DCharger68 None
March 5, 2014 11:52 p.m.

So I'm in a bit of a dilemma. I joined another forum site hoping to get an answer on a question concerning if a T3/T4 would be too small for a 307 Chevy that redlines at 5800 RPM. Unfortunately they didn't help at all. I'm aiming for 350-400 horsepower on a draw through setup. Any help would be greatly appreciated.

Kenny_McCormic UberDork
March 6, 2014 12:11 a.m.

The typical T3/T4 is advertized as a 300-400hp turbo, so I'd think you're good. I don't know much about turbos, but I'd think that spool pretty fast on a 5 liter V8, seeing as the T3 is a popular sub 2 liter import turbo.

DCharger68 New Reader
March 6, 2014 12:15 a.m.

You are literally the first person to give me an answer I was looking for. Thank you. I know the compressor side can feed it but the exhaust side is the part I'm worried about. I'm afraid that much engine would overspool it. Although the sub 2L cars that use a turbo run way higher RPMs than what I'm looking to do. It's going in my 77 Camaro as a mild street/strip car (it may not be that mild but I run with 550hp+ big block and boosted cars).

Kenny_McCormic UberDork
March 6, 2014 1:03 a.m.

I'm sure its far from ideal(seems this turbo is common in ebay twin turbo kits) but will probably work for what you want it for. Not like a (presumably stock) cast crank 307 is up for much more than that anyhow.

I'm sure come morning multiple people will chime in at varying higher levels of technicality of just how suitable a fit this turbo is.

chknhwk HalfDork
March 6, 2014 3:31 a.m.

Compare your volumetric efficiency of the engine and estimated intake flow to the compressor map of the turbo you are considering using. http://www.enginelogics.com/read-a-turbo-compressor-map/
http://www.not2fast.com/turbo/maps/all.html The more you start looking at the numbers and making informed decisions on your own the happier you'll end up! Compressor maps aren't all that hard to figure out once you get used to reading them.

Pat HalfDork
March 6, 2014 4:24 a.m.

T3/T4 is just the frame architecture...do you know the specific specs of the turbo you have there? Housings? Wheel sizes? Where do you intend on mounting the turbo?

edizzle89 New Reader
March 6, 2014 6:43 a.m.

any reason your going with draw through? with draw through you will have to change to a carbon seal in the turbo since it will be seeing vacuum since its downstream of the throttle plates.

also you wont be able to run an intercooler because it will cause fuel puddling and if theres a backfire through the intake it could become very bad very fast. not sure what your plans are, with low boost you could get away without one so that my not be an issue for you

pres589 UltraDork
March 6, 2014 7:16 a.m.

I thought it was more common these days to do blow-through with a carb that's been worked for boost. Quick Fuel sticks out in my mind as offering these sorts of things.

And it's a 307; I wonder if a Tuned Port Injection setup could be used, ala '80's Camaro, with a snail to good effect.

EDIT: I just remembered the Calloway "Sledgehammer" 'vette used a Tuned Port setup with turbos and skated in around 254 mph. So, yeah, that could be good.

DCharger68 New Reader
March 6, 2014 9:04 a.m.

Thanks for the help guys. I'm going with a draw through because of the cost of going blow through. I've looked at tuned port but I'm not sure how to tune it. And I think the ar on the compressor is .60

turboswede UltimaDork
March 6, 2014 9:16 a.m.

Tuned Port manifold + Megasquirt + TunerStudio = done.

From what I understand, a blow through carb solution requires a sealed box around the carb and/or carb mods.

edizzle89 New Reader
March 6, 2014 9:22 a.m.

yea you can run pretty much any carb if you use a carb box, just need nitrophyl floats so they dont crush. to use just a carb hat you need mechanical secondaries and a list of other things done to the carb


here is a full step by step on how to convert a holley.

if you could get a carb box made up for cheap i would think the cost would be equivilant to a draw through and gives you the option of the intercooler. but a draw though and a simple water injection set up would do pretty good i think

pres589 UltraDork
March 6, 2014 9:25 a.m.

