Big Bore Throttle 325i

[M3kuksport]

Hi, are the big bore throttle bodies worth fitting? I have a 325i Tech 1 Sport and was thinking of fitting one with a chip also.
Are they worth it? Ta Mike.

[flybynite]

https://www.e30zone.net/e30wiki/index.p ... tle_Bodies

[reggid]

nope fairly waste of time other than throttle response as its not a big restriction compared to other components

don't trust that review there is no way the throttle body gives gains at all rpm like that. it'll be a dodgey testing thing where they haven't controlled variables properly

[flybynite]

nope fairly waste of time other than throttle response as its not a big restriction compared to other components

Out of interest what else did Alpina do to make it worth while? or was it a waste of time on their engines too?

[reggid]

nope fairly waste of time other than throttle response as its not a big restriction compared to other components

Out of interest what else did Alpina do to make it worth while? or was it a waste of time on their engines too?

i'm not sure what size it is but it's not one of the key parts of the recipe

[M3kuksport]

Are preface and facelift bodies the same?

[fixedwheelnut]

nope fairly waste of time other than throttle response as its not a big restriction compared to other components

Out of interest what else did Alpina do to make it worth while? or was it a waste of time on their engines too?

Pretty sure Alpina reworked the ports on the cylinder head to make benefit of a larger throttle body.

Think of having a larger front door but leaving your hallway the same size, you won't get more people through it quicker until you make the hallway bigger as well

[flybynite]

Pretty sure Alpina reworked the ports on the cylinder head to make benefit of a larger throttle body.
Think of having a larger front door but leaving your hallway the same size, you won't get more people through it quicker until you make the hallway bigger as well

Well documented that flowing the 885 head does very little. Alpina did not do much to it either.

Very easy to mess it up and make it flow worse

i'm not sure what size it is but it's not one of the key parts of the recipe

64mm is what I measured

[steve_k]

well i know when i got hold of my stage 3 griffin motorsport head (885 cast) it came with a larger throttle body & the ports had been heavily reworked,

so there must be something it for them to do it.

[Lemon98]

Throttle body size matters when you want to reach a specific power and thus can calculate the amount of air needed to produce that power and subsequently the airspeed and flow that you need at your target RPMs.
The throttle body diameter limits your peak mass airflow so before boring it you need to know whether this is actually a limitation for your application/desired outcomes or not.

I have a 731 head from a 320i which I am using for my Motorsport Engineering dissertation and I am going to be running simulations based on airspeed and mass airflow calculations at the valve to then modify the head (and throttle body if required). I am going to be using the stock cams as I can't afford an aftermarket one but head modifications and a larger throttle body won't yield improvements unless modified to suit each other and your exhaust setup etc. It's all about volumetric efficiency basically.

If you are looking to optimise the intake setup on your engine then removing the AFM a potential redesign to a plenum-style manifold might yield better results but it is hard to tell what is the best route to go down without being able to accurately simulate the changes first.

My dissertation tutor is Hiroki Toyoda who developed the RB26, SR20, was head of Mugen, worked on the Honda F1 programme and built rally engines for Tommi Makinen so hopefully I should generate some good results!! I'm aiming for 150bhp from my B20. If I had more time and money then the B20 actually has a lot of potential for high RPMs due to it's better bore x stroke ratio than the B25.

[Lemon98]

nope fairly waste of time other than throttle response as its not a big restriction compared to other components

don't trust that review there is no way the throttle body gives gains at all rpm like that. it'll be a dodgey testing thing where they haven't controlled variables properly

Can you explain how a larger throttle body would improve response?

Air has mass and therefore inertia which is why individual throttle bodies offer better response because each throttle is smaller and thus there is a smaller volume (and therefore mass and inertia) of air which gets drawn into each runner.

If you think of the throttle being closed, there is low pressure on the engine side and high pressure on the atmospheric side. So with a larger throttle body there is a larger mass of air behind the butterfly. Getting this mass of air moving will take more time than a smaller throttle body.

From my understanding of thermodynamics the benefits of a larger throttle body are only felt when peak mass airflow is a concern ie WOT and high RPMs where response isn't the goal anyway.

