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Thread: My 68 Homemade Turbo Slant6 Dart

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    My 68 Homemade Turbo Slant6 Dart

    I have been working for the last 4 or so months completing this project. I turbocharged a slant six in my 1968 Dodge Dart. I have literally built the entire setup in the driveway.

    I am searching for answers on electronics and a few more tuning questions and happened across this forum.

    This is a daily driven car, and as such, it has been built with whatever safety and detonation limiting factors I can have. Right now - one of those - limiting the timing advance to 18* seems to be hurting performance when you're really pushing it. This car is already a rocket compared to what it was though, it's just that it can be better I think.

    The setup is a 68 Slant, all internal components are exactly factory. The head has been rebuilt, brand new valves, and surface shaved - not decked to anything significant - to keep the compression similar. I built a J-pipe and downpipe myself, and run a .50 trim t3/t4 style turbocharger on it, blown through an intercooler then a Holley 350 with Hangar18 modifications completed, and a cut off choke-tower. The distributor is a stock points type, converted to electronic ignition, then I welded the governor throws clsoed a little to only allow 8* advance, then set initial timing to 10* and left the vacuum advance hooked up. In the future I'll put a volvo 240t vacuum/boost unit on it instead after I finish sorting that out. I have an MSD6 ALN to put on the car if need be, but right now, it's not in or hooked up, I'm just utilizing the Pertronix ignition.

    There's a walbro 255lph electric pump feeding it through a boost referenced regulator with a return up front in the engine bay.

    Right now I'm pushing 8 pounds of boost, initial set of 4psi fuel pressure, that raises 1:1 with boost pressure. It also runs very smoothly at a 14.5 AFR in cruise, 22 with the throttle closed and a solid 11.8 when at WOT.

    I just dyno tested it, and am really really trying for a solid 200RWHP over the stock 95rwhp. At 8psi thought, it seemed to stop pulling after 3500RPM that i think is due to something in the ignition, or perhaps the wrong plug gap or something. It made 164rwhp and 234'lbs of torque @3600rpm. Basically I think it should be better at those numbers, so I want to crank the boost to 10, and see what other adjustments i can make to hit 200 without making the boost to out of hand. 10 is really where I want to stop on a daily driver. Basically I'm asking for advice on what i can do to milk that extra 40whp and maybe improve on what I have, while still leaving the slant itself "stock."










  2. #2
    Moderator Turbo Mopar Staff Vigo's Avatar
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    Re: My 68 Homemade Turbo Slant6 Dart

    I'm a little weak on the subject of how vacuum and mechanical advance interplay, but im assuming that if you are in boost your vacuum advance is giving 0 advance, so your total timing in boost will max out at 18 degrees?

    If that is true, it seems very low. If it were me, i would build a det-can or knock listening setup through headphones or something like that and see how much timing you can get away with on your octane level. It may be safer to turn the boost down to a very low number when first trying this until you are confident your 'mic' works and you know what you are listening to.

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    Re: My 68 Homemade Turbo Slant6 Dart

    Quote Originally Posted by Vigo View Post
    I'm a little weak on the subject of how vacuum and mechanical advance interplay, but im assuming that if you are in boost your vacuum advance is giving 0 advance, so your total timing in boost will max out at 18 degrees?

    If that is true, it seems very low. If it were me, i would build a det-can or knock listening setup through headphones or something like that and see how much timing you can get away with on your octane level. It may be safer to turn the boost down to a very low number when first trying this until you are confident your 'mic' works and you know what you are listening to.
    Yes, on boost the vacuum advance completely drops off leaving it at 18 degrees. This is limiting as you say but pretty much everyone I spoke to that has done their own slanted turbo has agreed that 18 is as high as it should be on any boost. My thought is with the Volvo unit (which I already have) I can tweak it so that I can pull maybe 26 advanced, and as the boost pressure raises, it will retard the distributor timing. It's off of a volvo240t from the 80s, and is right now attached to an electronic mopar slant six distributor. Once I get it apart I'll be able to weld the arm from the old pod to this one and hook one side to the vacuum and the other to the charge pipe reference, and hopefully that would ratard as pressure went up and put me somewhere near 18 as the boost hit 10psi.

