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P6 cam timing and setup advice

Discussion in 'Technical Q&A' started by Dandy_Don, Mar 10, 2004.

  1. Dandy_Don

    Dandy_Don Karting

    Dec 8, 2003
    102
    The Woodlands TX
    Full Name:
    Don McCormick
    Hello,

    I would like some advice on setting up the P6 cams in my rebuilt dry sump 308 (1976 engine) with all new valves and high compression pistons. I have done extensive research in the archives on how to actually set them up
    ( I have the dial indicator and the degree wheel etc) but thought that there might be some opinions/experience (especially from Phillip Airey ) as to what the range of settings might be for the cams.

    Last June Ted Gage- (TedMac) filed some interesting posts and laid out what he thought the P6 specs were and I have reprinted them here as best I can -the printing was very small and hard to read. The website that he listed in his post does not seem to contain the step by step how to do it he referenced but I have read enough at this point to feel certain as to how to proceed, I am just not sure as to the "best" settings and would like to take advantage of the experience on this board.

    P6 timing per last June posts

    Intake open 48 BTDC Intake close 62 ABDC duration 290 center 97 ATDC
    Exhaust open 64 BBDC exhaust close44 ATDC duration 290 center 80? BTDC

    I don't track the car but might want to if this thing works out well. Yes, I know that many have said that P6 are bad for power at low RPM and really don't want to get into that debate but am just asking for experience on cam settings/timing that the board might have before I put this thing back in the car. The engine is all built and I am a couple of weeks from reinstalling. Thanx Don
     
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  3. Matt Morgan, "Kermit"

    Matt Morgan, "Kermit" Formula Junior

    Nov 12, 2003
    405
    Ferndale, WA
    FWIW, I would set them @ the stock specs.
    A cam this radical is allready pushing the valve events to the far limits of what can be done, and in that respect, the usual methods of moveing the power curve around via tightening up the overlap, or widening it push the opening and closeing events farther into an area that is easily unworkable. Good luckwith running it. I would only suggest that you make sure that all of the elements are working together, heads exhaust, etc. as it will not work as well in conjunction with a stockmotor, as it would with a modified one.
    Kermit
     
  4. Dave

    Dave F1 Rookie

    Apr 15, 2001
    2,722
    Little Rock
    Full Name:
    David Jones
    Hi Don, Just wondering if you based your numbers on what someone else posted the P-6 camshafts profile to be, or did you spec the cams you have?
    My reason for concern being, the grind of the "P-6" cams you speak of changed over time...
    So it is important to check valve to piston clearances as the lift on these cams can differ...
    But I'm sure you already did that if you have already assembled the motor.
     
  5. Mitch Alsup

    Mitch Alsup F1 Veteran

    Nov 4, 2003
    7,077
    I would have thought a 290 degree duration cam would be setup nearer 35/75 than 48/62, even the 310 degree duration cams are setup closer to 40/80 than 48/62 in most cars. 92 degrees of overlap is a lot.
     
  6. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
    Chicago
    Full Name:
    Philip
    Don
    I've posted all of this before. Mine are factory grinds (they have the oil ways and were verified by Elgin) and set per the 1974 NART Le Mans GT4 specs (obtained from Pound) -- not "factory" P6 specs - the LM car ran 4 degrees earlier on the intake cam to help the low end a bit (Elgin's advice). This set up is also described (without conclusion) in Allen Bishop's book.

    We set operating clearances in line with stock cams. The race op clearance specs were tighter.

    "We" (Continental FM & Dema Elgin) spent a long time plotting, examing and "fixing" 2 lobes and then nitriding, heat treating, parkerizing etc followed by measuring, degreeing and so on to put them in right. All told it was not a cheap job.

    If you've done the whole motor (great), make sure your valve springs are in good shape. It will pull through redline and then some.

    To Dave's assertion of grind and versions. I have no idea if there are "other" P6 specs. For sure, there are non-factory P6 "look alike" grinds and who knows what the specs are. There are lots of non-P6 (and probably "better") grinds if you start from billets.

    Without wishing to offend anyone, there are lots of opinions on set up. All I can say is I spent time researching this and finding people that had prepared or had indepth knowledge of the race cars using the P6 cams.

    Good luck.
    Philip
     
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  8. Dandy_Don

    Dandy_Don Karting

    Dec 8, 2003
    102
    The Woodlands TX
    Full Name:
    Don McCormick
    Thanx for the replies,

    I have been assured by the builder that the cams are factory P6 cams and within original tolerances. I don't know what that means actually as I have not measured or degreed them myself but I will this weekend. The engine also has ported heads and the intake manifolds have been modified to match the intake porting.

    The timing specs that I quoted in the thread above are from Ted Gage not from any independent research that I have done myself. I have no problems with the clearances currently as the engine turns by hand (with the belts installed) but there appears to be some confusion about what the cam timing was set at by the builder and I would like to resolve it prior to installing the engine back in the car. I suppose my question then is do these values seem correct or are they in need of adjustment. Mitch and Phillip suggest that I might want to advance the intake cam timing to lessen the overlap which sounds reasonable while Kermit thinks that the cams should be set up at factory specs ( of course I am not even sure that the specs quoted are factory- they are just reputed to be by Ted Gage a year ago) I will determine the timing already in the engine this weekend and post it but was interested in anyone who might have experience in what these values ought to be.

