Yes. 100mm is very touchy. Not fun during your burnout at all. I had to design a progressive system. It helped out a lot.
What size throttle bodys are the stage guys running?
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Yes. 100mm is very touchy. Not fun during your burnout at all. I had to design a progressive system. It helped out a lot.
70mm = 672 cfm
90mm = 989 cfm
105mm = 1370 cfm
All with a recommended pressure drop of 1.5" Hg.
On an engine producing 850 hp, the difference between a 70mm and a 105mm TB can be 30 hp. For you big cube guys with hp to spare, I'm sure losing out on small hp numbers like that isn't a big deal. For the small cube guys, that's enormous.
Another thing to think about. If the target of your intake manifold design is to simulate an individual runner style intake to hope to get the widest torque curve possible, then large plenum volumes are key. Now, add to your plenum a throttle body(s), along with a section of up pipe(s) that is over-sized, and what have you just done to your plenum volume? Supersized it.
90mm = 989 cfm
105mm = 1370 cfm
All with a recommended pressure drop of 1.5" Hg.
On an engine producing 850 hp, the difference between a 70mm and a 105mm TB can be 30 hp. For you big cube guys with hp to spare, I'm sure losing out on small hp numbers like that isn't a big deal. For the small cube guys, that's enormous.
Another thing to think about. If the target of your intake manifold design is to simulate an individual runner style intake to hope to get the widest torque curve possible, then large plenum volumes are key. Now, add to your plenum a throttle body(s), along with a section of up pipe(s) that is over-sized, and what have you just done to your plenum volume? Supersized it.
Dusty Bradford
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Don. Do you feel these hp gain numbers represent a turbo engine? If a given throttle body is too small I can see a gain, for example a TSO motor running 8.30's with a 70mm. I can see it gaining hp from the extra airflow of a larger 80 or 90mm just due to the 70 being very restrictive. I think Ted A wouldn't pick up anything going from a 80mm to a 105mm in a forced induction 8.40 car. The #'s quoted look more suitable for a n/a car where the gain in hp is from a less restricive intake.
Pressure drop is pressure drop. Naturally aspirated or blown. A pressure drop in a turbo engine intake requires more boost to make up for it. More boost, more heat. More heat, less density. You get the idea.
Any portion of the intake system follows the same rules as an intake port. If the port is small enough to cause a 'feet per second' flow rate that is above a certain level, you will lose out on hp. 250 to 300 feet per second is the accepted max limit.
I agree, I have thought about increasing the piping size at some point. There is quite a bit of total developed length, plus quite a few bends. I'd say the benefit would be slightly less pressure drop from the turbo to the plenum, that also will drop exhaust backpressure. Might be worth a little, but like we talked about the first thing was effectively using the power I have so now it will be on to scrutinize the other areas and improve them, hopefully able to compare that data to data we have already obtained.
I still dont see how hp matters when choosing a TB. The column of air entering an engine is the same cfm regardless if its pressurized or not at any given rpm.
Once theres a pressure drop it will effect hp. The more the drop the more lost. No where near as much loss as an NA engine though. It would just take a little more compressor speed to make up for the lost boost. Just a little more heat in the air. I dont see a 70mm TB costing more than a few hp at 850hp even if there was a little pressure drop.
You should measure pressure drop to see if it is really substantial. I bet its a lot less than many think.
That's like saying the port and valve size of a head doesn't matter on a blown engine. Just stuff it in with more pressure. I might agree with you on that one though. Look at what I'm doing with M&A heads and 1.835/1.5" valves.
Dusty Bradford
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As long as the TB is large enough for the airflow put out by the turbo there will be no gains from anything larger IMO. Same is the case with head and valve size. As long as the head and valve size is not too small for certain combo, larger will not net any gain. For instance, a 70mm TB is undersized for 1200 hp and a 105mm is oversized. An n/a motor could possibly have .5 psi drop across a TB if it's undersized and could easily pick up 30hp from the properly sized TB. An 850hp turbo motor may pick up 30 hp from a 70mm to 80mm TB if the 70mm was choking it yet never see a gain going from the 80mm to the 105mm.
I like to run slightly larger charge tubing than the TB size. 4 inch tubing with a 90mm TB in my situation.
I like to run slightly larger charge tubing than the TB size. 4 inch tubing with a 90mm TB in my situation.
BetMinesFaster
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This post got quite complex........There are obviously alot of opinions on TB size, and many good points to back them up. The combo I will be running is a production chev 4.3 block, steel crank and H beams, steel splayed caps, Je pistons (targeting 8.5:1), bowtie 18* heads, TA headers modified for a 4.3, 76GTQ turbo, a GMPP daytona dash single plain intake converted to EFI by Wilson Manifolds, a 110* elbow with a ? TB and currently undecided roller cam. Looking like BS3 managment with COP. Im not looking for 1000 horse, just make good power on a milder tune than my 109...
