Turbocharger Sizing?

In reply to Ojala:

Well, the heads don't flow that well compared with what I'm used to, but the bottom end should be pretty stout on these.

Swank Force One wrote: I'm down with a t3 flange hx35 or hx40 in this case if you're looking cheap. 3076 will do your requirements but Vigo has a good point.

He could get a 3076 with the bigger exhaust housing A/R (84?) to slow down the spool and increase the top end flow where it will probably need it.

Need to do some flow calculations on the engine and learn to overlay that with compressor maps: http://www.gnttype.org/techarea/turbo/turboflow.html

Then go use a calculator or build out an excel spreadsheet with some calculations and overlay compressor maps:

http://www.squirrelpf.com/turbocalc/ or http://www.turbofast.com.au/TFmatch.html

and go talk to the junkyard turbo guys

OK, I did some more digging.

Flow chart for the 3.4 and the 3500 V6.

Apparently I need the 3500 heads, intake and plenum. The only problem there is that will put me at 11.5:1 CR using the 3.4 bottom end. That's probably a little high to be throwing boost on top. The quench also ends up at about .070. However, if I use the 3500 block and bottom end that will give me the forged crank as well as drop the CR to a more boost friendly 9.8:1

The 3500 is also 220-240 hp out the box. Kind of the easy button. It will necessitate building some funky mounts to put a FWD engine in a RWD car. Shouldn't be a problem though.

So, assume a 3.5L engine that flows like the chart above with a decent power band that will pull strong to 6500-7000 rpms.

In reply to Toyman01:

She'll be rattling like a belly dancer if you keep it up that high for very long.....but as you said, its possibly a better option. Or you can just boost the otherwise stock 3.4 for now and see how long she lasts.

This was hiding at the bottom of one of the pages Raze recommended.

www.gnttype.org/techarea/turbo/turbocalcs.xls

Just in case anyone is interested.

I'd rather have the power under the curve and quicker throttle response. Stupid big torque is easy to manage if it responds quickly to inputs and you have properly setup boost control.

Sure. Have you owned a 2300# car with 350 lb ft of torque at 3200 rpm? Just asking. My opinion is based on experience. It's fun when you're going straight and an absolute pain in the ass when you're trying to turn. Yes, you can do things to make it more manageable. In my opinion turbo sizing is one of the easiest things you can do if you're starting from nothing. The problem you need to avoid is having a 200 lb ft change in torque from 1/2" of pedal travel when you're busy trying to stay inside your traction circle around a turn. That requires a level of awareness and precision that detracts from fun rather than adding to it.

Vigo wrote:

I'd rather have the power under the curve and quicker throttle response. Stupid big torque is easy to manage if it responds quickly to inputs and you have properly setup boost control.

Sure. Have you owned a 2300# car with 350 lb ft of torque at 3200 rpm? Just asking. My opinion is based on experience. It's fun when you're going straight and an absolute pain in the ass when you're trying to turn. Yes, you can do things to make it more manageable. In my opinion turbo sizing is one of the easiest things you can do if you're starting from nothing. The problem you need to avoid is having a 200 lb ft change in torque from 1/2" of pedal travel when you're busy trying to stay inside your traction circle around a turn. That requires a level of awareness and precision that detracts from fun rather than adding to it.

I currently have 200ftlbs in a 2100lb car at 3000 rpm, and the goal is to have 300ftlbs once I put a tranny in it that wont explode at that power level. Proper boost control is key, if you make 15psi peak you need to be making 6-7psi at 50% throttle and it needs to happen instantly. If you can make the power easy to modulate then you want all the torque you can get everywhere, since you'll be able to use it in a straight line and in higher gears. Heck, better yet run a massive EWG and do boost by gear, and only make 5psi in 1st.

Better yet, run a big EWG and a light WG spring, and do boost by TPS.

bradyzq wrote: Better yet, run a big EWG and a light WG spring, and do boost by TPS.

Thats part of "good boost control"

JtspellS wrote: GT2871 or 3076?

You would not want a T28 on this, those are for 4 cylinder cars or twin turbo projects. The 3076 though would probably be perfect.

I only know going off of a VG30ET engine and the reading i've done on that, I can read compressor maps but only if I know everything about the engine it's going to be put on.

About really knowing how to read them and how to compare I don't need to know. People expect you to read maximum boost or know everything when how often are you going to select a turbo for a car? I would rather ask someone who knows that engine or people who are paid to know something like that.

Also there is this: http://www.squirrelpf.com/turbocalc/

But you have to know quite a few things to set it up properly.