    The other thing i wanted to experiment with is spark plug distancing and temperature to possibly control some ignition timing as well, but it's only stuff i read about - not really used at all. I'm running premium, which I believe is 91 here. I don't remember.

    I've never heard of a det can or having a mic setup - I'll have to look in to that. Since strapping a turbo to a slant is not widely done, a lot of my setup is based on others' builds and shying away from things they did that failed.

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    Moderator Turbo Mopar Staff Vigo's Avatar
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    Re: My 68 Homemade Turbo Slant6 Dart

    Well, unless the car made peak power at 3600 rpm before the turbo because of the head/manifolds/cam (which is possible but highly doubtful), then it seems like it MUST be in the ignition timing because you know that your AFR is good.

    The only exception i can think of to that would be if, because of the vagaries of inline-6 manifold design, some of your cylinders were actually much lower on power than others due to fueling differences. I would think that would show up on a plug read if done properly, or you could take a stab at it by pointing an IR pyrometer at each exhaust port on the exhaust manifold while the engine is running under boost (which is probably pretty difficult to do because you'd probably need the dyno again and im not sure all the exhaust ports can be shot with a point and shoot pyrometer). But, if anyone else has turbo'd their slant with the same intake manifold they should have had the same issue or something similar.

    The only way plug gap would have a major effect on power was if it was too big and was blowing out under boost which would probably show up as a grainy/choppy power line on the dyno graph.

    Also, which displacement is your slant?

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    Re: My 68 Homemade Turbo Slant6 Dart

    mine is the larger slant. 225 cubic inch. I've not heard of others having issues under boost like this using the same manifold. A lot of people move straight for the 4bbl carb intake though, wheras I think this 2 is adequate. It should allow enough CFM through it as it is rated for 350. On a 225 cubic inch, it only takes a little more than 300cfm to get it over 4k. 5k is the limit with a slant though. I think you are on to something with the timing, but the problem is what to do about it and still keep it safe? And I think the idea you have of being able to listen to knock is the only way to go.

    Here's the graph from that Dyno Pull video:

    IF you look at one run the RPM dropped off significantly at 3700 rpm. Also if you look near the peak of every run it's kind of a scribbly line. Is that what you mean by the choppy line?

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    Moderator Turbo Mopar Staff Vigo's Avatar
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    Re: My 68 Homemade Turbo Slant6 Dart

    It looks like the dyno operator only took one pull past ~3700 rpm? Why was that? I cant hear in the video if anything nasty was happening that made them back off, but the dyno plot does make it look like it was starting to break up right at the peak torque rpm. Could be spark blowout or minor detonation. Not sure if it's coincidence or not, but the one pull that went all the way to ~5k rpm with a pretty clean plot on the dyno graph also had a slower torque rise and if you look you can see that it's actually substantially lower at the rpm where the previous pulls were having issues. Since the torque line corresponds with cylinder pressure i am thinking you were getting either spark blowout or detonation at the peak torque rpm.

    The easy way to tell which it is would be to close up your plug gaps to .020 and see what changes. If nothing changes, it's probably starting to detonate at that rpm which you will be able to hear with a knock-listening mic setup which i think would be the next step after trying the plug gap change.

