Bore Intake Manifold? Pros and Cons?

[Route]

Anybody here bore their air intake manifold before? What are the pros and cons?

[Qr25vet]

have...i've done that to make the 60mm TB fit....stock for my car is 45mm...pros is good response,pickup and acceleration....cons is that idling will have issues(unstable) and might stall if too big... need to retune ECU also cos more air going in dosent mean that the ECU will auto supply more fuel to compensate....learnt it the hard way

[Route]

thanks :) so am i right to say that if i bore the air intake manifold and tune my ecu together to correct the air/fuel mixture, i'l be fine? :)

[Qr25vet]

yes thats correct...but u only bore intake manifold when u change to bigger throttle body or bore bigger throttle body...remember that when u bore the throttle body bigger make sure that the butterfly plate is changed if not it'll just make things worse...

[Route]

care to explain why not changing the butterfly plate will make things worse?

[Gcc_29]

yes thats correct...but u only bore intake manifold when u change to bigger throttle body or bore bigger throttle body...remember that when u bore the throttle body bigger make sure that the butterfly plate is changed if not it'll just make things worse...

 

 

Bro sorry do u noe where to bore the intake manifold?

 

[BMW320i]

care to explain why not changing the butterfly plate will make things worse?

 

Because its like widening a hole and not have a big enough cork to seal it.

 

Worst explanation ever I know. QR will have a better explanation.

 

Widening TB is ok but I prefer to buy a bigger aftermarket TB to begin with. Boring Intake manifold without widening TB is a bit of a bottleneck situation.

 

Like what has been mentioned before, ECU tuning is required because ECU does not automatically compensation for air flow and you may run lean otherwise.

[Chickensoup]

Bro sorry do u noe where to bore the intake manifold?

Forget it...if so good manufacturer already done it. They have calculated the diameter for optimise air flow , just like those variable length intake system. You are now eating with normal size spoon, if you change to bigger spoon can you eat more or faster? No right.

 

Your cylinder head inlet diameter still same, the inlet valve size still same....

[Qr25vet]

Because its like widening a hole and not have a big enough cork to seal it.

 

Worst explanation ever I know. QR will have a better explanation.

 

Widening TB is ok but I prefer to buy a bigger aftermarket TB to begin with. Boring Intake manifold without widening TB is a bit of a bottleneck situation.

 

Like what has been mentioned before, ECU tuning is required because ECU does not automatically compensation for air flow and you may run lean otherwise.

yes thats correct...and the velocity of the airflow will be disrupted as well..meaning that there'll be alot of turbulence which will make you lose power....and you're right...getting a bigger TB is better than boring out the stock one...

[Qr25vet]

Bro sorry do u noe where to bore the intake manifold?

just remove your throttle body from the intake manifold...u'll see that big hole which the TB is supposed to sit...thats where you bore it...not sure if its possible to bore an intake manifold thats amde of plastic though...

[Qr25vet]

Forget it...if so good manufacturer already done it. They have calculated the diameter for optimise air flow , just like those variable length intake system. You are now eating with normal size spoon, if you change to bigger spoon can you eat more or faster? No right.

 

Your cylinder head inlet diameter still same, the inlet valve size still same....

not really...if not why many aftermarket tuners change to bigger or individual TBs but using back the same sized valves? or why does BMW //M engines come with individual throttles instead of one throttle body? when a manufacturer designs an engine they have to take MANY factors into considerations not just performance...but mainly noise and emissions... enlarged TB helps but only to a certain extent...and with drawbacks like poor idling and increased FC (if u tuned it properly...getting better fuel economy from a bigger TB is a BIG sign that you're running lean!!) of course there are better ways to increase volumetric efficiency of engines without F.I....this one is just the best bang for the buck IMHO

Edited January 19, 2009 by Qr25vet

[BMW320i]

Forget it...if so good manufacturer already done it. They have calculated the diameter for optimise air flow , just like those variable length intake system. You are now eating with normal size spoon, if you change to bigger spoon can you eat more or faster? No right.

 

Your cylinder head inlet diameter still same, the inlet valve size still same....

 

Your analogy is flawed.

 

Just because the valve size is stock does not mean increase in air flow cannot be obtained.

 

By changing the camshaft with lobes that enable longer duration and higher lift, the valves are opened for a longer duration and at a higher lift.

 

Both duration and lift allows more air flow per revolutions.

 

Manufacturers have and always will tune factory cars conservatively. This is to ensure the longevity of the engine, drivetrain and other movable parts so that warranty cost does not spiral out of control.

[Chickensoup]

Your parameters for discussion have been changed. Just by opening the throttle body does nothing good unless you are very sure that the speed of airflow is too fast with a very small diameter intake. If increase just inlet manifold size, you drop air speed and less turbence. We assumed that the camshafts are still stock in this discussion.

 

What you had thrown in the reply is high lift cams, valve lap angle and duration increase. I dont suppose you are going to say bore up and stroke up also right.

 

 

[Chickensoup]

Hi Qr25vet,

 

You have also changed the parameter to the discussion. As manufacturers or engine designers, they take the whole picture into consideration. Like you mention, BMW introduce Vanos and Valvetronic as the whole system change.

