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-   -   twin spark conversion (https://www.alfabb.com/bb/forums/engine-conversions/652746-twin-spark-conversion.html)

sdamant 04-27-2018 05:12 AM

twin spark conversion
 
Hi I am looking for some technical advice :- I am in putting an Alfa 75 T/S engine into my 105 Coupe...I could do with some assistance :_

1. I am going to use Weber carbs and an 8 wire distributor which I am making using a Nissan cap & rotor with one trigger firing 2 Lumintion modules and coils. I understand the T/S engine needs less advance that the Nord engine about 28 degrees total ? ... so static at around 8 degrees and then 10 degrees mechanical advance at the distributor .... is that about right ?

2. Camshafts , I am doing away with the variator on the inlet cam...I believe the standard exhaust cam has timing of 68 / 34 with a 11.8 mm lift ... so if I use another exhaust cam on the inlet side and with a slight timing tweek I would have cams around 70/30 30/70 with a 11.8 mm lift , which sounds ideal for fast road performance.

Any thoughts ?? help welcome !

Stephen

bianchi2 04-28-2018 09:45 AM

why carbs?? F.I. is so much easyer to set up and use.. someone once told me all a carb. is...........is a controlled fuel leak..

Richard/SIA 04-28-2018 10:25 AM

...a computer chip/EFI is just sand with pretensions of grandeur!

When EFI fails you call a tow truck, when Webers have an issue you can still get home on your own or make the adjustment on the spot.
Lot more threads here for help with EFI issues than for Webers.

sdamant 04-28-2018 10:57 AM

T/S Coversion
 
Yes want to stay with carbs several reasons ...more original underbonnet appearance , I can fix them ! , want to stay away from electronics as much as possible which is also why I am going the 8 wire distributor route.

Anybody got any thoughts on my camshaft solution ?

iachella 04-28-2018 07:46 PM

Stephen:

On the first question, you are correct. 28 deg max advance is the commonly measured value.

I don't have anything on your second question because I have not gotten to the point of choosing a different cam for my TS. Here in the US, a guy in Washington state (Wes Ingram) has a cam for the TS that supposedly will work with the variator and if you switch it on at about 3K you will get a happy bump in the upper regions of your rev range. I am thinking of going that route. For you, that one would mean you have to have an rpm switch to activate it since you wont have a computer.

Did you get your engine with the EFI wiring harness? I'm looking to purchase a spare. Let me know if you have it and want to part with it. I don't need the ECU, though. Just all the wires.

hunttheshunt 04-29-2018 02:42 AM

Quote:

Originally Posted by iachella (Post 8185562)
Stephen:

On the first question, you are correct. 28 deg max advance is the commonly measured value.

What ? On a TS ? That´s nearly 10 degrees too much.

A properly improved Nord needs 28-30 degrees; TS needs way less.

Craig_m67 04-29-2018 04:39 AM

What's the benefit of a TS on carbs without variable cam versus a hot Nord?

Is there any?
This isn't a sarcastic post btw.. I'm interested in what gains are expected

Veep 04-29-2018 09:36 AM

a TS conversion will cost more than a good rebuild on a nord, with some tuning. Will simple work and good cam selection you get the same power for less money than the conversion. Besides that: TS wants a more classic look, that needs a 155 head without all the fitting points for distributors and VVT.
Contact RJR on cams with torque delivery. Also for the 75/155 btw... but for a classic look, and more than sufficient power: dont do a TS conversion..

Bertiebloke 04-29-2018 01:50 PM

Quote:

Originally Posted by Veep (Post 8186194)
a TS conversion will cost more than a good rebuild on a nord, with some tuning. Will simple work and good cam selection you get the same power for less money than the conversion. Besides that: TS wants a more classic look, that needs a 155 head without all the fitting points for distributors and VVT.
Contact RJR on cams with torque delivery. Also for the 75/155 btw... but for a classic look, and more than sufficient power: dont do a TS conversion..

