..... I have noticed from day 1 on the engine dyno that the datalogs were showing some vacuum at W.O.T. ... eg ... on a 101kpa pass , the MAP is dropping to 94kpa ... my 421 with a very light rotating assy likes to suck air through the 227cc intake ports and the professionally ported Victor E intake manifold topped with an Accufab 4150 1200cfm throttle body ... sooo ... I finally found a 1/2" adapter plate (hood clearance issues) to try a 2200cfm 4500 Dominator Throttle Body ... both TB's are 1 3/4" tall ... due to the proximity of the hood , the extra 1/2" might cause me to forego an air filter ... I presently have the shortest K&N 14" round filter @ 2 5/16" tall and a K&N filter lid on the 4150 ... Stay Tuned ! ... I will follow up with some intel on the change .....

 

There is so much to be had, lost from spacers. Its crazy how much they can change things for better or worse. I have a Holley book that shows alot of info on them. But it always ends up being affected by other factors that only the dyno will show....but ill be curious to see what happens!

 

Less is more in this case, but how much would be acceptable kpa drop during WOT?

 

..... But this is more adapter than spacer ... I agree that it is also there as a spacer by default because its the only way I can put a 4500 TB on a 4150 manifold ... at least long enough to see if doubling (almost) the flow through the mouth of the intake manifold will eliminate some if not most of the resistance/restriction ... or maybe help me to shift the blame further downstream ... I have a 1" spacer too , but I don't want to put the TB any closer to the hood than it already is for all of the same airflow reasons ... I realize that the best course of action would be to buy a 4500 flanged intake manifold ... but I have searched and they are all much taller than the 4150 and finding dominator intakes that are set-up or can even be converted to Fuel Injectors has been near impossible ... the only one I have found is a Bill Mitchell Performance manifold but then it would need to be ported and machined for injectors .....
..... Another path that could and might still be taken , would be to have a 4150 4bbl TB converted to 2 oval throttle plates ... I know a guy .....

 

..... I really don't know ... but I do know that 94 bugs me and I want it to be less (higher #) because that column of air pushing itself into my throttle body has more horsepower to offer .....

 

So first of all, note the KPA with the engine not running. Depending on the accuracy/calibration of the sensor, it may be let’s say 96-102 at sea level or close to it. Whatever the reading is, you can expect 2-3 KPA less with the engine running at wide open throttle. If you lose more than that at high RPM then you may have a restriction. Lower RPM’s would be a little bit closer to ambient.

 

when I saw the heading I thought you were going LS

 

LOL ... Not yet ! ... but never say never ... ...

 

Not sure how air is going to like the void then finding its way through the 4 hole deal? Keep us posted