Added plenum on tunnel ram.
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Re: Added plenum on tunnel ram.
Ok thanks. Thats likley a good idea. Might be good idea to flow it before and after to?
Re: Added plenum on tunnel ram.
You'd be better off testing it by running the engine and noting the effect on car performance.
You only get so far in making a effective working intake manifold based on air flow testing.
There is a lot more to it.
But when you do add a floor filler insert that has generous radiused port entries, you will see a increase in air flow on a flow bench.. Much like the effect of a radius putty on the intake flange of a cylinder head when flow testing the intake port.
The fuel in the plenum (some wet , some vapourized) is another big (and complex) factor.
The complex interaction of adjacent cylinders, port entries, is another.
You only get so far in making a effective working intake manifold based on air flow testing.
There is a lot more to it.
But when you do add a floor filler insert that has generous radiused port entries, you will see a increase in air flow on a flow bench.. Much like the effect of a radius putty on the intake flange of a cylinder head when flow testing the intake port.
The fuel in the plenum (some wet , some vapourized) is another big (and complex) factor.
The complex interaction of adjacent cylinders, port entries, is another.
Last edited by F-BIRD'88 on Mon Mar 26, 2018 1:07 pm, edited 1 time in total.
Re: Added plenum on tunnel ram.
As far as testing, there is nothing wrong with testing an intake manifold, it's done by the hundreds. If the heads are off it's best to have it bolted on the head with the head on a flow bench, pull on the head with manifold on a correct bore size fixture and then pull just the head and see how much air flow is lost thru the intake manifold. You can also at the same time flow your other intake manifold and see how they compare. It's usually enlightening! Air flow through spaces and shapes is still somewhat a "black art" and things you would assume or think it would do don't always work out that way. Contrary to what some think an engine is basically an air pump with fuel and if your engine is experiencing anything in the intake system that is not delivering all the air/fuel it wants and needs, you've got more work and experimentation to do! It's all in the details and not always obvious.
The Older I Get, The Dumber I Get
Re: Added plenum on tunnel ram.
Will be interesting to hear as you progress on this. I have a similar idea on this stuff using the Weiand Stealth Ram EFI base manifold (SBC vortec) and a custom made carb top plenum for my 406 SBC with vortec heads.
Re: Added plenum on tunnel ram.
The ur19 has what looks like a little straighter shot to head. Not sure if that affects anything!!
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Re: Added plenum on tunnel ram.
Heres weiand.
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Re: Added plenum on tunnel ram.
That UR19 will outflow that Weiand with that fabricated plenum all day long on the flow bench, but what it might create on the engine under full load at top rpms is a different possibility.
It would also have a lot less tendency to drop fuel out of the air/fuel flow out of the carbs.
Plenum volume is obviously smaller but if your engine will pull up to your top rpm under load without too much vacuum then it's a better system.
If the engine is already in the car and you are just changing out manifold and carb setups, then data log your vacuum at full rpms and see if you really need that plenum. JMHO
It would also have a lot less tendency to drop fuel out of the air/fuel flow out of the carbs.
Plenum volume is obviously smaller but if your engine will pull up to your top rpm under load without too much vacuum then it's a better system.
If the engine is already in the car and you are just changing out manifold and carb setups, then data log your vacuum at full rpms and see if you really need that plenum. JMHO
The Older I Get, The Dumber I Get
Re: Added plenum on tunnel ram.
Newold do you think the weiand with stock top 4hole has any gains over ur19? The ur19 on 438 cubes peaked hp at 6700. So not having to push to hard. Dual 1050 carbs. Would The big box move rpm up or down as compared to stock top?
Re: Added plenum on tunnel ram.
Where it will peak has more to do most likely with your cam and heads. If the intake is causing a peak it will show up with pulling some vacuum at that rpm. If it does then you've got to make it feed more air, That if it happens is probably being caused by the runners in the lower section having to little area and a bigger box plenum won't correct that. The intake manifold as such is a complete system and how much air it will flow and where it taps out is going to be determined by whether it can supply the air the engine wants with very little vacuum at peak rpm demands. This is a simple description of a "choke".
The Older I Get, The Dumber I Get
Re: Added plenum on tunnel ram.
Ok i see. I think we are a little light on cam. The head flow would likely wanna be in that mid 7500 rpm range. This was mostly a test to see what gains from adding another 1050. 54 hp and same rpm as single, so was a good shot in backside. We started pulls at 4100 and from there had a gain of 26ftlb. Over single carb.
Re: Added plenum on tunnel ram.
On a tunnel ram you are always best off with 2 carbs over a single carb.
Even 2 750's will out perform a single 1050. Even 2 eddy 750's will out power a single 1050
on a t ram manifold.
It takes a very specialized and tall tent like plenum top to make a single 4500 carb work on a tunnel ram even close to a 2x4 set up.
If you want max power with a tunel ram you want a BIG CAM too. and wind it up.
If BigJoe1 Joe Sherman was still with us, he'd tell you just that.
Even 2 750's will out perform a single 1050. Even 2 eddy 750's will out power a single 1050
on a t ram manifold.
It takes a very specialized and tall tent like plenum top to make a single 4500 carb work on a tunnel ram even close to a 2x4 set up.
If you want max power with a tunel ram you want a BIG CAM too. and wind it up.
If BigJoe1 Joe Sherman was still with us, he'd tell you just that.
Re: Added plenum on tunnel ram.
Thanks F-Bird. Well we'll experiment with setups this season and look at cam for next. Car is heavy so any low end tq extra is big benifit!!
Re: Added plenum on tunnel ram.
Hey one more question for ya. Will a typical tunnel produce more or less manifold vac?Or no different than good high style single plane!