325i throttle body on 320i

Tue Aug 28, 2007 5:25 pm

Hi Guys,

I have a 1990 E30 320i, which has a few mods, including a cold-air induction kit, a Superchips chip, Hartge sports exhaust, FSE Boost Valve and a 3.91 LSD. Oh, and it's got full M-Tech sport suspension and a pretty useful fast road brake set-up.

Anyway, the changes to the mapping and breathing have liberated a useful hike in power and torque, but I'm now wondering about bolting on a throttle body and inlet manifold. I know it's common upgrade, but can anyone tell me how effective it's been on their cars?

I'm new to the forum, but am a hardcore E30 fan. Mine's a keeper!

Cheers,

Richard

Tue Aug 28, 2007 6:29 pm

in a bmw mag last year they did a throttle conv on a 320 with a 325, but you would have to cut some room because the throttle butterfly would foul the manifold. with the manifold as well, along with all your parts it should go like a 325

Tue Aug 28, 2007 7:02 pm

With a chip it can give up to 15bhp.

Tue Aug 28, 2007 7:05 pm

I've got a spare 325i TB + manifold, PM me if you are interested.
Not sire what a cold-air induction kit is - the 325 runs cold air anyway as long as you bypass the TB heater pipes:

http://www.cutesphere.com/data/people/g ... .php?sid=0

Tue Aug 28, 2007 7:36 pm

just fit the throttle body not the manifold, youll lose out on torque low-mid range if you fit manifold due to the air not flowing as fast thru the manifold into the cylinders. ive fitted just the throttle body, had to die-grind out lots of ally out of the manifold, better off to take it off so all the little bits dont go into the engine. only noticed a small difference, but will compliment your excisting mods well particullaly fit you cam it too.........
im thinking of chipping mine, why superchips?? isnt it just a zonechip with 230 quid added to the price?

Tue Aug 28, 2007 8:02 pm

I've got a 325i TB on the standard 320i manifold - opened-out as per Murran's post above - and a wild chip.
I don't have any power figures, but as Ed said above, people talk of up to 15bhp. It's definitly more "revvy".
Alledgedly(sp?) a 320i set-up the same as mine is gave a few standard 325i's a good run for their money around the Nurburgring!

Tue Aug 28, 2007 10:23 pm

The 325i throttle body will fit on the 320i manifold without modification, the butterfly won't catch, main reason for grinding down to match is to aid airflow, otherwise the air flow will be disturbed by hitting the manifold.

If fitting the 325i intake onto a 320i, then again, the 325i inlet is bigger than the 320i head ports, and they would ideally need to be shaped to the same as the inlet ports.

Tue Aug 28, 2007 11:21 pm

Richard ,

In the articles area of our beloved E30zone is an article written by Iain Temple. Showing you the conversion process. I have done this but not fitted the manifold to the car yet.

enjoy

http://www.e30zone.net/modules.php?name ... tbconv.htm

lee

Wed Aug 29, 2007 7:24 am

a great man once said........... cut a long story short.. if you are going to fit a 325 inlet+throttlebody, leave it attached to the 325 engine

Wed Aug 29, 2007 9:22 am

Thanks Guys!

You've given me lots to mull over there. I've had my car run on the rolling road, and it's already pushing out about 140 brake with a quite a lot more torque in the mid-range. I had thought about sawpping the manifold for a 325i item, but it seems it may be better to just adapt my exisitng 320i one. I guess some of the piping from the airflow meter would have to change too.

I've seen the article posted on this site that covers the upgrade. I've also seen a link to the 'Big Bore' throttle bodies you can get. They might be going a bit too far...

Murran asked: why a Superchips chip? I was fittng the FSE Boost Valve at the same time, and got a good deal on rolling road set-up. The chip and rolling road session came in at around Ã‚£200.

Ah, the joys of thinking about more power...

Wed Aug 29, 2007 4:21 pm

e30bmlover wrote:a great man once said........... cut a long story short.. if you are going to fit a 325 inlet+throttlebody, leave it attached to the 325 engine

What was his name?