    It does look like even if everything went right that you are 'naturally' peaking power at 4000 rpm. If you dont plan to change that with cam/manifold changes i would consider running a 2stg boost control setup where you go to a higher boost level at about 4200 rpm using a second boost controller, a solenoid, and an rpm switch. Those cheap adjustable shift lights on ebay/amazon can be a good way to get an adjustable rpm switch for this. If you have an internal wastegate with an adjustable rod on the outside, you could adjust your minimum boost level to ~8 via the rod and then use a solenoid with only one boost controller to up the boost as the VE goes down to extend the powerband and up your peak HP number a lot. Torque, cylinder pressure, and detonation are all pretty closely correlated in the sense that engines are most sensitive to detonation at the torque peak and less so as the rpm rises and ve/torque falls. If your engine can make 230tq at 3600 rpm before running into detonation, you should be able to use more boost to keep the engine making close to 230 torque higher into the rpm range which equates to more horsepower. There are potential issues of heat gain if your turbo compressor becomes inefficient or your cooling system cant shed heat fast enough at higher rpm but your turbo's compressor is so understressed that i doubt you will have issues running it up to something like 12-13 psi in the upper rpm range.

    Most high-power setups get around the need for 2stg boost control by running such a large turbine that they dont make peak boost until well past the engine's 'natural' torque peak anyway, but you are running a very small turbine for the displacement (t3 based but you didnt say exactly what?) so you will have to intentionally limit the boost at peak torque rpm and raise it later to get the most peak hp without blowing up at 3600 rpm. Having said that, i think there is probably something you can change to get WAY more than 230rwtq peak at 3600 rpm. It's possible your ONLY issue at present is spark blowout. The plug gap change will tell.

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    Re: My 68 Homemade Turbo Slant6 Dart

    Nice build if mine i would find a 92 up 4.ol jeep fuel rail and injectors and throttle body might be able to swap distributor and tone wheel for the front of the crank then get a Megasquit3 that should unlease the beast

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    Re: My 68 Homemade Turbo Slant6 Dart

    Sorry I couldn't log on to Turbo-mopar for a while. Was the site down or something?

    Anyway. I changed the gap down as suggested and it seemed to help a little. I closed them to .023 and tried it. They were originally gapped at .028 Which I'd think would have been fine - but at both gaps the engine still has a noticable weird sound like frying bacon at about 3700rpm which might be why the operator was shutting down at that speed. You can hear it without a det can or mic.

    Currently it has a MBC that allows it to hit 8psi and that's where I have it set.

    I think I may need to control pre-ignition better here is the problem. I'm running premium. I also have the governor limited to only allow 8* advance. The vacuum advance I believe is not pulling off quick enough during boost. I have a volvo vac pod off of a 240t from the 80s that should actually retard under boost. I just need to adapt it to the arm on the dizzy now.

    The issue now though is i don't see how 18 advanced is too far to preignite.

    Could the temperature of the plugs also effect this? The ones i have are one step colder than a stock plug, but there are "colder" ones available.

    I'm looking to see how high it can get off the stock reciprocating assembly and cam. Others are "supposedly' making more power, but no dyno backup on any of that. Just - "Turbo stock slant 10psi= 250hp"

    It could be true and I just have my tune nowhere near complete. Fuel delivery is not an issue, and it is not running lean. The issue here seems to be electronic. The other control I have is a MSD6ALN I can add, and then later add boost retarding unit, but I haven't rigged that up yet.

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    Re: My 68 Homemade Turbo Slant6 Dart

    Nice project car! 4-door sleeper too!

    One of the Chicagoland Mopar Club guys, Dennis (Slantzilla maybe?) just runs nitrous on his and says everyone using a turbo has issues. I'd love for yours to prove him wrong!

    A couple thoughts...

    Mmmm Bacon! Can you get a video of this? Detonation sounds like a ping noise. A frying sound would make me think something else?

    At 3700 you power is dropping off on the dyno, is it possible its possible that its running out of fuel or getting choked on air (intake or exhaust side) somewhere so the opposite, too much fuel?

    What do the plugs look like?

    To diagnose if you think its breaking up due to pre-ignition/detonation, throw in some 100 octane or at least some octane booster to see if it changes anything.

    To diagnose if timing is too much, reduce your base timing and see if it changes anything.

    To manually control timing retard with boost, MSD makes a couple different models of BTM's (Boost Timing Master) that are adjustable from like 1° to 3° retard per pound of boost. At least a couple of the ones they have should work with your 6AL box.

