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I'm putting a 270 i my 31 chevy pickup project and originally had my sights set on 3-2s but now want to go with a turbo. what size turbo should i look for? plan on a 600 cfm 4 barrel draw through and mild boost 4-6 psi. thanks for any ideas Jay D.

What is your use case? Where do you want to make your boost/power?

How do you plan to keep that engine together at 7500 RPM so it will need a 600 CFM carburetor?
Jerry

Its just going to be a street driver, want the boost to come in the lower rpm range it will probably never see 5000rpms
Jay D.

Its not going to ever see 7500rpms. i have a 270 in a 53 sedan with a 471 on it runs about 10# boost with a Edelbrock 600 it RUNS LIKE A FREIGHT TRAIN! so why not a 600 on the turbo? my 53 270
Jay D.

Lets get this back on track and helpful.

Jay: Are you looking for a specific turbo recommendation? Or just some guidelines to look for?

Do you like where the 471 starts to spool up with the setup you have? If so, you could run another 471 and just wastegate it to 6psi.

If you want it to spool a little sooner, you could go with a 467.

I don't know of anyone here running a turbo inline 6, so I am not sure if you are going to get any firsthand experience answers.

Edit: your pictures hadn't loaded when I wrote this. I parsed your message as meaning a Borg Warner S471 turbo (which seemed pretty big for this application).

Thanks, looking at them, there mind boggling. size of inlet size of outlet compressor air ratio and so on. i'd like to get an idea of what i need i have no clue and simply buying one that you think might work might not. i've done a lot of searching on line and can't come up with anything solid as to how to size one to my engine. i have a 302, if i can find pistons reasonable for it i will use it instead of the 270.
THANKS Jay D.

Maybe take a look at this article and the T4 they discuss:
motortrend turbo I6

It is on a 292, not a 270 but it is a lot closer than other examples I have seen.

Do you have a 4bbl manifold for it already?

the 471 project was rather expensive. it runs PERFECT we have taken it on trips of 600miles or so, does about 10-13 mpg at 60 mph. maybe a hair more. the 471 makes boost a soon as the throttle butterfly's open. if i open it up a 2500rpms its got 10# boost. i'm at just about 0 boost-vac. at 2000- 2300 rpms cruse speed of 60mph.( 700r4 overdrive trans with 370 gears) like i said if i open the butterfly's i have 10# right now on up to 5000. the turbo will be something different for me. i should be able to match something up to make it run good. if you have any suggestions i'm all ears. or if you could put me onto someone that does it will be greatly appreciated.
Jay D.

A 270 at 6lbs of boost (~1.5bar absolute) at 5500rpm and a 90%VE is ~580CFM (40lb/min air) and roughly 380HP with ideal tuning.

That makes a few assumptions, but it is hard to avoid that without a lot of expensive equipment.

So when you are looking at turbo maps, you want to find one where 40lbs/min air and a pressure ratio of 1.5 fall in the high efficiency area. Something like a Garret GT40R would work, but it is going to spool fairly slowly because 6psi is near its bottom range.

Hi Jay D. It sounds like you are working on an interesting and fun project!

I would recommend you head over to "The Turbo Forums" and spend some time reading about how to size a turbo for your project: www.theturboforums.com/forums

Its a great group of users over there and they are happy to help.

I can tell you up front that based on what you plan to do (mentioned above in your first post), a turbocharger may not be a good fit. You might consider using a roots type supercharger like you mention above used on the 53 sedan.

There are always exceptions, but the general guide for street type use is anything less than 8 pounds of boost is typically more efficient and better suited to a roots type of supercharger, especially at lower RPM’s. Turbochargers really start to become efficient when you need more than 12 pounds of boost and you will be operating at higher RPM’s.

You will learn that anything between 8 to 12 lbs of boost is sort of a gray area for the decision to run a roots type supercharger or a turbocharger.

Again, there are many exceptions to this, but it will be brought up by people a lot smarter than I am when you start to learn more about this subject.

My intentions are not to discourage you in any way. I think what you are trying to do is very cool.

I hope this helps?

A forum dedicated to turbos would proobably be helpful.

