So I was looking for some engine info the other day and ran across this Pentstar discussion forum on line. Its not a big site or anything but seems friendly enough. Anyway I invited a guy who was responding to some propane posts I put in to visit us here. Be surprised if he isnt here under a different name because he apparently has a 76 powerwagon short box 4x4. But heres the thing. He says he has a stroked 383 (431 cid) that is getting 18 to 22 mpg. Thats with 3:55 gears, 10.5 compression on low octane pump gas, carter 2v carb, 906 ported milled heads, forged flat tops, doesnt rev over 5000, and full time 4x4 tcase. Now thats something. Cant see it myself, between detonation on 10.5 compression, or 18 to 22 mpg. But I'm no expert. Anybody think this is doable?
Pentstar web site?
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I was getting 19 20 mpg with the other tires and the bed covered tight, with the bed open the tail gate off the slightly heavier tires im getting 17 18 mpg, this is a 60 though on highway no stroked 83, i never build for mpg but none of my strokers get anywhere near that kinda double digits mpg, unless it's gallons to miles lol
And what do you think of 10.5 compression on cheap pump gas and getting that mileage? It might be possible to run 10.5 on lowest octane pump gas if you are spinning off the compression with the cam, but my understanding of that combination is a high reving engine producing max torque and hp at 6000 or better, low power in the lower ranges because of the cam. Somebody please correct me if I'm wrong.
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Hey guys
I'm one of the moderators at PentaStarPower.com, which has ample tech help if anyone needs...
I'm also the owner of the 431 in question. I didn't build the engine, my close friend and professional mechanic of over 35+ years built this engine, and he has a TON of tricks of the trade that even I don't understand, but this thing RUNS!
Even when we were building this engine, we had parts store guys, other mechanics all telling us that this wouldn't work.
I drove this truck out to Mopar Nationals in Columbus, OH in August 2000, with some other members of the PentastarPower.com forum. As a reference, I live in NW Iowa, so it was a long drive.
Anyway, locally I can get 18-22 mpg, usually around 18-19 but I have gotten as high as 22, more than once. On the big trip, even on the interstate at 70-75 mph, I still got upper teens (16-1
for most of the trip.
The cam is an RV style, set up for low end torque, doesn't rev much past 5000rpm. 2.18/1.84 valves, 906 heads, 2V Carter carb, milled heads and flat top forged pistons. Six Pack rods, stock forged 440 crank.
Does this help?
JS
I'm one of the moderators at PentaStarPower.com, which has ample tech help if anyone needs...
I'm also the owner of the 431 in question. I didn't build the engine, my close friend and professional mechanic of over 35+ years built this engine, and he has a TON of tricks of the trade that even I don't understand, but this thing RUNS!
Even when we were building this engine, we had parts store guys, other mechanics all telling us that this wouldn't work.
I drove this truck out to Mopar Nationals in Columbus, OH in August 2000, with some other members of the PentastarPower.com forum. As a reference, I live in NW Iowa, so it was a long drive.
Anyway, locally I can get 18-22 mpg, usually around 18-19 but I have gotten as high as 22, more than once. On the big trip, even on the interstate at 70-75 mph, I still got upper teens (16-1
for most of the trip.The cam is an RV style, set up for low end torque, doesn't rev much past 5000rpm. 2.18/1.84 valves, 906 heads, 2V Carter carb, milled heads and flat top forged pistons. Six Pack rods, stock forged 440 crank.
Does this help?
JS
I looked into (briefly) the chamber / piston coatings but didn't really run across anything very realistic. Not sure in a chamber how the coatings would do anything but keep the heat in anyway. I'm not calling anybody a liar by the way. I just want to know if this sort of power etc is really doable. Hey, your not JS on the other site are you?
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im not on the other site im on here and i browse moparts classifeds. well im also on turbododge and turbobuick. the theory behind ceramic coated chambers is supposedly so the chambers do not absorb heat. if the heat is all either used to push piston, or flown out exhaust, there is little residual heat to cause preigntion. also the principle for "polished" chambers. a completely smooth chamber has no bumps that cause hot spots, and is less prone to carbon build up. i ve been looking into this stuff due to the lil ol shadow. it has 8.2:1 compression. but under 10 psi of boost, effective compression ratio has reached 10.5:1 and under 20psi cr is almost 14:1. i had put in some 87 octane to make it home (only grade they sold) i had completely forgot about it. next day i got on it hard. maybe 12psi before i had remembered i got cheap gas. rectifed the situation with some 93 from shell like it should have. that car never said premium only, nor did it knock. new cramaros and fire birds have over 10:1 and run on regular so do many imports. it is possible. the technology does exist. i dunno about this but i wont completely say its not possible. btw bummo, incase ya didnt notice, Adventurer Sport=js. not joe swinehart=js. 
im on here and i browse moparts classifeds. well im also on turbododge and turbobuick. the theory behind ceramic coated chambers is supposedly so the chambers do not absorb heat. if the heat is all either used to push piston, or flown out exhaust, there is little residual heat to cause preigntion. also the principle for "polished" chambers. a completely smooth chamber has no bumps that cause hot spots, and is less prone to carbon build up. i ve been looking into this stuff due to the lil ol shadow. it has 8.2:1 compression. but under 10 psi of boost, effective compression ratio has reached 10.5:1 and under 20psi cr is almost 14:1. i had put in some 87 octane to make it home (only grade they sold) i had completely forgot about it. next day i got on it hard. maybe 12psi before i had remembered i got cheap gas. rectifed the situation with some 93 from shell like it should have. that car never said premium only, nor did it knock. new cramaros and fire birds have over 10:1 and run on regular so do many imports. it is possible. the technology does exist. i dunno about this but i wont completely say its not possible. btw bummo, incase ya didnt notice, Adventurer Sport=js. not joe swinehart=js.