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    Re: My 68 Homemade Turbo Slant6 Dart

    Stock timing, race gas, and about 4psi boost would walk all over what you have going on right now.

    If JT says that all Slant 6 turbos run poorly and you say that everyone with a turbo slant 6 says "You must never run more than 18 degrees advance in ANY boost" I think we have a correlation going here.

    Timing requirements are dynamic. Simply switching from regular octane to premium should get you the first 4 psi boost on stock timing. Then timing should bump down as boost rises once you near the boost limit allowed by the increased octane fuel. The rest of the timing map (I know there is no map) should nearly mirror the non boosted timing numbers @ WOT.

    Has your system been pressure tested? Carb likes boost?
    Brent GREAT DEPRESSION RACING 1992 Duster 3.0T The Junkyard - MS II, OEM 10:1 -[I] Old - 11.5@125 22psi $90 [U]Stock[/U] 3.0 Junk Motor - 1 bar MAP [/I] 1994 Spirit 3.0T - 11.5@120 20 psi - Daily :eyebrows: Holset He351 -FT600 - 393whp 457ft/lb @18psi 1994 Spirit 3.0T a670 - He341, stock fuel, BEGI. Wife's into kid's project. 1990 Lebaron Coupe 2.2 TI/II non IC, a413 1990 Spirit 3.0 E.S. 41TE -- 1993 Spirit 3.0 E.S. 41TE -- 1994 Duster 3.0 A543 1981 Starlet KP61 Potential driver -- 1981 Starlet KP61 Parts -- 1983 Starlet KP61 Drag 2005 Durango Hemi Limited -- 1998 Dodge 12v 47re. AFC mods, No plate, Mack plug, Boost elbow -- 2011 Dodge 6.7 G56

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    Re: My 68 Homemade Turbo Slant6 Dart

    Quote Originally Posted by BadAssPerformance View Post

    One of the Chicagoland Mopar Club guys, Dennis (Slantzilla maybe?) just runs nitrous on his and says everyone using a turbo has issues. I'd love for yours to prove him wrong!
    Wait, what?? Everyone??

    Check your trusty Turbo-Mopar data base These aren't too shabby...

    66 Valiant Signet225ci /6 Turbo IntercooledA727 (2.94:1)26x8.5x14 MT SlicksRyan Peterson (turbo66valiant) 1.57 6.86@100.48 10.74@127.47

    70 Dart Swinger3.7L /6 Turbo FMIC AlkyA904 (2.76:1)255/60/15 MT ET StreetsTom Wolfe (shaker223) 1.572 7.06@97.50 11.02@120.56




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    Re: My 68 Homemade Turbo Slant6 Dart

    BTW, if you find your problem is not fuel/ignition related, check the valves springs. IIRC they're awful weak on a /6, maybe only 50lbs on the seat, doesn't take much boost to float 'em...

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    Moderator Turbo Mopar Staff Vigo's Avatar
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    Re: My 68 Homemade Turbo Slant6 Dart

    ^Excellent point, the pressure in the exhaust ports could be causing the exhaust valves to float under full boost.

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    Re: My 68 Homemade Turbo Slant6 Dart

    I hadn't even thought of the valves floating like that. I believe the valves are stock replacement. When I had the head rebuilt the machinest put in new valve springs, new valves and seats, and cleaned the whole thing out, along with 12 new push rods and 12 new lifters. Not sure if the springs being new would help their strength unless they're still just rated for 50. The intake and exhaust are stock specs. I set both while the car was warmed up and idling.

    .010 intake, .020 exhaust.

