Effect of intercooler pipe diameter on performance?

While it's obvious that too small a pipe will choke performance, I'm curious about the other side ofht ecoin: How does an intercooler pipe size that may be too large affect performance?

I'm currently running a smallish FMIC with 3" piping on my Toyota 22RTE truck:

http://www.well.com/user/mosk/images/motor_02_08_04/motor_02_08_04-Images/0.jpg

The system works OK, but I believe I can do better. I recently picked up an intercooler that should offer better cooling and flow due to a larger frontal area and a more flow-friendly design, however, the new IC has 2.5" inlet/outlet piping.

My question is, what effects can I expect from downsizing from 3" to 2.5" piping? Will the greater velocity from the smaller size improve response, or will the smaller piping choke flow at WOT? I'm currently making 220 rwhp @ 15 psi (91 octane gas, no water injection), so the current 3" setup is probably oversized for my needs. However, I will be adding WI in the near future and hope to be able to run a leaner mixture and more boost (the motor is built for a solid 300 rwhp)...but 3" may still be too large for my motor, and i wouldn't mind tuning the system a bit for better low end response. And if I'm going to move to the new intercooler, I'd just as soon do it when I'm plumbing the WI...

Thanks for whatever feedback you can provide.

-Jeff

im just curious as to why you would want to run leaner when you run more boost even with water injection. sorry i cant help with you question though.

It's a good question, as you wouldn't normally expect to see someone asking about this, but my situation is probably different than most.

I'm running a F.A.S.T. standalone EFI computer with integrated closed loop wideband O2 correction. What this means is that I can continously monitor my a/f mixture in real time with a wideband O2 sensor, and the computer will make corrections on-the-fly to keep my a/f where I've specified it. Currently, in order to suppress detonation and reduce EGTs, my WOT fuel table cells are set to 10.0:1 @ 15 psi, which is pretty damn rich (max power is typically associated with 12.5:1 a/f, and max economy is usually seen in the 14:1 range). The extra fuel does a great job of eliminating detonation, but I'm robbing quite a bit of performance to keep the motor from damaging itself. However, I do have *more than enough* fuel to support the amount of boost I'm running.

What I will be doing to improve the situation is installing a complete Aquamist 2D water injection setup. Since my excess fuel is only being used for flash suppression, not combustion, I can replace the excess fuel with water and reduce the a/f mix to something more performance-oriented (~12.0:1 if I'm lucky). This will also let me run more ignition advance, which will lower my EGTs and give me better performance, too. Sort of a win-win-win scenario.

However, as long as I'm making all of these changes I want to reconsider my intercooler and intake plumbing. My current IC was chosen because it (mostly) fit the space in front of the grille. The new IC is an even better fit, and should also flow better. So the question becomes should I convert my 3" piping to 2.5" to match the new IC, or have new inlet/outlet fittings welded to the new IC to mate up with my current system?

-Jeff

First of all my car makes 456Hp and 609lb-ft at the wheels and it uses 2.5" plumbing to and from a FMIC. The kit is designed for up to 725 crank Hp. You should be a long ways from 2.5" creating enough restriction to worry about. Assuming you run a wastegate and it is referenced to the intake manafold it won't make any difference in power either way. The turbo will do whatever it takes to maintain the manifold pressure which is what determines power. Larger intake plumbing will however increase boost lag (takes a longer time to compress a larger amount of air). All of this is theory and may not make any noticeable difference either way so if it is any trouble, do whatever is the easiest.

I am surprised at only 15psi you have to run that rich. You must not have a boost friendly compression ratio.

Thanks for your reply regarding IC pipe sizing; it's in line with what my suspicions are.

Actually, I don't believe the compression ratio is the problem (I'm running an 8.0:1 CR, which I've verified). I can run more boost without detonation, but my EGTs rise to levels I'm not comfortable with. 15 psi at WOT will cause me to see EGTs of 1500°F as measured 2" from the exhaust port, which is pretty hot. I run forged pistons and have no problems with engine temp, but I don't feel comfortable running my EGT even this high...

I will encounter detonation if I add more timing advance, which I believe is due mostly to the shape of my piston crown. I went with a standard JE dished piston, and I don't think this has proven to be a good match for my combustion chamber. If I ever have the motor apart again I will try something different, but for now, I'm planning on making due with the current internals.

Of course, trying to wring max power from 91 octane pump gas (and crappy N. California gas at that) doesn't help. This is why I'm adding water injection, which will lower my EGTs, stabilize my mixture, and let me run more advance (and probably more boost as well). Historically, for my motor, I am within 40hp of what is reasonably possible on pump gas; I'm making double the stock power output, which is a pretty good benchmark. I think a few refinements will net me another 20-30hp while also making things more stable and improving my economy, all of which are good goals.

