True Twin Conversion Observations

I tried the temporary TTC hose method this evening to finally get an idea what it was like running in parallel.

 

I have a few observations which I'd like to make and see how other people's experiences compare.

 

- Exhaust has lost its throaty off beat, 6 cylinder rhythm.

- Off boost it now sounds more like a crappy 4 cylinder engine with an exhaust that is way too big.

- It is very droney at cruising and part throttle openings. (Off boost)

- Exhaust sound on overrun is also a lot more flat, boomy and uninspiring.

- Generally exhaust volume is greater at all engine speeds when off boost than in sequential mode.

- Engine generally feels very lazy and a bit like a badly tuned low compression NA motor, (hardly suprising).

- No pull at all to speak of below 2000rpm.

- 0.25 bar of boost produced by 2800rpm in 4th.

- 0.5 bar of boost produced by 3200rpm approx in 4th.

- Max boost of up to 1.2 bar produced by approximately 4000 rpm in 4th.

- No change in top end performance as expected.

- Relatively smooth power curve now that the prespooling dip in the torque curve has been removed. However there is still a wall of torque created at 4000-4500 rpm creating that hard pull.

- It seems like the 3000-4000rpm range is now much more useable however in comparison to the amazing low down pull from 1600rpm (with seq), I'm not sure if that trade off is a worthy one. I am sure the area under the torque curve must be less in TTC than in seq setup. (Igoring some curves I have seen with a horrible boost spike causing a brief torque peak in TTC).

- Fast cornering is far far more easier and safer in TTC than in a decatted seq setup. Gradually feeding in power between 3000 and 4500rpm range is totally predictable with no risk of a 2nd turbo kick whilst putting the power on when approaching the exit of a bend.

 

Anybody care to comment on this at all. I know this has been discussed before and many people prefer TTC to Seq (especially when hybrids are used and 2nd turbo kick becomes more and more savage). Others would never sacrifice the Seq setup and some go for the switchable ETTC.

 

I'm going to leave it for a day or so and see how it goes. I can't see me keeping it though as there seems to be no straight line performance benefit at all. Anyone disagree with this? The only upside for me pesonally is the ability to corner on the throttle better.

 

Biggest loss is the lovely sound that has now been replaced with a lazy low compression slug like drone.

well said and personally must agree (i'm ETTC) but i guess to each his own ..... i appears that for town driving, and if you're used to the sequential power delivery, it can take a bit of getting used but useful lowdown torque i find is crucial in this setting.

 

a caveat to add : i don't think the 2nd turbo ever comes into much play in stop/start traffic hence the importance of lowdown 1st turbo n the associated torque.

 

speaking for myself only, i cannot see myself going the single route because i am so used to the current set-up and when coupled with my daily traffic situation, it makes even less sense.

 

the drone is another thing i cannot live with (how on earth nur spec owners can is beyond me ) - just my own 2p ...

The first so called tuner to work on my car set it to TTC without telling me. I didn't notice because as soon as I picked up the car (completely standard) I left it with them for an exhaust, full decat, boost controller, FMIC etc. When I picked it up it up I was so taken with the noise and increase in power over standard that I didn't even notice until ChrisW pointed it out. I think the fact it's a VVT-i and has more torque over my old auto TT had something to do with it too. Anyway, he put it back to sequential and what a difference, so much more responsive!

 

The only benefit I can see for TTC is better fuel consumption when driving around town and more of a grin factor when the turbos come in. There's also fun to be had setting off car alarms with the decatted Hiper...

Originally posted by dandan

Biggest loss is the lovely sound that has now been replaced with a lazy low compression slug like drone.

 

Originally posted by Nick

The only benefit I can see for TTC is better fuel consumption when driving around town and more of a grin factor when the turbos come in. There's also fun to be had setting off car alarms with the decatted Hiper...

 

I missed the kick from the second turbo the most, that always puts a smile on passengers faces, as they arent expecting it, one minute your pulling hard (by most peoples standards), and then bang, here we go again, loved it.......

 

My Hyper set of alarms even when it wasnt in ETTC.........

the parallel setup can b improved quite a bit by remapping, the ignition map especially. my new ignition map is quite different to the sequential map. i certainly wouldnt describe it as lazy. there is definately an inital period of adjustment after only ever driving in sequential, at first i didnt like it, now i wouldnt go back to sequental. i think sequential is great for stock cars, but i dont feel the need for boost around town and i have no complaints regarding responsiveness. its very easy to drive around with a bit of boost to get a nice compression ratio and full on mental is only a gearchange away

 

my exhaust note has changed, but i wouldnt agree with yr 4 banger comments, theres a BIG difference between a 1.2ltr 4 and mine .

 

i'll have a full parallel conversion soon so i'll b able to do a good comparative test, egt, boost response etc. at the end of the day u cant expect it all to b set up perfectly in parallel just by swapping two hoses or wiring a valve open.

 

all my experience is with a manual car with ceramic turbos, with steel turbos and an auto on stock stall it could b alot different

I had mine converted to TTC a couple of years ago at the same time I had the e-manage, pump and hks pressure regulator fitted. The car was put on a dyno and the fueling and timing were mapped to suit the TTC. The car made 429hp on the rollers at 1.2bar, on stock j-spec turbos/injectors/hks cams. It would be interesting to compare this dyno sheet with a car with similar mods in sequential mode. I have since had bigger injectors fitted and had it remapped so that there is less of a drop off at high rmp's.