    Ondonti, I am not sure what you mean by pressure testing the system? It's been running on my slant for a while. I'm close to 3k miles on this setup and the motor seems happy enough with it. I wouldn't say it runs poorly, as it is a lot quicker than a stock slant 6 and gets nearly the same mileage. The carb is running off larger jets as opposed to having a functioning power valve, but it never goes lean under boost - always right around 11.8. -Sometimes 10. The next step I would do with it is I'll be making a BRPV for it, and utilizing a tube from the J-pipe to the power valve cavity to activate it. I've heard the pressure in the exhaust before the turbine is more than the intake side. Right now it's just a thought, and I haven't begun to actually change it because the car always seems to get adequate fuel. The carb itself seems to be doing fine. I get my pressure reading from the manifold so I know that the reading on my gauge is what is actually getting past the carb.

    Also this car isn't really going to run race gas. It runs Premium right now. I opened the governor on the distributor a little more and it made the frying bacon sound throughout the 4-8psi range.

    Right now I'm working on a bastardized electronic ignition distributor that has the Volvo 240T advance/retard pod on it. It should allow me to run a stock timing setup, and cause it to retard under boost. We'll see how it works out.

    Also as of today BasAssPerformance, I set the initial back slightly but left my more opened governor position which seems to allow about 12* of advance, over the 8* it did before and see what will happen tomorrow when i get a good chance to drive it around.

    Edit: ALSO - I just realized, at exactly 35 seconds in to the video I posted up top of my Dyno pull, you can actually hear the frying sound I'm talking about.
    Last edited by Serj22; 12-04-2014 at 10:32 PM.

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    Re: My 68 Homemade Turbo Slant6 Dart

    I mean pressure test between the inlet of the turbo and your engine. I want to know how your carb is dealing with boost and if you have leaks. I mentioned race gas only because I question the tune. Lots of people run race gas instead of getting the tune right. The simple bump to premium should allow you to run bone stock timing plus 4-6psi boost.

    New springs will be much stiffer than old ones. I would bet that when new they measure higher than required because its known they will relax over time. Other springs are like that.

    How did your ignition timing at 10psi compare with what timing should have been at WOT on an n/a slant 6 ? And what should it have been at varius rpms, like 2500, 3000, 4000, etc. Then what was it actually? Guessing your are running premium and stock timing calls for 85-87.

    Would you open up your wastegate and see how the car behaves with no boost? I would be interested to know your intake temperatures too. I think you jumped too far ahead in the boost game for a first attempt.
    Brent GREAT DEPRESSION RACING 1992 Duster 3.0T The Junkyard - MS II, OEM 10:1 -[I] Old - 11.5@125 22psi $90 [U]Stock[/U] 3.0 Junk Motor - 1 bar MAP [/I] 1994 Spirit 3.0T - 11.5@120 20 psi - Daily :eyebrows: Holset He351 -FT600 - 393whp 457ft/lb @18psi 1994 Spirit 3.0T a670 - He341, stock fuel, BEGI. Wife's into kid's project. 1990 Lebaron Coupe 2.2 TI/II non IC, a413 1990 Spirit 3.0 E.S. 41TE -- 1993 Spirit 3.0 E.S. 41TE -- 1994 Duster 3.0 A543 1981 Starlet KP61 Potential driver -- 1981 Starlet KP61 Parts -- 1983 Starlet KP61 Drag 2005 Durango Hemi Limited -- 1998 Dodge 12v 47re. AFC mods, No plate, Mack plug, Boost elbow -- 2011 Dodge 6.7 G56

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    Re: My 68 Homemade Turbo Slant6 Dart

    I initially had the turbo mounted with a huge exhaust leak that ran at 0psi, and the turbine barely spooled. Basically my old wastegate leaked like no ones business and no heat or pressure seemed to reach the turbo - just enough to spin it. Running without boost in that setup, I still managed the same AFR's so I know the fuel pressure reg is spot on (I think) since it's the same under boost at WOT, and cruise.

