Is it really worth the extra work to build a 383?

[jim_in_dorris]

Not sure if I titled this correctly, I am looking at both a 350 +.030 rotating assembly and a 383 rotating assembly with identical parts other than the stroke on the crank. Scat 9000 crank, H-beam rods, probe forged -12.5 cc dished pistons, new harmonic balancer, new heavy duty flex plate, rings and bearings completely balanced. I think I will use a Dart shp head, regardless. When I run the numbers on Comp-cams software (8-407-8 .. 252/258 .472/.480) I get .5 hp loss and 30 #/ft of torque gain for the 383 over the 350. When I run DD I get the same HP loss, but only about 25 #/ft of torque gain. I know that I am horsepower limited by my cam choice, but I want low end torque, the engine will rarely see rpm's north of 3500. What I did discover using my DCR calculator is that with a .045 quench setting, and 64cc combustion chamber I go from 9.4:1 SCR to 10.1:1 SCR. That's way more than I want. I can lower the CR by going with the 72cc combustion chamber version of the Dart shp heads, which puts my SCR back to 9.4:1. Is there a noticeable performance difference between the two sizes of combustion chamber if I maintain the same SCR? I thought that maybe I could use a bigger intake runner so I ran the numbers with 180 and 200 CC intakes, and it moves my curves up the RPM range, but doesn't seem to affect the total power any. Given that I am after dead reliable over power, does it make sense to even go to the 383? I know that this discussion has been beat up, but mostly for guys that want all out power. If I was after that, I would use a different cam, bigger heads, and go 383, but that's not what I want. Also, would I give up mpg with the 383 over the 350? I am building this motor for my alaska trip next summer, and will be towing a 22-24 foot travel trailer. I know I won't get great mileage with that much weight behind me, but after the trip, I will drive this truck daily.

[1project2many]

IMO, not usually.

I've built modern 383's for guys and while they make plenty of power and torque, they're just not my style. There's only one real reason why the 383 exists and that's because "back in the day" a guy could put the biggest factory crank into a 4" bore block and try to sneak it past the other racers as a 350. Like the 302, legend grew and the 383 gained popularity. With custom cranks you can build almost anything you want. I dynoed a 396 smallblock for a guy that made so much torque the friction brakes on our Dynojet would only hold the drums to about 20% throttle. The Impala SS that it was installed in was stupid quick for a large car and he smoked a couple of race built THM400s just playing around on the street. Yet it wasn't obnoxious at idle or low speed.

Large stroke engines like large flow heads. The old 383 stroker race engine would run out of power 1k rpm below the 350 with the same heads. It made torque so we'd gear the rear differently. Smart guys always figured something was up when we were keeping up with the pack (or leading it) but our engine wasn't screaming like theirs. But the point is the heads couldn't flow enough air for the 383 to be effective at the same rpm. Yes, we got the same job done or slightly better but I always looked at the opposite side... a lot of work and a lot more displacement but it didn't seem like a huge gain. If the Dart heads aren't great for flow, I'd stay with the smaller displacement engine or choose another head.

If the ring pack is closer to the top of the piston there's going to be some advantage for emissions and power, but it's slight. The increased rod angularity and resulting friction at the cylinder wall can easily offset it. You lose rod to stroke ratio as well and I feel that greater R:S engines tend to run smoother and get better mileage.

Try to keep quench small. .030" - .032" is the target. Reducing quench like this helps keep detonation at bay. Apply ceramic thermal barrier coating to the piston tops and the combustion chambers and you can run 10:1 with no worries. With those aluminum heads you're looking at, 10:1 is probably a non-issue anyway but I think you're going to play it safe at 9.5:1 or lower.

A trip to Alaska... sounds like it could be quite an adventure.

[gregs78cam]

I am running similar setup in the camaro but with 6" rods. I had my block decked to 0.000" to tighten up the quench. With aluminum heads I am running 10.5:1, but I have never tried to run 87 octane in it. Cam is a bit smaller than mine so a little less compression won't hurt. If you are building the engine anyways and there is room in the budget, I see no reason not to go 383. You basically give up very little and gain usable torque.

