323i inlet upgrade options

[H23]

Hi All,

I have an 84 323i with a standard head and Hartge Grind cam - using L-Jet...it revs cleaning to 6k+... (but usually change gears just after 5K when having fun)

I am after a little more HP/torque... no expecting a huge amount... but hopefully noticeable.

I also have a complete 325i inlet manifold with the larger throttle body (right through to the filter) from a later model e30.

Is it worthwhile (and possible) to swap everything over - complete manifold swap (Plumbing and deleting Mo-tron pipes as required) ...or is it better just to mod the 323i inlet manifold for the larger throtle body and pipe/filter?

Thanks
George

[flybynite]

There are a few things you can try but the general advice for the B20 still applies, There is a lot of work you can do for not much gain. You won't do much better than BMW did. The cam on an '84 323i was actually one of the better ones around so the Hartge grind probably wont do much.

Personally I would get the B23 running well and just drive it. Warmed up on good fuel it is an eager revvy engine and quite a lot of fun.

If you want more power you just need to bite the bullet and convert it to B25 and Motronic 1.3. Throwing random bits at it could actually make it worse.

[steve_k]

as above, get it running right, & then decide if you want to upgrade to the b25.

also, you have the key ingredient to build a 2.6 stroker (the b23 crank),
there are plenty of options it all comes down to budget & skill set.

[Lemon98]

There are a few things you can try but the general advice for the B20 still applies, There is a lot of work you can do for not much gain. You won't do much better than BMW did. The cam on an '84 323i was actually one of the better ones around so the Hartge grind probably wont do much.

Personally I would get the B23 running well and just drive it. Warmed up on good fuel it is an eager revvy engine and quite a lot of fun.

If you want more power you just need to bite the bullet and convert it to B25 and Motronic 1.3. Throwing random bits at it could actually make it worse.

It's a real shame that Covid has shut down my university buildings as I was going to simulate and modify a B20 (731) head to see the performance gains. What did you mean by better than BMW did because they homologated a 320i with engine modifications (the file is available on the FIA historic website) but it doesn't say what the power figures were unfortunately. This is something that I might be able to estimate with an accurate model and calculations of airflow. https://historicdb.fia.com/

With my dissertation supervisor Hiroki Toyoda (35+ years in WRC, F1 etc) reckons with work it could rev past 8,000 quite easily as it has a far more preferable bore:stroke ration than the B25.

With the practical part of my project no longer possible I am now only simulating modifications such as bore, valve diameter, ITBs etc and will post my results when it's all done.

Obviously it wouldn't have the low-end torque and driveability of the B25 but I think there is serious untapped potential in the B20 and it's my goal to find that out!! I think it would make for an awesome high-revving fast road motor and make drives in it feel more special and engaging. An aftermarket ECU would also been needed and I am working with the LifeRacing F88 with our formula student car & my new supervisor has on in his M60 swapped E30 and has just come from working at Toyota Motorsport GmbH mapping the WRC cars.


But yeah without changing to motronic or a standalone ECU, increasing the amount of air you have entering the engine is a bit futile because you can't increase the amount of fuel to match your potential power gains. More air without more fuel won't give you anymore power. Ideally you would need a wideband lambda/AFR and someway to tune the fuelling .

Screenshot 2021-01-18 110044.jpg

[flybynite]

as it has a far more preferable bore:stroke ration than the B25.

I am really interested in this one, as I have always understood long stroke engines to be low rev/high torque and short stroke engines to be the opposite. That has been the case with all the engines I have built over the years.

I think it would make for an awesome high-revving fast road motor and make drives in it feel more special and engaging.

If you throw enough money at it you can make any engine do anything, The old M10 did quite well in Piquet's Brabham BT52

Yes there is potential to make a 'screamer' because of the flat-top design but that takes work on inlet, engine and (most importantly on the M20) the exhaust side

I stand by the advice, throwing random bits at one area may make things worse. The M20 needs a balanced approach on all areas. The cost and effort to make it worthwhile are outweighed by the ease of simply putting in a B25 and motronic if you are not looking at huge gains.

Look at what Alpina did to the M20B23, they did a lot of expensive fiddling for the C1, then turned it into a 2552 for the C2 2.5

[Lemon98]

as it has a far more preferable bore:stroke ration than the B25.

I am really interested in this one, as I have always understood long stroke engines to be low rev/high torque and short stroke engines to be the opposite. That has been the case with all the engines I have built over the years.

I think it would make for an awesome high-revving fast road motor and make drives in it feel more special and engaging.

If you throw enough money at it you can make any engine do anything, The old M10 did quite well in Piquet's Brabham BT52

Yes there is potential to make a 'screamer' because of the flat-top design but that takes work on inlet, engine and (most importantly on the M20) the exhaust side

I stand by the advice, throwing random bits at one area may make things worse. The M20 needs a balanced approach on all areas. The cost and effort to make it worthwhile are outweighed by the ease of simply putting in a B25 and motronic if you are not looking at huge gains.

