

thanks

 

[Vettehead Mikey]

I now see where you're going with your search, I was just speaking from a Corvette-only point of view. Thought it might help in your search for details if the terminology was correct.

 

[pgtr]

Thanks Mike - appreciate the reminder. I was already aware of the ZQ3 Corvette factory code but it's not necessarily mainstream stuff.

If you do run across any interesting differences between the L48 and the ZQ3 variant of the L48 - definately please do share them! The only ones I'm aware of are bolt on external items but nothing about engine internals AFAIK. Anyway if there are any you discover I'm always up to learn more about L48s (ZQ3 or otherwise).

thanks!

 

[JohnZ]

Thanks Mike - appreciate the reminder. I was already aware of the ZQ3 Corvette factory code but it's not necessarily mainstream stuff.

If you do run across any interesting differences between the L48 and the ZQ3 variant of the L48 - definately please do share them! The only ones I'm aware of are bolt on external items but nothing about engine internals AFAIK. Anyway if there are any you discover I'm always up to learn more about L48s (ZQ3 or otherwise).

thanks!

The "ZQ3" wasn't an engine plant code - it was an internal scheduling option, only used from 1969-1972, which triggered an Engineering Bill of Material detail parts listing for the Corvette version of the L48 engine, which had its own sequence of engine plant suffix codes, plus the parts listing for all the other L48-unique parts required for the car; during those (and subsequent) years, there were as many as 26 different suffix codes during any given year for L48 engines across Chevrolet, depending on which car or truck model they were destined for. The Engineering releasing system for the Corvette was revised in 1973 to recognize L48 as the designator for the base engine, followed by L81 for 1981 and L83 for 1982 (when there were no optional engines). The GM #3896929 ("929") cam was used in all Corvette base engines from 1967-1979, and again in 1981.

 

[corvgreg]

The 70 LT1 piston is different than the 71-72. The 70 is domed and the 71-72 is flat top with a one large valve relief.

70 is 64cc heads, 71-2 is 76cc...the heads had the larger 2.02/1.60 valves and also screw-in studs and guidplates.
The L48 was 1.94/1.5 valves with pressed in studs.

 

[pgtr]

Thanks John for the clarification - I knew it was the L48 but wasn't sure of the explanation on the other code found on build sheets.

I'm impressed by the '929's lifespan - both 327s AND 350s, both pre emissions thru emissions - not too shabby. Curious about 1980.

While on the topic any recomendations for good aftermarket replacement cams on an early L48 like '71?

corvgreg - I thought '71 L48s and LT1s used the same '487' heads - did some have pressed in studs and others receive 3/8 threaded depending on the application? Same question on valves given the same '487' heads used on both engines? Did the '71 L48 have fully or partially dished pistons?

thanks,

 

[JohnZ]

'71 L-48 and LT-1 used the same head castings, but the L-48 had pressed-in studs and 1.94 valves, and the LT-1 was machined differently for screw-in studs, guide plates, and 2.02 valves.

 

[pgtr]

OK I understand. Thanks!

L48 ran a cast crank and all or virtually all are 2 bolt main vs the LT1s 4 bolt and forged(???) crank. Possibly different connecting rods too...?