Turboing an uncommon engine. A learn me thread.

Sooo...  I wanna add a turbski to my rx8.  

I'm currently rebuilding the 3.9 v6 since I starved a rod bearing of oil.  Boo.

However, I wanna turbo it at some point.  I want to do it cheaply, but reliably.  In other words, I want to do it "right", but as cheap as possible.

A couple of questions:

How do you size a wastegate?  Suggestions on reliable, but inexpensive ones are welcome!

How do you size a blow off valve? Suggestions on reliable but inexpensive ones are welcome!

Is a blow off valve (to atmosphere) an okay choice with the stock gm PCM and sensor setup?  Or, if I don't recirc, will it stall everytime I stop?

Should the MAF sensor be before or after the turbo?

If I am shooting for say 400hp, how big of an intercooler should I be looking for?  Any junkyard specials to seek out?  

Right now, I was planning on using the maxpeedingrods street GT35 turbo.  It looks like it would hit my power goals and work okay on a 3.9liter v6. (250 hp 250 tq at the crank stock).

I assume I need to upgrade injectors and fuel pump as well.  I've had good luck with DW pumps, so I'll modify the pump housing and slap one of those in. 

I am a little lost on injectors.  Preferably there is something plug and play that would fit in the stock location and support 500 hp (room to grow) and still idle normally.

I plan to run the stock ecu and hopefully find somebody to tune it.  Recommendations for a decent tuner in south carolina or within about 4 hours of me would be great!

Any help is appreciated!

One rule.  All the turbo.

HP = lbs/min of airflow. Everything is based on that. Yes, you will have to do math. There are a bunch of online calculators to help make it easier.

If that motor is not built for the stress is may make 400hp but not for long.  Maybe swap in a motor that has one already.

Can't help much with the plumbing sizes, but how you direct the air can cause problems with MAF systems, which is why you see most turbos go to speed-density designs.  

For instance, when your blow off valve opens and vents, the MAF has no idea and thinks all of that flow is going into the engine- which will flood it.   The wastegage is less problematic, but it can backflow up the intake, which also confuses the MAF unless it's designed to deal with back flow air.  Theoretically, that could be fixed by moving the MAF behind that turbo, but now you have pressurized air that the sensor isn't designed for- and it could break the sensor. 

Speed-Density doesn't really care about any of that- since both the wastegate and the blow off valve are upstream of the throttle so upstream of the manifold where the airflow measurement is made.

I'm sure there are groups out there who have good enough solutions for that, since your budget won't change the PCM.

porschenut said:

If that motor is not built for the stress is may make 400hp but not for long.  Maybe swap in a motor that has one already.

There are a few people running 600 plus hp on these engines with no changes.  By a few, I mean there are like literally 2 or 3 builds that I could find.

I'm not swapping the rx8 again.  One entire different drivetrain was enough for now.

wvumtnbkr said:

How do you size a wastegate?  Suggestions on reliable, but inexpensive ones are welcome!

More of a rule of thumb than anything else. A GT35 sized turbo doesn't demand anything particularly large. I'd probably use something in the 40-50 mm range.

How do you size a blow off valve? Suggestions on reliable but inexpensive ones are welcome!

These go by the volume of air you're trying to vent, and pretty much any of the aftermarket BOVs you'll see will be big enough here.

Is a blow off valve (to atmosphere) an okay choice with the stock gm PCM and sensor setup?  Or, if I don't recirc, will it stall everytime I stop?

This would work correctly if you have the MAF downstream of the BOV (and the turbo, of course).  If the BOV is downstream of the MAF, you will go rich any time it opens, and have the timing back down. This may not cause a stall, but is not ideal. You can avoid this by either recirculating the air or using speed density tuning and not running a MAF.

Should the MAF sensor be before or after the turbo?

Any MAF can go upstream of the turbo. Many of them can handle pressure and go after the turbo, although there are some plastic bodied ones I'd worry about not being able to survive boost. Or if your ECU can run speed density, the other possible answer is "Nowhere".

However, note that you will need a MAF that can handle 400 hp's worth of air. I don't know if the stock one can measure that. Which is another reason to consider speed density if your ECU can do this.

If I am shooting for say 400hp, how big of an intercooler should I be looking for?  Any junkyard specials to seek out?  

My usual method for sizing an air to air intercooler for a street car:

1. Measure how much room you have to fit an intercooler.
2. Use all of it.

While it is theoretically possible to have an intercooler large enough to notice drawbacks, it's rare you would be able to fit one into anything that has a production radiator core support and sheet metal.

I would not bother scavenging a junkyard intercooler. Most of the ones you'll see on recent cars have plastic end tanks with a lot of heat cycles on them, and there are a lot of cheap Chinese-made intercoolers on the market that work reasonably well.

I assume I need to upgrade injectors and fuel pump as well.  I've had good luck with DW pumps, so I'll modify the pump housing and slap one of those in. 

I'm not sure where a stock RX-8 fuel pump maxes out, but you'll definitely want an injector upgrade. And you will, of course, need someone who can tune your ECU for the injector upgrade.