    On my stock setup, i was running a 2 barrel Weber 38/38 and had it dialed in perfect for the slant. No afr gauge at that time so i was just reading the plugs on a regular basis. The initial timing I used on that setup was 12 degrees advanced. With the vacuum advance hooked up and revved to around 3000 it hit 32 and that's as far as it would go in the spectrum. AS far as slantsix.org is concerned, 32 should be spot on for maximum advance with a slant, and it operated well. I gave the pressure test a shot, using what I could find online which was have someone rev in drive and then shoot soapy water at the intake piping and such. I did that and there seems to be a slight bit of bubbling on the bottom of the carb, closest to the valve cover, and in one of the pipe silicone sleeves close to the carb hat. It's very small, and I'm guessing that's an issue... I did roll the ends of the pipes with a homemade beader so the hoses would stay on. Maybe they're cheaply made or something - I got the couplers from ebay and they all say "JDM" on them... wiped that off.

    The carb base I suspected would eventually have an issue. I had to mount it with allen bolts with a tapered head in an adapter specifically for the 2300 Holley. I'll disassemble and see what i can do to ensure those don't loosen up again.

    As far as the timing goes, retarding the initial a bit seemed to be very nicely met by the car - and it is super quick, but now is a dog after 70mph. I might get this other distributor finished soon and hook it up. It has the stock timing curve and a pod from a Volvo, that will allow it to retard if need be. I can leave that disconnected for initial testing though.

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    Re: My 68 Homemade Turbo Slant6 Dart

    Quote Originally Posted by spyder View Post
    Wait, what?? Everyone??

    Check your trusty Turbo-Mopar data base These aren't too shabby...
    Oh, I know there are quick ones out there, have even seen them, just not many

    Quote Originally Posted by Serj22 View Post
    Also as of today BasAssPerformance, I set the initial back slightly but left my more opened governor position which seems to allow about 12* of advance, over the 8* it did before and see what will happen tomorrow when i get a good chance to drive it around.

    Edit: ALSO - I just realized, at exactly 35 seconds in to the video I posted up top of my Dyno pull, you can actually hear the frying sound I'm talking about.
    12° total timing should be enough at high RPM... down low you'll want more though

    I watched it 3 times and unless I'm missing something by seeing video instead of live in person, the "frying" noise sounds like air pressure so maybe from the exhaust or from the carb?

    What size exhaust is it? For /6 I would think at a minimum 3"MB pipe to not choke it?

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  18. #18
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    Re: My 68 Homemade Turbo Slant6 Dart

    Quote Originally Posted by Serj22 View Post
    I initially had the turbo mounted with a huge exhaust leak that ran at 0psi, and the turbine barely spooled. Basically my old wastegate leaked like no ones business and no heat or pressure seemed to reach the turbo - just enough to spin it. Running without boost in that setup, I still managed the same AFR's so I know the fuel pressure reg is spot on (I think) since it's the same under boost at WOT, and cruise.

    On my stock setup, i was running a 2 barrel Weber 38/38 and had it dialed in perfect for the slant. No afr gauge at that time so i was just reading the plugs on a regular basis. The initial timing I used on that setup was 12 degrees advanced. With the vacuum advance hooked up and revved to around 3000 it hit 32 and that's as far as it would go in the spectrum. AS far as slantsix.org is concerned, 32 should be spot on for maximum advance with a slant, and it operated well. I gave the pressure test a shot, using what I could find online which was have someone rev in drive and then shoot soapy water at the intake piping and such. I did that and there seems to be a slight bit of bubbling on the bottom of the carb, closest to the valve cover, and in one of the pipe silicone sleeves close to the carb hat. It's very small, and I'm guessing that's an issue... I did roll the ends of the pipes with a homemade beader so the hoses would stay on. Maybe they're cheaply made or something - I got the couplers from ebay and they all say "JDM" on them... wiped that off.

    The carb base I suspected would eventually have an issue. I had to mount it with allen bolts with a tapered head in an adapter specifically for the 2300 Holley. I'll disassemble and see what i can do to ensure those don't loosen up again.

