[Mk2] [NA] ITB's + MAP sensor - Bit of a long post, but worth a read.

[jem]

I've been playing with this idea for the MR-2 in my head for a while now.

The Rev3 3S-GE engine has a two part inlet manifold, the top half housing 'ACIS' which is basically acts as variable length intake runners. The lower half is simply four intake runners.

Taking off the top half leaves you with this:



You can see that removing the top half leaves you with a perfect flange to make a matching flange from some 8mm alloy and then have alloy tube welded into attach these from a Suzuki GSX1000R to:



The intake runners on the lower half of the manifold look to be just over 40mm, the GSXR ITB's are 42mm, so should be a perfect fit and can be mounted to the flange tubes the same as they are on the GSXR using rubber tube and jubilee clips. The velocity stacks mounted in the same way, should give me something similar to this:



Clearly I've got to consider all the vacuum pipes and gubbins that are currently connected to the standard throttle body and manifold. I have a spare throttle body I can butcher for parts. The throttle cable should be quite straight forward as I can just cut the GSXR one off and weld the MR-2 one on. The throttle position sensor might be a little more tricky to mount to the ITB's but I cant see it being a problem. I will compare the resistance of the MR-2 TPS and the GSXR one, as they could give the same signal. The idle speed control valve is mounted to the underside of the standard throttle body, but I can make a small flange to attach a pipe to it and then branch that into four so it can feed air to the engine side of the ITB's. I can plumb the brake servo in the same way.

Now here's the main one I'm not so sure about. The standard ECU uses a MAP sensor so I should be able to take a vacuum pipe off each throttle body, or even tap a take off into the intake runners, then branch them into one and into the MAP sensor.

But would the standard ecu supply the correct amount of fuel? Theory would suggest the MAP sensor tells the ecu the vacuum in the inlet manifold so it can adjust the injector duty cycle accordingly. Surely it doesn't matter how that vacuum is controlled, be it one big throttle or four smaller ones:?:

Sorry for the long post, but I'm pretty sure this will work, and yes I know if I go further with cams and head work etc I'd then be looking at a stand alone ECU. But I can get GSXR ITB's for about £120 and the other bits I would need wouldn't cost all that much at all so would be worth doing. If I had to go stand alone ECU I'd be talking big money so not so worth doing.

[Nightfire]

Good idea but how would you stop the filters getting wet from the rain etc

[jem]

Good idea but how would you stop the filters getting wet from the rain etc

I can't see that being an issue, on the NA engine cover the rear is fully covered. The K&N 57i I currently have is much more likely to get wet.

If it worked, I may fabricate a plenum for the velocity stacks to sit in and feed that with a cold air feed.

[RST]

You can't realistically do this on a stock ECU. You'd really want to go ITB's after you fitted a decent set of agressive cams and lightened the drive train a little. In fact trying to do it on a stock ECU is crazy. Otherwise running MAP should be ideal. You should be able to take MAP and brake booster off a single inlet (separate for each). I always thought you needed to common up the lines but apparently a single inlet is good enough from the guys I know who've done it.

There's a few itb'd 3SGE's kicking about but tend not to be on MR2 forums. Look to some OZ sites (used to have some direct links but not any more since changing my works laptop) and I know a well known affilliate was provided the itb's in your 3rd pic for a gen 3 build on a gen 5 celica and they were less than complimentary on the kit and it needed alot of machining. Look for kit cars in the UK for itb some stuff and Jenvey do some things which fit.

If you're going ahead, check out the distance between the butterfly and the inlet valve face as that's apparently a critical length before throttle bores and length. I can't remember the forumla now as I had a custom manifold using black top throttles but it's a generic formula and out there on tinternet.

Ditch ACIS etc!!!! the whole point of going itb is to optimise the air flow so don't bother with any compromose stuff and you need a direct inlet runner. ACIS is based on varying the inlet manifold volume -DITCH IT WITH ITB's.

Try contacting Peter Gidden of Sbits -he's done an itb'd 3SGE (good luck getting info -I gave up after a year of promises of pics) other than that I sold my itb set-up to PROTOK, gen 4 set-up but the principles are the same. I'm pretty sure he'll help you.

