Re-Curve Distributor for Forced Induction?

[phebbler]

I am in the process of supercharging my Delorean and have been reading all the literature I can get my hands on concerning the process. I am only going to be applying 4-5psi of boost but I noticed in the Island Turbo install guide it mentioned that the distrubutor had to be sent in to be recurved to prevent pre-detonation. My first questions is with this little boost and running 93 octane fuel should I need to have the distributor modified?

The second questions is if it does, I have read in my service manual that the centrifugal advance is controlled by weights within the body of the distributor but they are not called out in the diagram on page M:01:01. I am familiar with other distributors that use weights and springs for mechanical advance but I again don't see the springs nor the weights listed as replacement parts. Can any one provide any information on if the weight(s) and spring(s) are accessable? I haven't removed the distributor yet just incase it doesn't need to be done.

Thanks

[WelmoedJ]

I am in the process of supercharging my Delorean and have been reading all the literature I can get my hands on concerning the process. I am only going to be applying 4-5psi of boost but I noticed in the Island Turbo install guide it mentioned that the distrubutor had to be sent in to be recurved to prevent pre-detonation. My first questions is with this little boost and running 93 octane fuel should I need to have the distributor modified?

The second questions is if it does, I have read in my service manual that the centrifugal advance is controlled by weights within the body of the distributor but they are not called out in the diagram on page M:01:01. I am familiar with other distributors that use weights and springs for mechanical advance but I again don't see the springs nor the weights listed as replacement parts. Can any one provide any information on if the weight(s) and spring(s) are accessable? I haven't removed the distributor yet just incase it doesn't need to be done.

Thanks

The iginition distributor used in the DeLorean has only one mechanical "balancer".
Volvo's 260 and 760 series distributors have two, making a more aggressive advance possible.
They are in the lower part of the distributor.
Usually parts for distributors are not sold separately, only a complete unit.

Volvo engines have a higher compression ratio (10:1).

I have no information about the need of or recurving.
If you are exchanging your D distributor for a Volvo type, you can change the advance from 13 to 11-10 degrees.
Maximum torque will be then available at some 2200 RPM instead of 2750 RPM.
These are the figures I have used on my standard D engine with a Volvo ignition distributor and Renault fuel distributor.

Hope this helps.

[David T]

The distributor does have to be "recurved" or modified. I will have to look up my notes and see exactly what was done and how. From memory I think the advance was just limited by sticking a screw into it to jam it. You have to be careful to avoid detonation, too much advance can make it detonate. If you are supercharging realize that it is not quite the same as the Island kit which is turbocharging. You could use how the Island kit was done as a guide but do not try to follow it exactly. The distributor does have to be removed to be disassembled and modified. On the Island kit the distributor was removed and sent to John Conway in Long Island and he did the modification and then returned it to the shop doing the kit install. I don't know if he is doing them anymore. The stock cast pistons can't take anymore than 5 psi without breaking the lands between the rings on the pistons. For more boost you must replace them with cast pistons.
David Teitelbaum

[Spittybug]

I thought Island made turbo chargers not superchargers, but it doesn't matter.

4 - 5 psi boost isn't that much, but I can see it having the effect of making a denser cylinder charge. At the same octane (and other operating parameters), this would have the effect of increasing the flame propagation through the cylinder, thus potentially requiring less advance to get the optimal ignition. Advance comes in two forms right? Vacuum and mechanical. Mechanical advance takes care of sending the spark earlier in response to the engine going faster and faster relative to a flame front that is going at a fixed rate (at a given octane). The vacuum advance is in place to accommodate changing charge density (flame fronts like denser packed molecules to chew through) so that when the engine is just coming off idle (our cars have zero advance at idle since the vacuum solenoid blocks it) and you are opening the throttle up and sucking in lots of air and gas, the vacuum advance is at its maximum (~20*). As you reach atmospheric (enough air getting in to significantly reduce the vacuum in the manifold), the charge is denser and the amount of advance is backed off. This is largely a pollution control feature more than performance.

By definition your boost won't kick in until higher RPM. The mechanical advance on our cars is fairly conservative (doesn't get all 20* in until about 4000rpm). I personally don't believe you will see the need to play with the mechanical advance. By running higher octane (93) you will be resisting the pre-detonation that the denser charge may incur. I would hold off re-curving to see if you need it since you will need to run it on the dyno to get it right.

As always, it's your car! I am NOT an expert on this, but have indeed played around with the timing on my EFI'd car a fair amount and have a pretty good feel for it. Use my advice at your own risk.