Happily proved wrong, that's just my way of thinking and understanding of the movement and manipulation of air. That's how it was explained to me of why the RB26 has ITBs for the GTR and all other variants use one throttle body, by the man that designed it...

[flybynite]

I have a 731 head from a 320i which I am using for my Motorsport Engineering dissertation and I am going to be running simulations

Have you read through the '2.8 development thread' ?

[Lemon98]

I have a 731 head from a 320i which I am using for my Motorsport Engineering dissertation and I am going to be running simulations

Have you read through the '2.8 development thread' ?

Not yet, will give it a look through!! Thanks for suggesting it

Got to set up my model first over christmas and do all of the literature review etc so that will be useful for it ahaha.

It will all be finished by April/May next year and will post my report then!

[flybynite]

Sorry I meant the "M20 Development thread" A lot of it is guessing at what is now well known, but the getting there is interesting to read.

The only thing that has really changed is the ease of availability of suitable pistons.

viewtopic.php?f=54&t=170822

[reggid]

nope fairly waste of time other than throttle response as its not a big restriction compared to other components

don't trust that review there is no way the throttle body gives gains at all rpm like that. it'll be a dodgey testing thing where they haven't controlled variables properly

Can you explain how a larger throttle body would improve response?

Air has mass and therefore inertia which is why individual throttle bodies offer better response because each throttle is smaller and thus there is a smaller volume (and therefore mass and inertia) of air which gets drawn into each runner.

If you think of the throttle being closed, there is low pressure on the engine side and high pressure on the atmospheric side. So with a larger throttle body there is a larger mass of air behind the butterfly. Getting this mass of air moving will take more time than a smaller throttle body.

From my understanding of thermodynamics the benefits of a larger throttle body are only felt when peak mass airflow is a concern ie WOT and high RPMs where response isn't the goal anyway.

Happily proved wrong, that's just my way of thinking and understanding of the movement and manipulation of air. That's how it was explained to me of why the RB26 has ITBs for the GTR and all other variants use one throttle body, by the man that designed it...

for a given throttle input more flow area is exposed with the bigger butterfly so its effectively like opening the stock one a bit more. In effect with a mild throttle increase its like a bigger throttle increase with the stock throttle. works kind of like an agressive DBW input demand vs output mapping. the mass difference between the smaller single TB and larger single one is negligible in comparison with plenum and runner volumes but the area change for a given throttle position is a much more dominant thing and is what you feel.

itb work because of the smaller volume of air between the butterfly and the valve so the engine sees the additonal airflow "sooner". the closer the butterfly to the valve the more responsive. With an itb system i noticed 50mm change in position of the throttles

[reggid]

well i know when i got hold of my stage 3 griffin motorsport head (885 cast) it came with a larger throttle body & the ports had been heavily reworked,

so there must be something it for them to do it.

thats not sound logic, im sure the gains are not zero but its not anywhere near close to what is shown in that graph and the money is better spent on more effective modiifcations first and foremost

[reggid]

Throttle body size matters when you want to reach a specific power and thus can calculate the amount of air needed to produce that power and subsequently the airspeed and flow that you need at your target RPMs.
The throttle body diameter limits your peak mass airflow so before boring it you need to know whether this is actually a limitation for your application/desired outcomes or not.

I have a 731 head from a 320i which I am using for my Motorsport Engineering dissertation and I am going to be running simulations based on airspeed and mass airflow calculations at the valve to then modify the head (and throttle body if required). I am going to be using the stock cams as I can't afford an aftermarket one but head modifications and a larger throttle body won't yield improvements unless modified to suit each other and your exhaust setup etc. It's all about volumetric efficiency basically.

If you are looking to optimise the intake setup on your engine then removing the AFM a potential redesign to a plenum-style manifold might yield better results but it is hard to tell what is the best route to go down without being able to accurately simulate the changes first.

