Jenvey TBs - straight to head or manifold?

[cyberface]

Question in the title! My mutating Ka / Puma project is now gravitating to getting another Racing Puma, retaining the 1.7 engine but adding big valve Super 1600-spec head, Jenvey TBs and DTA management.

Jenvey list indy TBs for the Puma with use of short inlet manifold. Assuming I'm not on crack again, I thought the Puma 1.7 engine is the 'Sigma' engine... and Jenvey's website list a set of straight-to-head TBs 'coming soon' for the Sigma engine.

Now I'm no expert - which would I be best going for? The proposed application is a fast road engine, nicely powerful and screamy at the top end for track days, but still tractable and usable round town (presumably the full management will give this, I'm not planning on mentalist cams).

Anyone out here know the pros and cons of both?

[Mikey G]

Not sure on your particular application but in general the shorter the inlet tract the higher the power ends up the rev range with a loss of torque lower down to go with it.
Horses for courses i'm afraid.

[cyberface]

Mikey G said:

Not sure on your particular application but in general the shorter the inlet tract the higher the power ends up the rev range with a loss of torque lower down to go with it. Horses for courses i'm afraid.

Is this not tunable with horns on the inlet end of the TBs though? I was simply wondering whether there was any other benefit to straight-to-head other than the possibility of the shortest possible inlet tract.

[Mikey G]

Yes it can be tuned with trumpet length. I suppose direct to head fitment would only benefit simple fitting in a tight space, but also better control over the injectors at such a close range. On the other hand if the injector is too close to the valve it may affect the fuels ability to mix in the port/chamber unless the spray patterns are spot on.

I may be wrong though.

[chuntington101]

have you concidered bike throttle boddies?!?!?

i know there are some companies that are making custome kits tha mount the bike 'bodies to custome manifolds. i will see if i can dig out some names and links if you like!

thanks Chris.

[cyberface]

chuntington101 said:

have you concidered bike throttle boddies?!?!? i know there are some companies that are making custome kits tha mount the bike 'bodies to custome manifolds. i will see if i can dig out some names and links if you like! thanks Chris.

Are they actually cheaper in the long run? I presume TBs from a scrapped bike will be much cheaper than the Jenvey gear, but will they require much more messing to fit / map?

I'm fairly clueless about the detail, just trying to select a bunch of components that work well together and not require constant fettling, and provide a good performance / driveability / reliability compromise.

[bor]

I would suggest straight-to-head. Advantages are
1.Less exhaust gas recirc if using large overlap cams.More stable idle and better low rpm torque as less inter cylinder interference.
2.Main advantage is theoretical better throttle response.
3.Easier to tune torque curve by varying length of the trumpets.

Disadvantages are limited to finding a suitable tapping for manifold pressure and brake servo (must be between cylhead and throttle body).

Do use an airfilter preferably with an airbox to stabilize air intake.