If you do want to go down the turbo path, maybe take a look at the S362SXE (https://powerdrivendiesel.com/product/borg-warner-s362sxe-2-2/).

I have a little turbo on my car that runs 6-7lbs of boost and it is a hoot, but not the most effective setup.

David, thanks! very interesting what you had to say. kinda what i'm looking for, information or where to find it. i'll be on that turbo forum. i have a roots engine but i would just like to play with something else. i had a chance to pick up a belt driven vane type supercharger (Paxton style) at a local swap meet. but past it by as like the turbo i don't know much about them and it was used. not that I'm opposed to buying something used i just didn't want something that i couldn't get parts for. another problem is the drive end with the belts i'm short on room in the 31 i allready stretched the engine compartment 3" to get the 270 in. something belt driven will add 2-3 inches or more. i just like the idea of the turbo because its only one throttle linkage, one carburetor, simple exhaust, no belts
Jay D.

Yep, i'm not looking for a ultra hi performance drag car. i just want to drive it and have some power when i step on it, at least more than a single carb with get me. i suppose one can lower the compression ratio then come up with the boost to make it a little more efficient it might get a little lazy right off idle just depends on what the turbo will do i realize its not going to be as quick as the roots.
thanks much for all your assistance! this didn't start out very good!
Jay D.

David, the turbo forum you suggested is great! thanks much.
Jay D.
This is how i would expect a forum to work, after the bad apples were removed thanks agian for all your help!

Hi Jay D.

It sounds like because of packaging issues under the hood, a turbocharger would be the better option. It’s my understanding that most OEM’s that use turbochargers on their "Daily Drivers" offerings succeed with lower than ideal boost levels with good results.

The thing that the roots type superchargers bring to the table is instant boost when you put the pedal to the metal. With a turbocharger, you have a slight lag before the fun begins.

Let the folks over on the Turbo Forums know your challenges and why you think a turbocharger is what you want to use with less than ideal boost levels. There is a user over there with the username bbi_turbos you might reach out to. From what I’ve seen, he is the most knowledgeable for something special like your project.

Also, expect to be in at least the 8 to 9 pounds of boost range to get a modest 50% gain in horsepower. This is taking in account for basic efficiency losses of the system.

Most OEM engines (that are in good shape) can reliably handle that kind of increase in power if you don’t rev it up too high. You mentioned you wouldn’t rev past 5,000 RPM. I think that is good advice. If it were me, I wouldn’t spin that 3 main journal crankshaft inline 6 more than 4,500 RPM with boost.

The 270 (and the other members 228,236,248,256 & 302 of that family of) GMC engines have 4 main journals.

Bill! My mistake. You are correct. My memory is not what is used to be...

David, its still a good idea! its an old engine, and its like trying to make a 80 year old man run the hundred yard dash in 11 flat. i run my blower 270 up to 5000 occasionally and thats about it. if i didn't back out of it i think it would rev until it scattered all over the place.
Jay D.

Specification: T-4 GT3582
Compressor wheel: 65.7/82.6/85.3mm
Compressor Housing: 0.72 A/R Anti-Surge, 4" Inlet, 2.5" Outlet
Turbine wheel: 68mm/62.3mm
Turbine housing: T4 Inlet, V-Band 3" Outlet, A/R 0.82
Oil inlet:7/16-24UNF THIS has been suggested to me what do you think????
Jay D.

You are going to be on the low side of the flow if you run that at 6psi. If you were willing to up your wastegate to 10psi you would get a lot more range and efficiency out of it.