    As far as the timing goes, retarding the initial a bit seemed to be very nicely met by the car - and it is super quick, but now is a dog after 70mph. I might get this other distributor finished soon and hook it up. It has the stock timing curve and a pod from a Volvo, that will allow it to retard if need be. I can leave that disconnected for initial testing though.

    Thats not really an answer about the timing. What is the stock WOT "zero" psi timing number at various RPMS. 2500, 3000, 4000. Then how do your current numbers compare. 12 degrees of total timing might work on a 4 valve head 2.4L at high boost but its not what a low boost engine needs. Nobody with a TD runs "low boost" and low timing...For TDers, low boost is more than you are running.

    If your OEM motor had 20 degrees of timing at WOT at 3000 degrees, then with premium grade fuel, you should get a couple psi boost without changing timing at all. then back off 1 to 1.5 degrees or so (very safe) for each psi of boost beyond 4-6 and you should be pretty close. 10psi should not radically change your spark requirements. There are probably guys out there running double or triple the boost as you and they have extremely different spark advance needs.

    Timing should increase eventually after peak torque which is what those govenors or whatever you welded would accomplish. Rereading, I think you should run 2 steps colder on the plugs when doing all this and gap them @ .022ish.

    "vacuum advance is not pulling off quick enough during boost" this would mean that its really not working at all then....or something greater than atmospheric pressure is fine.
    Interested to see how it runs with the volvo setup. I think I would rather run 100% stock and then have boost retard, however you accomplish that, MSD or the Volvo parts.
    Last edited by Ondonti; 12-06-2014 at 07:59 AM.
    Brent GREAT DEPRESSION RACING 1992 Duster 3.0T The Junkyard - MS II, OEM 10:1 -[I] Old - 11.5@125 22psi $90 [U]Stock[/U] 3.0 Junk Motor - 1 bar MAP [/I] 1994 Spirit 3.0T - 11.5@120 20 psi - Daily :eyebrows: Holset He351 -FT600 - 393whp 457ft/lb @18psi 1994 Spirit 3.0T a670 - He341, stock fuel, BEGI. Wife's into kid's project. 1990 Lebaron Coupe 2.2 TI/II non IC, a413 1990 Spirit 3.0 E.S. 41TE -- 1993 Spirit 3.0 E.S. 41TE -- 1994 Duster 3.0 A543 1981 Starlet KP61 Potential driver -- 1981 Starlet KP61 Parts -- 1983 Starlet KP61 Drag 2005 Durango Hemi Limited -- 1998 Dodge 12v 47re. AFC mods, No plate, Mack plug, Boost elbow -- 2011 Dodge 6.7 G56

  19. #19
    Moderator Turbo Mopar Staff Vigo's Avatar
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    Re: My 68 Homemade Turbo Slant6 Dart

    Vacuum advance should move basically faster than you could follow with the naked eye if you just flashed boost to it so if it's not moving quick enough it's broken.

    12 degrees total timing is NOT enough for an old---- combustion chamber at low boost. Timing requirements are a reflection of how much time it takes for combustion to finish and a newer 4-valve cyl head with the spark plug very near the center of the combustion space is going to take a lot less time than a slant6. I think it should have MORE than the 18 he has now if everything was working properly.

    So in my opinion the question is not 'does it need more timing' because i think the answer is yes, the question is what is keeping it from working better as it sits? I think exhaust valves floating from backpressure at peak boost is a prime suspect although i wouldnt rule out that other things are also having a small effect such as minor air leaks or the fact that it ran a little different with less plug gap. I just dont think those are the main issue.

    Dont push the red button.You hear me?

  20. #20
    Rhymes with tortoise. Turbo Mopar Staff cordes's Avatar
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    Re: My 68 Homemade Turbo Slant6 Dart

    I too would think that there must be a mechanical element at play to not allow for higher than 3.7K RPM.

    I would echo what JT said about the exhaust being large enough too. 200+cu.in. is way larger than our 153cu.in motors which most all of us run a 3" exhaust on and notice gains. A lot would be left on the table with anything smaller in a larger motor IMO.

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