flat tops, p90, and boost

[Brad-ManQ45]

Since he has Megasquirt he can program more advance when under light load - why screw w/vacuum advance?

[twogees]

my head is spinning... im still trying to get this car figured out..trying research to figure out exactly what i have and such but it is slow going process. i went back through the paper work and the receipt for the dist says 280zx dist w/ vacc advance not w/o. the wire leading to the vacc advance w/ the capacitor leading to the blk/white wire was hooked up so i would imagine it was working. the mechanical advance, i have to try and search for that cause i have no idea. as far as the timing i dont know what that was set at either. as far as what the timing was ..all i know is the msd was set between 2-3 on the retard dial and the dist was just about clocked all the way clock wise. it is still in the same position it was in when removed. i never did any timing readings in the short timee i had the car and it was running. im still trying to figure out timing and how to set it to get it running again with boost.

[twogees]

brad- unfortunately i dont have spark control on the ms just fuel.I haven't gotten that far.this car was built in 05' im sure alot of things on it can be done differently. thats the stuff im trying to figure out. A more efficient way of running this car than previously setup. A lot needs to be redone..but for now i just need this car mobile..im moving in a few weeks, time is limited and i cant tow it everywhere.

[Bernardd]

I have tuned a 8.8:1 cr L28 turbo engine and it could only take 17 degrees of total ignition timing at 8 psi of boost with 93 octane.

 

I would use the vacuum advance, as it help gas milage. boost will shut it down.

 

sounds like the distributor mechanical advance is locked (this is the typical setup for a retro fit turbo setup).

 

you need to figure out your ignition system, as this is critical for the engine to live on boost. check to see if the mechanical advance is locked, what the initial timing is, total timing, and what the msd is doing on boost (how much retard)

 

I can run 27 degrees of ignition timing on my 7.4;1 cr engine with 13 psi of boost on 93 octane. 8.8:1 cr at that same boost could handle maybe 12 degrees. (big difference).

 

better to run less compression and more boost and timing.

I've tuned a fuel only setup to 8psi as well on local 91 and it had no problems making 245hp on a mustang dyno with 34deg's. It had a meth setup with a small m8 nozzle on it at 60psi.

[Pyro]

isn't meth illegal?

just kidding.

 

But meth injection is not the same as running "just pump" gas.

[Gollum]

Basically in a nut shell what i want to know is , with the items and set-up i have, can a good re-tune get this thing working properly(not a band aid fix) w/a felpro gasket, or will i have to stick with the thicker head gasket to keep detonation from knockin at my door. I know i can run an additive like aces if i had to but id rather be on pump gas alone. http://www.americanc...ne_catalyst.php alot of guys i know run this in their performance boats with high comp heads. so i know it works.

 

If so, im buying that gasket tomorrow so i can get this thing purrin'

 

You'll be FINE!!!! I really wish this was more concrete on these forums as so many people have run these setups with no issues. The only problem people run into is with a BAD TUNE. The flat tops on a P79/P90 are actually LESS prone to detonation due to the increase in QUENCH but when you add a huge gasket you just REMOVED all that quench. Your setup will be BETTER on an OEM or Felpro gasket. I've been following turbo builds on this site since 2004.... The compression ratio with flat tops is still plenty manageable.

 

The guys that are running HUGE power numbers are usually running a custom flat top with an open dish under the chamber area, to allow for full quench to still be utilized. They might have lower compression than you'd end up with having a normal gasket, but they're also putting 400+ to the wheels. Search for Tim's setup.

 

 

 

I have tuned a 8.8:1 cr L28 turbo engine and it could only take 17 degrees of total ignition timing at 8 psi of boost with 93 octane.

 

I would use the vacuum advance, as it help gas milage. boost will shut it down.

 

sounds like the distributor mechanical advance is locked (this is the typical setup for a retro fit turbo setup).

 

you need to figure out your ignition system, as this is critical for the engine to live on boost. check to see if the mechanical advance is locked, what the initial timing is, total timing, and what the msd is doing on boost (how much retard)

 

I can run 27 degrees of ignition timing on my 7.4;1 cr engine with 13 psi of boost on 93 octane. 8.8:1 cr at that same boost could handle maybe 12 degrees. (big difference).

 

better to run less compression and more boost and timing.

 

 

 

From all the tests and dyno sheets I've read over almost the past decade, I'm actually more inclined to think the opposite at this guy's HP goals. Even at 300 wheel HP I think you're better off running flat tops. The flat top on the P90 doesn't NEED as much timing to make the same power. Timing is good, but it's not everything. An engine should only ever run as much timing as it needs to make power at the RPM you want. The higher compression and quench of using the flat top on this head makes the air/fuel charge burn FASTER, thus needing less time to burn it all. This means that if you add too much timing your peak energy of gas expansion will be before the piston reaches TDC.