As far as turbos that I have seen, that looks like a good choice for the low flow you are looking for.

thanks, i'm not afraid to try 10psi thats what the blower motor runs maybe just a tad more. i've only had one head gasket failure and after that i retorqued my head a couple times just letting it warm up then torquing it down agian. its been good for at least 30 k miles and some WFO runs. so yes id be in for trying 10 psi. i'm not sure of my static compression right now i have what is called a large port head but i've got to get it to the machine shop to confirm its good and have it rebuilt. so the combustion chambers are different so we have different cc measurements and different static conp. years ago it was explained to me buy a blower builder that you want to keep your static com. low and bring it up to to produce strong power with your boost. the ability to pump more air and fuel into the cyl. is where the power is. you'll get more effective hp out of 6.5 static comp. than you will 9.5 comp. you can pump more fuel and air into 6.5 for an effective ratio of say 10-1. you can't put much in if its allready at 9.5. BACK to turbos, so i can regulate my boost with the wastegate to 10 psi and still use a turbo of this specification? sorry for the questions, i'm just trying to sort this out in my mind and its worn out.
PS i use to have somewhere a book from BDS, Blower Drive Service that had a chart that took your static comp. and showed how it increased in actual comp. from pounds of boost, i can't seam to find it right now i'm still searching. they helped me a lot with my blower setup, GOOD people!!!
Jay D.

Yes. 6psi will put you at about the red mark and 10psi will put you at about the blue mark (at 5500rpm).

Lower RPM will result in lower mass flow, moving the values to the left into the more efficient range.

I think that should do you reasonably well. Based on the assumed VE and such on the engine and the compressor chart, I would expect it to give you boost from ~3000rpm up, so you won't really get any bottom end out of it. That is where the blower helps more.

That turbo will go a lot higher, but I would be hesitant to get too ambitious on the rest of the engine.

So the wastegate for a draw through will need to go in the exhaust side of the turbo?? also with the exhaust i know the turbo muffle's the sound some. i have a nice exhaust system i built with twin Flow Masters, i built headers and a 3- 2 carb setup. so what kind of exhaust do i need? can i plumb down to my existing 2, 2 1/4 header pipes and the Flow Masters? i would think one would not want much restriction on the exhaust side. maybe a straight pipe out the back??? or just dump out under the front fender!
Jay D.

Yes, A wastegate typically allows exhaust from inlet of the turbine wheel to bypass the wheel to the exhaust outlet.

THANKS, we have that taken care of.
Jay D.

What are your opinions on these turbos for my application?

https://www.cxracing.com/TRB-GT35-2-T4-81

Or this one https://www.maxpeedingrods.com/prod...turbine-housing-perfect-for-30l-60l.html

This would be for a 300ci engine ( 5 liter) inline six up to 10 psi boost and anything above 200 - 250 hp 300 is my goal, limiting rpms to 5000 i want the boost to come in low say 2500rpms. i have to wait until Monday and call to see if i can get one with carbon seals, as i want to draw through.
Thanks Jay D.

Tell me what you think of ths one: https://www.cxracing.com/TRB-T04B-5063-4B-RRB?search=TRB-T04B-5063-4B-RRB%20TURBO
Jay D.

Based on the descriptions, the last one seems like a better option to spool at lower rpm, but they don't give a lot of details so it is kind of hard to say for sure.

Edit: if you want it to start spooling at 2500rpm, you are going to need a pretty small turbo.

Thanks i'm really thinking strong about this one from CX Racing. plus he said the ceramic seals will be good for draw through. also if i don't like the way the draw through works, i can also use this one for blow through CORRECT? on the details did you scroll clear to the bottom of the description? i'm still in the dark about what all the numbers mean! the blower is so simple if one wants a little more boost just change the blower pully to a few teeth smaller and go for it.
Jay D.

I don't know anything about setting up a draw through turbo, so I can't comment on that part.

As far as what I meant by details, I have always specced turbos via compressor map and those are not provided on these ones. You can approximate that with the ratios they do provide, but I (personally) am less confident doing that.

I also personally really prefer blowers. I like the sound, the low end impact, and the easy of adjustment.

I'm with you on the blowers. i just don't have room for all the belts and so on. posibly IF i was doing a car like my 53 then i could put the elct. fans in front of the radiator, but with the 31 i can't have that. i've thought about doing another blower setup and put the blower on its side on the side of the engine sort of like the old jimmy diesels. any way thanks for all your input.
Jay D.

Centrifugal blowers use smaller/narrower belts.

Read my article:
http://victorylibrary.com/mopar/cam-tech.htm

1. call Precision
2. tell them what you're doing
3. give them your Visa #
4. done