My dissertation tutor is Hiroki Toyoda who developed the RB26, SR20, was head of Mugen, worked on the Honda F1 programme and built rally engines for Tommi Makinen so hopefully I should generate some good results!! I'm aiming for 150bhp from my B20. If I had more time and money then the B20 actually has a lot of potential for high RPMs due to it's better bore x stroke ratio than the B25.

the m20 already has a plenum style manifold, its well proven that on a stock m20b25 a nice IR setup is worth +35hp.
The 731 head can be improved 40% peak airflow at an achievable lift without excessive size increases so the port velocity is really good but only if done properly. Similary the 885 about 20-25% is an upper limit.

The B20 problem is the small bore. i would develop a M20B25 with 731 head and a flat top piston if i wanted a really high rpm M20 engine
i've done probably thousands of 1D simulations on the m20.

[BristolE30]

Throttle body size matters when you want to reach a specific power and thus can calculate the amount of air needed to produce that power and subsequently the airspeed and flow that you need at your target RPMs.
The throttle body diameter limits your peak mass airflow so before boring it you need to know whether this is actually a limitation for your application/desired outcomes or not.

I have a 731 head from a 320i which I am using for my Motorsport Engineering dissertation and I am going to be running simulations based on airspeed and mass airflow calculations at the valve to then modify the head (and throttle body if required). I am going to be using the stock cams as I can't afford an aftermarket one but head modifications and a larger throttle body won't yield improvements unless modified to suit each other and your exhaust setup etc. It's all about volumetric efficiency basically.

If you are looking to optimise the intake setup on your engine then removing the AFM a potential redesign to a plenum-style manifold might yield better results but it is hard to tell what is the best route to go down without being able to accurately simulate the changes first.

My dissertation tutor is Hiroki Toyoda who developed the RB26, SR20, was head of Mugen, worked on the Honda F1 programme and built rally engines for Tommi Makinen so hopefully I should generate some good results!! I'm aiming for 150bhp from my B20. If I had more time and money then the B20 actually has a lot of potential for high RPMs due to it's better bore x stroke ratio than the B25.

the m20 already has a plenum style manifold, its well proven that on a stock m20b25 a nice IR setup is worth +35hp.
The 731 head can be improved 40% peak airflow at an achievable lift without excessive size increases so the port velocity is really good but only if done properly. Similary the 885 about 20-25% is an upper limit.

The B20 problem is the small bore. i would develop a M20B25 with 731 head and a flat top piston if i wanted a really high rpm M20 engine
i've done probably thousands of 1D simulations on the m20.

What’s a nice IR? At 35hp extra I’ll take one

[reggid]

Throttle body size matters when you want to reach a specific power and thus can calculate the amount of air needed to produce that power and subsequently the airspeed and flow that you need at your target RPMs.
The throttle body diameter limits your peak mass airflow so before boring it you need to know whether this is actually a limitation for your application/desired outcomes or not.

I have a 731 head from a 320i which I am using for my Motorsport Engineering dissertation and I am going to be running simulations based on airspeed and mass airflow calculations at the valve to then modify the head (and throttle body if required). I am going to be using the stock cams as I can't afford an aftermarket one but head modifications and a larger throttle body won't yield improvements unless modified to suit each other and your exhaust setup etc. It's all about volumetric efficiency basically.

If you are looking to optimise the intake setup on your engine then removing the AFM a potential redesign to a plenum-style manifold might yield better results but it is hard to tell what is the best route to go down without being able to accurately simulate the changes first.

My dissertation tutor is Hiroki Toyoda who developed the RB26, SR20, was head of Mugen, worked on the Honda F1 programme and built rally engines for Tommi Makinen so hopefully I should generate some good results!! I'm aiming for 150bhp from my B20. If I had more time and money then the B20 actually has a lot of potential for high RPMs due to it's better bore x stroke ratio than the B25.

the m20 already has a plenum style manifold, its well proven that on a stock m20b25 a nice IR setup is worth +35hp.
The 731 head can be improved 40% peak airflow at an achievable lift without excessive size increases so the port velocity is really good but only if done properly. Similary the 885 about 20-25% is an upper limit.

The B20 problem is the small bore. i would develop a M20B25 with 731 head and a flat top piston if i wanted a really high rpm M20 engine
i've done probably thousands of 1D simulations on the m20.

