single throttle for 500hp plus ?

[spitfire4v8]

I'm trying to find a large single throttle body relatively cheaply (it's only for development purposes) which is capable of flowing enough air for over 500hp normally aspirated (the engine will be 500hp near enough but i want the throttle sized so it is definitely not a restriction) .. can anyone think of a large std throttle (preferably plentiful ie easy to get hold of, and cheap) that fits the bill?
many thanks.

[stevieturbo]

I could sell you a standard LS1, 75mm TB.

I wouldnt gaurantee it wont be a restriction at 500bhp though, although it certainly wouldnt be a big restriction.

Ideally n/a you might be looking to 80-90mm

But all such things cost.

pm me if interested.

[spitfire4v8]

Hi. 75mm isnt big enough .. that's only just enough for 320hp in my experience .. I think i'm looking for 100mm or so? Ive never run a single throttle for anything like 500hp so have no idea really how big it needs to be for no restriction. As its only a prototyping excercise at the moment i might make something that fits with 100mm tube and wire erode myself a butterfly. I only need it to prove something on the dyno.

[stevieturbo]

spitfire4v8 said:

Hi. 75mm isnt big enough .. that's only just enough for 320hp in my experience .. I think i'm looking for 100mm or so? Ive never run a single throttle for anything like 500hp so have no idea really how big it needs to be for no restriction. As its only a prototyping excercise at the moment i might make something that fits with 100mm tube and wire erode myself a butterfly. I only need it to prove something on the dyno.

standard LS1's can easily manage 400+ on 75mm, and with heads/cam etc etc a lot more.

A TB and intake can release more again.....but how much of the restriction can you actually put down to TB size ???

And what do you class as no restriction....absolutely zero pressure drop across the TB ?? or just a very minor pressure drop.

[spitfire4v8]

72mm throttles on the RV8 tests i've done are on their limit at about 320hp, we know this because if you go bigger you gain hp. Ls engines may well be making 400hp plus on 75mm, but theyd probably make more with more throttle area .. I need to make sure there's as close to no restriction as possible so I need a really big throttle. I think I'll make one, sounds easiest

[stevieturbo]

spitfire4v8 said:

72mm throttles on the RV8 tests i've done are on their limit at about 320hp, we know this because if you go bigger you gain hp. Ls engines may well be making 400hp plus on 75mm, but theyd probably make more with more throttle area .. I need to make sure there's as close to no restriction as possible so I need a really big throttle. I think I'll make one, sounds easiest

I think you'll find the Rover V8 becomes the limitation well before the TB. A point well proven by the fact a better engine, will make a lot more power on that very same size throttle.

[Pumaracing]

Good Lord, almost an interesting flow related question on here finally. The throttle body sizing for one choke per cylinder is well known from countless tests with DCOEs and fuel injection TBs on race engines. Four 40mm TBs are sufficient for about 200 bhp on a four cylinder engine and by calculating the increase in area 45mm TBs are sufficient for about 250 bhp.

When you breathe through a plenum and single TB you aren't actually restricting things much further because each cylinder is on its induction cycle at a different time. There is some overlap due to cam duration being greater than 180 crank degrees but this only occurs when the inlet valves on the consecutive cylinders are not very far open so in practice it makes little difference.

So we can see that with a plenum a single 40mm TB should still be ok for about 200 bhp and a single 45mm TB for 250 bhp.

Using the square law to calculate the TB area we can see that for 500 bhp we need a TB of sq root (500 / 250) x 45mm = 64mm

However TBs on standard engines are generally much larger than these sizings would suggest. Why? Partly because the flow efficiencies of the systems are not very high and partly because you can still achieve good part throttle tractability with larger single TBs than this so why restrict things any further?

When you go too large on a single TB it becomes very hard to achieve good low rpm and low throttle opening progression so the car leaps off the line or kangaroos when you try to feather it. This generally only occurs at much larger TB sizing than that which restricts power though.

A 75mm TB should be more than adequate for your needs.

[spitfire4v8]

Hi Dave. 75 seems small, although i fully understand what youre saying about each cylinder being on its induction stroke at a different time, so the throttle shouldn't have to flow more than one cylinder pull at any given time. I will let you know how I get on ..

if I have time I will try some different sized throttles and post the hp results. The engine is a 4.7 litre race TVR AJP V8 which is on throttle bodies as std, but I know these are restrictive at 400-420hp because when I do a bit of light modification (relieving the internal casting marks and thinning the spindles) they pick up hp every time .. this 4.7 AJP V8 has made 477hp so far but I'm looking to move away from the throttle bodies (which really can't be modified enough or would need expensive bespoke ones made, or fabrication for adapting another aftermarket set of throttle bodies to fit) .. I'm wanting a massive throtle area so I can see just what the engine is capable of, low speed driveability is not an issue at this stage I just want to see what it will make with an unrestricted throttle area. We're so close to 500hp with this engine (on my dyno anyway .. lol)

[GreenV8S]

If you're looking at it that closely then I suggest you bear in mind that you will *never* get the pressure drop across the throttle down to zero; the issue is how much is acceptable. If you're serious about optimising the TB size then I'd suggest putting a pressure sensor on each side and see how much pressure drop you're *actually* getting across the TB, air filter and so on.