Wed Aug 29, 2007 4:41 pm

Mosley's Garage in Llandeilo, South Wales -- owned by Vince Mosley. He's done a lot of work on my cars over the years, including a previous 325i Sport that I used to own.

I'll have to check the bill, but I got a good price on the Superchips chip.

Wed Aug 29, 2007 6:47 pm

yes that artical sounds about what sort of thing i did, sure i remember bodging more things than that! plus i found it nessasary to remove a bit of metal from the outside of the manifold cus the throttle switch didnt have clearance or sumurt.
oh and dont bother connecting up the two coolant pipes just link them together with sumurt. why go to all the trouble of your fancy cold air feed system then heat your inlet tract up??????

Thu Aug 30, 2007 9:58 am

Cheers, Murran. I'll try to pick up a TB and have a fiddle. Things is, the car runs pretty well now, so I'm kind of reluctant to tinkle. But, I can't help feeling that power is being sapped by the current restrictive TB... We'll see.

Thu Aug 30, 2007 11:37 am

I've done this conversion. The manifold stays on but you need to shove a few oily rags into the ports to stop swarf going in. If I was doing it again I would use the 325i manifold. Reshaping the six inlet ports to match the manifold is very quick and easy - just 30-40 minutes to do all six using a 325i inlet gasket. Grinding out the 320i manifold takes forever because the flange is so thick and to be honest it's not very satisfactory as you still have a huge step at the bottom. You can round it off, but it's not very good really. You will need to swap the 320i injector rail over to the 325i manifold.
Doing this without a rechipped ECU is a waste of time but once done it goes very well. On the start finish straight at the Ring a 325i Sport took longer than it should have to get past - and I was running a 3.64 diff. With the correct 4.1 it would have been better. I reckon 15 bhp for the manifold, TB and chip is about right.

Thu Aug 30, 2007 12:12 pm

Thanks, Andyboy. How much do you reckon the inlet ports need to be opened up by? I'd be kinda scared to get swarf into the head.

When you say: 'You will need to swap the 320i injector rail over to the 325i manifold.' Do you mean I'll need a 325i injector rail as well, or just fit my exiting one onto the 325i manifold?

My car is chipped, and the head, cams and all valvegear were replaced at great cost about 15,000 miles ago. So I'm looking to optimise what I've got instead of switching to an old 325i motor.

Thu Aug 30, 2007 3:17 pm

The 320i and 325i inlet ports are pretty much he same size, but the 325i ports are D shaped so it's a case of grinding two corners into the top of each port - literally 5 minutes per port. You need the injector rail and injectors from the 320i fitting to the 325i manifold - that's a pig of a job.

Fri Aug 31, 2007 5:55 pm

The top head is the 325 bottom is 323/320.

Mon Sep 03, 2007 11:56 am

Thanks for those pics. Can the grinding work be done with the head in situ?

And just to be clear, will my 320i injectors fit the 325i rail and manifold?

Mon Sep 03, 2007 3:22 pm

OK people: you lot have convinced me. I'm going to change the TB, manifold and the injectors.

Now, I need answers on this... Will I need to readjust the FSE boost valve to supply more fuel the bigger 325i injectors?

Mon Sep 03, 2007 5:58 pm

The injectors need 3 bar
Or is only 2.5 bar on the 2L ?

Mon Sep 03, 2007 6:29 pm

Standard 2ltr runs 2.5bar FPR.
I've never touched mine, it's been no problem in 20+k miles. OK, so I've never had the car on rollers and it could be fueling wrong at high revs, but now I'm running on LPG it's not an issue (if it ever was).

Mon Sep 03, 2007 9:45 pm

Have you measured the size of the throttle bodies and worked out the area increase?

There's no way a 320 will run like a 325 with just a chip and throttle body size increase.

Mon Sep 03, 2007 10:06 pm

tomstickland wrote:There's no way a 320 will run like a 325 with just a chip and throttle body size increase.