I am a little lost on injectors.  Preferably there is something plug and play that would fit in the stock location and support 500 hp (room to grow) and still idle normally.

This comes to around 63 lb/hr or 670 cc/min. The "idle normally" part should be no problem if you can get the injectors with data for your ECU; many suppliers that focus on customers who use tuned stock GM ECUs will have this data available.

I plan to run the stock ecu and hopefully find somebody to tune it.  Recommendations for a decent tuner in south carolina or within about 4 hours of me would be great!

With that being NASCAR country, there's a lot of dyno shops around, although I'm not sure who is able to work with your stock ECU. Hopefully someone else will chime in with recommendations there.

In reply to alfadriver :

How does the wastegate backflow through the intake?

So, as far as the BOV, couldn't I just recirc the air back in front of the turbo to avoid all of the intake issues?

MadScientistMatt said:

wvumtnbkr said:

How do you size a wastegate?  Suggestions on reliable, but inexpensive ones are welcome!

More of a rule of thumb than anything else. A GT35 sized turbo doesn't demand anything particularly large. I'd probably use something in the 40-50 mm range.

How do you size a blow off valve? Suggestions on reliable but inexpensive ones are welcome!

These go by the volume of air you're trying to vent, and pretty much any of the aftermarket BOVs you'll see will be big enough here.

Is a blow off valve (to atmosphere) an okay choice with the stock gm PCM and sensor setup?  Or, if I don't recirc, will it stall everytime I stop?

This would work correctly if you have the MAF downstream of the BOV (and the turbo, of course).  If the BOV is downstream of the MAF, you will go rich any time it opens, and have the timing back down. This may not cause a stall, but is not ideal. You can avoid this by either recirculating the air or using speed density tuning and not running a MAF.

Should the MAF sensor be before or after the turbo?

Any MAF can go upstream of the turbo. Most of them can handle pressure and go after the turbo, although there are some plastic bodied ones I'd worry about not being able to survive boost. Or if your ECU can run speed density, the other possible answer is "Nowhere".

If I am shooting for say 400hp, how big of an intercooler should I be looking for?  Any junkyard specials to seek out?  

My usual method for sizing an air to air intercooler for a street car:

1. Measure how much room you have to fit an intercooler.
2. Use all of it.

While it is theoretically possible to have an intercooler large enough to notice drawbacks, it's rare you would be able to fit one into anything that has a production radiator core support and sheet metal.

I would not bother scavenging a junkyard intercooler. Most of the ones you'll see on recent cars have plastic end tanks with a lot of heat cycles on them, and there are a lot of cheap Chinese-made intercoolers on the market that work reasonably well.

I assume I need to upgrade injectors and fuel pump as well.  I've had good luck with DW pumps, so I'll modify the pump housing and slap one of those in. 

I'm not sure where a stock RX-8 fuel pump maxes out, but you'll definitely want an injector upgrade. And you will, of course, need someone who can tune your ECU for the injector upgrade.

I am a little lost on injectors.  Preferably there is something plug and play that would fit in the stock location and support 500 hp (room to grow) and still idle normally.

This comes to around 63 lb/hr or 670 cc/min. The "idle normally" part should be no problem if you can get the injectors with data for your ECU; many suppliers that focus on customers who use tuned stock GM ECUs will have this data available.

I plan to run the stock ecu and hopefully find somebody to tune it.  Recommendations for a decent tuner in south carolina or within about 4 hours of me would be great!

With that being NASCAR country, there's a lot of dyno shops around, although I'm not sure who is able to work with your stock ECU. Hopefully someone else will chime in with recommendations there.

Thanks!

The intercooler advice made me actually LOL.

Thanks again!

wvumtnbkr said:

In reply to alfadriver :

How does the wastegate backflow through the intake?

So, as far as the BOV, couldn't I just recirc the air back in front of the turbo to avoid all of the intake issues?

You are right- but I seem to remember some issue with the WG... 

And it's the BOV that can backflow up to the maf.  So when you plumb it, try to make sure it's directed at the turbo, so the flow back up the manifold is minimized.

There are a lot of ECU options around $1000 or so that would solve a lot of these problems and allow you to run speed density like everyone else. Rewiring an engine for an aftermarket ECU is one of those projects that sounds way harder than it is, and makes your life so much easier.

maschinenbau said:

There are a lot of ECU options around $1000 or so that would solve a lot of these problems and allow you to run speed density like everyone else. Rewiring an engine for an aftermarket ECU is one of those projects that sounds way harder than it is, and makes your life so much easier.

Oh, it's not a difficulty thing.  It's a money thing.

I believe other people are using the stock pcm.  

What is the big advantage of speed density over just recirculation of the bov?

Is there another issue that I have missed?

Thanks!

Ring gaps can make or break your engine. Literally.

Rule of thumb:

NA 0.004 x bore

     <15psi -------- 0.0055 x bore

     15-30psi ----- 0.007 x bore

     >30 psi ------- 0.008 x bore

So, if I had a 4 inch bore, we are looking at .0055x 4 (looking at less than 15psi me thinks).

