As far as I know, there's really only one reason to lower the compression ratio - controlling detonation.

You could theoretically run 15:1 + compression if you liked, but the possibility of detonation increases considerably.

If you experience detonation, then your rods will snap, or your piston ringlands will break.

This is why you can run 7psi on a 10:1 compression motor. However, if you want to run 15psi on a 10:1 compression motor, you will have to retard timing by a lot in order to prevent detonation. This results in considerable amounts of lost power - especially on pump gas. The alternative is to run rich AFR's (11:1 or even lower), but that is no guarantee that detonation will not occur, although it will help. Your EGT's will skyrocket however, and your emissions will suffer badly (for a track car this isn't so bad....)

You could easily run 15psi with reasonable timing retard on your stock engine if you were running 115+ octane, however...

Of course, there is always methanol injection or water injection, then using an EBC to disable boost if you're running low on water. Lots of tricks you can play - but the physics can't be changed.

Then the question is, just how much stress can your stock rods and wristpins take?

 

I was speaking to Ed at Mongillo Motors and he firmly told me to not use an intercooler. I am trying to learn what I can about rear mount turbo's and Mongillo has done a ton of them. They have installed STS and many custom set ups. He said he tested cars both ways and found the intercooler hurt performance. I know this goes against common wisdom but he claims that with a rear mount turbo there is much less heat and the air forgets it was hot by the time it reaches the engine.

I am doing a lot of checking and am leaning towards a Garrett ball bearing turbo. I am now trying to understand how to find the right one for me. sizing is even more critical in a rear mount. I believe a critical factor with a rear mount is keeping the A/R on the smaller side.

 

Got an extra 10 minutes? I would like to know what you come up with.

5 Litre
10:1 compression
6250 redline
rear mount

 

The smaller AR and BB turbo will spool faster. I just can't see how a IC could hurt performance besides
a drop in boost pressure? Maybe heat soak from the front mount IC? Either way it will be plenty fast
and a handful to drive , LOL. Your right though, turbo selection is the most important thing in
usable power and there are plenty of options for every type of driver/car.

 

Lantana. I need to know how much power you plan making (max) redline of the motor and elevation where you live.

Yo have pressure drop across the intercooler because hot air takes up more volume. When it's cooled through the intercooler it becomes more dense (takes up less space) so it loses pressure.

Ar is a trade off. Smaller ar will spool sooner but it limits overall power potential. Larger ar will spool slower but has a higher power potential for the same turbo. Provided you aren't at the turbine or compressor wheel limits.

With rear mounts you loose thermal energy through the exhaust so it will spool slower anyways. You can ceramic coat and heat wrap the exhaust to make up for it.

 

I didn't see that you posted that lol ( on my phone) so I just need elevation and max power

 

The reason they say the intercooler hurt performance is because it spooled slower. It's a couple 100 rpm at most.

 

Elevation is 755

HP 533

I came to this HP number by figuring max boost at 9.5 (may end up a little lower or higher) and 6250 max RPM

Air temp of 110

Pressure ratio of 1.64
Corrected airflow 53.25lbs/min (85% of 62.7)

Does this help?

 

Yes. When I get home I'll post the compressor maps up.
You're going to have to go with a mid frame turbo due to displacement.
I did a quick plug with 550 and the best fits are a gt4202r and a t76.

I'll put in the new info when I get home and see if anything changes.

 

let me preface this by saying sorry if my posts are kinda incoherent, i spent last night/early this morning in the er for extreme kidney pain and im pretty much floating sowhere around pluto right now.

Based off of what you gave me here are some possibilities. (keep in mind the boost numbers are optimistic, you'll probably run less)

everything here figures a 14.4psi level and i did 130 degree intake temps because you never know with a turbo setup until you actually do it, so i gave some overhead

and also keep in mind, you are low on the maps because youre forced to run a large turbo due to the cfm requirements.

the points plotted, from left to right are 1000, 3000, 3400, 3800, 550, 5875, and 6250

gt4202r


gt4294r


gt4508r


gt4708


T-76


T-80


Borg Warner S362



those are the best fits.
For a street car, while keeping the price reasonable. the t76 is a perfect fit. You dont really have any growth room, but its ideal.
It will also be the most responsive out of the group, neck and neck with the gt4202r

which is also decent and has room for growth.

The T-80 is also perfect, because youre in the highest efficiency island at peak boost and rpm. but its an oddball turbo to find.

 

Thanks for the good info. It is still a litle confusing but I am getting up to speed. Can you explain the red plot points? I thought you just find where your presure ratio and corrected air flow intersect.

 

no, you have to plot the airflow and p/r across the rpm range.
the dots from left to right are rpm/pr and cfm. i used 3800 for full boost, it seemed like a conservative figure, taking into account acceleration boost curves, as well as higher gear highway speeds, etc

you never want to be left of the surge line or right of the choke line
honestly the t-76 would be dead on the money, and you can get them rather cheap and you have a ton of turbine housing options

 

I was on Ebay Looking at T-76's and there are a lot of options that I really don't fully understand.

 

Hey Lantana,

This is a lengthly read but it explains what formulas are needed in order to size a turbo. It also explains that there is information that you'd have to provide for example volumetric efficiency.

Maximum Boost - Turbocharger Systems - Bentley Publishers - Repair Manuals and Automotive Books

 

I like this statement in that read

"Multiple turbos imply more power. Power is, in part, a function of efficiencies. All other things equal, a big turbo is more efficient than a small one."

I thought the more turbos the better. Look at the Bugatti Veyron, no, not the one in the water from the cell-phone distracted driver. The ones on the road.

Or in my line of work with Volvos, the 2003-2005XC-90 has an inline 6 cylinder with 2.9l of displacement and 2 turbos with a power output of 286 hp. Seriously de-tuned to comply with Volvo's hardon, errrr.. I mean, commitment to safety. They feel slower is safer.

 

I believe smaller turbo's spool up faster and running two smaller turbo's make sure you don't lose top end. I think some multiple turbo's can be set up so that a smaller one comes on line first witha second one coming online latter. I think i will be fine with a single and am leaning towards a ball bearing turbo for quick spool up.

 

two turbos normally allow for high top end, but mid and low suffer.
they are also very in-efficient compared to what a single turbo is capable of.

post up the links of what you're looking at and i'll see if i can help.
I'm also going to tweak your map plottins slightly, by figuring out actual intake temp, but you'll still want to look at the t76

 

oh, theres a new garrett gt4508 chra on ebay, no housings for 650... thats a 2500 dollar turbo and housings arent hard to find

 

Thanks for the tip! This following link is a very helpful read. I read it all the way through and it is long but very comprehensive.

Build Your Own Turbo Kit

On the site they also have a great right up on rear mount turbo's. check it out!

Build Your Own Turbo Kit

 

Mongillo Motors who I have mentioned above sent the following information to me. Thoughts?

"T76 will be to big. You want to go with a T4 60mm or 67mm turbo. 60mm would probably use a .96 A/R housing and the 67mm would use a .83 A/R housing."

Ed at Mongillo thinks I should go for drivability instead of highest dyno numbers. One of my goals all along was to build a "German Corvette". A base Corvette puts out 430HP and the ZO6 puts out 505HP. I am a couple hundred pounds lighter than a Corvette but would like to smoke both of these models.