cjperformance wrote: ↑Wed Nov 15, 2017 8:33 pm
ptuomov wrote: ↑Wed Nov 15, 2017 7:43 pm
cjperformance wrote: ↑Wed Nov 15, 2017 7:22 pm
[b
]MPEFI on IR t-bodies[/b] would probably be your single biggest helping hand if he will go for it..
Bigger heads and wider lsa are going to help but even with a great carb and some vac advance etc running at 2Krpm and expecting a smooth ride is in reality asking a lot from a 650+ hp 427ci NA carb engine.
I think it’s the combination of large camshaft overlap, low rpms, and part throttle that is problematic for a plenum intake manifold, whether it’s carbureted or fuel injected. Individual throttle bodies, or even independent runner carbs, that have a very small volume between the intake valve and the throttle blade seem to drive very well at cruise rpm and at part throttle even with significant camshaft overlap. That’s what I believe, who knows if it’s true.
Exactly why i say mpefi on ir.
With enough cam and head to make 650hp that is not going to be a gem at 2000 in OD with any shared plenum intake, single OR dual plane, with an unlocked auto in OD yes but manual no.
The way I've rationalized this is that with high overlap cams, the cycle is unstable.
If the cylinder doesn't fill much, then there's small exhaust pulse and small suction, which leads to worse intake filling, which leads to even smaller exhaust pulse and even smaller suction, which in turn leads to even worse intake filling, etc. On the other hand, if the cylinder fills a lot, then there's a big blowdown pulse and big suction wave, which fills the cylinder better, which creates an even bigger blowdown pulse and suction wave, etc.
With a plenum manifold that has a large volume of air between the intake valve and the throttle, there's nothing keeping this unstable process in check. At part throttle and low rpms, the engine randomly surges or bogs down.
However, if we have an individual throttle (carb or EFI) very close to the intake valve, there's very small volume of air for the overlap period to draw from. This keeps the process stable and in check. The engine doesn't randomly surge and then bog down at part throttle and low rpms.