Quote:
Originally Posted by Beauwulf
On a DI engine, the MAF registers the total air through the intake and the ECU basically divides that amount by 6 and fuels accordingly. In a throttle body injected engine, the fuel is added to the airflow and mixed before it gets to the intake plenum area so, each cylinder gets all the air with fuel it can pack in. If one cylinder flows a bit more, the mixture is still the same.
In a bike engine, with individual carbs, each cylinder will still fuel for the amount of air it can pack into the cylinders. CV carbs are best at this because they work on vacuum in each intake so if one flows more air, it will still fuel more keeping the mixture right.
In our DI engine, (or FI motorcycle engine) if one cylinder gets more air, the ECU is still only fueling for 1/6th of the total airflow so, that cylinder could be lean. Add turbulence in the intake tract to that, which can cause incomplete burning of the mixture, and you could run way lean and hurt stuff... mostly exhaust valves. Better a safe tune than broke from buying new parts.
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I couldn't agree with you more there. I've seen too many threads on different forums talking about porting intake manifolds and that they are gasket matched. doing this is alot common on a lot of platforms, specifically in the older V8 crowd and there is merit to it when the runners are only ~1.5" long.
Another thing to consider would be to port match especially if you are not doing the heads, By port matching (not gasket matching) you allow the intake to perform as it was engineered. Remember, that engineers develop and draft out parts, then they get adjusted to allow for tolerances in the casting/machining process. By doing the porting we get it back to the engineer's original design. Gasket matching on the other hand is greatly changing the shape and not improving flow at all sometimes then you are even worse off as you now have a lip sticking in the path of airflow...
Im sure BSR has experience and I can only assume he know what he is doing and more kudos to you for even trying this out on your own
It really would of been awesome tho if you had a dyno shop around to know exactly if you gained, same, or lost any.
I am sending mine out next week to be ported so I should have some official before/after dyno numbers of what a tuned and ported IM will do to our cars.