Good luck with it. I had my itb's and got half way there with ECU and mild upgrades but nver got round to fitting my quads so sold them on. They were fitted within days and the car was putting out stonking power from basic mods and road mapping.

Sorry for the long post, but I'm pretty sure this will work, and yes I know if I go further with cams and head work etc I'd then be looking at a stand alone ECU. But I can get GSXR ITB's for about £120 and the other bits I would need wouldn't cost all that much at all so would be worth doing. If I had to go stand alone ECU I'd be talking big money so not so worth doing.

...itb's will give good results on a 3S engine but save your £120 if you haven't dont the preparatory work and got an ECU set-up IMO, you're way short of the mark of gettng them working.

[Century Motorsport]

At a glance, the runners look far too long ... I guess it's a case of trial and error.

Map & brake line can be taken from individual ports, no need to group them as RST said.

You'll need a piggy back ECU minimum to make them work properly, but the STD ECU would read the MAP on itb's as it would the plenum setup .. the mapping would be way out though.

[Protok]

Also expect some rather horrible fuel economy at idle even with a mapped ECU.

Power though is really night and day between the old 3SGE to this and the sound when it comes on cam is even better.

I did once consider what you are doing, it is actually a great idea in theory but (always a but) it's nearly all custom work so it gets expensive in that respect.

[LimeyMk1]

FYI Triumph Triple ITBs are nigh on a perfect match for the inlet ports of a Rev1 3SGE head. You'd need to make your set of 4 out of 2 sets of 3 but it's something I'll be playing with once I've finished the V6 (whenever that happens ) as I've got a couple of sets and a spare Rev1 head floating about .

Nice thing about ITBs is you don't need an uber fancy all the bells and whistles, makes the tea, ECU. Unless of course you have something stupid tike VVTi.

[Protok]

Yea but last I checked the Triumph ITBs were rather expensive.

You can get GSXR ones for £80 if you look hard enough, hell you can have my silvertop ones for £100 if you wish. Throttle bodies aren't so expensive really, just finding a set in good condition, at the time I was looking I couldn't find any so I ended up getting some from the states.

[LimeyMk1]

Yea but last I checked the Triumph ITBs were rather expensive.

You can get GSXR ones for £80 if you look hard enough, hell you can have my silvertop ones for £100 if you wish. Throttle bodies aren't so expensive really, just finding a set in good condition, at the time I was looking I couldn't find any so I ended up getting some from the states.

I think I got my 2 sets for about £120 all in, maybe a bit less. They're pretty chunky beasts and have an angled flange which might cause an small headache but I think it'd be worth it to have a good smooth flow.

[RST]

Also expect some rather horrible fuel economy at idle even with a mapped ECU.

...I wouldn't be so sure about that. If it's done correctly then that doesn't necessarily have to be the case. For the kit car guys slapping on carbs to 3S engines then maybe so -but that's not the smart way to do it in my mind.

[jem]

Cheers guys.

I'm going to try it, if it works on the standard ECU then great, but I'm under no illusion that it will work but it's not going to cost anything to try. If it doesn't work I'll just go for something like a Link G4 ECU.

Today I took the top half off my spare engine and got the gasket that sits between the two. This is basically a template for the flange I need to get made up. The inside diameter of the four holes is identical to the intake runners, quite surprised that they are 50mm though. Does that mean that 42mm ITB's will not be big enough?

[pbmr2]

If you're going ahead, check out the distance between the butterfly and the inlet valve face as that's apparently a critical length before throttle bores and length. I can't remember the forumla now as I had a custom manifold using black top throttles but it's a generic formula and out there on tinternet.

this is THE main thing with ITBs. it is also a function of the revs you run to and this also moved the injecter location too.

go for it! but don't expect the best results without doing your homework first.

i don't think it'll run on the standard ecu, but i'd love to be proved wrong

good luck!

[jem]

i don't think it'll run on the standard ecu, but i'd love to be proved wrong

good luck!

Cheers, I will be surprised if it runs ok on the standard ECU too, but it's got to be worth a try. If it does seem to run ok I will get it on a dyno to firstly check the air/fuel ratio is ok and also to see if there are any improvements in power. I had my car on a dyno earlier this year and it's making a healthy 175bhp.

