Bigger TB for (modified) 1.9 8v ?!

[DamirGTI 323]

Thinking about this for some time , if it's even worth the effort/experimenting with different than standard size/bore TB's or not .. me thinks likely not but , not sure .

 

So slightly different than std. , with the base NA engine reworked from standard by head porting , reworked OE inlet manifold (as deep as it was possible to reach) and OE TB , running around 10.8/11.1 dynamic CR , and some other bits and pieces different than the std.  ... would fitting bigger bore TB (possibly different shape too) made any gain optimizing air flow and reducing turbulence inside the inlet manifold or likely just barely or none at all ?! kinda think it'll just shift around the throttle response opening/closing progressives .

 

I can see it being beneficial for turbocharged engine , but how about the NA ?

Anyone tried bigger/different TB than the standard one ?

 

I remember late mr. Guy Croft (RIP) did some flow-bench experimenting with this , can't find the links (sadly site/forum is no longer available) , but i remember that he himself hasn't found much if any gains by swapping OE TB's for bigger ones even on tuned NA engines ..

Also remember while chatting with him about this he sincerely said , he hasn't made really "in depth" testing/analysis and stated it's one of hes weak areas in engine tuning and modifying thus said to me depending on the engine specifically - maybe on this particular setup/engine, try and see what happens .

 

Some engine tuning books i read tend to advise going bigger , even adding one more TB on the opposite side of the manifold/plenum ! but that sounds to me like making some major airflow issues within the manifold/inlet tract .

 

 

D

 

EDIT: http://www.guy-croft.com/viewtopic.php?t=679

 

 

 

 

Edited August 17, 2021 by DamirGTI

[petert 549]

Good question. It’s certainly a thing to do in V8 land. Mustangs, Chev etc. Why not make an adapter for a GTi6 TB and find out?

[Thijs_Rallye 86 4 Cars]

I've had a different TB (alfa romeo) on a slightly prepped 8v engine*, no dyno results unfortunately. The car seemed to be more throttle happy but I really couldn't notice much power gains overall. I think the more throttle happy response is due to the bigger opening area vs throttle pedal input. But it messes up the delta p in the intake tract which causes the AFM to read incorrectly, since that is fixed for a certain stock VE. (and yes, the cam f*cks that up as well)

 

I am now running the exact same engine in my ex-daily, but instead of the jetronic with big TB it is now running on the motronic management with the STD throttle body and it runs fine. Maybe if I got some time to spare I can dig up the other TB and have a go with that to check what it does.

 

 

(* 3 angle seats, DFZ pistons / D6B head, catcams 4900365)

[welshpug 1,621]

have you dispensed wjth the afm?  if not there isn't much point as the afm is the restriction  (if it even is too small for the power level? )

[Thijs_Rallye 86 4 Cars]

@Mei, the AFM isn't really a restriction on these engines. They managed to do 170 bhp+ (on stock engines) back in the day with similar sized ones. They've done a lot of experimenting in the BMW (E30) scene and they've found it really doesn't limit the power in any way. Even MAF conversions have been tried with lots of trial and error, only the engine response improved but in regards of torque and power nothing was to be gained. From memory at about 75% load it is fully open anyway.

 

Also the Gr. A PTS did around 160 bph with original TB and AFM. (although PTS re-clocked the spring, but more in regards of getting the fueling right for the applied load)

[boldy205 74]

Is this not a solution? Not sure Miles is producing these still?

 

[welshpug 1,621]

2 hours ago, Thijs_Rallye said:

@Mei, the AFM isn't really a restriction on these engines. They managed to do 170 bhp+ (on stock engines) back in the day with similar sized ones. They've done a lot of experimenting in the BMW (E30) scene and they've found it really doesn't limit the power in any way. Even MAF conversions have been tried with lots of trial and error, only the engine response improved but in regards of torque and power nothing was to be gained. From memory at about 75% load it is fully open anyway.

 

Also the Gr. A PTS did around 160 bph with original TB and AFM. (although PTS re-clocked the spring, but more in regards of getting the fueling right for the applied load)

so in essence,  not really an avenue worth going down,  just go straight to itb.

 

or more valves

[Thijs_Rallye 86 4 Cars]

1 hour ago, welshpug said:

or more valves

This basically. But I also do understand where Damir is coming from, having a semi prepped 8v myself .

[DamirGTI 323]

16 hours ago, petert said:

Good question. It’s certainly a thing to do in V8 land. Mustangs, Chev etc. Why not make an adapter for a GTi6 TB and find out?

 

Yes , was in search for a GTi6 TB for some time here but found - zero ! .. will have to import .

 

I have Webber 1.9 Mi16 TB but , missing the intake pipe ... also , very hard to find here , and the oval'ish shape is weird on it's own making harder to find some similar hoses from other brands/makes as an donor piece .

 

How about a 2.9/3.0 PSA V6 TB ?! found a few of them .. but dunno how big of a bore they are .

 

D

Edited August 17, 2021 by DamirGTI

[DamirGTI 323]

5 hours ago, boldy205 said:

Is this not a solution? Not sure Miles is producing these still?