 

Now over here, someone is asking if just by boring the inlet better does it help? All other components remains stock. The simple answer is No.

Edited January 21, 2009 by Chickensoup

[BMW320i]

Your parameters for discussion have been changed. Just by opening the throttle body does nothing good unless you are very sure that the speed of airflow is too fast with a very small diameter intake. If increase just inlet manifold size, you drop air speed and less turbence. We assumed that the camshafts are still stock in this discussion.

 

What you had thrown in the reply is high lift cams, valve lap angle and duration increase. I dont suppose you are going to say bore up and stroke up also right.

 

There can be no one particular modifications related to air flow without changing 1 variable. A combination of compensation to eliminating air flow restrictions has to be carried out.

 

Hence explain why I brought camshaft into the picture because I am under the impression that you felt that because valve size is factory, all other components that propagate air flow is redundant.

 

I don't think you get understand factory engine set ups.

 

Factory engine set ups are never tuned for maximum volumetric efficiency. The closest ever I have come across are cars like E46 M3 CSL which runs 280 deg camshaft and Honda S2000 F20C.

 

The M3 and the S2000 are both running very high volumetric efficiency because it all becomes very obvious that after all that CAI, pod filters, 3" exhaust, advancing ignition timing till its no longer feasible, you soon come to realise the horsepower gain is minimum.

 

More drastic modifications are needed to squeeze horsepower out of them but I won't mention what and how we are able to do so for the purpose of staying on track.

 

Back on the topic of volumetric efficiency, most factory cars are mainly restricted by air flow and hence are not running optimum efficiency. This gap can be narrowed if less restriction is imposed on air flow.

 

When you remove air restrictions, you are enabling the engine(NA) to take in as much air as it wishes to.

 

In addition you need to look at various engine load relative to rpm. Just because you are running at 30% engine load with little air restrictions, it does not mean that there will be just as little restrictions at 100% engine load.

 

At higher piston speed or rpm, the amount of air flow demanded is increased. Simply changing to pod filter does not help much because at higher engine load, intake pipe diameter becomes too small to allow air flow. Restrictions are further imposed at the throttlebody size as well as intake manifold.

 

If you want to fully maximise volumetric efficiency, go ITBs.

 

As to whether boring the intake manifold would help ? The answer is no. You need to do a whole lot other things. Its just like asking whether chucking a T04Z would increase horsepower ? The answer is no as well. Without some form of ECU tuning, changes made to air flow instruments, fuel supply, there can be no horsepower gained.

 

Simply boring the intake manifold alone without looking into other aspect of is simply being tunnel visioned.

[Freifeit]

There can be no one particular modifications related to air flow without changing 1 variable. A combination of compensation to eliminating air flow restrictions has to be carried out.

 

Hence explain why I brought camshaft into the picture because I am under the impression that you felt that because valve size is factory, all other components that propagate air flow is redundant.

 

I don't think you get understand factory engine set ups.

 

Factory engine set ups are never tuned for maximum volumetric efficiency. The closest ever I have come across are cars like E46 M3 CSL which runs 280 deg camshaft and Honda S2000 F20C.

 

The M3 and the S2000 are both running very high volumetric efficiency because it all becomes very obvious that after all that CAI, pod filters, 3" exhaust, advancing ignition timing till its no longer feasible, you soon come to realise the horsepower gain is minimum.

 

More drastic modifications are needed to squeeze horsepower out of them but I won't mention what and how we are able to do so for the purpose of staying on track.

 

Back on the topic of volumetric efficiency, most factory cars are mainly restricted by air flow and hence are not running optimum efficiency. This gap can be narrowed if less restriction is imposed on air flow.

 

When you remove air restrictions, you are enabling the engine(NA) to take in as much air as it wishes to.

 

In addition you need to look at various engine load relative to rpm. Just because you are running at 30% engine load with little air restrictions, it does not mean that there will be just as little restrictions at 100% engine load.

 

At higher piston speed or rpm, the amount of air flow demanded is increased. Simply changing to pod filter does not help much because at higher engine load, intake pipe diameter becomes too small to allow air flow. Restrictions are further imposed at the throttlebody size as well as intake manifold.

 

If you want to fully maximise volumetric efficiency, go ITBs.

 

As to whether boring the intake manifold would help ? The answer is no. You need to do a whole lot other things. Its just like asking whether chucking a T04Z would increase horsepower ? The answer is no as well. Without some form of ECU tuning, changes made to air flow instruments, fuel supply, there can be no horsepower gained.

 

Simply boring the intake manifold alone without looking into other aspect of is simply being tunnel visioned.

Bro, mind to share what is ITB?

 

[Iliketodrive]

this is itb

Edited January 21, 2009 by Iliketodrive

[Qr25vet]

i didnt mention valvetronic...i said volumentric efficiency.....boring the inlet ALONE without changing to a bigger throttle body or vice versa isnt gonna do any help in fact make things worse...but if both are done and givent he correct fueling...there will be an increase in power cos u're making the engine breathe in easier thus increasing its volumetric efficiency....valvetronic is a different thing althogether...its variable valve lift and cam phasing combined...so dont mix it up...