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Hey Bummo
I am JS, I post as AdventurerSport on most boards (Moparts, Scatpack, TurboDodge, etc.) but use JS on PentaStarPower, that's the handle I used to use on the old Dallas Mopar board as well...
What details do you want? Forged pistons, six pack rods, 2.18/1.84 valves, 500cfm 2V Carter (off a late '60s C-Body, Newport 383-2V), stock electronic ignition, NAPA Belden cap/rotor/wires, Bosch Platinum plugs, and we set timing by ear/sound, so I can't tell you (in degrees) where the timing is at exactly.
JS
I am JS, I post as AdventurerSport on most boards (Moparts, Scatpack, TurboDodge, etc.) but use JS on PentaStarPower, that's the handle I used to use on the old Dallas Mopar board as well...
What details do you want? Forged pistons, six pack rods, 2.18/1.84 valves, 500cfm 2V Carter (off a late '60s C-Body, Newport 383-2V), stock electronic ignition, NAPA Belden cap/rotor/wires, Bosch Platinum plugs, and we set timing by ear/sound, so I can't tell you (in degrees) where the timing is at exactly.
JS
This isnt anything but an attempt at getting some details. You said its not a ross kit so what pistons are you running. A 440 crank in the 383 block interests me. What rods and what bore is the block. The pistons are flattops with very little milling of the heads so they gotta be pretty much zero decked, right? 906's with nice sized valves are nice heads. 383 stroked is a nice engine. Its just some specifics that would be nice. What rpm did you get 358 hp and and what rpm did you get 656 torque on the dyno. How old was the rebuild when you put it on the dyno. What hints and suggestions can you give us. Thats all I can think of. Thanks.
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This wouldn't be a quench motor by chance, would it? If it were, running 10.5:1 on 87 would not likely be a problem. Forgive my V8 head casting ignorance, but are 906 heads closed or open chamber heads?
-SM
-SM
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OK, let's see...right off the top of my head...
I'll look up the dyno sheet, but it was back in early 1998 when it was dyno'ed (Feb or March '9, and the engine was initially built in Dec. 96, so about a year old, with less than 10,000 miles at the time (around 8000 I think)
358 hp around 4000-4300 rpm range, and 656 ft-lbs in the 17-1900 rpm range...I think...
Pistons were ordered thru local NAPA store, and rotating assembly was balanced at the NAPA machine shop. Turned 440 crank, six pack rods.
Stock 383 block, bored .030 over for 4.28" bore, with 3.75" stroke, so 431 cubic inches.
Flat top forged pistons, milled 906 heads, with 2.18/1.84 valves.
Steel shim head gaskets, not sure of the thickness and not sure if I have that info around...?
And, yes, 906 heads are open-chamber. '68-up. '67-down closed chamber big block heads, like the 915s on my '67 440.
JS
I'll look up the dyno sheet, but it was back in early 1998 when it was dyno'ed (Feb or March '9
, and the engine was initially built in Dec. 96, so about a year old, with less than 10,000 miles at the time (around 8000 I think)358 hp around 4000-4300 rpm range, and 656 ft-lbs in the 17-1900 rpm range...I think...
Pistons were ordered thru local NAPA store, and rotating assembly was balanced at the NAPA machine shop. Turned 440 crank, six pack rods.
Stock 383 block, bored .030 over for 4.28" bore, with 3.75" stroke, so 431 cubic inches.
Flat top forged pistons, milled 906 heads, with 2.18/1.84 valves.
Steel shim head gaskets, not sure of the thickness and not sure if I have that info around...?
And, yes, 906 heads are open-chamber. '68-up. '67-down closed chamber big block heads, like the 915s on my '67 440.
JS
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Open chambers nixes the quench motor. Impressive this combo doesn't have any problems with pre-detonation. Sounds like the builder made a good cam choice
-SM
-SM
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specs are very vague so it leaves a lot of open space. hell this carb could be nascar spec'd. there is no mention of cams. some people have been reporting good numbers with the hughes/engle cams. and what exactly has been done to the heads. the numbers are well within the range of possibility depending on the level of the engine builder. torque does seem a bit high but i will not deny its possibilty. i ve read a good engine builder shoots for 1.3 ft lbs per ci on a n/a engine built for racing. which could easily put numbers into the 550+ range without too much trouble. i dunno though. would love to hear what the engine builder has to say.
I'm trying to learn as much as possible before my rebuild. The mileage is good. Not impossible to get on a full time dodge truck, but pretty engine / gear dependant. But the compression number on 87 pump gas is real tpough for me to accept. Also how do you get 10.5 compression on flattops with open chamber 906's with very little milling? Flat tops would be out of the block would'nt they? Which I guess is ok if you can keep the rings low enough. I dont know, and its this sort of thing that I would like to know. Also 656 lbs torque at 2000 rpm or less with a 500 cfm 2 barrel carb doesnt make sense to what I know about how this sort of power is obtained. Now I'm not calling anybody a liar. I dont know enough to do that, and I dont like that anyway, but this aint making sense to me. Somebody who knows how this can be done please let me know. And what pistons are those? Its a b block with a 440 crank and 440 rods, right?
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