 

.. that's the least problematic , i have an handy machinist here locally who makes all kinds of stuff for me for years now :)

[DamirGTI 323]

2 hours ago, Thijs_Rallye said:

This basically. But I also do understand where Damir is coming from, having a semi prepped 8v myself .

 

Indeed ! engine conversion - not a problem , i have a few of them 16V and turbo ... traffic law/"stamp man" is the problem !!

 

ITB's - too expensive for eastern EU standards ! would need 6 months wages invested .. and then again , the same problem as above - needs paperwork/certificate/testing/inspection to make it road legal .

 

So back on simple (but harder) options ...   Thijs , which Alfa-Romeo TB was that one you've had ?

 

Looking back , reading old posts here .. few old members back in the days did some testing on AFM flow , and found it to be capable/flowing much more than it seems like it is .. thus , really not as much of restriction . A lot of big old BMW's had the same size vane AFM's and with excess of 200hp .

 

Anyhow , myself , will be going Motronic 3.1 this year for sure .. for other reasons but the intake (need digital ignition) .

 

D

Edited August 17, 2021 by DamirGTI

[welshpug 1,621]

51 minutes ago, DamirGTI said:

 

 

How about a 2.9/3.0 PSA V6 TB ?! found a few of them .. but dunno how big of a bore they are .

 

 

same (solex?)   t-b as a gti6.

[Thijs_Rallye 86 4 Cars]

9 hours ago, DamirGTI said:

Thijs , which Alfa-Romeo TB was that one you've had ?

Tbh it was a really long time ago and I don't remember. After having a look at the Dutch 205 GTi club forum it appears to be from a Alfa 164 twin spark, but don't take just my word for it . http://www.205gticlub.nl/forum/viewtopic.php?f=2&t=1025&hilit=alfa

[DamirGTI 323]

17 hours ago, welshpug said:

same (solex?)   t-b as a gti6.

 

Really ? .. cheeky Frenchman's !

 

Yeah , earlier manual/non FBW 2.9/3.0 TB's .. so yes , Solex ones mainly .

 

But seems to be a few of them .

 

From an old ZP 3.0 V6 :

 

And later ES 2.9/3.0 V6 (the Solex one) :

 

 

D

 

[DamirGTI 323]

8 hours ago, Thijs_Rallye said:

Alfa 164 twin spark, but don't take just my word for it . http://www.205gticlub.nl/forum/viewtopic.php?f=2&t=1025&hilit=alfa

 

I did and was looking at some old Alfa's TB's , seemed kinda big ... also interesting options , as Italy is near , there's usually a lot of second hand Italian car parts here .

 

Shame for this "influenza madness" , as i could've done some digging at the Italian scrapyards near the border area .. used to go there a lot in the past as it's close to my local , about 1.30/2h of driving .

 

D

[welshpug 1,621]

yeah the early es9 throttle body I mean, its the same size as the gti6, flows enough for over 200 bhp easily.

[camgti 56]

The smaller one will have better velocity speed anyway which is what you want for response and efficiencies over a wider band. An Xu10 mi16 TB is tiny and they still make great power. 
 

Spend money eleswhere. Can be a fun path to go down but unlikely there are any real gains. 

[DamirGTI 323]

Agreed , myself thinks so too .. probably won't do much difference if any at all .

 

Anyhow , V6 TB can be found for much less money than the 306-6 item , so will see if i can find some and maybe try it out then just for s*its and giggles .

 

Was thinking carbs for a while , but then no .. not really .

Shame as i really did my best with the head work (re-did it 3 times trough the years) , feeling it has more to give but the OE inlet is holding it back . Must invest in a TIG welding machine , have some weird visions of stuffing/welding shapes and correcting the insides of the manifold/runners , or making my own DIY inlet manifold .

 

D

 

 

[pug_ham 240 3 Cars]

I spoke to Miles about using one of his adapters & a GTI-6 TB on my mildly worked 8v a few years ago but we decided it wasn't worth it, they are quite a bit bigger than the standard one iirc.

 

They are probably more suited to a turbo application, unless you are running a high road spec engine, by which point you'd probably be looking at a standalone ecu & ITB's for the next development & to make the best of what you have anyway imo.

 

g.

 

[DamirGTI 323]

Indeed , no doubt it must've been good/beneficial for turbo .. for NA , no so much if at all .

Suppose the OE 205 TB is good for around 160/170 ponies pushing on NA as it is .. only the manifold is problematic , that'll need come cutting reshaping and welding to correct .

 

Curious why they went for such an big TB and "fancy" inlet (and tubular exhaust) manifold with trumpets on a 306-6 ?! , contrary to the 2.0l M16 with small TB and much disliked "active" ACAV inlet manifold (and cast/heavy exhaust manifold) .. like the 306-6 having all the "fancy add-ons" , and 2.0l Mi16 more "de-tuned tan tuned" and yet the difference between the two of them is not miles away in terms of power/torque , you'd expect the 306-6 being far off/better with all that "fancy equipment" .

 

D

Edited August 22, 2021 by DamirGTI