Or, .022" ring gap.

Just a set of feelers for measurement?  Or does it need to be more accurate?

Basically take the piston rings off, put them in the bore down about 1 to 1.5 inches.  Use a piston to make sure they are square and measure gap with feeler gauges.  Right?

Thank yall!  Keep it coming!

This year, the car will be underbudget, but next year....  turbski powah!

Edit.  Bore is 3.90.  So that would be .02145 gap.  Right?

Is this an okay piston ring filer?

https://www.amazon.com/Proform-66785-Piston-Filer-Manual/dp/B000630J8E

wvumtnbkr said:

porschenut said:

If that motor is not built for the stress is may make 400hp but not for long.  Maybe swap in a motor that has one already.

There are a few people running 600 plus hp on these engines with no changes.  By a few, I mean there are like literally 2 or 3 builds that I could find.

I'm not swapping the rx8 again.  One entire different drivetrain was enough for now.

 

well then the motor is built to take it.  There are som NA motors that will take boost safely.  But trying for 400 from a 3.9 v6 sounds like a lot.  Good luck. 

porschenut said:

wvumtnbkr said:

porschenut said:

If that motor is not built for the stress is may make 400hp but not for long.  Maybe swap in a motor that has one already.

There are a few people running 600 plus hp on these engines with no changes.  By a few, I mean there are like literally 2 or 3 builds that I could find.

I'm not swapping the rx8 again.  One entire different drivetrain was enough for now.

 

well then the motor is built to take it.  There are som NA motors that will take boost safely.  But trying for 400 from a 3.9 v6 sounds like a lot.  Good luck. 

Thanks!

There is actually a crazy dude with a 3rd gen camaro running 10s on stock hardware and gaskets with just a cam and spring swap (to eliminate vvt).  Hasn't opened the motor from the junkyard at all.

These are built like mini ls engines.  Cross bolted mains and all.

The simple way to deal with a blowoff valve is to not run one.  There were tens of thousands of Buick Grand Nationals, turbo 2.3 Fords, turbo Subarus, etc that did not use one.  They are strictly so the driver doesn't hear turbo giggle as this is considered to be NVH.

In reply to Pete. (l33t FS) :

It can be hard on the turbo if you're running big boost and slam the throttle body shut, but with reasonable boost levels it's surely not mandatory. I think only one of my turbo cars had one and I've never broken a turbo

In reply to Peabody :

Never had an issue up to 30psi.

If a guy wanted the benefit of a blowoff valve with out fanboi noises, you cauld always plumb in the Volvo one they used on the 700 cars, which loops the air and doesn't draw a bunch of spare air through the MAF and cause a bunch of over-reporting of air flow.

But then you don't get the stupid noise.

Without the BOV you don't get the cool pssss turbo sounds. 

wvumtnbkr said:

So, if I had a 4 inch bore, we are looking at .0055x 4.....

*snip*

Yes, all of that is correct.

I have the same ring filer.  I did my 4" bore to 0.026" in anticipation of running 22psi, but found out much later that my PCM can't do 3-bar tables, so I have more gap than I need.  Which is safer than too tight, I guess.... 

... Though I have since found a way to still pull timing once outside of the 2-bar spark table.

Streetwiseguy said:

If a guy wanted the benefit of a blowoff valve with out fanboi noises, you cauld always plumb in the Volvo one they used on the 700 cars, which loops the air and doesn't draw a bunch of spare air through the MAF and cause a bunch of over-reporting of air flow.

But then you don't get the stupid noise.

The recirc valve built into the mighty K24-7400 in my Volvo sounds like one of the doors in the original Star Trek.

I took the spring out and stretched it reeeeeally long to minimize how much it works.  I'd like to just disconnect the hose but it looks like it does need boost pressure to keep it shut, too.

I did the same thing to the little Mitsubishi TD04-12T (the T stands for tiny) in my S40... which interestingly looked like the same built-in recirc valve as the KKK turbo in the S60.

Stampie said:

Without the BOV you don't get the cool pssss turbo sounds. 

One of my favorite turbo noises ever was from a 66mm Precision turbo in a BGN.  Da Boss brake torqued it to about 22psi in the parking lot and let off the throttle.  The turbo chuffed and chattered for what seemed like minutes.  (Well maybe 2-3 seconds in reality)

If there is no airflow, there is no load on the turbo and it keeps spinning.  If there is airflow through a blowoff valve, the turbo is flowing air and loaded down so it slows down faster.

A very simple intercooler setup:

Fiesta ST or Explorer ST. Both have inlet/outlet on either end pointed back toward to engine. Both are small but thick and are readily available from people looking to get rid of the stock one. It does have plastic end tanks but you will find most are VERY low on mileage as that is one of the first things people upgrade.

They do heatsoak on the stock vehicles at 200hp/400hp respectively. So i dont know how much bigger you would need it. 

For the price(might get one free?) its hard to pass up.