Build ideas for an '88 - MPG considerations Q-jet retrofit
 

My title doesn't make sense - Sorry

I have an 88 Silverado K1500 and I have a fresh build coming up that is in the planning stages.
I'm considering a 383 or a 350 with a 4bbl (Q-Jet)
The gearing is 3.73:1 and with the tires I'll be using it will turn at about 1900 RPM @ 60 MPH with the 700R4 in OD locked up.
I'd like to hear what other guys are getting MPG - wise
Mine used to get about 18 MPG with the TBI. But a fire toasted the wiring and I went to a carb.
I'm mainly concerned with fuel efficiency on the hwy
I'd like to get more mid range torque with this build - Up to maybe 4700 RPM, Just to make it a bit more sporty feeling to drive when I'm in the mood to play around.
But without hurting the fuel efficiency if possible... Nothing too extreme

You should go back and edit the title of your post by putting a comma after "88" and adding an apostrophe before the "88". This might get more people looking at it.

As it is, I clicked on it because I thought 'What sort of crack-pot thinks they can get 88 mpg out of a Blazer??" :icon_lolsign:

I'm gonna have to delete the post and start over
It won't let me edit the title
I may be a crack-pot, but I'm not crazy enough to expect to get 88 mpg

I'll edit it for you.

I'm assuming that your current setup is throttle body injection. As far as mileage goes, TBI should be a better fuel-miser setup. 18 sounds fantastic and I would be doing whatever you have to do to get back to TBI if that's what you were getting.

I have had good luck with Q-jets, but I have been messing with them for over 30 years and know them quite well. If you are going for a refurbished carb, then you shouldn't have much trouble, but you have to watch out for the fuel well plugs & throttle shaft vacuum leaks (wear). You can't go wrong with a 600 or 650 cfm holley either.

My '74 with 3.73's, 350 v8, q-jet, & 33x12.5 mud tires gets around 8mpg.

Did I mention that I went to a carb cause my engine caught fire?
There was enough left of the wiring harness to find a hot ign wire and convert to a dist/carb set up.
The amazing thing was that after I jetted the Q-jet it still got good fuel economy on the hwy with the 700r4 in OD/lockup.
That was with the original 350 long block

This truck is 31 yr old now and the most recent engine transplant is a 327 with a 204 deg @ .050 cam (That I used just because it was there waiting)
Unfortunately, this engine lacks the torque at cruising RPM on the hwy to pull OD
It will pull it on level ground, but the gearing is pretty high, and on any grade, even a slight one, I have to give it gas and the vac ga drops way down into the carbs power range.
I hoped that the 327 would get good MPG like the 350 but it doesn't because I have to keep it out of OD.

So I'm gonna build a fresh engine
My main question is: Would a 383 be a good choice, considering what my goals are?
I'm pretty sure that I can build a 350 to do the job
A 383 would obviously have more power, but would the displacement be advantageous or not, as far as fuel economy goals are concerned?

I saw that after I posted.

Lots of trucks in the junkyards with the engine side harness that would be a direct plug-in installation to get you back to TBI, but if you're already running a modded motor, then you have to get into ECU tuning to compensate properly. The ECU setups in those trucks can be finicky when it comes to changes in displacement/heads/cam/etc.

At some point I will get around to swapping the TBI 350 from the '90 'burb donor in my barn into my '74, but that currently is a larger project than I have time for as I also plan to move over the entire dash, HVAC, and main wiring harness for power windows/locks/etc. into the '74 as well.

As far as your goals go, engine displacement isn't going to impact your efficiency goals all that much, but higher displacement usually gives you higher torque output down low. Your choice of cam, heads, & compression will have a bigger impact. You should be able to go with something in the 9.5-10.5 CR with a mild cam and middle of the road heads (flow wise). You are seeking good low end torque which will help move the somewhat heavy truck on down the road.

If you aren't averse to it, a carb'd LS will show you better gains in efficiency than an older small block, however, you will likely spend more to get there. I also have a LM7 5.3L LS engine from a 2004 Tahoe sitting on the shelf in the shop that I picked up dirt cheap. It needs a crank and a set of rods, but I only paid $30 for it and it came with a new set of knock sensors & harness that I already needed & used on my old 2004 Tahoe ($290 value) so I came out way ahead with it. I've been toying with the idea of building that engine into a turbo motor for my '70 Chevelle.

I have a storage unit where I have a bunch of usable Gen1 SBC engine parts that I can play around with. So although the LS engine sounds tempting... This stuff is paid for.
I still have to pay for it with my time.
I'm throwing together a roller 350 with a ring/bearing job just to see how that does
I've even be thinking that if I put some iron exhaust manifolds to replace the headers on my 327, then that might give it enough bottom end to pull overdrive
But I really want to get as much torque as possible without killing the fuel efficiency. And I haven't made the purchase of a stroker crank, yet.

The 383s like bigger cams
My 72cc Dart heads with 2.02 valves 165cc intake volume, would give me over 9.5:1 CR with a 383
I think that it would be about 9.2:1 CR in a 350... Smaller cam = cheaper valvetrain parts.
I'd use a performer intake on either engine
I think I'd use a 215 intake duration cam with a 383
But I'm using a 206 deg hyd roller cam on my 350 build - That cam maxes out my valve springs @ .490" lift

I have decided that I have to give my 327 a fighting chance, and I'm going to try putting some 64cc heads on it - maybe some Vortecs, to replace the 8.5:1 CR smogger heads.
I'm 100% certain that there will be a noticable gain