-Jeff

Rule of thumb here is for every one degree of intake temp drop, you get one degree of EGT drop. Your EGTs are so high because you are running so rich. Just try taking your AF to 11.5:1. If you get detonation, I guarantee you it is not because of lean conditions. Timing would be your next problem if detonation is the case. What is your timing as of right now? The FAST system can control timing correct?

One of the guys on another forum made 400whp with a 2" hotpipe and a 2.5" coldpipe. Bigger pipes create more lag. A good rule of thumb is keep the piping the same diameter as the compressor outlet. Same flow with the same velocity.

^^amen

Rule of thumb here is for every one degree of intake temp drop, you get one degree of EGT drop. Your EGTs are so high because you are running so rich. Just try taking your AF to 11.5:1. If you get detonation, I guarantee you it is not because of lean conditions. Timing would be your next problem if detonation is the case. What is your timing as of right now? The FAST system can control timing correct?

One of the guys on another forum made 400whp with a 2" hotpipe and a 2.5" coldpipe. Bigger pipes create more lag. A good rule of thumb is keep the piping the same diameter as the compressor outlet. Same flow with the same velocity.

Nissanfanatic,

Thanks for your feedback, but I don't think my rich a/f is entirely to blame for my high EGTs. I believe my high EGTs are a direct result of not being able to run enough spark advance. (The rich A/F is necessary to keep the mixture stable at max boost).

Here's my current spark table:

http://www.well.com/user/mosk/images/jm_spark_table_1-8-05.gif

As you can see, beginning at around 12 psi (183 kPa) of boost I'm only able to run 11° of timing. More timing would lower my EGTs and make for a more responsive motor, however, I am limited by the quality of the fuel I'm running. Once I complete my water injection setup I can reduce the amount of fuel I'm using, increase my advance, and perhaps increase my boost.

When I worked with the professional who tuned my motor (Dan Fodge, a FAST dealer/tester/tuner and all-around EFI genius) we tried a number of different scenarios, altering fuel, timing, and boost. The current combination was the one that yielded the best overall drivability -- the lowest EGTs with the most timing, but still a few degrees away from detonation. Dan's first recommendation was altering the piston crown design, ditching the standard dish in favor of a design that conformed more to the combusiton chamber for less volatility, reducing detonation. Since I didn't want to dive back into the motor, he suggested a good water injection setup as an alternative, and this is the path I plan on following. I'm pretty confident that with WI I can drop my EGTs by 50-70° while raising my AF to something in the 12:1 range.

FWIW, this is what my current AF table looks like:

http://www.well.com/user/mosk/images/jm_af_1-8-05.gif

Anyway, thanks for your suggestions regarding IC size. I went a bit overboard when I was laying things out initially, and see this as a chance to correct my previous mistakes. (And hey, if it wasn't for mistakes I'd probably never learn anything.)

Cheers,

Jeff

The rich condition isn't completely to blame. If you have to run AFs and timing like that, it sounds like you have hot IATs. What are the size and specs of that intercooler you have? I see what you're saying about why you have to run those AFs and timing, but that just means you have another problem. Pistons or not, 10:1AFs are not correct for a turbocharged engine. Thats more like a nitrous tune. And with that low of a comp., the timing shouldn't be that low either. Good luck.

Have you looked into Alcohol injection?

The rich condition isn't completely to blame. If you have to run AFs and timing like that, it sounds like you have hot IATs. What are the size and specs of that intercooler you have? I see what you're saying about why you have to run those AFs and timing, but that just means you have another problem. Pistons or not, 10:1AFs are not correct for a turbocharged engine. Thats more like a nitrous tune. And with that low of a comp., the timing shouldn't be that low either. Good luck.

Have you looked into Alcohol injection?

My old FMIC is only a 13" X 6" X 4" core. The new IC has a core that's 18" X 9" X 2.5". With the old FMIC, IAT's run about 40°F over ambient at WOT @ 15 psi, which seems pretty reasonable, although I'm hopeful that the new IC may run a bit cooler.

One thing to keep in mind is that my motor, the 22RTE, is a SOHC that was originally designed as a forklift (!) motor. Toyota sold several generations of the 22R motor in pickup trucks and Celicas, and it was produced in various forms from 1983-1995 (and longer if you count the 20R motor that proceeded it). However, Toyota only produced a factory turbocharged version for three years, 1985-88, after which they introduced a normally aspirated V6 as an alternative to the normally aspirated inline 4. So this is pretty old technology, and it was not designed from the ground up as a turbo motor, or even a particularly advanced motor: in bone stock form, this motor made 136 hp at the crank @ 6 psi boost, on a stock CR of 7.4:1, and got around 17 mpg.

