Calling All 383ci Trucks

[VDOG]

Originally Posted by WorkinLonghorn

VDOG, there's something way off here. I don't have time this morning to figure it out but you are either in 2nd gear or you have a MUCH lower gear in the diff.
I have 3.73 and at 65 I'm at 2600 or so.
My last truck had 3.07 rear (33" tires) and it cruised at 60 at 1875 RPM.

Ok FT size 15x8 255x60x15 26 1/2 tall tires in the back
RT size 275x60x15 27 1/2 tall tires on 3:08 gears and Th 350 trans with a 283ci motor. 4000 might be high but its in the high 3's easy

[mrein3]

Originally Posted by WorkinLonghorn

VDOG, there's something way off here. I don't have time this morning to figure it out but you are either in 2nd gear or you have a MUCH lower gear in the diff.
I have 3.73 and at 65 I'm at 2600 or so.
My last truck had 3.07 rear (33" tires) and it cruised at 60 at 1875 RPM.

I agree. Something is way off in your calculations or actual readings. My engine has never seen 4000 rpms and I drive down the slab in a 70mph zone all the time.

I didn't write it down but the last time I was out in a 70 mph zone, I think I was taching around 3200 rpms.

Again I have 3.73 rear end gears and 28" tall tires. Assuming I'm seeing 3200 rpms in my truck at 70 mph, 3.08s with 28" tall tires should be seeing approximately 20% lower R's or 2500 - 2600 R's.

[68GMCCustom]

Originally Posted by WorkinLonghorn

VDOG, there's something way off here. I don't have time this morning to figure it out but you are either in 2nd gear or you have a MUCH lower gear in the diff.
I have 3.73 and at 65 I'm at 2600 or so.
My last truck had 3.07 rear (33" tires) and it cruised at 60 at 1875 RPM.

I agree. I have 275/60-15 tires on mine with fairly new 3.73 gears. my truck runs in the low 3k rpm range at 60-65.

[mr48chev]

I've been collecting pieces to build a 383 out of the original 4 bolt 350 that Came in my 71 GMC C2500 that I use to tow and haul on a regular basis.
Plans include Vortec heads, Comp 268 Cam, intake intended for torque and a carb in the 650 cfm range but I am leaning towards aftermarket fi.
I'm currently chasing a 3.54 Posi Dana 60 to replace the 4.11 that is in it now.
This is the last full sized truck I intend to own and the plan is to own and drive it for a long time. I would like to be able to pull better fuel mileage with it though.

I think the main thing is to sit back and view exactly what you do and intend to do with the truck and go from there.
If all you haul is luggage, cooler and lawn chairs to head to a rod trot or other event a mildly modified 350 is probably a better bet. If you tow a trailer on a regular basis the 383 may be the better option in that you would have the extra torque an power to pull the hills and handle the load. And it just might let you run with the big dogs without straining.
With the correct cam you shouldn't have to change anything in the drive train.

[Gray Ghost]

I had my 350 built for $1100 here locally & saved a ton of money! Mine gets 12mpg without OD [TH350 soon to be changed to a 700r4]. The motor is a very strong one that has a mild cam [pulls from 1000 rpm for towing]. The tranny is rebuilt as well.

The 383 will be much more fun, but I think for your application a stout 350 is all you really need.

[mrein3]

A 383 is a no-brainer in my opinion if you are sticking with a small block. You can build a 383 for ALMOST the same cost as a 350 since the 383 parts are so common now. I managed to get mine done for a touch over $1200. I used a 350 block out of a Monte I used up years ago. My rebuilder had a 400 crank he was saving for such a project. The rods are out of the Monte. The rebuild kit with the correct pistons was +/- $20 of the cost of a 350 kit. If you have a small block in your truck now EVERYTHING else is the same on the truck. (You state you have a 283 so you're good to go).

I run mine in a 4x4 with 3.73 gears. The only thing I would (actually am going to) change is the tranny. Right now I run a th350. The rpms are a tad high on the highway in the 70 mph zones. A well built 700r4 would be just the ticket and is on my list. With 3.08 gears you will be fine with a th350. In fact I read on these pages that people with 3.08 gears got worse mileage after switching to a tranny with OD.

For me the benefits of the 383 far outweighed what I could get out of a 350. I pull my boat a lot. I pull stuff like docks and boat lifts out of the mud bottom of the lake. You really notice the difference. I just stuck a snow plow on the front of it for the winter. We'll see how that goes.

If you're just going to drive around the city, nevermind. Get a 350.

[VDOG]

Originally Posted by mrein3

I run mine in a 4x4 with 3.73 gears. The only thing I would (actually am going to) change is the tranny. Right now I run a th350. The rpms are a tad high on the highway in the 70 mph zones. A well built 700r4 would be just the ticket and is on my list. With 3.08 gears you will be fine with a th350. In fact I read on these pages that people with 3.08 gears got worse mileage after switching to a tranny with OD.