[David T]

It is a lot more complicated than you say. 5 LBS of boost translates into a MUCH higher combustion chamber pressure, more than the cast pistons can handle. Detonation is ignition occurring before it should and has nothing to do directly with timing advance since the ignition didn't start the combustion process yet. The Island kit IS two turbochargers. Turbochargers are driven by exhaust gasses. A supercharger is driven either directly by the motor or by an electric motor. Then there is passthrough or pull through the metering unit. The Island kit pulls through the metering unit. Premium fuel will delay detonation but can't prevent it. The Island kit doesn't have intercoolers so the fuel/air charge is hot which increases the chances of detonation. The higher the boost pressure the hotter the charge, the closer you get to detonation. You *could* add water/methanol injection so you can increase boost pressures but now you are flirting again with detonation. As you can see, this can get complicated in a hurry.
David Teitelbaum

[Spittybug]

Hey, well David is the "guru" as his avatar points out, so go ahead and spend the money. I was under the mistaken belief that there were several members running such modest boost with stock internals.

[SS Spoiler]

I've had a BAE turbo on my car since I bought it in '88. [PO installed] Replaced engine [new out of box]
at 70,000 miles,because of a massive coolant leak into oil pan. Probably head gasket or liner. Core went back to Don at DMCCA. Since then at 150,000 miles i'm getting blowby that will lift the oil fill cap an inch. Lots of smoke to. Maybe time to think of forged pistons. Stay tuned.....

[David T]

I should have said 5LBS boost is the maximum you should do for longevity. The stock pistons can handle that but realize that is still a LOT of combustion chamber pressure and ANY hint of detonation will push you over the edge and damage the pistons. I looked in my notes and I did not find exactly what the "recurve" is. There is also a pressure switch that forces full enrichment on the Lambda system. Timing should be set to 10-12 degrees BTC at idle, vacuum disconnected and you should use the highest Octane fuel you can get. I seem to remember mechanical advance was limited. BTW going higher than 5LBS boost with forged pistons, the next weak link is the input shaft on the transmission. The coupler is pinned and it breaks where the shafts are drilled for the pins. The fix there is a one piece shaft of the correct length.
David Teitelbaum

[DCUK Martin]

Okay let's get some facts straight here....

1: Forced induction means a hotter, faster and more powerful explosion in the cylinders. Ignition timing needs to be retarded because of the extra speed of the burn.
2: Higher octane fuel burns more slowly which allows you to achieve higher combustion chamber pressures without pre-detonation (knock). So it WILL help, though isn't a magic bullet.
3: the "recurved" distributor recommended in the island kit is a BODGE. It retards as a function of engine rpm and only "works" because, being turbocharged, the higher boost only occurs at higher RPM. This is not the case with a supercharger, assuming it's positive displacement.
4: The island kit is hardly a "bible" for forced induction. For example it recommends taking out the advance solenoid, even though under boost it'll have absolutely no effect whatsoever.
5: DeLorean pistons are perfectly strong enough for moderate boost. The Renault 2.5 turbo pistons are also cast and apart from a 0.5mm thicker primary ring, have an otherwise identical ring configuration (the pistons are taller with a thicker crown however). What kills DeLorean pistons under forced induction is knock because it's near impossible to get timing and fuelling correct.
6: There is no "good" way to boost a stock DeLorean engine. Unless you work out a way of retarding ignition as a function of boost and fuelling correctly under boost. I've toyed with the idea of using a wastegate actuator to rotate the ignition distributor under boost, and I've successfully used the stock CPR to drop control pressure under boost. Without changing at least the camshafts for a forced induction profile however, you'll never get as good performance as from the native turbo engines in the first place. MFaulks has achieved 275hp and nearly 300ft-lbs from the 2.5 with a different cam profile and back cut valves. We're putting that config into #2727 and adding twin chargecoolers so watch this space. (#2727 had an island TT but the only original parts now are the exhaust manifolds)


the next weak link is the input shaft on the transmission.

Still banging that drum eh? The input shaft coupler is good to 300hp (@ 300ft-lbs) as seen in the Alpine A610, Venturi 300. The only input shafts I've heard of breaking in DeLoreans have chevvy conversions, and the Esprit V8 where 5th is actually the weakest point, followed by the input coupler.

David, please cite some evidence as to the weakness of the DeLorean transmission. It is limited, but not in the context of all but the most insane PRV.

[David T]

The DMA had Fred Dellis as a speaker and Mark Levy has been in touch with him. He was the owner of Legend Industries and his company had the contract to do the R & D to create the turbo version of the PRV for the '83 Delorean. Fred said they were able to get the HP up to any level they wanted (I remember he said they recamed and used forged pistons) but the limiting factor was the transmission input shaft. They had to make the conversion very robust because they had to be able to warranty it since it was being sold as a new car. They were working on that problem when everything stopped. The Island kit was developed by a former employee of Legend and he made the Island kit a bolt-on affair so he had to limit the boost because of the stock pistons, cams, and input shaft. I agree the Island kit is not the be-all-end-all but it is a proven time tested install. Fred said they blew a lot of input shafts! Maybe Mark will add to these comments. Or you can contact him directly, he may be able to put you in touch with Fred. Legend Industries was going to get the contract to add the turbo option to the Delorean once it was developed. When DMC went bankrupt they owed Legend so much money that it went down too. Legend was well known for their expertise in adding turbo power to motors.
David Teitelbaum