Yeah the B20 is 80x66mm bore and B25 is 84x75 which gives the B20 a ratio of 1.21 and the B25 1.12 so for choosing a high performance base engine I would go with the B20 and then work the cylinder head and redesign the cam to take advantage of higher revs.

And as they both have the same block, it's possible to bore out a B20 to 84mm and have a ratio of 1.27

I do agree though, throwing random parts that haven't designed to work together and get the best from each modification is a waste of time and money. Again true with the cost of doing all the machining to a B20 I still want to do it because it gets no love hahah. I like being different from the rest and it would be cool to say I have an 8000rpm E30 (that's not an M3)

[flybynite]

also, you have the key ingredient to build a 2.6 stroker (the b23 crank),

Hi mate, Good Idea but as you probably remember I looked at this really hard and in reality no way to do it right without a custom piston. just not worth it money-wise for what you get.

I also have doubts you could use the block as those early 80mm blocks don't take well to boring out. crank would be about all you could use.

I would still like to see a 76mm B26 done properly but for the amount of money that would take I would sooner work with a bigger forged crank to make it worth while.

[Lemon98]

* I also should add that I'm looking at all of this from more of a "race car" perspective and maximising performance as I am doing motorsport engineering where £5-10million per year is spent to extract an extra few bhp in WRC so my angle and opinion on this is to get the most out of things.

I know it's the easiest and makes most sense to swap in a B25, not discounting that route at all!! I want to explore what's possible and having the software and resources to do so I find it interesting I'm seeing what's possible in a theoretical manner too.

So it comes down to whether you want driveability and more low-end torque for driveability or a wild high revving engine not for daily use lol. My preference is the latter and is just that, a preference

[Lemon98]

also, you have the key ingredient to build a 2.6 stroker (the b23 crank),

Hi mate, Good Idea but as you probably remember I looked at this really hard and in reality no way to do it right without a custom piston. just not worth it money-wise for what you get.

I also have doubts you could use the block as those early 80mm blocks don't take well to boring out. crank would be about all you could use.

I would still like to see a 76mm B26 done properly but for the amount of money that would take I would sooner work with a bigger forged crank to make it worth while.

Ooohhh this is news to me, do the B20 and B25 not share the same block???

[flybynite]

Yeah the B20 is 80x66mm bore and B25 is 84x75 which gives the B20 a ratio of 1.21 and the B25 1.12 so for choosing a high performance base engine I would go with the B20 and then work the cylinder head and redesign the cam to take advantage of higher revs.

Yep, I was talking about the OP’s B23, you were talking about the B20, those 5.8 millimetres make a difference

And as they both have the same block, it's possible to bore out a B20 to 84mm and have a ratio of 1.27

As I said above just be wary of pre325-era 80mm blocks I think there are differences in jacket thickness.

Be an interesting project, Poor old B20 needs all the love it can get

[flybynite]

Ooohhh this is news to me, do the B20 and B25 not share the same block???

Yes but all B20 blocks are not the same

Yeah the B20 is 80x66mm bore and B25 is 84x75 which gives the B20 a ratio of 1.21 and the B25 1.12 so for choosing a high performance base engine I would go with the B20 and then work the cylinder head and redesign the cam to take advantage of higher revs.

B20 is 80x71mm

I have a B20 crank kicking round for scrap if it is of any use to you

[Lemon98]

Ooohhh this is news to me, do the B20 and B25 not share the same block???

Yes but all B20 blocks are not the same

Yeah the B20 is 80x66mm bore and B25 is 84x75 which gives the B20 a ratio of 1.21 and the B25 1.12 so for choosing a high performance base engine I would go with the B20 and then work the cylinder head and redesign the cam to take advantage of higher revs.

B20 is 80x71mm

I have a B20 crank kicking round for scrap if it is of any use to you

I bought a complete late M20B20 last year for £100 (again benefits of an unloved engine lol) so I have all the spares I need thanks.

Which B20 blocks are different?

& according to the FIA and BMW the M20B20 engine has a bore of 66mm

320i bore stroke.jpg

& that's from 1983

** the link to all of these homologation papers is in my first reply **

[flybynite]

Which B20 blocks are different?

As said above, early blocks. The place that does my engine work said they have broken through on some early blocks going to 84mm. They do good work so I trust them. There are differences outside I can see from my '83 B23 and the '90 B20 block I have but have not stripped the B23 down to check with any accuracy.

& according to the FIA and BMW the M20B20 engine has a bore of 66mm320i

You are correct at 66mm, that teaches me to read the Wiki without looking it up properly But that is STROKE, they all (B20 B23) have BORE of 80mm

It is the M10 that has stroke of 71mm

[Lemon98]

Which B20 blocks are different?

As said above, early blocks. The place that does my engine work said they have broken through on some early blocks going to 84mm. They do good work so I trust them. There are differences outside I can see from my '83 B23 and the '90 B20 block I have but have not stripped the B32 down to check with any accuracy.

Well that is useful to know luckily I have a late model so should be fine when I eventually bore mine out if I manage to find a job after graduating lol