Intercooler Piping Routing Under the Car- Pic

[Tony D]

"As for lag, if the only way you use the throttle is to mash it to the floor at the start of the run and to let off again at the end of a quarter mile, then you guys are right. Once the turbo spools up and the motor is at full power than that extra length of pipe probably doesn't matter.

 

But if you actually try to use the throttle and engine power to negotiate the car through a turn, then I simply cannot believe that increasing the volume of the intake plumbing by an amount almost equal to the engine displacement won't be noticeable.

 

Think of the intake plumbing as a storage reservoir on an air compressor. The larger it is, the longer it is going to take to pressurize, the more stored energy it will contain, and thus the longer it is going to take to depressurize. None of those things will contribute positively to throttle response."

 

I will have to disagree only from the point that the way most kids have their BOV's setup today...to make noise, and not function properly, then you might have a point.

 

But for a properly operating compressor bypass valve that lifts and allows the compressor to keep up at speed and constant flow, as soon as the throttle would be changed the bypass will close and pressurization will immediately happen. A compressor bypass will keep the turbo flowing at peak flow, making form linear power delivery when modulating underboost. It's not an 'all or nothing' proposition, the BOV doesn't drop that intake line to even atmospheric pressure unless the engine is drop-throttle closed for a considerable amount of time. Under throttle modulation on-boost it will be some middle ground where the engine may be seeing slight vacuum between the throttle plates and engine intake valve, but the plenum will still have pressure in it. It's a wierd phenomenon, the compressor bypass valve should lift fully and relieve pressure in the piping, but at the same time it will relieve load on the compressor section by allowing N/A operation directly shunting the compressor section allowing it re respeed in almost a vacuum. The setup on the HKS Type 2 Surge Tank did this pretty well---basically once you're on-boost, modulation is occurring without a drop in turbine/compressor speed, you dump your excess overboard and keep the wastegate closed to allow for instant response.

 

With the "Fast and Furious" BOV's dumping 'hard' you semi-stall the compressor for auditory effect, and then since it dumps overboard, and not to the compressor inlet (speeding up the wheel) you loose response.

 

A lot of myths surrounding Turbo Operation come from people running horribly designed systems (even though they make copious amounts of power!)

 

The contention about Mass-Flow is really at the crux of it. In a properly operating compressor bypass system, the mass flow through the compressor will remain constant under lift-throttle with the excess being vented overboard, and being immediately available for use when the throttle position changes open again. Pop's contention is based on the F-N-F style dump, where the compressor is stalled, all pressure in the intake piping is dropped off, and then the turbine is then called upon to speed back up to the prpoer operational point on its mass-flow chart and then start delivering through the piping again.

 

It's a problem of blowoff design, rather than piping system design that solves the issue.

 

This can be seen every day at any air separation plant using cryogenic distallation columns. The cold box must have an uninterrupted mass-flow through the columns or things get all out of whack. The solution to keep the colums balanced is to run the excess air out a bypass that will open instantaneously on switch from "Column A" to "Column B" allowing for constant mass-flow to the point of use, even though the switchvalve operation momentarily stops flow thorugh the column. You watch the Turbocompander's tachometer during these events and the thing stays very steady...a function of the same mass flow being pushed through it. If anything, the Capacitance of a larger piping system makes drop-throttle control of mass-flow through the system easier as you can use a slower opening blowoff, with a much more sensitive closing ramp!

[proxlamus©]

damn genious.. jeesh Tony.

 

thanks for taking the time to type that!!

[Clifton]

Well you sure have a drop dead gorgeous car, whereas I have never built a turbo motor. So a good point of reference for me. 26 psi seems like a lot of boost, too.

 

Do you any type of pop off valve to relieve intake pressure on quick down throttle?

 

On my 73's, originaly no. I do know though. I don't run one on my 71'(road race car. They don't dump intake manifold pressure, that's what the throttle does. Just gives the turbo somewere to move the air so it doesn't surge when the volume isn't used my the engine. Low cfm and high pressure = surge. They are not designed to prevent stall, they aren't postive displacement. Infact on my truck the turbo is pretty loud when spooled, not exhasut, just from the compressor. I don't run a bov and have stalled the truck a few times at the dunes under full load, boost dropping as the revs drop, a downshift just kills it on a steep hill. With the engine stalled, you can still hear it whisstle for a few seconds, throttle closed and no rpms. It won't just stall with froma a shut throttle.