It's easy to have an opinion on what size tubing or throttle body is right for what, but when it comes down to nuts and bolts, it's simple everyday fluid dynamics. Gas flow through a tube.
Diameter and length must both be taken into account.
The amount of airflow that a certain hp target demands will tell you the cfm that is needed.
The required cfm must be delivered within a certain air speed window through the tubing and throttle body. As the air speed moves out of that preferred window, flow losses will result. I'm not making this up. It is simple fluid dynamics. The same principles that every engineer must follow. I can give you several turbocharger related books that hammer this subject home, if you're interested.
Diameter and length must both be taken into account.
The amount of airflow that a certain hp target demands will tell you the cfm that is needed.
The required cfm must be delivered within a certain air speed window through the tubing and throttle body. As the air speed moves out of that preferred window, flow losses will result. I'm not making this up. It is simple fluid dynamics. The same principles that every engineer must follow. I can give you several turbocharger related books that hammer this subject home, if you're interested.
BetMinesFaster
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Im interested.....Do these books have any equasions or formulas that will help nail this down? I know there are some formulas in this thread..But im curious if there are more?
Yes there is. Maximum Boost by Corky Bell. I use a software simulator so I'm not used to working through the particular formula in this particular book that pertains to the thread subject.
Everyone should already have this book. Very, very good reference.
If theres little to no pressure drop through the tb then bigger wont help. It is the speed and ci of the engine that will really matter. I wonder how much air is lost in the overlap period though? Id bet some of the really high output turbo engines have a higher manifold pressure than exhaust pressure. Those are really small valves in those heads.
You can't know whether there might be a pressure drop or not without at the very least sitting down and doing the math. Better yet would be to perform a pressure drop test, but that would mean that you've already picked a size, bought the parts, and installed the system. Once the system has been installed, chances are, you're not going to change it. Even after you perform a test that shows you that there is a pressure drop.
Do the math before spending the money to make sure you won't be sorry with your setup later.
That is where a computer simulator comes in. That can be taken into account.
The central theme of my project was to see how much power I could squeeze from these heads using the valve sizes they came from the manufacturer with. The whole idea was to see if camshaft and manifolding design could make up for the imagined shortcomings of these heads. Add to that the smaller displacement I'm using compared to most everyone else and it's turned into quite a challenge. Every aspect of the engine design has come about with the heads being the central consideration. There are actually many tricks that can be used to make a relatively small port and valve head act as if it was bigger. Air speed through the intake port was a big factor in the configuration of the engine.
If max hp had been the target, it would have been max displacement and stage II heads. But then, everyone else has done, or is doing that already.
I'm trying to show the small guy that you don't need to have the killer heads to make respectable hp. And to do that you need to pay very good attention to the efficiencies of every support system on the engine.
Dusty Bradford
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I understand what your talking about Don. I'm saying boost pressure changes everything. A 90mm TB will flow a certain amount at 5# and flow alot more at 30#. Picking a TB size by a flow rate is only part of it. You would need to know what pressure it was flowed at. Just like flowing heads. The standard is 28 inches of h2o. Put 40 inches on it and watch the flow skyrocket. The only way a turbo car will pick up 30hp from a TB swap is if the TB was originally undersized. I remember when Kenne Bell was advertising 30hp from a 70mm TB. How many people swapped from the stocker to the KB 70 and never gained anything....I know it was a bunch.
I do agree a TB must be sized properly for the set-up but Ted A has proven how far a 80mm will go. 8.40's at 30# of boost with plenty left. If his TB is smaller than his charge tubing he could possibly see a gain from a larger unit.
I do agree a TB must be sized properly for the set-up but Ted A has proven how far a 80mm will go. 8.40's at 30# of boost with plenty left. If his TB is smaller than his charge tubing he could possibly see a gain from a larger unit.
Every system of the engine must be looked at as a package. If you make a change, such as the KB example you brought up, you must look at the rest of the systems in place to determine if there might be an improvement or not.
Yes, more pressure will increase flow through a given tube size. To a point. The big question becomes, how much more pressure does it take to flow a target cfm through a tube compared to a tube that has a little bigger ID? When a certain air speed has been reached regardless of the pressure, more pressure will have to be used to increase the flow, until a max air speed has been reached where any flow increase becomes very small no matter how much pressure you use. It's called approaching max mach number. Efficiency drops rapidly in the range of .6 - .8 mach number. Maximum efficiency is in the range of .3 to .5 mach number with no tuning effects (pressure pulse tuning).
Again, flow in feet/second becomes very important. If you have to increase the pressure to move the target cfm through a given tube, you are unnecessarily heating air and reducing density.