See im not pulling anything, car, boat nothing like that. And Im going to have to disagree with you on the revs of the 3:08 gears. On the freeway at 65mph im taching out at 4000 rpms with those 3:08's and TH350 trans.

[piecesparts]

385 Cu In stroker motor with Comp Cams roller cam and rocker arm setup, Edelbrock Performer RPM intake, "Carb Shop" billet dizzy, Edelbrock AVS 650 carb, and Moroso 7 quart oil pan.

This is the second engine that I have built like this and the driveability is better than a normal 350 and has more low end torque than needed. I am running a 700 R4 with 3.73 gears and 28" rear tires. Highway RPMs are at 2500 RPMs at 70 MPH with the gas mileage at 15 MPG. I have had this truck all over the country on numerous Hot Rod Power tours.

[VDOG]

Originally Posted by piecesparts

385 Cu In stroker motor with Comp Cams roller cam and rocker arm setup, Edelbrock Performer RPM intake, "Carb Shop" billet dizzy, Edelbrock AVS 650 carb, and Moroso 7 quart oil pan.

This is the second engine that I have built like this and the driveability is better than a normal 350 and has more low end torque than needed. I am running a 700 R4 with 3.73 gears and 28" rear tires. Highway RPMs are at 2500 RPMs at 70 MPH with the gas mileage at 15 MPG. I have had this truck all over the country on numerous Hot Rod Power tours.

Thats a helluva motor. Im convienced, 383 it is. Cause I do want the torq and power and if I get it built for reliablity and for light to light, I should be ok.
Thanks.

[ratpackv8sonly]

I have a 383 in my 69 as well. 700R4 with 4:11s and on the hwy it was getting 18mpg. Offey intake with a Q-jet and points. Its a good truck engine with alot of torque an you should be happy with it in yours even with the 3:08 gears. But then there is nothing wrong with a good 350 engine.

[piecesparts]

Originally Posted by ratpackv8sonly

I have a 383 in my 69 as well. 700R4 with 4:11s and on the hwy it was getting 18mpg. Offey intake with a Q-jet and points. Its a good truck engine with alot of torque an you should be happy with it in yours even with the 3:08 gears. But then there is nothing wrong with a good 350 engine.

Wow, 18 MPG with 4:11 gears, the tires must be pretty tall, to get that. That is a good thing, that you can do that. The Q-jet is part of the combination that helps in that area.

With a set of 3.08 gears, don't overdo the cam choice. The gear ratiio will kill your take off and screw up the gas mileage. My son's truck had 3.08 gears and when we put an OD tranny in it, the RPMs fell to just under 1800 at 70 MPH. The mileage also dropped off. We put a set of 3:73 gears in it and gained back 2 MPG and it is a strong running 350 truck.

[VDOG]

Options Options!!
I just know its time to get out of the 283!

[68Stepbed]

VDOG, you won't have to change your gears with a 383. The 3.08's will be fine as long as you don't get too radical with the engine and cam selection.

My suggestion would be this:
383 with Vortec heads, an RV cam, NO bigger than a 600 cfm carb, a dual plane intake, a good HEI ignition system, and a decent set of headers.

This combo should be very similar to the GM crate engine noted above, but alot less money. It would have great street manners with a smooth idle and still provide about 300-320 hp which is plenty enough to smoke tires when you want.

[VDOG]

Originally Posted by 68Stepbed

VDOG, you won't have to change your gears with a 383. The 3.08's will be fine as long as you don't get too radical with the engine and cam selection.
My suggestion would be this:
383 with Vortec heads, an RV cam, NO bigger than a 600 cfm carb, a dual plane intake, a good HEI ignition system, and a decent set of headers.

The parts you mention above is what I had planed for a 350. About 9 to 5 compression with Vortec heads, RV cam and add my HEI and Headers with a Vortec Intake and my 600 Carb. I figured that would be a good strong motor with ok gas mileage, and decent power.

[special-K]

Is it the longer stroke makes it less suited for highway and you`ll get less miles argument?It`s not that significant of a stroke over the 350 to matter there.It`s not like it`s in a whole new rpm range.Plus,you`ll get better power from lower rpms so that makes up for the extra travel on the piston at a given rpm.

[Slik69]

All I can say is prior to buying my 69, I often used my dad's 70 which has a 383.. and the one thing I dreaded the most about using his truck was replacing the gas I used. Sometimes the cost of replacing gas outweighed the use. 'Seriously'. He also has a Victor Jr. Intake a Carter 850 AFB carb, and Dart heads. Way too much IMO. I think if he changed carb and intake he would see an improvement in gas mileage.. but not much, but I think it will lose some zip.

This motor was built for an El Camino, but was quickly taken out because the car would not go in a straight line at any speed. It was simply too much motor for a light car. Put in in a 3/4 truck loads of difference on behavior. Stall is something you'll have to add also. Why add the power if you can't get it to the ground. His truck is nice and you can hear it coming and going.. but I want something different for my truck. I will be going with a mild-stout 350. It drives plenty good right now with a very tired 327 in it.. so a freshly built 350 will be that much better. It's a 1/2 ton truck and only weighs 3780.. that's pretty light for a truck. Has a TH350 behind it and gets decent gas mileage since switching over to HEI.