 

I prefer the smoother power delivery of the TTC, it takes a little getting use to at first but you soon adjust your driving to suit. Wouldn't agree about the comments about the engine noise, I can assure you mine doesn't sound like a 'crappy 4 cylinder' :flame Dev

The car does feel like it needs a serious dose of ignition advance below 3000rpm.

 

I was not saying TTC is a waste of time and even with careful mapping it would be no good. However, when used in ETTC or hose type method this is not possible.

Obviously the stock ecu is mapped for the sequential system. Resetting the ecu will never change that fact, granted some small amount of ignition and fuel adjustment will take place.

 

My comments regarding the exhaust tone all relate to off boost driving, such as light cruise and over run. Off boost the exhaust does indeed make a droning sound which just conjures up images of NA motors with drain pipe exhaust on. The urgency, barble and energetic feel from the exhaust sound is now non existent in off boost conditions.

 

A full remap and dedicated manifold design would no doubt help to pull up some of the lost lower torque but you'll never replace the Seq pull below 3000rpm, it's not possible. Again it's down to personal preference, the rewards being a useable mid range power band withh TTC rather than the characteristic dip and rush of decatted seq cars.

 

To be perfectly honest I find the exhaust tone now a little embarassing, I wouldn't say it is much louder at car park speeds than before; just flatter, dronier and less sporting.

 

There will be no gains from TTC in the high rpm bands compared to seq as in both cases two turbos will be running at full operating speeds in the high rpm range.

Originally posted by dandan

To be perfectly honest I find the exhaust tone now a little embarassing, I wouldn't say it is much louder at car park speeds than before; just flatter, dronier and less sporting.

Agreed. I tried TTC last week and although I liked the power delivery I couldn't live with the crap sounding exhaust. It doesn't sound sporty or nice in any way. I had folks telling me that my exhaust had blown!

 

Also my Mrs refused to drive the car sounding like that (so it wasn't all bad )

Originally posted by dandan

A full remap and dedicated manifold design would no doubt help to pull up some of the lost lower torque but you'll never replace the Seq pull below 3000rpm, it's not possible. Again it's down to personal preference, the rewards being a useable mid range power band withh TTC rather than the characteristic dip and rush of decatted seq cars.

 

im making reasonable boost at 2krpm, but generally i dont race folk from 2krpm in 4th

 

which exhaust do u have?

what decats?

Eyefi,

 

I don't race from 2000rpm either but it's unavoidable off the line in a manual. Also the ability to just squeeze the accelerator slightly at 2000rpm and ease past any cars or just accelerate smoothly and rapidly is only due to that 1st turbo. Impossible to generate that sort of torque with an 8.5:1 NA motor through mapping alone. It makes rapid progress so easy without the need to rev over 4000. I'm not talking about all out hammering in in any of these posts really, more the off boost chaacteristics.

 

I have a CW 1st decat pipe and an HKS lower decat pipe, coupled with a Trial exhaust.

 

How much boost do you make at 2000rpm in 4th on a flat road?

 

Also that audible 1st turbo whistle has all but gone now, as had my dump valve dumping in low revs as there's nothing there to dump.

eyup dan, please dont take this the wrong way, im aware it could b but i just cant b arsed rewording it

 

Originally posted by dandan

I don't race from 2000rpm either but it's unavoidable off the line in a manual.

 

i launch with boost from the line and im hoping when the cars back together i can get a bit more

 

Originally posted by dandan

Also the ability to just squeeze the accelerator slightly at 2000rpm and ease past any cars or just accelerate smoothly and rapidly is only due to that 1st turbo.

 

yep, u definately loose a bit of low end response. my arguement is big deal, i dont drive it like that and i dont miss that. i also dont have to hit 4krpm just to pass something.

 

Originally posted by dandan

Impossible to generate that sort of torque with an 8.5:1 NA motor through mapping alone.

 

that would b true, but its not an na motor. i touch the throttle and the boost gauge responds. mine is not dead in that respect, i can b cruising off boost use the throttle and its generating boost straight away. if i want more boost i drop a cog. dont get me wrong im not saying its just the same as the sequential mode cos its not, but neither is it a dead lo CR 8.5:1 na.

 

Originally posted by dandan

I'm not talking about all out hammering in in any of these posts really, more the off boost chaacteristics.

 

so am i and the transition to on boost.

 

Originally posted by dandan

How much boost do you make at 2000rpm in 4th on a flat road?

 

nothing cruising (static accel), accelerating from - i'll dig out some logs.

I did the ETTC mod a couple of months ago, and was unsure about parallel mode at first, but after a couple of days of the stunning kick in the arse when both turbos come on line, I loved it, and was hooked. I only flicked back to sequential when I was up against something 'nippy' off the line...

 

Yes there is a lot less power below 3500 but I could easily live with it.

 

I pretty much kept it in parallel mode until Sunday night when I fitted my RSR. I have swithced back to sequential, because as stated by others, the exhaust note IS embarassing It's droney and seriously loud.

 

I'm thinking of putting my baffle in and switching back to parallel to see what that's like...

Originally posted by eyefi

accelerating from - i'll dig out some logs.

 

2600 i have 0kg/cm gauge.

3700 i have 1.2kg/cm gauge

Ah right,

 

That sounds more like it. I thought when you said reasonable boost by 2000rpm you we're gonna come back with 0.25 - 0.3bar.

 

So yours makes no boost below 2600rpm?

 

I am genuinely interested as I know you've been spending some time on a dedocated TTC setup, something I was considering.

 

Mine makes approx 0.25bar by 2800rpm, 0.5 bar by 3200rpm and 1.2 just under 4000rpm. These are not "sixth gear up hill figures", they are approx 3/4 throttle on flat road 3rd, 4th, 5th.