I've had a lot of fun with this project, and I've done just about everything that you can think of to this motor short of nitrous. It's currently making 222 rwhp on 91 octane pump gas, gets 15-17 mpg, and it's very drivable -- nice idle, smooth to drive, but with very decent power under the right foot. That's approx. double the stock power output, which ain't bad. Not sure if I would choose this motor again as the basis of a big buildup, but this project was my first introduction to turbo motors, and so seven years and several large bags of money later, here I am...

Anyway, I do agree with you, 10:1 A/F is not where I want to be, which is why I'm adding water injection, or water/methanol injection, and we'll see what that does. As for something else being the culprit, I'll stand by my assertion that the piston crown/combustion chamber interface is the cause of my high boost detonation; water injection will keep the mixture stable for a longer period of time, and this will be good enough for me. It isn't a solution that addresses the root cause, but it's good enough for what I'm after. I'll be happy to post here again in a couple of months after I get all of the new parts installed and retuned.

Thanks again for your feedback,

Jeff

IATs seem very reasonable. What type of plugs are you running? Maybe a step colder is in order.

Very small cam huh? 136 BHP @6psi just doesn't sit right with almost 2.4l of displacement. I would look into cams for more power. But like you said, it is a "forklift," engine.

I'm running one step colder than stock now. I've tried two steps, and it really didn't help the problem (and with my current AF, two steps fouls more easily...) I will probably play with plugs again after the WI is installed.

Actually, the stock cam on this motor isn't too bad. I'm running a much more aggressive, custom, turbo-specific cam, but the cam isn't the limiting factor on this motor until you get above 180 hp.

In stock form, Toyota delivered a turbo motor that had *exceptionally* low compression, an intake optimized for low end torque, only modest boost, and a so-so turbo. Also, this was one of Toyota's first generation digital EFI motors (earlier EFI motors were analog), so the spark and fuel tables weren't very sophisticated. Finally, this motor (in stock form) used a flapper-door AFM...oh, and it had an exhaust that narrowed to 1-7/8" at the BEFORE the cat. So there are many things that have to be addressed to make decent power.

I won't go through the litany of what I've done to get to this point, but you can take me at my word: I've looked at every component on this motor, and to the extent I've been able, I've chosen the best part. If you want more detail, here's a blog of the buildup, with pictures:

http://www.well.com/user/mosk/blogger.html

Anyway, thanks for the comments.

-Jeff

If you got problems with high exhaust temperatures there are usually two reasons for that.
1. You're running lean.
2. You use to little spark advance.
This is often the result of too low octane/too high boost or compression ratio. A small turbocharger also make it worse.

A 3 inch intercooler pipe will be good for a least 1000 hp.

The "temperature" of the plugs doesn't have anything to do with exhaust temperatures, they just control the operating temperature of the plug. Too low and you will get deposits on your plug, too hot and it overheats and can cause surface ignition.

40 degF over ambient, not good but it could have been worse.

If you got problems with high exhaust temperatures there are usually two reasons for that.
1. You're running lean.
2. You use to little spark advance.
This is often the result of too low octane/too high boost or compression ratio. A small turbocharger also make it worse.

A 3 inch intercooler pipe will be good for a least 1000 hp.

The "temperature" of the plugs doesn't have anything to do with exhaust temperatures, they just control the operating temperature of the plug. Too low and you will get deposits on your plug, too hot and it overheats and can cause surface ignition.

40 degF over ambient, not good but it could have been worse.

Thanks for the reply. The following responses should be in order:

1. As established above, I am not running too lean -- my injectors and pump are more than adequate for the airflow I'm seeing, and fuel-wise, I have enough headroom for at least another 7 or more psi of boost.

2. I *am* running insufficient spark advance. I know this. Because I am determined to make do with 91 octane pump gas (philosophical decision), I am paying the price in terms of my advance curve and boost level. I will be augementing this with a well designed water injection system, and this will allow me to run more advance. This will address the problem, but it obviously won't afford me the same lattitude as running 116 octane racing gas.

Turbo is properly sized for this motor: T3/T04E, 50 trim compressor, Stage II exhaust, .48 A/R housing, full 3" downpipe and exhaust (keep in mind that this is in a truck, and the motor has a 6500rpm redline, with an effective powerband of 2800-5800rpm).