 

 

But if you actually try to use the throttle and engine power to negotiate the car through a turn' date=' then I simply cannot believe that increasing the volume of the intake plumbing by an amount almost equal to the engine displacement won't be noticeable.

 

Think of the intake plumbing as a storage reservoir on an air compressor. The larger it is, the longer it is going to take to pressurize, the more stored energy it will contain, and thus the longer it is going to take to depressurize. None of those things will contribute positively to throttle response."[/quote']

 

It's not the intake manifold volume you are increasing, it's just the area in front of it. No different than the atmospheric pressure on a n/a car with a throttle closed except the pressure is just a little higher higher on a turbo car. It is still pressure though.

[Tony D]

"They don't dump intake manifold pressure, that's what the throttle does. Just gives the turbo somewere to move the air so it doesn't surge when the volume isn't used my the engine. "

 

That is only part of the equation on the dump valve, it is more to prevent the turine wheel from slowing down out of peak efficiency range, and 'surge/stall' are interchangable terms when referring to centrifugal compressors. There is a minimum mass flow of air that a compressor must flow in order to have stable operation. If you fall below this point, you will stall/surge the compressor. The airflow delaminates from the blades, and the airflow reverses instantaneously.

 

Otherwise, I agree on everthing said by Clifton in the last post. Things people attribute to 'turbos' are totally accepted in an N/A car. "Coming on the cam" is one of them. You just drive in the power bump region. Same for a turbo, you drive above boost threshold rpm (usually around 3000rpm, no biggie) and the problem becomes on where to put the excess air than waiting for it to 'come on boost'.

 

Driving a non-BOV equipped car that runs high boost will reveal some really strange things, like 3-4psi at small throttle openings, going instantly to say 20 psi at WOT. It modulates just like the power delivery of an N/A car when driven like a hot-cammed N/A car.

 

It's just that people get lazy with their driving and expect the turbo torque to pull them out of everything no matter what the RPM, and they pick the wrong gear entering a corner, so at exit and throttle roll-on they are below boost threshold...and then the dreaded non-linear power delivery comes on.

 

Incidentally, if you cam and match your components correctly, even then this won't happen! Your car will drive like a N/A monster of MUCH larger displacement, but usually the components are so poorly matched to the application you get a non-linear bump because 'strapping a turbo onto it for more power' screws up the dynamics of even a stock cam.

[Clifton]

[quote name=Tony D;802642

Driving a non-BOV equipped car that runs high boost will reveal some really strange things' date=' like 3-4psi at small throttle openings, going instantly to say 20 psi at WOT. It modulates just like the power delivery of an N/A car when driven like a hot-cammed N/A car. [/quote]

 

BOV should be closed under boost. Difference between the bov and non at 4 psi and 20 psi would be the same.

[Tony D]

"BOV should be closed under boost. "

 

This is the common misconception! Not necessarily! The BOV shuold move almost in a mirror image of the throttle plate. If you keep 20psi in the plenum, and through throttle modulation you only have 3-4 psi in the inlet between the T/V and the Intake Valve...something is wrong with your BOV setup and you are slowing the wheel and affecting turbo response. In this instance, when you go WOT, you will notice a dip in plenum pressure before it regains to 20psi. This should not happen and won't if your BOV is set up correctly.

 

If the BOV was relieving mass flow at partial throttle, under the same scenario, the turbine would be up to full speed, and delivering full mass-flow for the engine needs, the BOV would simply be diverting the overage during a partial-throttle condition. In this setup, when you went to WOT, there would be NO dip in boost pressure noted in the plenum, nor the resultant 'lag' associated with a lower pressure in the inlet plenum.

 

People think the BOV is either and 'all or nothing' proposition, and it's simply not the case. A majority of people set it up that way through ignorance of the things proper function...but when you lift the throttle even slightly the BOV will crack and divert pressure not being needed by the engine to the vent line---allowing the turbine to remain totally spooled and providing full mass flow.

 

Sure, once you got WOT, it will shut. And if you drop throttle completely it will dump pressure from the plenum like most people do. It's the partial-throttle response that gets buggered up when people set the thing to respond.