[stevieturbo]

low speed driving....but for any race engine, throttle control is rather important.

It's a bit pointless having a TB blade that only give a change in performance over say 50% of its motion, and the rest of the time it makes no difference.


If you dont care about throttle control, and just want to see a number on a dyno. Just remove the throttles entirely, fire a few open stacks onto the head with nice trumpets, and no throttle blades at all.

Just open pipes. You can load the engine up with the dyno to control rpm.


or for a laugh....make this large plenum intake ready for a TB....and just stick something over it to restrict whilst on the dyno. Wy worry about a throttle at all ?

Edited by stevieturbo on Saturday 6th June 18:27

[spitfire4v8]

I'm worried about the throttle because unlike your suggestion i'm not gung-ho on my dyno and i respect that the car's owner has invested a lot of money in his engine, I want to be able to control the engine to some extent .. and if i get the results I want i'd like to try and take the opportunity to map the part throttle and make it driveable enough for racing too if possible. If it doesn't work out then so be it, but nobody ever achieved anything by sitting on their arse so I'm keen to see if it works. I know the std inlets aren't enough so this seems the easiest/cheapest way of getting a (largely) unrestricted inlet .. and if it's driveable enough it's a winner (metaphorically and literally hopefully).

[spitfire4v8]

GreenV8S said:

If you're looking at it that closely then I suggest you bear in mind that you will *never* get the pressure drop across the throttle down to zero; the issue is how much is acceptable. If you're serious about optimising the TB size then I'd suggest putting a pressure sensor on each side and see how much pressure drop you're *actually* getting across the TB, air filter and so on.

Hi Peter .. that approach is great but rather suggests making a few throttles up and testing them to find what has best hp for the smallest throttle size. As this is an excercise in high numbers at the moment I was hoping there might be some info out there that would fast-track me to an appropriately sized inlet so I don't have to waste time making several different sizes. If i go too big I presumably can just fit a series of different sized restrictors over the mouth of the TB intake to simulate going smaller on the bore size .. if I find I can go significantly smaller without costing hp that suggests I would be better with a smaller TB to start with .. if however go slightly smaller than my chosen TB size and the hp drops immediately that would suggest I'm about right or havent gone large enough to start with. For this reason I think I'm inclined at this point to go with something very large so I know it isn't restrictive, then restrict down and see what happens.
It's a freebie for the car owner because I'm keen to see what the engine is capable of, so that does rather mean getting to the conclusion as quickly as possible.

Hope that makes sense.

[taz turbo]

Surely when the engine is on the dyno, you will get to a point where further throttle opening will not increase the power output, if you were to make a note of what minimum angle the throttle butterfly is when producing maximum power you could from that calculate the 'effective' size of TB?

On the flat plane AVJ V8 how many cylinders are on induction at any one time, and where are the cylinders on their stroke, mid stroke pulling lots of air or near the top/bottom pulling little air? Just a thought regarding the size question.

Regards,

Chris.

[GreenV8S]

spitfire4v8 said:

GreenV8S said:

If you're looking at it that closely then I suggest you bear in mind that you will *never* get the pressure drop across the throttle down to zero; the issue is how much is acceptable. If you're serious about optimising the TB size then I'd suggest putting a pressure sensor on each side and see how much pressure drop you're *actually* getting across the TB, air filter and so on.

Hi Peter .. that approach is great but rather suggests making a few throttles up and testing them to find what has best hp for the smallest throttle size.

I was thinking more along the lines of installing one is cheap/convenient and big enough that you think it might be OK, and then see whether the pressure drop across it at peak power is enough to justify the work to fit a bigger one.

[B19GRR]

Hmmm, I may be over complicating things but I have a cunning plan Why not build a plenum that uses a multiple smaller TBs (motorcycle carbs may, thinking cheap), you could then block off a number of them whilst doing dyno runs to see what effect that makes and maybe help narrow things down as to what cross section you'd eventually need on a single TB.

Caveat, I've been known to not have a bloody clue about things I'll shut up now.

