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Technical Anyone running an L79 in their daily???

Discussion in 'Traditional Hot Rods' started by Shaggy, Jan 7, 2014.

  1. Shaggy
    Joined: Mar 6, 2003
    Posts: 5,208

    Shaggy
    Member
    from Sultan, WA

    I need a new motor for my daily(65 el camino), well not "need" but I want. I basically have almost all the makings for a L79 longblock, and I know the cam is a great cam, I was wondering how much your stuff likes the 11to1 compression, I know they have a lot of bleed off due to the slow ramp of the cam.

    Btw, this'll be full traditional dress, edelbrocks c4b, Mallory rev-pol dual point, early t-10, holley 4bbl, camel humps, vette covers, ect.....
     
  2. tfeverfred
    Joined: Nov 11, 2006
    Posts: 15,792

    tfeverfred
    Member

    They have the gas up there for it?
     
  3. Shaggy
    Joined: Mar 6, 2003
    Posts: 5,208

    Shaggy
    Member
    from Sultan, WA

    That's what I'm wondering, I figure with the l79 cam it should have a lot less compression at the rpm's/load's that compression really fucks you due to the bleed off. Ive ran a close to 10to1 350 and I'd assume it should be similar but I don't know
     
  4. rustang
    Joined: Sep 10, 2009
    Posts: 710

    rustang
    Member

    I run a 327 with old TRW 11:1 with 461 heads,LT1 solid cam. It runs great, just can't get too aggressive with timing. Needs min of 91 octane or will ping, but as long as decent fuel it runs well.... Not an L79 but pretty close fwiw.


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  5. I think your CR is pretty high for a Daily Driver with an L79 cam.

    I had an L79 in my 350 SBC powered '55 Chevy. It could've been a perfect DD.

    It's beauty was its combination of consistent parts. The rest of the package consisted of a 625 cfm Carter AFB, Edelbrock Performer intake, camel hump 461 heads, and blockhugger headers. CR was only about 9.5:1 and it would run well on a steady diet of 87 octane.

    Drivetrain was a Muncie M-22 4-speed and 3.55:1 rearend. The only thing that I would've changed was replace the tranny with a T-5 for interstate cruising.

    Hope this provides a good data point.
    -Gary
     
  6. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

    As long as the car isn't too heavy, and you dont run a stupid tall gear, I would think you will have no problem with this, even on the crappier gas you have down there. Cold air intake (not underhood air) will help, and block the heat risers. The best deal would be flat tops, heavily angle milled heads, and real tight squish, but with the 114 lsa and ULTRA lazy ramps on that cam,I wouldn't even consider less than 10.5/1. I dont think you will have too much to worry about, what do you guys have there, 91?
     
  7. In the late 80's I ran a stock L79 in my 65 vette with 3.70's. Sent the distributor out to get recurved and an electronic conversion. Ran crappy 87 octane gas with the timing set at 4 or 6 degrees. Ran ok.
     
  8. joel
    Joined: Oct 10, 2009
    Posts: 1,900

    joel
    ALLIANCE MEMBER

    I had the same parts you have and cut .040" off the piston domes and ran it. I used Rhodes lifters on the L79 cam because I had a th350 with a stock converter. Premium pump gas no problem and that was with a 3.08 gear. It was a pig until I got it wound up, but triple digits were no problem. If I would have changed the gear, it would have been great.
     
  9. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

    I decided to figure out the dynamic compression ration on this deal. You would think it would be easy to find seat timing numbers for the 151, considering how long its been around, and how popular its been over the years, but you'd be wrong. I found .050 numbers easy enough, but no seat timing numbers. Normally, you could take the intake closing number @ 050, add 15 degrees, and be reasonably close, but with the 151 having such slow ramps this is a non-starter, so I calculated the closing point from the factory 312 seat duration and the 114 lsa.
    I'm getting a dynamic compression ratio of 7.06/1 for this combo, which means you are gonna have no problem on 91. I wouldn't cut the domes, and I'm gonna revise what I said earlier about blocking the heat risers, you'd probably be ok without it. In the unlikely event that it DOES ping a little, its pretty easy to pull the intake off, and block them with a thin piece of stainless.
    Another thing to keep in mind here, when the 5cc dome motors left the factory, they werent at the advertised 11/1, they were closer to 10.6-10.7/1. God only knows how many times your 327 has been decked over the last 45 years, but you will probably be below 11/1, especially if you are using modern composition gaskets instead of the factory .015 steel shims.
     
    Last edited: Jan 8, 2014
  10. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

    Just for shits and giggles, I just looked up the factory tune up specs on the L-79 in my old Motor manual, it says 160 psi cranking, which is more or less in line with the above. That should put this one to bed.
     

  11. no ! :(
     
  12. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

    According to this, there are two stations in Vancouver WA selling ethanol-free 92. I dont live there, so cant vouch for its accuracy...

    http://pure-gas.org/index.jsp?stateprov=WA
     
  13. Shaggy
    Joined: Mar 6, 2003
    Posts: 5,208

    Shaggy
    Member
    from Sultan, WA

    Thanks for the info, I think I might try it probably around 10.5 to 1 or so, worst case I guess I can de-tune it.
     