In reply to turboswede:

Older carb tech did require a box. That's been fixed. I haven't read how that was done in any detail because I've no interest in these setups, but I see them in magazine write-ups and they seem to work. Like this thing;

DCharger: A few years ago Car Craft wrote about a 350 they built up using a TPI setup with SLP runners and some other little tweaks. They controlled it with a Megasquirt. As I remember they came away very impressed with the unit. There is more money here, of course, but it might be worth looking in to. And there's a lot of places online to find support, including here.

DCharger68 New Reader
March 6, 2014 10:02 a.m.

Well so far this is the only forum to help me and not say I'm a dumb kid trying to do something that won't work. I'll check out that car craft article and see what I can do. I'm just looking for a lowish dollar way to turbo the little motor. I figure I'll run it until it blows and then replace it with something better like a 400. Thanks again for all the help guys.

Edit: I forgot to ask, what exactly is a carb box?

PseudoSport HalfDork
March 6, 2014 10:03 a.m.

I used turbo calculator on http://www.squirrelpf.com/turbocalc/ and quickly plugged in some numbers. Assuming you are using a 60 trim T3T4 (largest map listed) and are looking for 400hp it looks like that turbo will be too small. Grated I did guess at how it would spool and a few other numbers but I only used to the calculator to get a rough idea.

A better match might be two 50 trim T3T4

DCharger68 New Reader
March 6, 2014 10:13 a.m.

Alright. I think I can make that work.

pres589 UltraDork
March 6, 2014 10:15 a.m.

In reply to DCharger68:

Here's a carb box;

This is used so the carb bowl and venturi's all see the same pressure. It makes it easier to get the carb happy with internal and external air pressures so it will still work. One of these boxes plus the right floats and power valve (and jetting...) will get you a carb setup that functions as it should. They've been around for a long time.

DCharger68 New Reader
March 6, 2014 11:07 a.m.

How hard is it to set up a carb box compared to a draw through? And can a Qjet work in one?

David S. Wallens Editorial Director
March 6, 2014 11:10 a.m.

Just wanted to say, thanks, everyone, for helping out a new forum member.

tuna55 PowerDork
March 6, 2014 11:20 a.m.
DCharger68 wrote: How hard is it to set up a carb box compared to a draw through? And can a Qjet work in one?

No, I am pretty sure you want mechanical secondaries for a non-box app.

DCharger68 New Reader
March 6, 2014 11:42 a.m.

What about a holley dp if I can find one fairly cheap? I asked about the Qjet because I already have one

edizzle89 New Reader
March 6, 2014 11:53 a.m.

as far as i know any carb can work in a carb box with the correct floats, vacuum or mech. secondaries. but mechanical secondaries is a must when just using a carb hat like pres589 posted

edizzle89 New Reader
March 6, 2014 11:58 a.m.

also carb boxes are ridiculously expensive, having one made is probably the cheapest route, the tricky part is just getting a seal around where your throttle cable come into the box

DCharger68 New Reader
March 6, 2014 12:08 p.m.

So about the best way to keep it fairly cheap is to sell my Qjet and buy a holley dp and modify it for blow through or to build a good carb box?

pres589 UltraDork
March 6, 2014 12:14 p.m.

Can I go and be the huge jerk in the room and say that if you are at the end of the budget scale to where selling a used Q-jet is going to provide noticeable funding assistance to this project, you may be smart to hold off on this project and just get the 307 running really well as a naturally aspirated engine?

Here's my logic; the 307 has fairly trash heads from the factory. Are you still on factory heads? They have lower compression that deals with boost well but I don't know how strong the pistons and rods are...

How much do you have to spend on all of this, do you know exactly what the turbo is / has the turbo been purchased or are you still working on that as well, etc etc? The more I think about a stock 307 bottom end (especially one that's had real mileage on it) dealing with ~350hp, I'm not sure how mechanically sound this plan is.

edizzle89 New Reader
March 6, 2014 12:14 p.m.

yep pretty much, or do the draw through and get a carbon seal for your turbo. but if your wanting big power i'd say go straight to blow through

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