My dad still has the truck and I can't tell you the last time it was driven.. He calls it the beast. He too complains about the gas and says "that's why it's sitting there". He'll be making some changes soon that I mentioned above.. but the base will still be 383.

Bottom line, it's your truck so you can do what you want to do. If you can afford to gas it and go COMFORTABLy,, then build the 383 and drive it like you stole it. If you want a better balance of the two, then 350. I'm going 350 route with my build. Will not be towing anything either, but in the event I do, I am confident the 350 will be able to handle it. Once you get up to speed the stress is pretty much off the motor anyways. I will be going with a 200/700, or leaving the TH350 in I already have. Doing this research now. Folks seem to like the TH350 over the overdrives. Anyone know why?

[mrein3]

Ha! We posted at almost the same time.

[Blackbird66]

Sound more like a 4.11 gear. I too have 275/60r15 with 3.73, and I'm spinning 3-3.5k on the interstate. As far as gas milage........I've run a stock 307 2bl hopped up 283 4bl, and now a gmpp 350 ho. All three motors got nearly identical gas milage on the interstate.

[70rs/ss]

A vortec block and heads (roller cammed) can be found for a core price ($100-150) and it'll get you a set of heads, as well as a vortec roller cammed block, buy a balanced 383 kit that'll drop into the block for like $8-900 and all you'll need is a bore/hone and some small reliefs in the block for clearance. Get a mild roller cam and use the factory roller lifters, etc and the heads will ahndle up to .500 lift/flow so a .480-.500 lift cam would be fun smaller is OK and then you'll have an honest 350-400hp and over 400lb/ft of torq. With a 3.08 and a th350 you should be able to smoke em for as long as you want, get decent MPH and MPG on long road trips and it'll last forever under 6K RPM, so why not build one?? With a complete kit, you can do this for about $1500-1800 tops and as mrein3 said it can be done even cheaper, but the piecing it together can get pricey for a balance, whereas the balanced kits come ready to use, so a little more $$$ = less work and headaches?? Do I have one, yep, and it'll be north of the 450hp range with 500lb/ft of torq and a HUGE cam, but so what it'll outrun most anything I come across and I'll be OK with frequent stops for premium fuel, cause the smiles per/gallon is all I am worried about!!

[WorkinLonghorn]

70rs/ss; I'm sure this has been beaten to death elsewhere but if he uses Vortec heads, will his accessories bolt up or not?
Also he'll need vortec intake.

[70rs/ss]

Originally Posted by WorkinLonghorn

70rs/ss; I'm sure this has been beaten to death elsewhere but if he uses Vortec heads, will his accessories bolt up or not?
Also he'll need vortec intake.

Accessories will bolt like any SBC, they have the same bolt holes as all SBC heads do, and they take a normal or reversed water pump so , litterally the 67-72 accessories bolt on and work as is. Yes, he'll need a Vortec intake $130 new, so no real increase in $$$, but all the benefit outweighs the extra $$ IMO since a roller cam, and never worrying about a flat lobe in and of itself helps me sleep at night.

[68Stepbed]

I'm gonna have to agree about the numbers being off on your calculations. I have a TH350 and 3.73 gears and I turn about 3350 at 70. It would turn 2500 at 70 with 3.07 gears. I'm also thinking you have 4.11 gears.

How did you determine you have 3.08's?

Check your calculations here.

[VDOG]

Originally Posted by 68Stepbed

I'm gonna have to agree about the numbers being off on your calculations. I have a TH350 and 3.73 gears and I turn about 3350 at 70. It would turn 2500 at 70 with 3.07 gears. I'm also thinking you have 4.11 gears.
How did you determine you have 3.08's?
Check your calculations here.

The original engine for this truck was a 305, 2bbl carb. Also when I removed the gears to install 3:73s I had the numbers refference, and from talking to a few people here, I found out they were 3:08's.
I also learned the hard way that 3:73's out of a 1970 6cyl 12 bolt truck will not fit in a 69 12 bolt truck. Would not line up and when installed one axel went in further then the other. (See attached inner drum pic.)
Notice how the lip of the drum on one side has a lip while the other side is flush.
So the guy rebuilt it to the stock gears, 3:08's

[68GMCCustom]

isn't that because there are 2 carriers for truck 12 bolts....1 for 3.73 down...and one for 3.73 up? ...or something like that.

[VDOG]

Originally Posted by 68GMCCustom

isn't that because there are 2 carriers for truck 12 bolts....1 for 3.73 down...and one for 3.73 up? ...or something like that.

I cant remember what the gears were, either 3:55's or 3:73's, one of the gurus here can tell me for sure because I forgot. The reason for the difference in the spacing, 1970 rearend and axel tubes are longer.
1970 uses different length axels.