3. My current intercooler pipe is almost certainly oversized for my current power levels. Hence this thread...

4. I do understand the difference between "hot" and "cold" plugs, and their actual effects. That's why I said I was running one step colder than stock, and going two steps colder affected low-speed drivability as they fouled more easily.

5. 40°F over ambient is what I have now. Once I get the new intercooler installed, I'll hopefully see a drop. Not sure what a good IAT would be for an air-to-air FMIC, but it doesn't strike me that 40°F over ambient is all that bad...

Thanks for your reply,

Jeff

Piping Choices

Most installations are plumbed with thin wall mandrel bent steel tubing. This tubing is available at race fab shops in various radii and diameters, generally in U or J configurations, which can be sectioned to fit together into the desired shape. It is relatively inexpensive and can be TIG or gas welded. Aluminum tubing can also be used but is harder to find and more expensive. Piping diameters are dependent mainly on engine airflow which is a function of HP. For engines up to 350hp, 2.25 inch tubing works well. 350 to 500 hp installations should use 2.5 inch. Engines above 500hp should use 2.75 or 3 inch tubing. Some means to take up vibration and engine movement to chassis mounted intercoolers is required. This usualy means flexible couplings. Moulded radiator hoses are available in larger diameters and various shapes and are generally safe at the temperatures and pressures required for street applications. You may have to cut or enlarge holes in your sheet metal for the piping to run to the intercooler. Watch hood clearnce and ground clearance to the pipes if they run over or under the radiator. Silicone hump hoses are also available to take up movement.

Figured that would be useful to you.

http://www.sdsefi.com/techcooler.htm

The "temperature" of the plugs doesn't have anything to do with exhaust temperatures, they just control the operating temperature of the plug. Too low and you will get deposits on your plug, too hot and it overheats and can cause surface ignition.

I just asked because I thought that it could have been one of the causes of his detonation issues when running proper AFs.

I still blame AFs, but you had it tuned by a pro, so go with what he recommends. Good luck with the water injection. Hope it solves the problem.

Figured that would be useful to you.

http://www.sdsefi.com/techcooler.htm



I just asked because I thought that it could have been one of the causes of his detonation issues when running proper AFs.

I still blame AFs, but you had it tuned by a pro, so go with what he recommends. Good luck with the water injection. Hope it solves the problem.
A hot plug won't cause detonation but it can cause surface ignition. That's not the same thing tho.

A rich air/fuel mixture is typically used to cool the exhaust temperature.

I see know that he says the exhaust temperature is 1500 degF at 2" from the exhaust port.
First of all I would like to comment on where the exhaust temperature is measured; on a turbo engine you usually want a reading from the turbine inlet where the temperatures usually are highest.
Secondly 1500 degF at WOT isn't high. Stock Saabs operate with exhaust temperatures of 1800 degF and I know that some tuning companies have had problem with high exhaust temperatures with the Saab engines, but then the temperature readings was above 2000 degF.
A temperature of only 1500 degF is infact so cold that even a variable geometry turbine turbocharger from a diesel engine can be used. Allow at least 1650 degF turbine inlet temperature.

Another thing I forgot to mention, look if there is any ethanol fuel availible where you live. Ethanol requires a modification of the fuel system but does otherwise offer an octane increasement. Since it's more envirnonmental friendly taxes are often lower on it, so even if the fuel is more expensive it can be economic to run on it.
Some aviation (piston engine) fuel or aromatics such as toluene or xylene mixed in the regular petrol isn't wrong either.

A hot plug won't cause detonation but it can cause surface ignition. That's not the same thing tho.

A rich air/fuel mixture is typically used to cool the exhaust temperature.

I see know that he says the exhaust temperature is 1500 degF at 2" from the exhaust port.
First of all I would like to comment on where the exhaust temperature is measured; on a turbo engine you usually want a reading from the turbine inlet where the temperatures usually are highest.
Secondly 1500 degF at WOT isn't high. Stock Saabs operate with exhaust temperatures of 1800 degF and I know that some tuning companies have had problem with high exhaust temperatures with the Saab engines, but then the temperature readings was above 2000 degF.
A temperature of only 1500 degF is infact so cold that even a variable geometry turbine turbocharger from a diesel engine can be used. Allow at least 1650 degF turbine inlet temperature.

So you're saying that I should have mounted my EGT probe close to, if not in, the turbine inlet, and that I can feel good about temps as high as 1650°F for WOT bursts? This would certainly cast some of my concerns in a different light.

In my experience, EGT probe location and acceptable EGT temps are subjects about which no two engine builders can agree. Certainly, in my experience, no two agreed on either ideal probe location or acceptable max EGT for my motor.

