SBC 383 500ft/lb torque build

[GARY C]

Serious question to other engine builders here. Who is honestly prepared to build a tow engine (not talking diesel) going into a heavy load situation where you know it will be subject to extended WOT-( because thats what will be required to do the job , not fairy tale it will do it at 1/4 throttle etc) - usage on a regular basis in possible high ambient temps and driven by possibly some one who has no sense of things like pinging let alone knowing what station has decent fuel etc AND send it out the door with warranty?
I will say that I certainly am not. Fact is that given these parameters a small cammed engine will do the job, and a small cammed engine with good heads (for the rpm range ) and intake, exhaust etc for the rpm range does not require a high C/R to pull WOT at lower rpms and fact is that if you sit an 'on the edge' CR engine in these conditions with joe average behind the wheel and have him WOT pull it up thru a hilly/maintain area in high ambient temps with heck knows what fuel he dumped in out of the fuel can for the stationary generator as he could not be bothered stopping for fuel on the way home ,, that you are asking for trouble. Even then if you can refuse the warranty due to proving that it was due to abuse you will still look like a dick in the eyes of the all knowing customer.
Build as much TQ safely as the engine parameters allow and gear it right for the actual road speeds and use that it will see and it will do the job well for a long long time.

Why would it require WOT? That would only be the case if it were under powered or over loaded.

[B Original]

Serious question to other engine builders here. Who is honestly prepared to build a tow engine (not talking diesel) going into a heavy load situation where you know it will be subject to extended WOT-( because thats what will be required to do the job , not fairy tale it will do it at 1/4 throttle etc) - usage on a regular basis in possible high ambient temps and driven by possibly some one who has no sense of things like pinging let alone knowing what station has decent fuel etc AND send it out the door with warranty?
I will say that I certainly am not. Fact is that given these parameters a small cammed engine will do the job, and a small cammed engine with good heads (for the rpm range ) and intake, exhaust etc for the rpm range does not require a high C/R to pull WOT at lower rpms and fact is that if you sit an 'on the edge' CR engine in these conditions with joe average behind the wheel and have him WOT pull it up thru a hilly/maintain area in high ambient temps with heck knows what fuel he dumped in out of the fuel can for the stationary generator as he could not be bothered stopping for fuel on the way home ,, that you are asking for trouble. Even then if you can refuse the warranty due to proving that it was due to abuse you will still look like a dick in the eyes of the all knowing customer.
Build as much TQ safely as the engine parameters allow and gear it right for the actual road speeds and use that it will see and it will do the job well for a long long time.

What cylinder pressure or dynamic compression do you consider safe for these conditions on pump gas?

[cjperformance]

I dont recount ever having driven a true heavy use tow vehicle that does not require the use of frequent WOT when fully loaded. Particularly in hilly areas. Not so common of late due to the popularity of turbo diesel stuff but i have done a lot of tow engine builds and even stout build 460ci BBF's in F250/350's with big trailers or goosneck trailers that are within tow rating still will see times when WOT is used. And therefore must be built to suit warranty.
Im not saying you cant run high comp in a tow vehicle, im not saying I havnt done it and I would do it for myself or someone who was a switched on driver.
I was asking a serious question to other engine builders who build and warrant engines for average joe.

[cjperformance]

Serious question to other engine builders here. Who is honestly prepared to build a tow engine (not talking diesel) going into a heavy load situation where you know it will be subject to extended WOT-( because thats what will be required to do the job , not fairy tale it will do it at 1/4 throttle etc) - usage on a regular basis in possible high ambient temps and driven by possibly some one who has no sense of things like pinging let alone knowing what station has decent fuel etc AND send it out the door with warranty?
I will say that I certainly am not. Fact is that given these parameters a small cammed engine will do the job, and a small cammed engine with good heads (for the rpm range ) and intake, exhaust etc for the rpm range does not require a high C/R to pull WOT at lower rpms and fact is that if you sit an 'on the edge' CR engine in these conditions with joe average behind the wheel and have him WOT pull it up thru a hilly/maintain area in high ambient temps with heck knows what fuel he dumped in out of the fuel can for the stationary generator as he could not be bothered stopping for fuel on the way home ,, that you are asking for trouble. Even then if you can refuse the warranty due to proving that it was due to abuse you will still look like a dick in the eyes of the all knowing customer.
Build as much TQ safely as the engine parameters allow and gear it right for the actual road speeds and use that it will see and it will do the job well for a long long time.