 

No, some might argue "But running race gas allows me to run more timing advance, so I must be loosing power on pump gas with my pulled timing"

 

That's misleading. Race gas burns SLOWER, so it NEEDS more timing to make it's power. And the slower burn is more controllable, and you can normally run more fuel, both equating to the increase in power. It's not the timing alone that sees any power increase.

 

Food for thought: F1 uses extremely low octane fuels, because race gases burn so slow they'd never burn complete at F1 RPM. An F1 engine can actually run on pump gas and not detonate.... because they simply outrun detonation at those RPM levels. This should show you that in F1 the battle isn't getting enough timing or anything like that, it's getting fuel that burns fast enough to run the tight timing they NEED to.

 

And so I'm back full circle. If you want HUGE numbers, then run CUSTOM pistons that still allow full quench to be utilized. Used these heads for what they're GOOD for. Start with a flat top and have the dish area be ONLY under the area of the chamber. Then you can run a lower 8.5:1 which is pump gas friendly, and then you can use race gas/ethanol to get your 400+ wheel hp numbers.

[Gollum]

my head is spinning... im still trying to get this car figured out..trying research to figure out exactly what i have and such but it is slow going process. i went back through the paper work and the receipt for the dist says 280zx dist w/ vacc advance not w/o. the wire leading to the vacc advance w/ the capacitor leading to the blk/white wire was hooked up so i would imagine it was working. the mechanical advance, i have to try and search for that cause i have no idea. as far as the timing i dont know what that was set at either. as far as what the timing was ..all i know is the msd was set between 2-3 on the retard dial and the dist was just about clocked all the way clock wise. it is still in the same position it was in when removed. i never did any timing readings in the short timee i had the car and it was running. im still trying to figure out timing and how to set it to get it running again with boost.

 

Please just take some detail pics of the dizzy and post them.

 

I think this might be the reason you're having troubles.

 

More people blow up their engines from spark control rather than fuel. I can't count how many people have put a turbo on their flat top/P79 setup and blew it because the NA dizzy is just poopoo for turbo application. Even the turbo 81' CAS dizzy has blown it's fair share of motors. You want to run the 82/83 turbo dizzy with the corresponding oil pump shaft. Stock timing curve is only good till around 250 wheel hp, then it's highly recommended to get some type of programmable unit on that dizzy (which is fine, many people run these dizzys with MS and have seen very impressive numbers).

 

And actually since the 82/83 dizzy is electronic (not vacuum+mechanical) you'll need some type of controller for it. I'd recommend this one:

 

http://www.msdigniti...on_Control.aspx

 

Also, if you were to go that route, with the MSD you could also just setup a hall sensor on the crank and just remove the dizzy altogether.

Edited September 27, 2010 by Gollum

[twogees]

Please just take some detail pics of the dizzy and post them.

 

I think this might be the reason you're having troubles.

 

More people blow up their engines from spark control rather than fuel. I can't count how many people have put a turbo on their flat top/P79 setup and blew it because the NA dizzy is just poopoo for turbo application. Even the turbo 81' CAS dizzy has blown it's fair share of motors. You want to run the 82/83 turbo dizzy with the corresponding oil pump shaft. Stock timing curve is only good till around 250 wheel hp, then it's highly recommended to get some type of programmable unit on that dizzy (which is fine, many people run these dizzys with MS and have seen very impressive numbers).

 

And actually since the 82/83 dizzy is electronic (not vacuum+mechanical) you'll need some type of controller for it. I'd recommend this one:

 

http://www.msdigniti...on_Control.aspx

 

Also, if you were to go that route, with the MSD you could also just setup a hall sensor on the crank and just remove the dizzy altogether.

 