  14. At it again huh ? :p
     
  15. George Miller
    Joined: Dec 26, 2008
    Posts: 413

    George Miller
    Member
    from NC usa

    My 66 vette is a L79 has many miles on it. I drove it to work from 1970=1992. It has been a great engine. Still runs very strong. It is hard to beat a 327-L79.
     
  16. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

    If someone asks a reasonable, well thought out question, I have a hard time not answering.
    A little more on this. Rather than running the thicker head gaskets to drop the compression back, I would lay the chamber wall back to the bore around the intake valve. I do it by hand with a egg shaped carbide cutter. Blue the deck surface around the intake valve, bolt the head on the empty block, turn it over and scribe a line along the bore, adjacent to the intake valve. Stand the head up plug side down, and grind the chamber back to the bore line around the intake valve, but taper the cut out and just change to a light re-shaping as you sweep around to the the 8 oclock position relative to the valve. The casting is thin there, and prone to cracking through to the adjacent water passage in the deck, if you remove too much material in this area.
    Some guys do this using a cutter on a Serdi or milling machine, I do not recommend this, as it will not taper the cut out in the thin spot, and the head will probably crack in use.

    The chamber shape with the low plug position in the camel bumps combined with the 5cc pop-up is pretty abysmal, this thing will need a lot of timing as compared to doing the same compression with a more modern, smaller chamber, better plug position and flat-top, somewhere in the area of 5-6 degrees more, total in the low 40s as compared to mid 30s.

    One way to help this a BIT is to think in terms of generating some swirl when you port the pockets. When you do the pockets, bias the cut between the guide and pocket wall towards the pushrod side of the port, and tilt the shape of the pocket slightly towards the center of the bore. What you are trying to do is encourage the flow as it approaches the valve seat to turn slightly towards the center of the bore. This will hurt high lift flow numbers, but with less than .447 at the valve, thats not as much of an issue, and it will encourage swirl, which will help keep fuel from dropping out of suspension against the backside of the chamber, and make the engine a little less detonation prone.

    You really want to keep as much of the piston/head clearance in the bore, not in the gasket, as the gap between the top of the bore, the fire ring of the gasket and the flat of the cylinder head creates a little pocket that will collect a/f mixture at the end of the compression stroke, which will be drawn back into to bore as the piston passes tdc, and creates potential for a second flame front to start. You cant eliminate them entirely, but you really want to do as much as possible to limit end gasses in a high compression/pump gas deal, and using the thinnest gasket possible, with the smallest bore size possible is a big help in this area.

    I dont know if you already have a cam, the Crane #967601 Blueprinted 3863151 is reputed to have a little bit faster ramp (less seat duration same 050 number) than the chevy cam. The Crane HMV278 is even better, is sort of a modern version of the 151,still on 114 LSA, similar duration at 050, much shorter on the seat, VERY aggressive ramps, and a really good cam, I have used it in the past. It'll actually idle better than the 151, and it'll walk all over it, to the tune of around 20 hp on top, and roughly 5-8 ft lbs across the board. But if you want to stick with a "period" cam, I get that, just throwing it out there.

    Another thing to keep in mind, you can dial in the cylinder pressure by advancing the cam, and cylinder pressure will translate directly into more idle vacuum and increased part-throttle fuel economy. Altitude also plays a big role in cylinder pressure/octane tolerance, depending on where you are in WA, you may want to keep that in mind. The dynamic compression number I gave is calculated at sea level, as you move inland, it will drop.
    One other thing, I dont know if the heads you have are 1.94s or original 2.02s, you are better off cutting 1.94s for 2.02s than starting with original 2.02s, as you will be cutting the seats on fresh material, no sunk valves to contend with.
     
  17. I can only get 90 octane with no ethanol here in Seattle.
     
    Last edited: Jan 9, 2014
  18. 66tintop
    Joined: Nov 7, 2012
    Posts: 450

    66tintop
    Member
    from Canada

    Have a look at gm performance 290hp crate, pretty sure the cam in it , is very similar to l-79 cam , I think so but might be wrong
     
  19. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

    Thats grim. We are so spoiled up here, with Chevron 94 all over the place. Its not like they cant make decent gas, they just choose not to. I think at 10.5/1 with the 151, he will be ok, even on 90. The HMV 278 might be another story...
     
  20. RainierHooker
    Joined: Dec 20, 2011
    Posts: 2,018

    RainierHooker
    Member
    from Tacoma, WA

    There was a 76 station in Snohomish that had Non-Ethanol 92 Octane. But I havent been up there in a year or two...
     
  21. Its a Cenex now. Still 92 ethanol free.
     
  22. Yeah, we've checked them out. Only 1 exists and it is a cardlock dealer commercial only. There is supposed to be one in Camas too but not confirmed.
     
  23. falcongeorge
    Joined: Aug 26, 2010
    Posts: 18,341

    falcongeorge
    Member
    from BC

    Is that this one? Looks like they will let you use their card, but only 7-5, monday-friday. Not very practical.

    http://pure-gas.org/station?station_id=1411
     

  24. Going to check. Sounds like the same company name but wrong address.
     

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