setup for more boooost please

[KEV 5 GT]

right before i start im looking for as much advice as possable / stock engine with uprated cam and fuel pump so ive been told not sure which ones....its running stock turbo with gt tuning intercooler...ive just fitted a side exit with enlarged elbow 2/12 downpipe and lc1 afr kit fitted...i think carb is stock im running 10psi im looking to raise this to 16psi on stock turbo till i get a t25 so what settings am i looking for i tested afr kit today and on tickover was reading 12.5/8 ive never used one before so id like to know safe readings also what best to do to carb ???

[GTphil]

Give the carb article a read then as a basic guide

idle wants to be 13.5 use the mixture screw to adjust this, as for the boost you will need a standard main jet and more than likely everything else apart from the second stage jet, you will more than likely need to drill this 1.25/1.3mm.

As for afr's for that boost, you want to be foot to the floor in fourth gear right upto your desired revs and it shouldn't go any higher than 12.2 afr.

[KEV 5 GT]

is it just a case of droping air correcter to a 0.9 and see how i go from there ?

[casper]

You wont need to change the a/c jet for that boost level and t2.Assuming its a 1.25.

[KEV 5 GT]

so if im running a stock carb you saying i can crank the boost up to 1.6 and wont have any trouble

[casper]

No mate standard jetting is only good up to 13psi.For the boost level you want you will have to enlarge the 2nd stage.This is a fixed bush that needs drilling.

[KEV 5 GT]

so you saying stck to stock jets but enlarge the one your on about ? where is this jet ?

[casper]

Yes.:agree:Look in the article sectionall will be revealed.:agree:

[KEV 5 GT]

so its all about the 2nd stage jet then ? where is this located and will i need to drill it out to say 1.25/130 mm and just leave the other carb bits alone keep stock ?

[Big Supes]

From the articles for you mate:

What the gurus say....


Here's Scoff (http://www.rtoc.org/members/member.asp?Memberid=10236)s carb setup and comments:

"As for an ideal setup, really, there isn't one, all carburettor setup involves compromise somewhere or other. I run a 26mm choke with a 1mm air corrector, a 1.2mm 2nd stage with the spring shimmed by 2mm(ish), an 0.6mm 1st stage, a 1.5mm main jet and a 2mm needle valve to keep the fuel level up. This is good for 28psi on my car before AFR creeps up to mid 12's (which means starting to go too lean). On an engine that doesn't have as good a VE (volumetric efficiency) as mine this setup may be good for higher boost. The reduction of the 1st stage helps hugely, not something alot of people seem to try. I also find that the standard needle valve is too small on a lot of big-powered GTTs, but I think often the AFR leaning at higher rpm's just isn't noticed by the owner until somone with wideband points it out to them! Quick blurps on the rollers don't show a thing. Foot to the floor in 5th gear on a real road sure does though!!

It must be understood that my setup may not be all that ideal on somebody else' engine. On my car at 20psi the AFR is very rich in the low 11's! A smaller main and everything else remaining would probably show an improvment across the board on a car not running as much boost as mine. I think after 1.2/1.3mm in the 2nd stage not alot happens.

Maximum power at any time is made at around 13:1 AFR, I've never really wanted to go much leaner than that. I think if I did I might find that the far-from-smooth transitions between stages might make things run overly lean at points and cause hesitation. With the AFR at 13 to 14:1 litte gaps in the fuel curve get covered up. Even the standard carb is far from perfect. How many gtt's suffer from a hesitation just before boost comes on ? A lot it seems!

Using a Wide Band Lambda sensor and making enough power for sub 13 sec 1/4's. 28psi, but It lives at 25psi now, it wants to pink at any more boost than that with the new cam.

I use the standard fuel pressure regulator. Actually, I use 2 in parrallel! I once got a bit paranoid about it leaning off as I managed to blow a h/g because of it suddenly leaning before I could re-act (screaming up B roads, trying to keep the car in a straight line and watching the laptop at the same time is rarther tricky). It really isn't required, but I suppose should one of the (20yr old) regulators die, the other will keep the car alive. Really I just havn't bothered undoing the pipework.

The 2mm needle valve does a good enough job of keeping the bowl full. Aparantly the 2mm valve doesn't work well on some cars, causing stalls during gearchanges or after hard pulls, possibly down to the accuracy of the home-drilling causing them not to seal properly, but worked fine for me. With an adjustable fuel pressure regulator I think maybe it doesn't take alot of extra pressure to force the needle open when it should be shut. A bigger needle is going to be even more sensitive to that you'd think. If the bowl overfills then you can imagine it would have exactly the symptoms of popping and spluttering.

I tried a 2.5mm needle valve this week, Oct06, in my car. Although the jet sealed with the usual pressure to the ball bearing, it didn't seal in the car, and fuel overspilled the bowl. I imagine there was too much fuel pressure for the float to contend with at 2.5mm! However, a 2.3mm worked ok. It didn't at first as the drilling was perhaps not absoloutly perfect (stubborn swarf on the inside of the hole?), so I applied some pressure and turning motion to the ball-bearing (needle part) of the valve in such away that it cut itself in, a little like cutting a valve into a valve seat. The result was a perfect sealing needle jet. I ran the pump for 10 minutes and had no over-fill. Nor do I have any unwanted symptoms during driving. Something worth trying the next time you can't get that drilled needle to seal.


Here's Ant@Backyard Racing (http://www.rtoc.org/members/member.asp?MemberID=11566)s comments:

I found some interesting results messing with my carb using an LM-1 widenband lambda meter.

I was using 140main jet, 1.0 a/c jet, 25mm venturi, 23psi boost manifold.