What cylinder pressure or dynamic compression do you consider safe for these conditions on pump gas?

I dont really like using dcr as so many factors can alter it, just an exhaust system change will alter your DCR.
Altitude, combustion chamber shape/efficiency etc.
Eg an open chamber factory 351C head will not tolerate the same baseline dcr on the same fuel as a modified closed chamber etc. And a thousand other variables.
But talking a baseline dcr that i would target on a high loaded tow engine for joe average that i would warrant and tell the customer to use 95 fuel (australian octane rating) knowing full well they will cheap out and run 81 octane, i will go for no more than 8:1 dcr. Yes thus depends on the actuall engine and chamber, intake etc etc but thats where my thinking will start for a 'joe average tow engine with warranty'. And i know that working with this works and is warrantable with confidence on my part. I will push for more ci before i will be talked into warranting higher CR. IMO cubic inches are king in true "tow" high TQ N/A engines.

[randy331]

Serious question to other engine builders here. Who is honestly prepared to build a tow engine (not talking diesel) going into a heavy load situation where you know it will be subject to extended WOT-( because thats what will be required to do the job , not fairy tale it will do it at 1/4 throttle etc) - usage on a regular basis in possible high ambient temps and driven by possibly some one who has no sense of things like pinging let alone knowing what station has decent fuel etc AND send it out the door with warranty?
I will say that I certainly am not. Fact is that given these parameters a small cammed engine will do the job, and a small cammed engine with good heads (for the rpm range ) and intake, exhaust etc for the rpm range does not require a high C/R to pull WOT at lower rpms and fact is that if you sit an 'on the edge' CR engine in these conditions with joe average behind the wheel and have him WOT pull it up thru a hilly/maintain area in high ambient temps with heck knows what fuel he dumped in out of the fuel can for the stationary generator as he could not be bothered stopping for fuel on the way home ,, that you are asking for trouble. Even then if you can refuse the warranty due to proving that it was due to abuse you will still look like a dick in the eyes of the all knowing customer.
Build as much TQ safely as the engine parameters allow and gear it right for the actual road speeds and use that it will see and it will do the job well for a long long time.

This all spot on.
I got 3 truck/tow engines that I've pushed the comp on but I wouldn't do it for others.
The average driver would probably have them all 3 in trouble at some point. Radiator gets a little clogged, fan clutch goes bad, etc.

I like my new 1982 suburban engine. 9.5 comp with little cam. Pulled the suburban across us36 in MO. into a head wind with 2 adults, bags, tools, a iron headed big block, extra parts, at 80-85 MPH and got 14.5 MPG doing it. It would stay in overdrive and lock up on every hill. Got 16.6 on the way home at a little more reasonable speed. LOL

Randy

[groberts101]

Serious question to other engine builders here. Who is honestly prepared to build a tow engine (not talking diesel) going into a heavy load situation where you know it will be subject to extended WOT-( because thats what will be required to do the job , not fairy tale it will do it at 1/4 throttle etc) - usage on a regular basis in possible high ambient temps and driven by possibly some one who has no sense of things like pinging let alone knowing what station has decent fuel etc AND send it out the door with warranty?
I will say that I certainly am not. Fact is that given these parameters a small cammed engine will do the job, and a small cammed engine with good heads (for the rpm range ) and intake, exhaust etc for the rpm range does not require a high C/R to pull WOT at lower rpms and fact is that if you sit an 'on the edge' CR engine in these conditions with joe average behind the wheel and have him WOT pull it up thru a hilly/maintain area in high ambient temps with heck knows what fuel he dumped in out of the fuel can for the stationary generator as he could not be bothered stopping for fuel on the way home ,, that you are asking for trouble. Even then if you can refuse the warranty due to proving that it was due to abuse you will still look like a dick in the eyes of the all knowing customer.
Build as much TQ safely as the engine parameters allow and gear it right for the actual road speeds and use that it will see and it will do the job well for a long long time.