[Rad Dad]

I have had two DeLoreans with the Island kit. I put over 50,000 miles on the first car after the kit was installed and never had any engine problems. I ran 7 lbs. of boost. My current DeLorean has logged over 120,000 miles with the Island kit installed. I have it running at 6lbs. Again, no engine problems attributed to the turbos. Yes, I get a 'bit' of blow-by if I really tromp on it, but nothing to be concerned about. If I ever need to go into the engine, I will use Total Seal rings and I believe that would resolve any blow-by problems.

I have seen no negative engine wear effects from the turbos.

[FABombjoy]

6: There is no "good" way to boost a stock DeLorean engine. Unless you work out a way of retarding ignition as a function of boost and fuelling correctly under boost.
I've never examined a DMC or Volvo distributor closely, so pardon if this is a bit naive, but Volvo at the time used vacuum advance canisters that were also boost sensitive. Would it be possible to refit the stock distributor with a similar mechanism?

Thanks for posting your list. It reaffirms a lot of things that I've observed about the Island (and BAE) instructions but didn't feel like having an argument about. I especially like how they have you adjust boost by lengthening the wastegate actuator arm.

I'm going with the MSD 5462 on my Island setup to control ignition retard. It has to be altered for odd-fire, right now mine is sitting in the RMA queue at MSD.

In the Island manual, the advance is reconnected to vacuum at instructions #39 & 40. If I'm reading it right, I think they have you bypass the thermo vacuum switch and connect the distributor directly to manifold vacuum. Honestly I've read it 50 times and I can't tell what they're trying to accomplish or what's supposed to become of the enrichment function of the WUR. Connecting it to ported would make more sense but the instructions don't read that way (to me).

[Ron]

3: the "recurved" distributor recommended in the island kit is a BODGE. It retards as a function of engine rpm and only "works" because, being turbocharged, the higher boost only occurs at higher RPM. I am reassembling a basket case turbo car and any info particular to a BAE distributor recurve would be appreciated. (PO lost all of the paperwork and I'm getting mixed stories as to whether this particular distributor was sent out and recurved correctly or simply had the tabs bent to limit the advance and it was called "recurved".) What was the practice originally WRT to having one recurved when purchasing the setup...was it part of a kit, the customer had to sent it off, or what?

[DCUK Martin]

Fred said they were able to get the HP up to any level they wanted (I remember he said they recamed and used forged pistons) but the limiting factor was the transmission input shaft.


Yes - I completely accept he said this, but without knowing more about the testing they were doing it's a bit of a leap to claim the transmission is weak based on one opinion given that there are production cars putting a truly violent performance through the standard transmission without a problem (Venturi 300, Alpine A610 both with 3 litre turbos). It's very likely that in their testing, they weren't trying full throttle accelleration in 5th gear, or they've have discovered that was an even weaker point than the input shaft!




They had to make the conversion very robust because they had to be able to warranty it since it was being sold as a new car.



And 2 years later Renault started doing exactly that, putting 200hp through it (and the Renault 25 subsequently gaining and excellent reputation for a donor drivetrain for mid engined kit cars). Later the A610 came along with 250hp and a lot more torque.



I agree the Island kit is not the be-all-end-all but it is a proven time tested install.


I'd disagree with that - you read many stories of both turbo kits killing engines. There's one higher up in this thread...

Oh and as a side note, forgetting all the internals limiting boost pressure, anything above about 5psi and you risk blowing the injectors clean out of their holes. Ask me how I know....

[DCUK Martin]

I've never examined a DMC or Volvo distributor closely, so pardon if this is a bit naive, but Volvo at the time used vacuum advance canisters that were also boost sensitive. Would it be possible to refit the stock distributor with a similar mechanism?



My experience of Volvo (and Renault) 013 dizzys is the only difference is the shape of the advance weights.



I especially like how they have you adjust boost by lengthening the wastegate actuator arm.


I had a copy of the destructions from Dave Stragand somewhere but haven't seen them for ages. The bit about the vacuum solenoid had me thinking they didn't really have a clue. Using the hobbs switches too is a bodge.



I'm going with the MSD 5462 on my Island setup to control ignition retard.


Let me know if you want to talk about using the CPR to enrich.... (there is some calibration work to do but it's relatively straightforward).



In the Island manual, the advance is reconnected to vacuum at instructions #39 & 40. If I'm reading it right, I think they have you bypass the thermo vacuum switch and connect the distributor directly to manifold vacuum.


That can't be right or you'd be running either stupidly retarded under normal circumstances, or stupidly advanced at idle... (depends on how you set up the timing!)