My car was heavily over-fueling, so I was reducing jet sizes and re-testing, anyway I started by dropping the main to 130, and to my supprise to made VERY little differance, however when I put the original 125 a/c jet in that made a huge differance, and leaned right off, and was much better off boost, i.e. not in the 10`s AFR anymore.


Here's frytol (http://www.rtoc.org/members/member.asp?MemberID=12686)s comments:

I've noticed in my engine when testing with too little boost; ~17.4psi with 140 main jet (original venturi and a/c) is that AFR was starting from eg 11.5 when at ~7.3psi and going as low as 9.5 when 17.4psi.

So the AFR was going down when revs and boost were going up.

In my opinion not using AFR and EGT sensors (on RR first before road test) when setting up your car with some 'bigger' mods is big mistake and even in Poland it's basic methodology when setting up almost any engine.

To rich is maybe not so dangerous as getting your AFR 13 or 14 but it's dangerous too. When going too rich it's possible to brake oil film and destroy your pistons and liners without propper lubrication/smearing.


Here's Supersonic (http://www.rtoc.org/members/member.asp?MemberID=2286)s comments:

Exactly what I found when I first started using a wide band lambda. I was running a 28mm venturi with 150 main, 0.9 a/c & enlarged 2nd stage enrichment, etc, etc with 20+psi. After hooking up the lambda the spec became 135 main, 1.1 a/c, etc, etc, & reading high 11 to low 12 AFRs. Leave the 1st stage enrichment alone. 2nd stage is where it all happens while on boost. Amazing results after many years of over sized main jets!


Here's Ave (http://www.rtoc.org/members/member.asp?MemberID=10038)s comments:

I have a Mike48 carb, although I always had problems with leaning out due to the float chamber emptying too fast.

As the drilled up needle valve didn't seal, I created this (http://www.rtoc.org/library/file.asp?id=31326) setup.

Now it works, it's a quite flat 12.2 A/F all the way through the rev range on full boost. But I have to admit it runs very rich on part throttle.


"14.7:1 is fine for idling and off boost but at WOT the AFR should be about 12.5:1 on our cars. Why is this?"

Lee-H (http://www.rtoc.org/members/member.asp?MemberID=11608): 12.5:1 is as lean as you'd want to go under full load/full throttle conditions. This is the mixture that should yield the most power whilst keeping det at bay.

14.7:1 is known as stoichiometric. Any less and it's considered rich, any more and it's considered lean.

The most efficient burn occurs at stoich, but when the engine is under load or full throttle then more fuel will be required to prevent the det that would occur at stoich.

Modern EFI systems try to maintain 14.7:1 under part throttle conditions using info from the map, TPS and Lamda sensors, i.e, in a closed loop. As soon as you floor it, you shift to a completely different map, efficiency kinda goes out the window and (especially on turbo'd cars) fuel is dumped in to some degree to provide a safeguard against det.

frytol (http://www.rtoc.org/members/member.asp?MemberID=12686): From theoretical (scientific) point of view to burn 1kg of fuel you must use 14,7kg of air. Then it'll be stechiometric mixture.

14.7 AFR is ok when idling (truth is that is ok up to 1.5k rpm).

The best AFR for turbocharged engines is 11.0 - 12.5, and the best AFR for N/A engines is 12.5 - 13.0.

Bigger values mean too lean mixture which explodes with bigger temperature (measured by EGT sensor) resulting in 'knocking' and in extreme cases burning your pistons, valves, head - generally destroying your engine.

Hope this helps. :agree:

[Big Supes]

Not sure if someone can point it out on here...

http://super5gtturbo.s.u.pic.centerblog.net/dwdcs5w8.jpg

[KEV 5 GT]

cool thanks mate im hoping someone will point me in the right direction i need to get back on top of things it was along time since ive tinkerd with things on a 5

[Big Supes]

No worries, I know the feeling having recently got back in a 5 GTT. I must have missed the constant tinkering. :D

[Markey Mark (BD)]

For 16psi I wouldn only take the 2nd stage to 1.1mm, any bigger and it'll be running too rich on boost

[Alex]

My carb spec is all standard bar 1.3mm second stage and a 1.00 air jet. That's running 15 psi @ the manifold on a T2/T25 turbo. The AFR's are about 12.1 @ WOT.

[KEV 5 GT]

can anyone point out where the 2nd stage jet is that needs to be drilled

[gardner51]

undo these 3 bolts on the right, remove part,

http://i667.photobucket.com/albums/vv31/gardner51/DSC_2272_zpsb01c8ea6.jpg (http://s667.photobucket.com/user/gardner51/media/DSC_2272_zpsb01c8ea6.jpg.html)

in the middle youll see the brass jet, this is the 2nd stage

http://i667.photobucket.com/albums/vv31/gardner51/DSC_22752_zps1e0140a9.jpg (http://s667.photobucket.com/user/gardner51/media/DSC_22752_zps1e0140a9.jpg.html)

[KEV 5 GT]

is it removable ? or do i have to be careful not to mess the carb up ? also how much should i drill out 1.1/1.25/1.3

[GTphil]

Start at 1.1 and up the boost slowly, if it goes above 12.2 flat out in fourth then it will need to be drilled out more.

once it's done it's done, unless its drilled and tapped for an air corrector jet so as to make it adjustable.

[LiamR]

I recognise those hands ;)

[gardner51]

i wasn't trying to pass them off as mine lol, cheers for for them though :)

[LiamR]

i wasn't trying to pass them off as mine lol, cheers for for them though :)

It's cool mate. I didn't think you were :agree: I was just being a dork.

Anyone can use any of the pics I put on here :)

[KEV 5 GT]

where can i get such fine drill bits from ? can anyone recomend

[GTphil]

micro drill bits in the search function on e-bay;)

[SCHWARTZ]

any decent decent modeling shop will do them, so that excludes modelzone.