Cheers,
Rob

[Pumaracing]

spitfire4v8 said:

Hi Dave. 75 seems small, although i fully understand what youre saying about each cylinder being on its induction stroke at a different time, so the throttle shouldn't have to flow more than one cylinder pull at any given time. I will let you know how I get on ..

if I have time I will try some different sized throttles and post the hp results. The engine is a 4.7 litre race TVR AJP V8 which is on throttle bodies as std, but I know these are restrictive at 400-420hp because when I do a bit of light modification (relieving the internal casting marks and thinning the spindles) they pick up hp every time .. this 4.7 AJP V8 has made 477hp so far but I'm looking to move away from the throttle bodies (which really can't be modified enough or would need expensive bespoke ones made, or fabrication for adapting another aftermarket set of throttle bodies to fit) .. I'm wanting a massive throtle area so I can see just what the engine is capable of, low speed driveability is not an issue at this stage I just want to see what it will make with an unrestricted throttle area. We're so close to 500hp with this engine (on my dyno anyway .. lol)

I take it you mean the engine is on 8 individual TBs at the moment. If so then you are going to create a completely different pulse tuning scenario with a plenum and single butterfly which will most likely knock a lot of power off the engine and prove very little about optimal TB size. Designing a plenum system is not very easy without extensive R&D. Both shape and volume considerations come into play.

On average when you replace the plenum system of a standard road engine with a single butterfly per cylinder system you gain between 10% and 15% power. Now it's certainly possible to claw back most of this with a properly designed plenum system and competition engines restricted to a single butterfly or orifice spend a lot of development time in this area. In essence the plenum needs to be big enough that each cylinder treats it as being open air like at the end of a single butterfly per cylinder system. The pulse tuning then takes place between the inlet valve and the end of the plenum runner rather than between the inlet valve and the single butterfly feeding the plenum.

In your situation I would say you would be much better advised to optimise your existing system than start playing with a plenum and single butterfly.

There's a lot of info on my web site www.pumaracing.co.uk

If you've achieved 477 bhp so far then 45mm TBs should be just about ok although 48mm would be better. If your current ones are smaller than this then yes it's no surprise you'll pick up power by streamlining spindles and suchlike.

Formula 3 engines are 2 litre four pots breathing through a single 26mm diameter orifice and still produce about 210 bhp like this. Scaling up you can calculate that 500 bhp should be possible through a single 40mm orifice. Call that a 45mm butterfly to account for the restriction of the spindle and other gubbins but you see where this is going. It's not the orifice or butterfly size that generates the bhp limit you think you're encountering but the shape, volume and flow efficiency of the plenum and runners downstream of it.

Behind the 26mm orifice F3 engines have a huge plenum which feeds the engine's cylinders so as to allow the orifice to see an almost constant pressure drop rather than a fluctuating one. This allows it to operate at maximum efficiency all the time. Lose that plenum volume and each cylinder would just see a single 26mm diameter hole to breathe through every time an inlet valve opened.

http://www.autoblog.com/2007/12/10/martinelli-unve...

http://www.italiaspeed.com/2007/motor_shows/bologn...

That's maybe 20 to 40 litres of plenum volume to feed a 2 litre engine just to make the orifice work properly. All the pulse tuning is done in the runners inside the plenum.

Standard engines have plenums with only 2 or 3 litres of volume. That means the engine sees the butterfly as the restriction which is why fitting bigger ones gains power. It's for entirely the wrong reasons though, or at least the reasons are generally misunderstood.

Dave Baker
Puma Race Engines

Edited by Pumaracing on Sunday 7th June 11:56

[spitfire4v8]

This is the system as it stands (not the exact car but this shows the inlets perfectly in this pic.

The throttle bodies will stay but with the butterflies and spindles taken out, it's easy and then you have a path with less obstructions. I've got a set of pipes coming which will stand being under vacuum on closed throttle from high rpm(hopefully). The f/glass airboxes wont be man enough to hold themselves under vacuum, plus they leak so I'll be fabricating some agricultural boxes to mimic their effect that I can link to a common throttle. As I say this is just an excercise in what difference it will make, but if i'm retaining the 8 inlets leading into a largeish plenum on each side then as long as I have a big enough throttle to simulate going to atmosphere I can't see at this moment how this can be worse for airflow/hp than whats on at the moment. I will keep you informed. Pipes will be here in about 3 weeks

Cheers for your contributions Dave and also thanks all for all replies so far, I might be sad but i really enjoy this side of things

[GreenV8S]

spitfire4v8 said:

I've got a set of pipes coming which will stand being under vacuum on closed throttle from high rpm(hopefully).

I suggest you try to rule out the 'hopefully' part of that. If one of the plenums collapses you'll get a load of debris sucked into the engine potentially (depending how you are managing the engine) followed by a full power runaway.

[rev-erend]

As the AJP is a flat plane crank and essentially runs as 2 * 4 cylinders .. why not just 'try' 2 plenums, one on each bank. The front area of the air box could be easily modified to take a large - say 65mm throttle .. and I believe the AJP already uses 2 throttle pots anyway. 65mm would be way more than enough air..

[chuntington101]

whilst you are doing all this work, why not straighten out the intake path to?? isn't it what the AJP race engines do??

Chris.