[RobPhoboS]

Just out of pure curiosity, what did you decide to do Jem ?

[jem]

Time to revist this thread now I have these:thumleft:





They are from a Pulsar GTiR, so for an SR20, but the ports match the 3S-GE head very closely. Ports 2 and 3 are very close to lining up perfectly, maybe 0.5mm shaving of here or there to port match, 1 and 4 are only about 3mm off, and there is enough metal to be able to port match them on one side, the other side will need some material added to be perfect.

as you can see the head face on the throttle bodies has loads of room to drill holes to match the head studs, so very close to a straight bolt on directly to the head.

The injectors on the 3S-GE are mounted to the head and inject directly into the port, so no need to worry about them at all.

The Toyota throttle position sensor looks like it will bolt on with a little fettling of the GTiR mounting plate, so nice and easy.

And there are plenty of vacuum connections to be able to feed the MAP sensor, brake servo and sort the idle speed control valve:thumleft:

Only problem I can see is that engine in the MR-2 is mounted with the intake side facing the rear bulk head, and tilted over by about 15º, so the throttle bodies will be sort of down behind the engine. There does look like there is enough room for some short velocity stacks with sock filters over them, but I would rather have slightly longer velocity stacks so the power doesn't end up all at the top end, so might have to look into finding/making some velocity stacks that curve upwards.

[jem]

I've just taken this picture of the intake side of the head on my spare engine. As you can see the ITB's should bolt up pretty easily:thumleft:

[RST]

I'm going to try it, if it works on the standard ECU then great

...no offence mate but if that's your aim then I think you'll be dissapointed. Nothing wrong with stock ECU but a new one should be very first thing on your list before even attempting this kind of mod. Get the ECU sorted and you can muck about all day with the 3SGE/GTE, if you want to keep the stock one then why are you trying anything more than it can handle which is pretty much an exhaust and induction kit? After a new ECU your only hold back is re-mapping it, without one you're pretty much stuck with running the map for a stock car and not bing able to make any changes whatsoever. Piggybacks are just money watsted when you need a standalone for this.

...if it were me I'd spend the monty this way on:

Lightening the drive line, lightweight wheels, lightweight flywheel and an uprated clutch to take the bite at a higher rpm all the time. Stock ECU will be fine with that though maybe a bit quirky at lower revs without the fly mass
ECU and a full conversion to MAP, this sets you up for allot of mods after
ITB's, proves everything is fine running MAP also
Cams, go as wild as you like I guess, re-map to take account of them
Further lightening and maybe looking at fuelling, at this point you'll be wanting to seriously upgrade the rev cut which is no bother on the new ecu
Improving cooling, even early on in the mods I listed mine needed a lower temp thermostat, engine bay ventillation improvements help also

...monitoring everything peoperly, can use gauges but aftermarket ECU's often come with options for diasplays for not much more than a bank of gauges so makies sence to use them for me.

...You'll have a very lumpy idle (maybe even none on a stock ECU LoL) and it'll be quirky but you'll love holding gears and still pulling past the usual 7,200 limit when you get it to work

It's addictive but I'm going to say a good ECU and good map in there is going to be the jey as there's plenty of power to free up in there. It's just going to takr the "finess" to get it out peroperly.

[pbmr2]

hahaha gtir throttle bodies.. everybody seems to use them for everything.

i half think that this will run (not perfectly) on the stock ecu but i also think the idle is going to be the hard part.

rather than adding material to the ITBs to make them fit the ports, why not make up an adaptor plate so they you don't have to port match the head or ITBs. just port match the adaptor to meet both.

you can then tune the thikness of the adaptor plate to get the perfect intake runner lengeth for the system. you need to do the maths to work out what that lengeth will be on your setup with a 7250rpm rev limit. but the overall result will be much better if you get this right. it will also make fitting the ITBs easier.

balancing the ITBs on the pulsar was hard enough, on the mr2 stock ecu i'm sure it's going to add complications with the idle.. but good luck, i hope you at least get it running even if it's not really a go-er for road use without a standalone ecu.