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ITB's on K20's seem low ?

thesmileyone

thesmileyone

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27
On most cars a set of jenvey ITB's will add around 10hp (at the flywheel) per ITB, ie 40hp for a 4 cylinder, 60hp for a 6 cylinder etc.

But with K20's people are lucky to see 10-20hp, why is this ?

It seems awfully low especially some of the dynos i have seen in a search where with cams and ITB people only get 210hp ?
 
I think you've got to think about what the ITBs do, get fuel and air into the cylinders individually.

Now of these other cars that you have mentioned, that get a 10bhp per cylinder gain, are they kicking out 100bhp/litre from the factory NA? Probably not.

I would imagine that the inlet mani and throttle body on the K20s are not as restrictive as some other engines when it comes out of the factory.

I wouldn't get too hung up on dyno figures of 210bhp either, as different dynos will give different figures. Before and after figures are more important. Have the cars you've seen with ITBs and cams got before and after dynos, or are you just assuming they have gained 10bhp because the output figure is now 210bhp? A car with ITBs, cams and a decent exhaust and manifold combination and a remap I wouldn't be surprised to be giving 210bhp at the wheels, which is vastly different from at the flywheel.

A K20a2 comes out of the factory with around 197bhp at the flywheel, which would probably be around 155-165ish at the wheels.
 
ITBs aren't about headline figures.
There will be alot more torque across the range, therefore more real world performance :twisted:
 
I know of a guy that had a TODA Racing stroker kit in his K20, it was making good power, upwards of 290HP.

He got tired of the fuel consumption and jerky nature of his Jenvy ITB's and eventually swapped back to an RBC intake manifold. He lost about 10HP peak but picked up alot of low to mid torque, more usuable power in this instance.

Those particular ITB's were sized to make good peak power, but you can have them made any way you like, if they make more mid range, thats because they were sized to make good mid range, it's not that the nature of ITB's in general make more power in a certain area over another.

Check out Kinsler Fuel injection, they make some really good stuff ;)
 
It may also be due to cylinder head design, the K20 has a pretty keen head so ITB's wont actually yeild that much more compared to a different/******* engine.
 
k20 head flows ~270cfm @ .50"
RBC flows 290cfm

so unless you are running 'stage 4' cams, +1mm valves and a race port - a plenum manifold is more cost effective.
 
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