[jim_in_dorris]

1project2many, I chose the heads because of budget constraints, and the fact that they have EGR crossovers. I don't really want a race engine, like I said. The dart heads are a medium flow head, nothing like AFR or TrickFlow, but I should be able to sneak them past the smog nazis. What head gaskets should I look for to reduce my quench space. I am having the block decked at .005 in the hole, and most head gaskets are about .040 that I looked at. I don't really have the budget for ceramic coatings, and really want to keep the CR down so I can run mid-range gas. In a go-fast project, I probably would be doing the opposite, and spending the money. The Alaska trip is to visit the daughter, hopefully she will be moving to Anchorage from Juneau this spring so we can drive to see her. Of course, the sights and fishing that go with it are just icing on the cake. Over 2700 miles each way.

Greg, like I said, if this was going in something like your 78 camaro, it would be a totally different build, and I probably would go 383 or bigger without thinking about it. I kind of like the thought of a 406 or bigger small block. Does the Dual TBI feed the beast? Sounds like a lot of fun.

[EagleMark]

For a rig like that and the aventure planned I would run a very stock TBI motor, maybe an L31 Vortec to TBI? Cause I just tuned one in a 1990 Chevy TBI truck. Reliable, cheap, easy to repair on road if need be. Depending on tire size gear it! My Suburban is stock other then ECM. Has 235/75r-15 tires and 3:73 gears with towing package. Loaded, 40 gallons of gas, 40 gallons of water and a 22 foot travel trailer full! It pulls the mountain passes here fine and still gets 10 plus MPG. I only used OD on flatlands to 60 MPH, pulls most passes at 45-50.

No lean cruise for towing!

[1project2many]

1project2many, I chose the heads because of budget constraints, and the fact that they have EGR crossovers.
But why aluminum? And if I read correctly, those heads don't use a fast burn chamber??


What head gaskets should I look for to reduce my quench space.
You're much more limited if using an aluminum head. With iron you could use an old Chevy stamped steel gasket.



I don't really have the budget for ceramic coatings
I just bought a bottle of heat barrier and a bottle of dry film lube. Together they cost $62 with shipping. A cheapie harbor freight airbrush like I started with is maybe $30


and really want to keep the CR down so I can run mid-range gas.
Done correctly, with or without coatings, you'll be able to run low range gas.

I have friends living in Homer, AK but I've never gotten to see them. I think the trip is nearly double the mileage for me, though.

[RobertISaar]

FWIW: 95 monte carlo, 9.6:1 static compression with aluminum heads, runs on the intended 87 octane, no kind of heat barrier coating. the chamber design is relatively great though(for it's age), so i don't know how it would compare.

[jim_in_dorris]

1project2many, I found this picture of the Dart SHP compbustion chamber on the Dart web site, I thought it looked pretty heart shaped?
2987
Aluminum was just because that's what was offered. I would love to be able to put a vortec head on my truck, cost wise, but the california smog nazis make it very difficult. I would have to basically convert from TBI to the spider type injection and go to OBD2, way more than I want to do. I know that there are a couple of options on head gaskets, I guess I will have to look a little more. Everyone on here has reinforced my gut feeling that the 350-30 over route is the way I want to go.

Mark, lean cruise while towing..... Yeah, probably not going to happen, besides, doesn't lean cruise require the engine to be in fairly low map ranges to enter?

[EagleMark]

You can adjust then MAP qualifying parameter. Can be done but not something I would recommend for towing.

[RobertISaar]

while towing, pretty good chance you would very rarely even come close to hitting the MAP threshold to enter that you would use while not towing.

[EagleMark]

The way I have done it before, hands on so I knew what was happening! Is set it to work while cruising no trailer and note MAP reading at 60 MPH. Hook up trailer and same streach of road pulling trailer and note MAP reading 55 to 60 MPH and set it under that. Still works without towing.

It may enter Lean Cruise while towing but only long downhills where it is safe. Benifits would not be seen...

This is a really bad idea unless you have the tune dialed in! Going Open Loop Lean cruise if your not running very close to 128 BLM can leave you very Lean!

[1project2many]

http://www.jegs.com/p/World-Products/World-Products-SB-Chevy-Sportsman-II-Heads/746700/10002/-1
Emissions legal in 50 states. Flow like a bastahd. Takes stock plugs for truck.

Bare cost is similar. Purchase inexpensive valves and appropriate springs (http://www.pbmperformance.com/store.php?catId=628) and assemble at home. (Note that current pricing on assembled heads puts them within $70 per pair of SHP assembled heads and bare heads are $60 less per pair than SHP bare casting). Ports are a bit big but if you were considering the 200cc SHP this should work as well.

Afterthought: Send your daughter the paperwork and have her register the truck in Alaska. Smog Nazi's be damned.

