I was wondering if there could be any power loss from going from a large MAF, say 80mm, and tb of the same size, to: the same MAF, but using a 70mm tb. I was talking to someone and he made the comment that it is important to keep air speed velocity up going from the filter to the tb.

Also, is it possible for one runner, on an EFI engine, to steal fuel and air from another just from the vaccum created by the first runner by the valve opening? Is this a big concern, especially on a long runner intake(e.i. TPI, LSx, 5.0)? Also, do intake pressure waves travel from one runner to another if they are exactly across from another in the plenum?

thanks
Jeremy

 

Your airflow is only as good as your smallest area downstream. So upping the MAF size and downsizing the TB doesn't seem like a logical approach does it?

On the second part of this question....
Yeah, the pressure wave interaction in the plenum can cause distribution problems in a carb setup. Don't doubt there's some reverse flow in an EFI setup but I don't think it's near as pronounced... just judging by EGT's I've seen from port EFI engines.

The plenum area kind of acts like a buffer to pressure waves but there's still some cross-talk. Kinda like having a bucket of water and throwing a pebble in it. The waves lose energy as they travel but they still interact with other waves and they eventually make it to the perimeter. At least that's my take on it.

-Mindgame

 

The idea on the MAF and TB size was to taper the intake track to get as much airflow in while keeping air speed up. I guess the same idea that is used in the LSx intake for the runner designs. I just never thought that air speed to the TB to be an important thing when choosing a CAI or designing one.

 

I think of the plenum as a storeroom for the air from which all the cylinders draw in order. You need to keep the plenum full to keep from starving individual cylinders, so restricting the flow with a smaller TB seems counterproductive, as Mindgame said. That's probably why ported LS1 TB's show small increases in power. LS2 has a much larger (90mm) TB than the LS1/4 (75mm). I double many 90s will need porting until hp gets REALLY high.

My take is that taper belongs in the individual intake ports, not "upstream" in the plenum or plumbing leading to it. This runner taper is on the order of 1 degree or so.

The tuning exists in the individual runners. If there is "cross-talk" it may be that air or mixture is rushing toward the only open hallway, say cylinder #5 during it's intake stroke. Part way thru that stroke the inlet valve of #7 starts to open and maybe some of the air gets diverted. OTOH, since the flow in the plenum is already heading that way, maybe it helps fill #7.

Perhaps on a 4-7 swap, especially on a single plane carbed engine, the mixture is heading toward the rear of the plenum for #8 when #7, also at the rear asks for mixture. Air has significant mass, so it doesn't start and stop moving or turning as quickly as the cylinders are demanding it at high rpm.

Just my thoughts.

 

If you have a 1000 or 1300CFM TB you need the air intake in front of it to flow what your TB flows,or you will be defeating your purpose.That includes air cleaner.Look at a K&N CIA and you will see what it takes to get the flow.It will flow in excess of 1300CFM with the right filter.The 7" filter flows about 750CFM so you have to go to a larger filter to get 1300. The tubing is OK to 1300CFM

 

On a somewhat related note...

Anyone have approxamate CFM figures for a single bore 90mm TB, like the lsx/ford style accufab ones? I havent ever seen published figures, but guessing in the 1250cfm range?

 

Well since no reply, did some researching.

ACCUFAB 90MM RACE
TESTED @ 3" - 449 CFM
CORR @ 20" - 1158 CFM
CORR @ 25" - 1297 CFM
CORR @ 28" - 1369 CFM

 

That's pretty stout.

28" H2O is ~1psi and considering that most engines make best power at between .8-1.2 psi, that Accufab could go over 1400cfm. That's enough to support just about any small block.

-Mindgame

 

Yes i was very suprised to find out they flowed that well. Cant wait to get mine on and running. ETA, next week I still need to get the filter end of my CAI worked out, ive got the super small Moroso filter (its about 6 inches long, yuck). Thinking of trying to run 2 filters, or cutting out some of the plastic and getting one of the jumbo generic truck KN filters and making it work.

http://home.cinci.rr.com/atljar/New%...r/PICT0104.JPG