Becore mounting my probe I attempted to get opinions from the people who I respected, and most recommended mounting the probe in the exhaust runner, at a distance that approximates the diameter of the runner itself. The difference between mounting the probe in the runner vs. mounting the probe in front of the turbine inlet is that the probe in the runner has a chance to cool a bit between exhaust pulses, whereas the probe in the runner tends to heatsoak from the combined exhaust gasses of all the cylinders. This was my decision, based on the data I had available.

As for acceptable EGT temps, I have also heard the gamut on this issue, but for the most part, the consensus I've seen has been that the probability of melting a piston or worse increases dramatically above 1550°F. Yes, I know that rotary motors run EGTs in the 1800°F range, and I also know that running forged pistons (which I am) provides a much greater range of acceptable temps. But I am not trying to tune my motor to the edge in order to wring a few more hp out of it. My goal has been to build a motor that makes good, sustainable power, a motor tuned for power, but NOT to the edge of detonation and meltdown.

-Jeff

PS: IIRC, some/all Saabs are quipped with sodium filled exhaust vales, which makes a big difference...

EGT are measured in the turbine inlet in turbocharged engines, this since the temperature is higher there than a few inches from the port. This has to do with the gas is still burning (especially on wankel engines) in the pipes and that some pulse energy is converted to heat in the collector. When the exhaust then passes the turbine there will be a heatloss which will be higher than the heat gain seen in the compressor. The heat lost in the turbine is what powers the compressor.

Another reason for placing the EGT sensor in the turbine inlet is because this is the limit that the turbocharger manufacturer sets. This depends on the materials used in the turbocharger but is typically 900 to 1050 degC (1650 to 1920 degF). With the first value the industry standard inconel materials are enough while the latter requires a special Mar-M 247 turbine.

If more than one EGT probe are used, additional ones can be placed a few inches after the ports on each cylinder.

High exhaust temperatures is bad for the turbocharger, exhaust manifold and exhaust valves. The pistons sees much higher temperatures during the combustion so for them there aren't any danger. What usually causes piston damage is a too lean mixture and detonations.

As for heat lost by radiation and convection from the exhaust manifold it's low, typically around 5% of the total heat is lost.

No newer Saab engines are using sodium filled valves, with a few exceptions (ecotec based engines). Some engines are however fitted with exhaust valves of nimonic. Nimonic was used before they wanted to go down from 7 to 5 mm valvestems and thereby being able to reduce friction and fuel consumption.

A hot plug won't cause detonation but it can cause surface ignition. That's not the same thing tho.

A rich air/fuel mixture is typically used to cool the exhaust temperature.

I see know that he says the exhaust temperature is 1500 degF at 2" from the exhaust port.
First of all I would like to comment on where the exhaust temperature is measured; on a turbo engine you usually want a reading from the turbine inlet where the temperatures usually are highest.
Secondly 1500 degF at WOT isn't high. Stock Saabs operate with exhaust temperatures of 1800 degF and I know that some tuning companies have had problem with high exhaust temperatures with the Saab engines, but then the temperature readings was above 2000 degF.
A temperature of only 1500 degF is infact so cold that even a variable geometry turbine turbocharger from a diesel engine can be used. Allow at least 1650 degF turbine inlet temperature.

Surface ignition A.K.A. hot spots correct? But this can lead to detontation right?

And I was under the influence that rich AFs lead to higher EGTs because the unburnt fuel would ignite in the exhaust manifold and raise EGTs to very high levels. Thanks for clearing things up.

BTW, I read the part about rich AFs leading to high EGTs in Hugh Macinnes Turbochargers.

Surface ignition A.K.A. hot spots correct? But this can lead to detontation right?

And I was under the influence that rich AFs lead to higher EGTs because the unburnt fuel would ignite in the exhaust manifold and raise EGTs to very high levels. Thanks for clearing things up.

BTW, I read the part about rich AFs leading to high EGTs in Hugh Macinnes Turbochargers.
With a rich mixture the extra fuel can't burn unless air is added. So unless you got air into your exhaust manifold some way the rich mixture cool down the air/exhaust just like water injection.

Surface ignition isn't the same as detonation. With surface ignition the mixture is ignited from a separate heat source, the "hot spot". Surface ignition can be separated into post ignition and pre inition.
Detonation on the other hand does only occur after the mixture have been ignited by the spark. When the spark ignites a mixure a flame front starts to travel from where the spark occured. This means that heat will be released and as the flame front comes into contact with the unbuned mixture it too starts to burn and the flame travels outward from the plug. When a detonation happens this is unlike the normal combustion a very fast combustion, almost like an explosion. Detonation is when the endgas ignites by the heat and pressure in the cylinder and not the flame front.