[jim_in_dorris]

1project2many, I thought about the alaska registration, but since I live close to the Oregon border, all the cops here look for out of state plates, then check where you live and bust you if they can. Cali will do anything they can to fine you to help fill the state coffers. I talked to my machine shop today, and he wants me to build a 406! I don't want to give up my roller cam. He also thinks that the Dart heads are too much head for what I want to build. I think he just wants to sell me machine work. He did mention using a marine cam and a marine TBI intake, so I will at least look at that, not convinced.

[1project2many]

Marine cam is horrible to clean up and make smooth at idle. Marine engines run stupid rich and marine cams can be a real fight to get through emissions. Marine TBI intake has no EGR which I'm sure the smog natzi's would love to catch.

Those heads do have large ports but they're similar to what you're looking at. Port volume of 170-180cc is more like what I'd run. Vortec heads came on 96 OBDI one ton vans with TBI. Edelbrock TBI Vortec intake is same as OE GM intake for that setup. Will that combination be accepted as emissions legal in your truck?

Machine guys can be tough to work with. 406??? Why? How about a 350 4 bolt block, inexpensive L99 (4.3 V8) rods and crank, flat top forged pistons, nice cam with advance timing and little overlap. Add boost. You'll get 302 ci making 400-550 h[p fairly easily. Total cost will be lower than 406 and results will be more pleasing to wallet and seat of pants dyno.

[gregs78cam]

Greg, like I said, if this was going in something like your 78 camaro, it would be a totally different build, and I probably would go 383 or bigger without thinking about it. I kind of like the thought of a 406 or bigger small block. Does the Dual TBI feed the beast? Sounds like a lot of fun.

You can build a torque monster 383 and not HAVE to wind it up. An aluminum head only GIVES you the ability to run a higher compression, doesn't mean you have to. With 180cc runners and the size of cam you are talking I think it would be great combo. I went just a little wilder than your specs because obviously it was going in the camaro, but even mine makes more torque than hp. And yes two TBI's are more than adequate. That cam should be no problem to tune either way.

[jim_in_dorris]

Well, the marine stuff is out, not only after 1project2many's comments, but my research. The 302 idea would work if I saw high rpm's, however using my handy dandy self made excel spreadsheet, with my 3.73 gears, 700R4 and 265/70/15 tires, at 2350 rpm in 3rd gear I am doing 55.5 mph, 80 in overdrive (not that I would tow in OD). if it kicks down to second, 3500 rpm is 51 mph. I need torque in that kind of range. The 406 was a torque monster on DD, but I give up a lot when I switch back to a standard flat tappet cam. The trailer loaded is going to be somewhere just under 5000 lbs. loaded, so I will need lots of torque. I guess my real question is with the 350, I get about 415 #/ft of torque from 2000 to 4000 rpm. Will that work? The 383 gives me 450 #/ft of torque from 2000 to 3500 rpm. obviously this is DD, so results may vary. My question is mainly if I have over 400 #ft of torque at the flywheel, will it do the job towing? BTW, thanks everybody for chiming in, I really appreciate talking to people that aren't trying to sell me something but have real world experience with the kind of motor I am interested in building.

[1project2many]

Relax! :)

Youre trying to build an engine with more torque than most production engines. It will pull your trailer ok. You've got more to worry about in the driveline, trans, cooling system & etc. After all, you're increasing factory torque by what... nearly 100%?? And you're expecting to apply that force for long periods of time. Torque breaks stuff!

If the 406 is your cup of tea then don't sweat the roller cam. DD makes assumptions about roller cam profiles that aren't correct for many of the street hydraulic rollers. It's not uncommon to find a street roller with a profile like a flat tappet cam... mild ramps and small duration at the peak. Not what a roller's about but nice and quiet and doesn't wear out guides. A retrofit roller is available if that's what you need, even though it costs a fair amount. DD also makes big assumptions about exhaust systems with headers. Can be hard to figure out a real world duplicate of their model. If you really want the roller cam block accept the limitation of a 4" bore and call it a day. DD also has old design turbo maps, or at least my version does. The information to properly map the turbo in DD isn't always available and the ones they offer often look very unappealing on mild engines.

If I can find it, I'll try and dig out my DD 600hp 302 turbo build when I get home. IIRC power was all in by 6K and the torque curve wasn't too bad. Parts combination was fairly mild.