This all spot on.
I got 3 truck/tow engines that I've pushed the comp on but I wouldn't do it for others.
The average driver would probably have them all 3 in trouble at some point. Radiator gets a little clogged, fan clutch goes bad, etc.

I like my new 1982 suburban engine. 9.5 comp with little cam. Pulled the suburban across us36 in MO. into a head wind with 2 adults, bags, tools, a iron headed big block, extra parts, at 80-85 MPH and got 14.5 MPG doing it. It would stay in overdrive and lock up on every hill. Got 16.6 on the way home at a little more reasonable speed. LOL

Randy

@ cj. Your point is well taken but since this OP is doing his own motor and obviously wants to push the envelope I would question the need to dumb it down too far for fear of warranty or pr related issues. And does a lower compression motor making 475 ft/lbs of torque @ 3,800 rpm need to be run at full throttle for extended periods of time? And would a higher compression motor of similar design but having higher torque output need more throttle or less? If it does I'd question the sanity of the guy pulling my car around on the back of his truck like it's a gumball rally to get it there faster than any speed limit.

@ Randy. Unless that motor was literally riding on the ragged edge and detonation was emminent?.. why would another 3/4 to full point of compression increase require you to push the motor much harder to cause higher damage potential? Maybe the higher compression motor would then require slightly reduced throttle angles to achieve similar performance. Thus requiring slightly reduced fuel mixture density and overall heat production to help offset some of that higher compression ratios inherently greater cylinder temps? Maybe even slightly improved economy as well?

All this stuff can be contextually twisted around to meet whatever rationale people like or prefer to believe in. But history has taught us many times that a larger combustion space with lower compression ratio can INCREASE detonation potential over another motor using much more compact combustion spaces with considerably higher squish and burn rates. And from there we get into combustion space temperature saturation directly relating to the time it takes for an engine to accellerate. Ie:.. lower torque output motors rpm slower through the gears and saturate the space more quickly than another higher compression motor which spends less time accelerating through the gears and requiring less throttle and fuel to do it.

[cjperformance]

At the end of the day TQ is TQ regardless of CR, if one engine with 475lb/f does X work at 3800 then the next engine with 500lb/f expected to only do the same work will obviously use less throttle.
I wasnt trying to dumb down the OP's subject , just asking a Q to other builders about the parameters i threw out there at the same time explaining why i choose that route.
To be honest I have not read right from the start as yet but i will when i get a chance.

[groberts101]

At the end of the day TQ is TQ regardless of CR, if one engine with 475lb/f does X work at 3800 then the next engine with 500lb/f expected to only do the same work will obviously use less throttle.
I wasnt trying to dumb down the OP's subject , just asking a Q to other builders about the parameters i threw out there at the same time explaining why i choose that route.
To be honest I have not read right from the start as yet but i will when i get a chance.

Sorry if you interpreted as any kind of attack.. wasn't my intention at all. By using the term "dumbed down" .. I was only pointing towards your implication of increasing safety margins related to abuse or poor maintenance or whatever.. that may potentially come back to bite the builder. Not that you were dumbing his subject down, per say.

Not a tow truck but still a heavily loaded motor pulling around a lot of weight. Back around the late 80's I owned an 429 SCJ powered '71 Torino GT and was getting pretty heavy into collecting the 385 series stuff because of it. My uncle's best friend talked me out of one of my sets of D0VE heads to put in his mid-70's 30+ foot motor home along with an older design Weiand stealth intake manifold. Motor was a little tired to begin with, even puffed a little smoke, but after bumping compression almost 2 full points?.. with a little powerbraking trickery that thing could light up one sides set of dually tires and shift into 2nd gear doing it! Never would have believed if I hadn't seen it with my own eyes. He said it was amazing how much easier it would go up steeper hills. Also got better mileage than ever too. Granted we detuned the ignition curve a bit to help it live.. but was still far superior to anything the 8 or 8.5:1 smogger heads could offer no matter how well we tried to tune it.