    Phillip, I appreciate the amount of effort that you went to to set up your engine and hope that you would be willing to share that information with me. Whether your data and particulars work for my particular situation is my risk etc etc. If you prefer that I call Continental Motorsports myself perhaps you would be so kind as to tell me with whom you spoke as it would greatly reduce the time spent.

    Don
     
  9. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
    Chicago
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    Philip
    Don
    Let me see what I can find in my files. It has been a year.
    Philip
     
  10. Dandy_Don

    Dandy_Don Karting

    Dec 8, 2003
    102
    The Woodlands TX
    Full Name:
    Don McCormick
    Phillip Thanx I got word from my engine builder today that he thinks the cams should have been set to the following:

    Intake opens 42 BTDC closes 71 ABDC
    Exhaust opens 67 BBDC closes 40 ATDC

    This would serve to reinforce what Mitch has said about lessening overlap from that associated with the timing reputed to be "P6 factory" earlier in this thread.

    Phillip, anything that you find would be greatly appreciated. I understand how the details tend to slip away after some time has passed.

    Don
     
  11. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
    Chicago
    Full Name:
    Philip
    Don
    Attached is an extract from the "308 Special For Le Mans" LM GT4 build specs I received over a year ago. They related to Chassis # 08020, engine #00010. Page 2 (below) has the specs for the cams. Intake is 51/58 exhaust 64/44 all at checking lash.

    The "factory specs" for the intake are 48/62 and exhaust are 64/44. Unfortunately I can't upload the file as it is too big to show you this.

    Bishop's book has a section on 308 tuning by Mark Dees at the end. It references the LM GT4 having the P6 intake cam timing set 4 degrees earlier than "specs".

    As you may know, given the profiles (see pic below) determining the precise start of the ramp is a little challenging - hence the difference between Bishop's book (implying 52) and the ML specs (51).

    I set my intake cam to LM specs -- as I mentioned, Dema Elgin (of cam profiling fame) recommended an earlier close to help low end torque (I run stock compression).

    I set my cams to "street" operating clearances rather than the race specs. Bill Pound believed the greater seat time would give the exhaust valve a chance to dissipate some more heat.

    Your call where you choose to set them. I had no basis to override the factory experience.

    I hope this helps. Good luck and keep us posted.
    Philip
     
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  13. Dandy_Don

    Dandy_Don Karting

    Dec 8, 2003
    102
    The Woodlands TX
    Full Name:
    Don McCormick
    Phillip, Thank you very much for the info. I would like to ask some questions about the LM car and engine setup.

    Did this car run higher than stock compression?- I have approx 10.5 :1 ,I am told.

    The carb build sheet shows 40 DCF whereas mine are 40 DCNF (stock) Any difference that you know of? Any idea what the 35-37-37-38 means after the 40 DCF designation?

    Did you modify the progression holes in your carbs to match the values listed and if so do you know what the stock values were? and do you know which hole corresponds to which value- as I recall there are indeed 5 progression holes in each carb

    What plugs do you run? The Champion N60Y would appear to be different than the stock Champion plug

    I will start tomorrow and set up the cams and will send pictures etc.

    Lastly, did you get the impression from Elgin that if one had higher compression pistons, one would not need to close the intakes earlier as you have with the stock compression?

    Thanx for your info.

    Don
     
  14. pma1010

    pma1010 F1 Rookie

    Jul 21, 2002
    2,559
    Chicago
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    Philip
    Compression ratio. I do not know CR of the LM car although I believe the Borgo pistons ran 9.5 or 9.7:1 in the comp Daytonas and the comp 308s were, I believe, similar (same?). Perhaps someone else knows. Piston was 251F/140174 Borgo 7709. 81 mm overbore. 310 g weight.

    Carb type. DCF is typo, s/b DCNF ("DC" = twin choke, "NF" relates to the material of construction of the carb). LM car ran stock carb bodies but with very different jetting and 36mm venturis.

    Series #s. 40 DCNF 3X series were stock carbs on the GT4. Progression holes are different on 3x from 4X or 5x series. Hole positioning also inter-relates to ET specification.

    Plugs, jetting etc on the LM car are all for running flat out on Mulsanne for 24 hours without the motor imploding (i.e., very rich jets, very cold plugs). Not likely to be useful for dialing in for street or typical track use. FYI, I run NGK "6"s. There are many threads on jetting (a different topic from the cam timing thread, here) that will provide you with background and a starting point.

    Cam timing. I don't feel qualified to give you an opinion. Could you run a later closing of the intake valve given you have higher static compression and therefore higher dynamic compression than me. Yes. Would I move away from the Ferrari specs? Personally, not without a lot of engine dyno testing and a very clear understanding with the builder of where I wanted the power band to be.

    HTH. Good luck.
    Philip
     
  15. Dandy_Don

    Dandy_Don Karting

    Dec 8, 2003
    102
    The Woodlands TX
    Full Name:
    Don McCormick
    Phillip,

    I thank you very much for the information and your opinions. I shall keep all in mind as I set the engine up this weekend. I will also post some pix this weekend of the engine and the cams. Your thoughts on jetting make a lot of sense to me. The main jet and idle jet sizes on the LM sheet did look awfully big (rich ) to me. I too have been following the jetting discussions that you and Russ Turner have been having concerning his 3.2 mondial with the webers. Again thanx Don
     

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