Is twin plugging worth it?

[dzlndan]

I have a naturally aspirated twin weber, twin plug 3.0 but building a 3.0 turbo (changing pistons/cylinders for lower compression) but wondering if it would be worth using my twin plug heads off my current motor? any thoughts?

[Mick_D]

How much extra power did twin-plugging the N/A motor give you?

[IMR-Merlin]

twin plugging a turbo is not about power (more or less) but rather to avoid detonation.

[Mick_D]

Twin-plugging anything is mostly about that, to be honest. THe Chrysler Hemi 5.7 is twin-plugged for that reason. Doesn't hurt the emissions either. I was just wondering if it was any different with the air-cooled motors.

[dzlndan]

Originally Posted by Mick_D

How much extra power did twin-plugging the N/A motor give you?

Don't really know I bought it with the set up.

[dzlndan]

Originally Posted by IMR-Merlin

twin plugging a turbo is not about power (more or less) but rather to avoid detonation.

Right, so less chance of unburnt fuel detonating under high compression from high boost and the rich mixture open throttle. So this is a very great case for Twin Plug setup. Thanks for the input.

[IMR-Merlin]

Originally Posted by Mick_D

Twin-plugging anything is mostly about that, to be honest. THe Chrysler Hemi 5.7 is twin-plugged for that reason. Doesn't hurt the emissions either. I was just wondering if it was any different with the air-cooled motors.

It's even more important in the aircooled cars to keep the flame front moving in the right direction and getting even burn. Aircooled cars don't cool as well as water cooled heads, so the less "hot spots" you create the better. You also run less timing in the twin plugged cars, I would assume it's because the flame is coming from 2 directions.

[JFairman]

That's correct.
Twin plugging lights off the mixture from both sides of the combustion chamber instead of from one side with single plug so the two separate flame fronts meet somewhere in the middle and complete combustion happens faster or in less time.

Because of that ignition timing should be a little later or less advanced with dual plugs using the same fuel and that makes for less chance of detonation.

[kenikh]

Whats your static compression ratio and camshaft profile. You can't authoritatively answer this question without knowing these.

[jwasbury]

I like this little write up on the topic by Steve W at rennsport systems

Gasoline, Timing & Twin-ignition | Rennsport Systems | Porsche Performance Systems and Support

[TurboKraft]

Example:

1982 Turbo, 3.4L, EFI
Recent tune, then converted to twin plug and tuned again, all on west coast "91-octane" junk fuel
Before: 493tq/532hp at the wheels
Twin plug, no tuning, 4deg timing removed: 497tq
Tuned: 505tq/541hp, 2 degrees added back

12tq and 9hp doesn't sound like much, huh?

Midrange 3800-4800rpm gained 20-30tq.
Engine has noticeably more pull, feels more snappy and responsive. And at (very) high speed cruising going to RRV the economy was ridiculous, like mid-20s, up about 4mpg -- a nice perk on top of it all.

[Hams930T]

Interesting; didn't know you'd pull out a little timing with a twin-plug setup. The reason makes sense however. Learn something new every day!

- Chris.

[Craig 930 RS]

Nice thread! Good stuff. Twin plugged here :-)

[dzlndan]

Originally Posted by TurboKraft

Example:

1982 Turbo, 3.4L, EFI
Recent tune, then converted to twin plug and tuned again, all on west coast "91-octane" junk fuel
Before: 493tq/532hp at the wheels
Twin plug, no tuning, 4deg timing removed: 497tq
Tuned: 505tq/541hp, 2 degrees added back

12tq and 9hp doesn't sound like much, huh?

Midrange 3800-4800rpm gained 20-30tq.
Engine has noticeably more pull, feels more snappy and responsive. And at (very) high speed cruising going to RRV the economy was ridiculous, like mid-20s, up about 4mpg -- a nice perk on top of it all.

Excellent data, thank you for sharing. I do have to admit. I did experiment with just a local test drive and on the non-turbo the response on twin plug is brilliant. But I also understand the reason to twin plug on a high compression dome piston is almost a necessity to get ignition on both sides of the cylinder.

[dzlndan]

Originally Posted by kenikh

Whats your static compression ratio and camshaft profile. You can't authoritatively answer this question without knowing these.

Can't answer that yet. I'm still in the planning mode but I have a 81 3.0 SC motor with broken head studs, a set 3.3 piston/cylinders and all the OEM components for the top end of a 3.3 turbo motor. If I stick with the 97mm 3.3 p/c and the short stroke of the 3.0 the CR should be little less than 7.0:1

Still doing the research.

[Bucketlist]

My twin plug setup (installed by a PO) gives me piece of mind. I run a 40 year old cis system in 100* Texas heat. I feel this alone has saved my engine several times when conditions were out of my control.

[voitureltd]

Originally Posted by kenikh

Whats your static compression ratio and camshaft profile. You can't authoritatively answer this question without knowing these.

My experience. I have two old school 77 930s, twin plugged CIS w 934 distributers. Both @ 7.5 compression, one a 3.2 liter by Andial with recently installed factory 993 sport cams, the other a 3.2 liter cam's unknown. Both pull strong to redline and running 29 BTDC, 15 PSI and always use leaded race gas at least 100 octane for regular use and 112 if really pushing it. I have put around 8K miles on each with no problems,,,, so far.

[kenikh]

The key point is twin plugging is always better. The nuance is that the magnitude of benefits you'll see very much depend on compression and cam.

[boosted79]

Later timing with twin plug makes more torque because the combustion pressure is pushing back against the piston for a shorter time before TDC vs single plug. Twin plug allows this because of two flame fronts so less time is req'd to reach max BMEP. The ideal ignition timing would be just past TDC but due to flame front time requirements that doesn't work with today's fuels. If Porsche could have made the 911 with a hemi head and central plug location then twin plugging may not have been necessary.

[pkabush]

Twin plugging isn't cheap but just having the heads drilled is only around $300. You could have that done while the heads are off and fill the holes with dummy plugs until you can afford the t/p ignition system.