Moral of that story is this. Despite higher compression/higher combustion pressures increased tendency towards detonation.. the much more efficient combustion spaces improved burn characteristics can easily compensate and at least partially offset some of the negatives associated with running higher compression. Basically, efficiency improves enough to ALLOW getting away with higher than normally accepted SCR with a small'ish cam. Been a long day.. hopefully I conveyed that well enough to get the point across.

[GARY C]

It's all about the correct tool for the job, you can use one of these but would you?

[cjperformance]

No offence taken, not seen as an attack at all, just clearing up my point as i had gobe off topic a little!
Yes upping the CR on the mud 70's 385 stuff is a big plus, as low CR along with the horrid retarded cam was just terrible for hp/tq, made mockery of a big ci engine for sure!

[gmc406]

Lol, for setting up bearing rolling torque when rebuilding a gear case, I still do.


.....but I get your point, not head bolts and such.

[cjperformance]

 This is the spec on a torque oriented 383 sbc I sent out, had to run A/C and P/S, sound good but not radical, have nice street manners run pump fuel and move a lardy vehicle and have warranty. (Not really aimed as a tow engine per say but had to be torquey)

Trick flow super 23 195cc,
EPS intake just quickly tidied up , Edelbrock 750,  1/2" 4 hole on top of 1/2" open.
4.030" x 3.75"
5.7" i beam rods.
 Crow Cams HR # 757, 214/218@.050" , 123/124@.200" , 280/280 adv, .311" lobe, 110 lsa. (Valve train friendly and quiet)
1.6/1.5 rockers- .497"/.466" valve lift.
 I believe the custom pipes the owner made based on my suggestions ended up at 1-5/8" primaries , 1-7/8" secondaries into 2" choke and straight out to 2.5" then x pipe, 3" resonators and intermediate pipes and lukey ultra flow mufflers, 2.5" tailpipes.
 @ 10.3:1 SCR will run our Australian 91 octane but using our 98 ran 11.98 @ (i think )112ish mph in a 1967 Parisienne, 2800 stall, T700 3.9 rear.
I only got to start/run test the engine on the jig before crating it out and it sounded nice, thru borrowed 1.75"-3" 4 into ones with mufflers jugged on the collectors, good and responsive on the throttle. Apparently drives  and cruises really nice too, happy customer.

[Newold1]

If you can and will use some of the great programs on engines we now have you can do something pretty simple, it will eliminate a lot of "Wagmars" and you can plan that SBC specification and build it in pretty simple fashion.

Torque is the muscle for a work heavy engine and it is that force that gets work done.

For a great performing SBC "WORK" engine try and determine the rpm and range of gearing (final drive ratios) that this engine will operate at when it is doing its heavy work. Then use the program that can tell you based on stroke and bore for that cubic inch range, compression, camshaft specification, cylinder head specification, etc. to put the maximum torque range within that "Work" range and I think you are going to achieve a pretty good result.

How you drive (use) that torque will pretty much determine how successful your SBC will perform in your work use as any well designed and built engine can be misused and abused by the operator.

JMHO

[Scotthatch]

Have you seen this build

http://jmacperformance.com/?cat=21

[Scotthatch]

The goal in a high torque build is more about getting the airspeed to peak at a lower rpm ..... a longer runner would help but if you stick to a duel plane runner length is kinda set in what fits ... flow wise I think about 200 cfm at Max lift is the tipping point as the camshaft would have to be small as to not contaminate the charge at low of idle rpm and a 600 cfm carburetor ..... to much airflow and the rpm shifts up ......