[DCUK Martin]

I am reassembling a basket case turbo car and any info particular to a BAE distributor recurve would be appreciated.

I believe I saw a BAE instructions set some tie ago and no mention of the distributor was included. The Island kit had you send the dizzy away.
Changing the "curve" can only be a function of engine RPM and never a function of boost pressure, which is what it should be.

[FABombjoy]

My experience of Volvo (and Renault) 013 dizzys is the only difference is the shape of the advance weights.
Mainly I'm looking at the green books that cover Volvo's B21FT and B23FT, as they are K-jet turbo. Volvo addresses the issue of retard with a 2-way canister on the distributor. I've seen them aftermarket as well. Mainly I'm just thinking out loud, wondering if the DMC dizzy could have it's canister swapped for one of these.


I had a copy of the destructions
I LOLed


Using the hobbs switches too is a bodge.
I wasn't sure where to go with this. My feeling was that a pressure switch that shorted the WOT throttle switch when under boost might be beneficial to keep the lambda computer from pulling fuel. Based on the DMC manuals description of what the WOT switch does, this seemed like a better approach than routing the O2 sensor through the switch. You don't think it's necessary at all?


Let me know if you want to talk about using the CPR to enrich.... (there is some calibration work to do but it's relatively straightforward).
I was considering it, once everything was together and I had some road tests (I'm set up for wideband logging). I would very much be interested in your experiences. I'm also set up for wideband o2 logging.


That can't be right or you'd be running either stupidly retarded under normal circumstances, or stupidly advanced at idle... (depends on how you set up the timing!)
Yeah, I just facepalmed a little and read on. There are a lot of things about the island kit that I don't get.

My kit is still on the bench but it's coming together. Next stop is to find a shop to have the manifolds cleaned up and extrusion honed or at least internally deburred. They have seam slag that can be removed by finger. I cannot believe that the original purchaser of this kit did not have a chunk of iron run through a turbine.

[FABombjoy]

I am reassembling a basket case turbo car and any info particular to a BAE distributor recurve would be appreciated. (PO lost all of the paperwork and I'm getting mixed stories as to whether this particular distributor was sent out and recurved correctly or simply had the tabs bent to limit the advance and it was called "recurved".) What was the practice originally WRT to having one recurved when purchasing the setup...was it part of a kit, the customer had to sent it off, or what?
The BAE manual also has you "decurve" the distributor. I did a quick OCR on that page:

Remove the distributor, place on distributor machine. With no vacuum line connected run the distributor at idle. Slowly increase the RPM's. Watch what RPM level it starts advancing, usually around 1500 to 2000 RPM's and continues advancing until 3000 to 3500 RPM's. Continue increasing RPM's until 5000 RPM. It will start advancing again. This second advancing mode is what has to be stopped. On the side of the distributor you'll find a pressed on view plate, the lower one of the two is the one you want. Rotate the distributor by hand, notice the arms that have no springs connected to the top of them. With a hammer and a punch bend one of the arms in just a little, in order to figure out that the one you bend is the right one. What your bending is the centrifugal weight stop. If you bend the wrong one pry it back out to the same position. Bend the other arm in until the advance at 5000 does not advance any more. Set the timing to stock specs.

[Ron]

The BAE manual also has you "decurve" the distributor. I did a quick OCR on that page:Thank you very much!!!

Any chance of getting a full copy to keep with his paperwork? (...PM me ?)

[David T]

I have a copy of a BAE manual if you need it. It has a procedure to "recurve" the dizzy. I agree the timing advance was never great for the Island or the BAE turbo, it left a lot to be improved. The fuel enrichment too. More work in these areas could yield more performance and with today's control systems it can be done a lot easier. I would do away with the whole ignition system and go to a custom engine management system computer based and also do the fuel system. This way you can map the whole RPM and prevent detonation. The UN 1 is capable of a LOT more than 200 HP. In the Lotus V-8 stock is 350 HP and there are some running much more. The problem has to be shock (dynamic) loads on the coupler. There is a one piece input shaft that may be part of the solution. I have seen UN 1 transmissions out of the V-8 Lotus with the teeth ripped off the crown wheel so there are limits to what you can do with the UN 1.
David Teitelbaum

[FABombjoy]

Any chance of getting a full copy to keep with his paperwork? (...PM me ?)
They're both in the DMCNews Yahoo file archive:

http://autos.groups.yahoo.com/group/dmcnews/files/Turbo%20Install%20Manuals/

If you can't get in, PM me your email and I'll send them to ya

[Ron]

Got em' both, Thanks Again!!!!

[FABombjoy]

I'm going with the MSD 5462 on my Island setup to control ignition retard.
Nevermind on this, I just received my 5462 back from MSD stating that it can't be modified for odd-fire. Even though a tech confirmed that it could be. Twice.