 

Just because the manifold is 'on boost' does NOT mean the BOV is totally closed! Perhaps at WOT that is true, but any other time all bets are off. If you are not at WOT, there is no reason to have full pressure in the inlet plenum, and ideally under the perfecct setup the turbo would be fully spooled for full boost, the BOV venting the excess overboard, and throttle plate pre and post probes will show the same boost pressure.

 

If you think about that setup, that is a no-lag situation, but because people are so misinformed about how a BOV should be working, and the common fad is to set it up for 'noise production' instead of finesse in a corner for throttle modulation you get a lot of junk setups out there that don't function nearly as well as they should.

 

There are some systems currently on vehicles...and dammit I can't say why/how I know this, but commercially it should be available some time in the not-to-distant-future, that will let a BOV be controlled on a similar loop like the Wastegate. In fact, the BOV and the Wastegate will be tied together in a common controller, with an input from the TPS. With total electronic control of these items through either stepper motors or pneumatically controlled solenoids the boost response will be amazing for people accustomed to the 'Whizz-Woosh-Boom" style of BOV Actuation popular today. A BOV should sound like a big guy sighing when you feather the throttle, if it doesn't it's set to harsh and you are loosing turbine speed and tip-in boost response...you're opening way too late, and dumping way too much.

[proxlamus©]

so Tony.. what BOV would you consider to be a well designed unit?!

 

Just curious as the Greddy Type RS unit is very nice.. and was pricey.. probably for the "Greedy" name..

[Tony D]

I haven't bought or even looked at one since the early 90's. At the time the Cartech unit and several HKS bypass valves were avaliable that functioned really well. I have been told the Cartech unit from BEGI is no longer available, which is sad it was a really good one. My HKS unit from the mid 80's has a 50mm orifice and nice flow design...when you consider my boost piping is around 2.5", that orifice will take much of the flow directly.

 

From what I have seen the emphasis seems to be on smaller, smaller, smaller, and I see that as a problem. The flow speeds through that orifice not only make noise...they cas get downright turbulent and that hurts their flow ability.

 

For me on the BOV, bigger is better. It has to be able to flow a lot of air and relieve the plenum pressure with decent resolution without going overboard. They all may be 'well designed' but I think they are being misapplied---most of this stuff looks to be for small four cylinder applications and not suited to flow the air required for bigger engines. I think maybe the Vortech stuff for the V8 Superchargers may hold promise, but I haven't looked too closely at them. I think the problem is in application, more than design engineering.

 

Turthfully I haven't looked in years since I'm happy with the few I bought back then. A Bell (Cartech), Two HKS units, Two SK's from their turbosystems, and one that I have no idea who made it, but I bought it in Japan in 1987 or 88 at a speed shop. It was supposed to be good for bypass on twin applications to 600ps...though is only slightly bigger than the HKS unit on my Type 2 Surge Tank.

[datman]

Tony, funny you should talk about electronic control of a BOV, My brother has set his race car to use his brake servo as a vacuum resevoir..this connects to his BOV via a 3 way solenoid valve...the solenoid valve is controlled by the ECU to open the BOV before the throttle shuts to keep the turbo spinning and response high out of corners. This was his idea.....I not entirely sure how he has it plumbed in.

[Tony D]

Like I said, it only takes proper controls!

Once the turbo is up on the boil, there really is no reason not to dump excess in copious volumes rather than let it slow and re-spin to optimum speed. The throttle response on-boost is much better doing it that way.

[boardkid280z]

I wonder if your brother's using a TPS like signal to control the position of the blow-off valve according to the position of the throttle...

[WizardBlack]

You could probably use an amped up DFCO-like signal to determine when and how to open it. On a side note, during shifts I seriously doubt it's going to have the turbine energy to keep it spinning 'at full boil' unless you are talking about ignition retard (two-step or antilag). About the best you could do would be a tapered in and out bypass such as the solenoid controlled bypass valve would afford. Some BOV's offer a 3-port design that you could use the third port with a simple electric-pneumatic on-off solenoid. This could also actually be implemented just like a standard pwm solenoid for boost control. Many ppl buy one (from an industrial electronics company) to hook up with standalones for boost control. I've seen some threads on aempower.com that are relevant to this.