The twinspark vs Nord decision was one I had to make last year and I was pretty open to both options. The Nord option was always going to be substantially lower cost and thanks to a helpful AROC member I managed to source a well built lightly tuned and balanced engine with a bit of head work but standard valves and 12mm C&B cams and 123 distributor. With standard 40mm carbs and exhaust/ manifold it puts out 160hp at 5300rpm with a pretty flat torque curve from 2300-5300 rpm. I think that's probably not too far from a mildly tuned twinspark at lower cost.

Factors that affected my decision were
  • I wanted to keep the sound and feel of carbs
  • Originality was a factor
  • There was some faffing around to get speedo to work with twinspark plus more modifications
  • Nord works best with injection which I felt mitigated against my first 2 points
  • It was actually quite difficult to find a twinspark and a good Nord came available
  • The Nord option was several thousand lower cost
I think if I'd wanted 180hp + car then I'd have gone Twinspark but I'm very happy with what I've got which pulls cleanly from tickover to redline. It's enough for a semi daily driver.

sdamant 04-30-2018 10:54 AM

hi, I am pretty sure I am right about the advance that's 28 degrees TOTAL , so say 8 degrees static and then 20 degrees mechanical

Stephen

sdamant 04-30-2018 11:01 AM

Ok my reasons for going the T/S route , my NORD engine is very tired , needs a rebuild...I have a pristine T/S engine , and then ultimately with development I will be able to get more usable power from the T/S. I am keen to keep the under- bonnet looking as original as possible hence the plan to use carbs and an 8 wire distributor . The cams issue has become "interesting" in that apparently I am right about the standard 75 T/S exhaust cam timing and as I have another T/S engine I will use the spare exhaust cam on the inlet which as far as I can see will give the same timing/ profile as the C&B cams listed as performance street .

sdamant 04-30-2018 11:05 AM

Hi, I will be back in my workshop mid May and will have a look to see what I have in the way of wiring harnesses....over the years I have collected two T/S engines one was bare but the other came with a large box of "bits"...if I have a harness I will let you know and you are welcome to it.

Stephen

nealric 04-30-2018 01:33 PM

Quote:

Originally Posted by Richard/SIA (Post 8184730)
...a computer chip/EFI is just sand with pretensions of grandeur!

When EFI fails you call a tow truck, when Webers have an issue you can still get home on your own or make the adjustment on the spot.
Lot more threads here for help with EFI issues than for Webers.

The thing is, properly setup EFI doesn't really have issues. The help threads you see on the BB are mostly for stone age Bosch L-Jet stuff. A modern aftermarket EFI eliminates all of the disadvantages other than complexity of initial setup.

hunttheshunt 05-01-2018 02:21 AM

Quote:

Originally Posted by sdamant (Post 8187866)
hi, I am pretty sure I am right about the advance that's 28 degrees TOTAL , so say 8 degrees static and then 20 degrees mechanical

Stephen

On a TS you´re pretty sure way wrong; especially when modified and running with 2 plugs.

ianellisalfa 05-01-2018 03:08 PM

I have a twinspark in my road legal track car running on TBs & stand alone ECU (Emerald) whilst in my daily driver I have a twinspark on Webers with the original Alfa (Bosch) ECU running the ignition (twin distributors) and a throttle pot (the variator is hard-wired by a switch on the dash). The latter was much cheaper to build & install, albeit about 35bhp less powerful but is ideal for road use - the most unreliable aspect being the 3 Bosch relays that control the ignition & fuel pump!
I also have a Giulia Ti with a tuned 1750 (oversized to 1.9) pushing out about 150bhp (i.e. stock 2.0 twinspark bhp) which looks great, but cost more to rebuild, and isn't as easy to drive in traffic due to the light flywheel & slight stumble at low rpm...
For me a twinspark on original EFI just doesn't sound like an Alfa!


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