What’s a nice IR? At 35hp extra I’ll take one

individual runner intake manifold (i.e. itb style). it makes a bit more if you fit a nice airbox to. it has far superior geometry than the stock crab manifold

[BristolE30]

the m20 already has a plenum style manifold, its well proven that on a stock m20b25 a nice IR setup is worth +35hp.
The 731 head can be improved 40% peak airflow at an achievable lift without excessive size increases so the port velocity is really good but only if done properly. Similary the 885 about 20-25% is an upper limit.

The B20 problem is the small bore. i would develop a M20B25 with 731 head and a flat top piston if i wanted a really high rpm M20 engine
i've done probably thousands of 1D simulations on the m20.

What’s a nice IR? At 35hp extra I’ll take one

individual runner intake manifold (i.e. itb style). it makes a bit more if you fit a nice airbox to. it has far superior geometry than the stock crab manifold

Ah I see. Are there any on the shelf options? Or is it all custom jobbies with lots of fiddling

[reggid]

What’s a nice IR? At 35hp extra I’ll take one

individual runner intake manifold (i.e. itb style). it makes a bit more if you fit a nice airbox to. it has far superior geometry than the stock crab manifold

Ah I see. Are there any on the shelf options? Or is it all custom jobbies with lots of fiddling

https://racehead.com.au/product/bmw-m20-itb-kit-e30/

[flybynite]

the m20 already has a plenum style manifold, its well proven that on a stock m20b25 a nice IR setup is worth +35hp.

Stock M20B25? log manifold and no standalone ECU?

The 731 head can be improved 40% peak airflow at an achievable lift without excessive size increases so the port velocity is really good but only if done properly. Similary the 885 about 20-25% is an upper limit.
The B20 problem is the small bore. i would develop a M20B25 with 731 head and a flat top piston if i wanted a really high rpm M20 engine

I thought it was proven on an actual flow bench that although the 731 could be improved by a greater amount, most of that improvement only brought it up to the flow of an 885. An 885 head flowed similarly was still able to do more.

I am not saying Alpina got everything right but they did not put ITBs on the M20. They got to the point of diminishing returns then either put a bigger engine in it from something else or slapped a turbo on it. There has to be some logic to that.

I bought a whole running 75K 330i Msport with MOT for the same price as that RHD kit

The 2.7 will cost me enough to do right, I'm only going to be throwing stupid money at one M20

Out of interest, however

would you hemi the head on your flat-top 731 screamer?

[reggid]

the m20 already has a plenum style manifold, its well proven that on a stock m20b25 a nice IR setup is worth +35hp.

Stock M20B25? log manifold and no standalone ECU?

The 731 head can be improved 40% peak airflow at an achievable lift without excessive size increases so the port velocity is really good but only if done properly. Similary the 885 about 20-25% is an upper limit.
The B20 problem is the small bore. i would develop a M20B25 with 731 head and a flat top piston if i wanted a really high rpm M20 engine

I thought it was proven on an actual flow bench that although the 731 could be improved by a greater amount, most of that improvement only brought it up to the flow of an 885. An 885 head flowed similarly was still able to do more.

I am not saying Alpina got everything right but they did not put ITBs on the M20. They got to the point of diminishing returns then either put a bigger engine in it from something else or slapped a turbo on it. There has to be some logic to that.

I bought a whole running 75K 330i Msport with MOT for the same price as that RHD kit

The 2.7 will cost me enough to do right, I'm only going to be throwing stupid money at one M20

Out of interest, however

would you hemi the head on your flat-top 731 screamer?

Standalone is the proper way to do it, though have seen war chip used with a Maf

The 731 and 885 will end up flowing about the same, the 731 starts out smaller so needs more work to get there. In both cases you are limited by the casting wall thickness.

With Alpina The bbtb was about 1 of 10 performance modifications.. They had a certain goal and it met their expectations.

No the hemi head is a redundant design that’s good for top fuel engines. The semi hemi 885 or 731 head are a better combustion chamber mostly due to being smaller and being able to generate squish and good compression ratio without a huge dome. There’s a reason no one makes an actual hemi anymore.