Gollum- thanks for the reply. OK that's what i thought. i figured, hell as long as i get a good tune done, then i figured the drop in comp should be ok. just wanted some confirmation.. I do like the idea of those pistons you described. i will try to look into that. the msd unit you posted the link for, is that the same/similar as the msd btm i have ? just with a rev limiter/2 step? give me a few mins and i will post some pics of the dist. my whole goal is eventually upgrade my M.S. to control spark(whole nother can of worms!!) then i wouldnt need to worry bout a dist if i go distributor less. Then I could get rid of the msd btm. I do know thats my weak link now(and most important go figure).. but with the power levels i would like to achieve right now in this car i thought it should fair well up to 300 hp or so( i just cant let my boat have more hp than my car)lol... plus i thought id keep it mild for now its a rust bucket. don't want it falling apart. i have no actual goal..what ever the car can run at w/o blowing up is what it ends up. there's no reason to blow it up from trying to boost beyond the cars means. Doesn't make sense.(i do have a bigger turbo and another block i plan to put in my other 280) I had looked into doing the crank trigger but the mods ive seen are for a pulley w/o A/c. I live in fl, there's no way im getting rid of that. my fuel side (knock on wood) should be good the MS was already programed for this setup already aside for lower comp, and i relocated the intake temp sensor to in front of the throttle body instead of in the air filter before the turbo. so its gonna need a tune for sure. I really plan on having it tuned as soon as i can get it to the dyno. im only waiting for $$ for head studs, a few bolts, odds n ends and i should hopefully have it running again very soon. So as far as the timing, now i should put the timing chain on crank and stock cam gear like normal, set dist at tdc aswell so timing is all at 0, but should i leave the BTM where it is, or should i make it 0 aswell to start out with?

Edited September 27, 2010 by twogees

[twogees]

[twogees]

 

heres the wire and capacitor hooked up to the vac part of the the dist i believe.

 

 

heres the pick up connected to the msd

 

[Gollum]

According to these specs:

 

http://www.newprotest.org/projects/510/dizzy_specs.htm

 

your dizzy doesn't have a whole lot of advance, which should be ok as long as you set it very conservatively. This actually isn't so bad though, since it won't be able to pull timing under boost. But it's going to give you fairly poor mid-range feel. And with a stock T3 you might not get full vacuum advance on the freeway.

 

It's workable, just be careful, and definitely get the thing tuned by someone who knows their stuff, and then learn for yourself. Megasquirt is much easier than some of the other EFI's out there to tune, and it would benefit you well to be able to do your own tuning.

[twogees]

OK sorry for the stupidity in advance(no pun intended).... i thought i didn't want advance, since it is turbo? i thought i wanted it to retard, thats why i had the msd btm to retard (x) amount of timing per psi of boost? I should set what conservatively? the boost level? and by "pulling" timing under boost you mean pulling it advance or pulling it retard? yes i am a retard. lol. so what should i do now as a fix to this ? run a 82-83 dist w/o MS for now? or just stick w what i have til i can get MS/S working and controlling spark? basically any tuner should know what to do (if they are good)? yea it doesnt seem like i have been able to find anyone else running the same stuff i have like the pick up, dist i have, and btm. it must be an outdated way to run , but its what i have .no wonder ive been having trouble trying to figure this out.

Edited September 28, 2010 by twogees

[Pyro]

http://www.xcceleration.com/cr-boost%20101.htm

[Gollum]

OK sorry for the stupidity in advance(no pun intended).... i thought i didn't want advance, since it is turbo? i thought i wanted it to retard, thats why i had the msd btm to retard (x) amount of timing per psi of boost? I should set what conservatively? the boost level? and by "pulling" timing under boost you mean pulling it advance or pulling it retard? yes i am a retard. lol. so what should i do now as a fix to this ? run a 82-83 dist w/o MS for now? or just stick w what i have til i can get MS/S working and controlling spark? basically any tuner should know what to do (if they are good)? yea it doesnt seem like i have been able to find anyone else running the same stuff i have like the pick up, dist i have, and btm. it must be an outdated way to run , but its what i have .no wonder ive been having trouble trying to figure this out.

 

You have this setup because someone didn't want or have the means to do a full turbo motor swap.

 

I'd say keep it the way it is for now, and tune it conservatively. Run the MSD BTM at 2-3 degrees per PSI, and run the idle timing to around 5-8 degrees. That should get it running decently, but you'll be leaving a bit of power on the table, which I'd consider "ok" until you get MS controlling spark as well. And if that's the plan then I'd skip looking for a 82-83 turbo dizzy, since using a crank trigger will be more accurate and cost effective in the long run.

 

You can ALWAYS take your crank pulley and have a machine shop bolt/weld a EDIS 36-1 wheel on it. You can keep AC, not a big deal.

 

 

Oh, and the link/article posted above by pyro is a good article worth reading, just remember that it's far from a comprehensive article on the subject and there's a lot more to it, such as the camshaft you run, how well the head breathes, your RPM range, combustion chamber shape, rod/stroke ratio, intake temps, chamber temp conformity, chamber hot spots, amount of quench, fuel atomization, fuel type, etc. But the basis of the article is solid ground. More boost = less compression you want to run. IMO the easiest way to get around this, is to increase the flow of the head. Then you don't need as much PSI for a desired HP level which means lower PSI levels for a given HP output, which means you can run higher compression, and have a faster spooling turbo and more HP before boost comes on. But head work can get pricey, but it's usually worth it to a point.