Reversion issue with quad Ida's and 108 lsa

[Ljtigers]

Hi All,
I'm new to this site- just after opinions on something I am trying to do.
I have a rover 4.6 litre engine with approx 300 bhp - heads: int .450 lift 185 cfm- exh.450 lift 135 cfm - camtech hyd cam (ct37-517a) 274deg int & exh- 110 lsa & .471 lift with 1.6 rocker ratio. 10.5 comp with edelbrock 3.51 intake- 450 holley mech second- block hugger extractors with elec ignition. This goes really well in a small MGB-

However, I would really like to run downdraught 44mm Ida's with a mech flat tappet cam- something with similar lsa of 108 degs and a little more overlap but also more lift as webers do like that. I will be fabricating my own IR type manifold for each barrel/intake port - but as you know there is the reversion issue with such overlap and timing.

I am proposing to build this manifold with each IR 10 inches long - will this be long enough to quell the reversion problem - ie; as to absorb the reverting exhaust & fresh intake- similar to a mini plenum in a typical manifold with a plenum - or is it a waste of time based on the cam being the principle issue in that it having not enough lobe separation?

Any ideas on this would be great.

Thanks
Ljtigers

[modok]

Keep the overlap below 25 degrees at 050, i don't think there will be any problem.
If you want to run a more radical cam then it should have proper headers, and if they are proper then there won't be any problem either.
I do not know if making the intake runners longer would help, but I suspect it would not.

[modok]

yeah pretty sure it would not.
The problem which I think you are anticipating, is you can't go WOT until you get above the RPMS the reversion presents itself, because the sharp reversion pulse makes the carbs go rich or just go nuts. Keeping the throttle half closed....blocks it.
Lengthening the runner would mean it takes longer to get there but the shock would still be a shock, and it would still reach the booster.

[Ljtigers]

Thanks for your opinions- i think i'll get the exhaust little more free flowing but also opt for a greater lsa- around 113 and less overlap- just try to run a bit higher lift- not too much.

Thanks!

[Geoff2]

Ford used IDAs on their small block in the 60s, IR manifolding, & the engine produced some healthy HP #s back in those times. I have only seen pics of the engines, but from what I recall, the intake tracts were not particularly long. You might be able to find pics on the web.

From personal experience, I use cams that select the LSA using David Vizard's 128 rule. When I find someone else who has tested 10,000 cams like DV has, then I will use their rule.....
I also have a V8 street car with quad 48 IDFs, on a home made IR manifold. Intake tracts are quite short because I wanted to use an air cleaner AND also fit under the bonnet without holes in the bonnet. Does it suffer from reversion? Don't know. All I know is that performance is great. I run 106 LSA cams.

[Truckedup]

yeah pretty sure it would not.
The problem which I think you are anticipating, is you can't go WOT until you get above the RPMS the reversion presents itself, because the sharp reversion pulse makes the carbs go rich or just go nuts. Keeping the throttle half closed....blocks it.
Lengthening the runner would mean it takes longer to get there but the shock would still be a shock, and it would still reach the booster.

On bike engines reversion can be reduced a bit if the part throttle fuel mixture can be leaned out ...