[datman]

Yes I think he has some chart on his MOTEC ecu to control the solenoid at certain TP. He also keeps the throttle open 30deg and cuts the spark or fuel to keep the turbo spinning....it's a bit of an animal to drive. 470BHP out of a 1.8 Audi engine...that's de-tuned to lower it 470bhp!

Previoulsy he tried an offset throttle body on the inatke side of the turbo, unfortunately his turbo didn't have carbon seals and sucked a lot of oil into the intake...not good

[Tony D]

On a side note, during shifts I seriously doubt it's going to have the turbine energy to keep it spinning 'at full boil' unless you are talking about ignition retard (two-step or antilag).

 

If you drop all restriction, and bypass the compressor so it's in a 'vacuum' the decrease in wheel speed is MUCH different than if you are actually pumping air. WRC Cars do use retard, but that is because they are 'flat shifting' at WOT and using pretty sophisticated ECU interactions to control the ignition to turn the exhaust manifold into a gas turbine combustion can, powering the turbine differently than when on normal boost. You are actually engaging in combustion in the manifold, not in the combustion chamber...

 

What we are talking about is a 'lift throttle' situation where turbine energy is decreased, and at the same time you drop pumping air on the compressor end. This allows basically a 'free float' of the wheels with very little deceleration, if any.

 

If you alter timing at the same time, you would need far less retard because it is operating in a 'bypass' as well as 'free field' mode of compression.

[datman]

Well it must be working to some extent as I watched him race this weekend, he won his class 2wd turbo (3rd overall) 1st and 2nd were 600BHP Mitsi Evo's......4th was also a 600hp Evo.

[Tony D]

There were some efforts early on in Datsun Turbo Development to use a linked throttle body to dump boost because of the defficient/inefficient turbo designs present at the time.

If you will recall, E-Motive ran a twin turbo setup without much success, going back to a single for the 83 car, and had much better success. But they had some seat time with the new 'TEC1' that was developed.

 

On older, inertia-soaked wheels, a blowoff such as I'm describing was the only way to insure the minimum of turbo lag (actual re-spin time) was kept to an absolute minimum. In today's cars of titanium wheels, ceramic ball bearings, and electronic controls, many other things can be done to help keep the thing spinning fast (if not even producing boost under drop-throttle conditions as Datman points out!)... But this does not mean that a properly designed blowoff won't help the situation, either.

 

"We digress..."

 

I'm counting my days left till I hop the plane for Spa and attend the 6-Hour.....

[jonus079]

The air is moving at over 300 ft/sec.....an extra couple feet is nothing. The slight increase in volume is the other issue, but that would only impact the turbo lag. Again, given the velocity, the flowrate would be such that the incremental increase in volume would have a minimal impact.

 

As for the bends, there are no more bends in this setup than there are in a convential behind the fan setup - 4 bends for the inlet, 3 bends for the outlet. As a matter of fact, my outlet bends are very smooth. One 90 degree and two 45 degree. The bend coming up from under the engine is a 70 degree bend.

 

i completely agree. i think the extra 2 feet would be barley noticeable (if at all). i don't understand why people take so much time and effort into making the charge pipes as small as possible. i mean come on, i see rear mount turbos making big power, just think about how many miles of charge tubing are in those setups.

 

the only reason why i would take time and effort into shortening the charge pipes is because i think it looks better but i must say i like that setup allot, very clean!

 

-Marcus

[WizardBlack]

they are 'flat shifting' at WOT and using pretty sophisticated ECU interactions to control the ignition to turn the exhaust manifold into a gas turbine combustion can, powering the turbine differently than when on normal boost. You are actually engaging in combustion in the manifold, not in the combustion chamber...

Yep, that's a form of antilag. I've driven a rally car with it before and set up two-step for street cars.

On a side note, some EVO's (Jap versions for one) use a BOV that dumps the air (from IC piping) into the exhaust manifold runners from the factory. Another interesting way to benefit.

[mcmike280z]

First off I have to say how sweet everything looks....it's hella sweet! I have a ? for you (KTM) and Pyro as well. Did either of you have issues with how you clocked your compressors and the frame or steering rod? I have mocked mine up like Pyros and I am wondering if I should change it like yours.

[ktm]

No issues with the steering shaft or the frame rail, though it is a tight fit. The silicone reducer from the compressor to the first charge pipe touches the frame rail, but I could rotate the compressor smidge more if I was really concerned.