Here is some examples of maps on a SOHC 3.0 V6, the VG30ET mentioned above, probably will give you similar results. http://www.mygen.com/users/dbruce/myz31/TurboMaps/VG30ET%20Engine%20Air%20Flow%20and%20Turbo%20Compressor%20Maps.htm

Zombie thread, revived from the dead because I'd like advice in choosing turbos for a 3.4L flat six. I'm looking for throttle response and improved low end torque. Static compression ratio is: 11.3:1, so I'm planning to add only around 4-6lb of boost. Bonus points if I can keep it cheap with junkyard turbos. I want twin turbos because it's a flat six. Maybe Audi S4 K26s?

Pick the amount of power you want, then pick the smallest turbo that will achieve that. However, if this is an air cooled engine there's more to it than that.

In reply to Leafy:

It's water cooled, and my goal is 400hp at the crank

For that in the Cheap you have a ton of factory turbo to choose from. Td04 is another one to pick from. The volvo variant is probably the best for you. But either with any of these you won't be happy with only a few psi, something more like peaking to 20 as low as possible and then tapering to 10ish would get you what you want with any of them pair of small turbos. You'll need something way bigger than stock turbos on anything but a diesel truck to get 400hp with 4-6psi.

ditchdigger wrote: Oooh! can I play too? Which cheap and easy to find in the junkyard turbo for a 2.8 or 3.3 6 cylinder?. Low power goals of 200 to 250hp.

A Mitsubishi 20g would work. They can be found on Fuso trucks.

moparman76_69 wrote: I'd say a hx35 would be kinda small. also they are designed with divided housings so unless you're willing to build headers with that in mind, you'll lose spool. Maybe a hx35/40 hybrid would work.

from what i've seen people say that the hx35 is just about right for a totally stock 302, anything more and you would want a bigger turbo. So i think the hx35 would be a good option for the 3.4 and they are cheap and plentiful

it also somewhat follows this very primitive rule of turbo sizing since the hx35 is on a 5.9L diesel:

Fueled by Caffeine wrote: Ready. Here is my horrible quick and dirty turbo sizing. If it works on a 6 liter diesel at 3000 rpm it should work ok at 6000 rpm on a 3 literish gas motor. It's all about the gas flow. And I don't mean uncle morty after a bowl of chili and two natty lights.

Yeah, we also have a member here who had valve float at 4000 rpm because the backpressure from his turbine section was so ridiculous it was holding his exhaust valves open. Picking the smallest turbo that will hit your power goal, in my opinion, sounds like a terrible idea.

Although, a rear engined car would have a lot easier time coping with loads of low-rpm torque than most as far as traction goes. Unsafe at any speed is too strong a term! It would be more like 'unsafe to spin tires while turning at any speed while not on a closed course'.

That sounds like a tuning failure. Opening the waste gate more in that case would generate the same amount of boost but with less back pressure because you're just trying to spin the compressor faster than the turbine is capable of. Not something you can do with a manual boost controller. Anyone with a reasonable power goal (IE noticeablyn more than you can reasonable get n/a bolt on) isn't going to run into that problem unless they get some bizarre sized turbo.

Twin IHIs from a turbocoupe?

What type of vehicle is this going to be for?

In reply to 92dxman:

Porsche Boxster that's geared way too tall. Turbos desired to overcome unreasonably long gearing

That sounds like a tuning failure. Opening the waste gate more in that case would generate the same amount of boost but with less back pressure because you're just trying to spin the compressor faster than the turbine is capable of.

The problem was the turbine discharge section. Which just adds to the idea that it's more complicated than 'smallest thing you think will work'. I'm not trying to make it sound intimidating, but if anyone is going to be operating on vague generalities, just don't spend a lot of money on the first go round or you might wish you hadn't listened to (literal) one-liners about turbo system planning.

In reply to Vigo:

Most off the shelf turbos aren't going to run into that issue unless you make them by tuning like a dufus or sucking at fabricating your exhaust. Most are designed with turbines and compressors that match and as long as you don't do something really dumb like put a 250hp turbo on a 3 liter you'll be OK. And that's where the reasonable hp stipulation comes in, if I have to make the guideline more specific, that reasonable hp minimum is ~125% of bolt on power.

The kits I've found for my application (TTP, Lotec, etc) all use Borg Warner K24 turbos. I'm only second guessing their selection because K24s are commonly found as OE turbos on old (1986-91) VW diesels. Turbo technology has to have improved significantly since the last 1991 Jetta 1.6L diesels were built. My friend, and GRM regular, "carbon" is something of a turbo wizard and he tells me I should use a pair of modern aftermarket Garrett turbos.