Most important thing about this is my car is it's my daily driver and has been since '87. It's an original Az car, second owner, nice car, not hacked at all. Currently have a Tq monster 406 with pro prepared Torquer S/R heads, about 175cc port, 72cc chamber. Has real short roller cam, prepped HEI, prepped Q-jet, 200-4R GN transmission and 3.73 12 bolt. Car runs good but bad gas mileage even with carefully tuned Q-jet and HEI. I'm a carb guy.

What I want to do is dump the 406 shortblock, keep the really nice heads. I'd like to go to a 302 built in a splayed main cap 350 block (I have one already), steel crank, good rods, SRP pistons. keep the heads, headers, etc. With those heads and flattops it would be down near 8:1.

Currently this car will idle in gear with the A/C on all day in Phoenix in July/Aug. I want to hang on to most of that and get better gas mileage. I'm not a leadfooted driver in my daily driver car. So, figuring simple intercooler, move to Holley blowthrough, what turbo should I be looking at? I want quick response, not mega top end power. Most of the stuff I see on here is oriented towards big turbos and massive top end power. I'm sort of leaning in the other direction. I cruise around 2000-2200 a lot.

Anybody got any bright ideas? Anybody with experience in this type setup or similar

 

DD since 87!!

 

yeppers.

Paid top dollar for it in 87, $1700. Just an old used car then. Put about 200K on it, it's just about to roll over to 300K. Haven't had a car pmt since owning this car. Do the math on that. How can I afford to drive around in a classic car? How can I afford not to? I just want it to get a little better mileage hauling it's 4000 lbs around.

 

I wouldn't go under 8.8 comp...
12 Lb should be enough to fry...

 

What about a 3.08 gear and turbo the 406 with twins.
I guess in AZ they don't rust away. My dads truck was rusted away @ 400k. The motor then went into my old chevelle.

 

What I really need here is some kind of guidance on what specific turbos might meet my stated goals in the first post. Not really looking to put twins on the 406 or anything similar to that. I've gone to a few of the turbo calc sites, they want more info than I know how to tell. As noted, I'm really more interested in response than top end HP. With the gearing I"ve got the engine rarely sees' the far side of 4500.

Interesting, I ran across a guy who has a 400 crank with 2.75 stroke. Has a damaged main journal, so what, weld it up. That would yield a 298" engine with more room around the intake valve. I could re-use the existing block.

What type of turbo do I need to look at?

 

No way in hell I would switch the crank out for something that small unless you are racing in an under 300ci class. If you want more options then just run bearing spacers and you will have the whole realm of 350 journal cranks to chose from. For the turbo you are going to have to first off decide if you are going to build a 400ci or 300ci engine as that will greatly affect the turbo size. Your current engine, especially when backed by a 200-4R shouldn't be getting that bad of mileage. If mileage is really what you are after then you should be trying to learn the most about proper carb tuning than to be trying to shrink the motor. Even a 302 will get shitty mileage if it isn't tuned properly.

 

or maybe think about some fuel injection... put lower numerical gears in like a 3.08 to get the revs on the highway down... at least if going the carb route, have it tuned a bit better, turbo or not

 

Well, guess I give up onthis forum for now. Apparently none of the people that answer questions can read or are not familiar with the term "daily driver."

So nobody here has any idea what might be a good turbo for a ~300 cu in Chevy V-8 in a heavy street only car?

 

TayI guess where everyone is confused is why would you drop 25% displacement. There are guys on here with 363 and glides getting 16-18 mpg.
As for a 300 ci motor look at master power, you could run up to the 70 easy with a few turbine housings to tailer the boost.

 

dont give up, just look at the options and cost youre thinking about. i would rebuild that engine with pistons to lower the CR, put in 3.08s and get a new carb, or redo that one to handle boost. then youre ready for the turbo.

one thing you may cosider for turbo size is you dont want the thing to be spooliing when youre cruising around anyway, the more power the engine is making, the more fuel its going to use at your cruise rpm. face it, youre putting the turbo on to have fun with it. if it doesnt spool til 3500rpms, is that really a bad thing? if youre dead set on building a smaller motor, then go right ahead, but i just think youll be throwing more money into it than needed. i run a t72 on my 306 and i love it, even tho most people would consider it way too big for the motor

 

If you went with a 350 crank and you would lose some friction from stroke length and reducing piston speed as well, but not be giving up as many cubes. You are talking about a crank that will take a $800 set of custom pistons just to be able to put them in the 400 block, after you buy a set of 6" or 6.125" rods, and I doubt that's what you want. Your goals are pretty simple, but if you are blaming the engine size on the fuel mileage then you are blaming the wrong thing. We are here to help, but we can't read minds or know how fat your wallet is.

 

i must be a hater, but id just go with a ls 6.0 or 5.3 get 20+mpg and add some rod bolts get a tune and be very very happy. those stock ls heads probably out flow yuur heads anyways. so sell your stuff and go ls genIII sbc and never look back.

 

thanks guys for replies.

from the OP, "prepped HEI, prepped Q-jet," HEI initial is 16, total mechanical 36 at 2700-2800, plus 15 vacuum advance at cruise. Q-jet with extra altitude compensation circuit being used for adjustable part throttle, cruise is 16:1, power is 12.5 - 12.8, idle is 13. Passes Az roller emissions with flying colors.

I want to get better gas mileage, this current setup is pretty well optimized, pings if I push it any harder. Cruise RPM is is 2000 at 60 or so, the 200-4R previously mentioned has .67 OD, I could go to a 3.42 but the cruise RPM would drop down to 17-1800, getting pretty low even for the the very mild roller cam I have. 3.08? Dunno where he's coming from, It would cruise OK at Bonneville I guess.

It takes a certain amount of air to run a 406 at 2000 - 2200 in a heavy car, and that air will require a certain amount of fuel to give a usable A/F ratio. I've already leaned it out as far as practical, over 16:1. If I put on the 20 vacuum advance it rattles too bad for me to listen to. IOW, it's sort of maxed out.

So, I want to go to a ~300 inch engine, it'll require appox 25% less air and fuel from the start. If I put a decent small turbo that doesn't spool up until 2500-3000 or so I can hopefully cruise in econo-mode but still build a little boost if I want to nail it.

Is there a turbo that would be nice and quiet till about 3000 on a 300 inch engine but still build 15lbs at RPM?

the reason I'm interested in that crank is that it has 400 mains, fit in my existing block which is align honed, parallel decked to 9.000, bored and honed with Tq plates, has ARP head studs, etc, etc and gives me ~300 inches?

I need some actual model numbers to work with, things like "run a 70 and try a few different housings" don't mean anything to me, I have no turbo background.

 

What you could do is build your econo motor to your mpg standards, then inquire about tubocharging that motor.
Once you increace tq. with a turbo you can pull 3.08 gears.

Ex. (I've got a mag with a Vette that has a 8.1 400 cube roller motor, twin 58mm turbo's. It gets better than 20mpg and makes
1000hp on pump gas with 1200 on race fuel.)

 

i would vote a 350 just to keep it cheaper and simple,a 302 will not have the torque to loaf along and get mileage in a haevy A body.if it was a light chevyII maybe the 302 would work.

 

my t72 is fairly quiet if you keep it 1/4 throttle or under... but any more than that itll start making a couple lbs of boost and youll hear it spool. and mine even has the bigger .96 housing. that was with an open downpipe, so well see how it sounds once the weather warms up so i can take it out with the new exhaust.