Noddle Posted April 7, 2010 Share Posted April 7, 2010 With this timing light I could easily build up a timing map of degrees advanced versus engine rpms. If you do a timing map, can you upload it please, any chance to add what kpa (vacuum) as well. I just want to compare a standard dissy with what my MS II is running. Nigel Quote Link to comment Share on other sites More sharing options...
ozconnection Posted April 7, 2010 Author Share Posted April 7, 2010 If you do a timing map, can you upload it please, any chance to add what kpa (vacuum) as well. I just want to compare a standard dissy with what my MS II is running. Nigel Hi Nigel, I didn't even think about "at what vacuum", that shouldn't be too hard as I have an autometer vac. guage under the bonnet for dyno sessions, checking vacuum to see when the power valve cuts in, for example. Im just thinking at what rpm intervals I will test at? Suggestions? What are your intervals on the MS II Nigel? Quote Link to comment Share on other sites More sharing options...
z-ya Posted April 7, 2010 Share Posted April 7, 2010 Thank you gentlemen for all your inputs so far. My timing is verified by an Innova timing light, one of those fancy jobbies that tell rpms, dwell and volts along with the actual number of degrees advanced. Lovely bit of gear! With this timing light I could easily build up a timing map of degrees advanced versus engine rpms. I could then test another dizzy (thanks Pete, I'll take that L24 unit ) and do the same with that one. I can look at the character of the curve and test both in car to decide which one responds better. As for the cam, I could try retarding it a bit, and test that. I have so many cams here it's silly, all bought for projects I haven't built yet. I really need to get a wriggle on and build an engine with a decent static compression ratio so I can try some of 'em. I can't believe that 10 to 1 compression with a stock cam gave you 215 psi cylinder pressures at 28 degrees advance without ping. Was that a flat top, stock piston with with a stock N42 head? (All bets are off if the head was modified though). When I had a stock cam in my 10:1 (flat tops, N47) motor cylinder pressures were in that region. I couldn't run much over 25 deg advance without ping. With a 460 lift 280 duration cam I can run close to 30 degrees, and the cylinder pressures are about the same as with the stock cam (+- 5psi). It made around 160WHP with the stock cam, and just over 180WHP with the performance one. As for my camshaft drive, it was all replaced when I first bought the car some 40K km's ago so I'm happy it's still all in good, serviceable condition. As for L28ET's running 180 psi cylinder pressures, their camshaft is so mild, isn't it just like the one I'm currently using? Just how do you get a decompressed 7.5:1 engine like that to run 180 psi though? Not sure why, but my stock L28ET has cylinder pressures in the 170-180 range. I just stopped to think about this situation again and came up with "the" question I guess I'm trying to ask. What is the highest static compression ratio I can go with a stock profiled camshaft? Caveats are pump gas, no turbo or super charging and no nitrous. (have I just spoilt the party for any of you? ) You can run 10:1, you just need to retard the timing to prevent detonation. So as you might expect, this limits the potential. This CR vs. max advance trade off discussion is all over this board. I still believe that even though you can't run as much timing, a higher CR will always get you more power in an N42/47 headed L28. With performance cam and 29 degrees advance: With stock cam and 24-25 degrees advance: Quote Link to comment Share on other sites More sharing options...
ozconnection Posted April 14, 2010 Author Share Posted April 14, 2010 (edited) I went ahead and did some recording of my currently installed 280zx distributor (P71) and also a spare one (S67). The results are with a warmed up engine and the vacuum advance disconnected and plugged. The two distributors are D6K8-02 9105 part #22100-P7101 and D6K9-05 3605 part #22100-S6706 The P71 was tested first and then immediately swapped for the S67 which is still in the car now that I'm here writing this. Just as a side note, the vacuum advance canisters add a further 16 degrees @ idle connected to manifold vacuum. 700rpm 14/14 850rpm 14/15 1000rpm 14/16 1200rpm 17/17 1400rpm 18/18 1600rpm 21/21 1800rpm 24/23 2000rpm 26/25 2200rpm 30/26 2400rpm 32/26 2600rpm 33/26 2800rpm 34/26 3000rpm 34/26 degrees ATDC. The first number separated by the / is from the P71, the other is from the S67. When you graph these out, there's a huge difference! As far as engine vacuum is concerned, vacuum was high due to me just opening the throttle via the idle adjusting screw on the Holley. It never fell below 16 inches. (idle is 19 inches in neutral). Things I need to consider is the amount of advance that the vacuum advance mechanisms add. The idle is very 'rough' with 36 degrees at idle with the S67. 20 degrees static is acceptable, with 32 total from 2200rpm!!! I'm thinking of connecting the vacuum advance back up to the ported vacuum port on the Holley since connecting to manifold vacuum, it's too advanced IMO. Thoughts? Edited April 14, 2010 by ozconnection Quote Link to comment Share on other sites More sharing options...
Tony D Posted April 14, 2010 Share Posted April 14, 2010 (edited) Distributor Mechanical Advance Curve is abvailable in the FSM. I can't recall if they have a chart for vacuum advance as well, but I think they do. Yes, I'm still up, I haven't reverted to the west coast time in the USA... I only returned on Friday. Sorry I didn't get a chance to call and say 'bye' Mark... I went to Fours -vs- Rotaries and did some posed photos in front of Atlas Copco Blacktown that third weekend. And I did get my shirts at HD B-Town before I left. Pete, you didn't answer the phone... Yes, 0404611119 was me! (Expired on the 13th....I've been using my excess Vodaphone Minutes here in the USA to make international calls---you know how Vodaphone offers "$1200 in call credit" and you figure nobody will EVER use that much? In a bit over a WEEK I made a concerted effort and have gotten it down to $200 by my calculations...muahahahaaaaaa!) Maybe next startup... Edited April 14, 2010 by Tony D Quote Link to comment Share on other sites More sharing options...
ozconnection Posted April 14, 2010 Author Share Posted April 14, 2010 Distributor Mechanical Advance Curve is abvailable in the FSM. I can't recall if they have a chart for vacuum advance as well, but I think they do. Yes, I'm still up, I haven't reverted to the west coast time in the USA... I only returned on Friday. Sorry I didn't get a chance to call and say 'bye' Mark... I went to Fours -vs- Rotaries and did some posed photos in front of Atlas Copco Blacktown that third weekend. And I did get my shirts at HD B-Town before I left. Pete, you didn't answer the phone... Yes, 0404611119 was me! (Expired on the 13th....I've been using my excess Vodaphone Minutes here in the USA to make international calls---you know how Vodaphone offers "$1200 in call credit" and you figure nobody will EVER use that much? In a bit over a WEEK I made a concerted effort and have gotten it down to $200 by my calculations...muahahahaaaaaa!) Maybe next startup... Hey, no problemo...see you again next time! I will have to instal my MSD timing controller next. I just need to figure out how to lock this distributor. Hmmmm, did it with an older point type, not with the electronic ones. I thought about using a rubber hose again to expand the weights out to maximum. That way if something goes wrong, the dizzy won't advance any more than it already is. Should work again methinks. Quote Link to comment Share on other sites More sharing options...
kolonelklink87 Posted April 14, 2010 Share Posted April 14, 2010 Pete, you didn't answer the phone... Yes, 0404611119 was me! Pete me pete? I don't recall getting that missed call... if so i was probably at the hospital and in lab and forgot to call back... sorry!! next visit? I'll have plenty to show off by then. Quote Link to comment Share on other sites More sharing options...
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