No-one's saying it will run like a 325i. It's just a worthwhile mod for people who can't (for whatever reason) or don't want to swap their 320i engine for a 325i one.
An extra 15bhp for less than Ã‚£100 and no hard work involved - can't be all that bad, can it?
The extra power will put the 320i into 323i performance territory - ie not that far behind the 325i.....

On the start finish straight at the Ring a 325i Sport took longer than it should have to get past

Tue Sep 04, 2007 7:31 am

The extra power will put the 320i into 323i performance territory - ie not that far behind the 325i.....

and a 323 in to 325i performance territory

Tue Sep 04, 2007 8:19 am

TBH, I'd be very suspicious that a throttle body alone will add 15BHP. In fact, I'd bet on it if someone went to a decent rolling road for a before and after. It will help though.

Tue Sep 04, 2007 8:29 am

I guess I'm going to find out. I may put the car on rollers after I've completed all the work. I know for a fact that my car is pushing out 140 bhp as it is. I'll certainly keep you posted.

In any event, I reckon it'l probably bost torque more than outright power, which is no bad thing.

Any ideas for plugging the inlet ports before grinding?

Tue Sep 04, 2007 11:16 am

I looked at doing this but the throttle from a 25 is obviously a lot big than a 320 one which is the point, but...
the hole in the inlet manifold is the same size as the old body so i didnt see the point in doing it without changing the inlet because your still restricing the air that flows into the engine.
So really its the same difference.
And will just thr rottle body make a differnce on its own, I have a few of them in the garage and if it does ill fit one to the 320 touring but otherwise ill stick them up for sale.

Tue Sep 04, 2007 12:16 pm

tomstickland wrote:TBH, I'd be very suspicious that a throttle body alone will add 15BHP. In fact, I'd bet on it if someone went to a decent rolling road for a before and after. It will help though.

Nobody said it would - it would need an ECU remap to get the fuelling up. As it is a 320i runs mega lean as all plastic bumper E30's are catalyst prepped. Just a rechip will make a pretty noticeable difference and as with every engine ever made, more fuel and more air equals more power.
A 320i is still a 2 litre engine with pretty big valves and ports. After a bigger throttle body it would need more valve lift and duration but that's Ã‚£Ã‚£Ã‚£Ã‚£ and not worthwhile. Even so it'd be interesting to see what a stock 2 litre with a hairy cam and throttle bodies would do. Probably 170-180 bhp.

Tue Sep 04, 2007 1:04 pm

You're right Andyboy. And a 320i with 170+bhp would have presented the BMW marketing men with quite a challenge in flogging the 325i. I've always felt the 320i was 'strangled' for this reason to avoid a bad case of sibling rivalry.

Personally, I prefer the sweeter nature of this so-called 'lesser' M20 to the 325i...

Tue Sep 04, 2007 1:35 pm

Virtually all BMW engines are strangled and it's mainly to keep cars in a certain insurance bracket. That's why an M30 2.5 engine gives 150 bhp and not the 170+ it's actually capable of.

Tue Sep 04, 2007 1:44 pm

oes this mean that for instance, the Zone Shop Big Bore TB's are not a straight replacement?

They list an 318iS Big Bore, is that just a straight bolt-on?

Tue Sep 04, 2007 10:11 pm

So just the TB and a chip should do the job?

Wed Sep 05, 2007 10:48 pm

Do you think that the Zone would loan me a big bore throttle body? I'm happy to spend Ã‚£50 on a rolling session for a before and after.

Thu Sep 13, 2007 12:04 pm

Right, here's an update of progress on my car. I've fitted the TB, manifold, and injectors from a 325i onto my slightly modded (and chipped) 320i. I've opened up the inlet ports, and had the car on the rolling road. And the results are disappointing...

Power is the same as before at 110bhp at the wheels. Only now, it arrives at 6,250 instead of 6,000. Power and torque are both down at every other point in the rev range.

Oh dear! Apparently the car isn't overfuelling with the bigger injectors, but I'm just wondering if i should switch back to the smaller 320i items... Anyone got any ideas?