[jim_in_dorris]

1project2many, thanks. I have already rebuilt the 700r4 to handle more power, rebuilt all the driveline with new stuff (hopefully that works) and will be upgrading the cooling soon as I have a coolant leak at the filler neck of the radiator. Yes it is a lofty goal of increasing torque. Part of the reason for asking all the questions is that I completely understand that DD doesn't always make good assumptions. Does Comp-Cams software do better or worse? I suspect worse because they are trying to sell something. The bottom end of the engine isn't that much rocket science except for getting quench right, but the cam selection and heads make up for it in sheer numbers of variables. If DD is way off on torque specs for this roller cam, maybe I do want to look at flat tappet cams. I just want lots of torque down where I would be using it. Thinking about it, the shape of the torque curve has a lot to do with what I want. I tend to like flat torque curves not peaky torque curves.

[1project2many]

You're putting this kind of torque through a 700!!!??? <whistles> Get a big cooler. Get a beeg, beeg, beeeeg cooler. Also consider using fittings from a later 4L60E (if they fit) to use 3/8" cooler line.

Does Comp have engine dyno software? I've used their cam selection software to pick cams before. It worked ok but cams have come a long ways since the '90s. I use Engine Analyzer Pro for modeling but it asks for a lot of variables that aren't always available if you don't have parts on hand to measure.

DD makes assumptions about the lobe shape that may or may not match a real cam. If you're looking at a spec card for a cam use the cam math section to enter as much data as possible and generate a more accurate model. Last I knew DD couldn't even model asymmetrical lobes. The way I see it is this: If DD gives numbers you like, try to ensure you can get a cam that matches DD's model.

[RobertISaar]

IIRC, the software used by comp is more or less a spinoff of desktop dyno.

engine analyzer pro? last i knew, that was not cheap....

and that kind of torque while towing, i would be looking at 4L80s(if staying automagic), just saying.

[gregs78cam]

CamQuest has a very similar feel to DD, and they seem to be very close on the numbers. If you can get actual head flow numbers they can be 'more' accurate, but it's all relative. I would look into a stroking a factory roller block.

A 700R4 should be ok, as long as it's not setup to shift hard at greater throttle openings, that is what breaks parts, more line pressure is ok, and more of what you want than hard shifting. But I agree with Robert, 4L80E.

[jim_in_dorris]

Nobody loves my 700R4 Boo Hoo LOL. I am hoping that the tranny builder (who has done a couple of trannys for me and really knows his stuff) is right when he said he built it to handle 500 hp.
I have been looking at flat tappet cams and kind of like the Lunati Voodoo 60101 cam, I think I might forgo the roller cam just to save the money to put into better heads.

[1project2many]

If your trans survives this trip, I swear I will sacrifice a Honda in it's honor. :)

Too bad the Bowtie Vortec's aren't an option. The small port version is ideal for your engine.

[jim_in_dorris]

I can't even begin to tell you how may 700r4's I've scattered across the pavement. I think we went thru 9 in our first s10 blazer. The 2.8 V6 just couldn't support it. I plan on flogging the truck after the initial break in period with lots of local towing, we have a few 6% grades around here that are pretty brutal on tow vehicles. If it even looks like I am having a problem, I might have to learn $0E code. And I am just barely getting a handle on $0D. And be sure and make a video of the Honda sacrifice, I would watch it over and over and over...... LMAO!

[1project2many]

History lesson. GM's Hydramatic Division designed transmissions from the early '60s to 1990 They sold transmissions worldwide to customers such as BMW, Jaguar, Rolls Royce, Daewoo heavy equipment, and many others. They designed nearly legendary transmissions such as the Powerglide, THM350, THM400, and 4L80E which are still in use in many applications today. They know their stuff.

in 1979 Chevrolet executives looking for a new four speed automatic told Hydramatic to pound sand and proceeded to design one of the most problematic and expensive transmissions ever released by a GM division. Chevy spent 6 years trying to fix it but it was eventually given to Hydramatic to straighten out. Hydramatic spent another 4 - 5 years working it over and in parallel, designing an electronic version of the trans. It took until 1992 to achieve "not too bad" status and other than the name, there aren't many parts shared between the early and late transmission. I have a list at home of all the updated parts beginning in the original trans and ending with the last 700R4. There are 2 1/2 pages of part numbers.

Also, don't forget that the torque converter provides torque multiplication and the gears do the same. If you are fully loaded in 1st gear you could be providing 400ft/lbs * 2.25 multiplication through converter * 3.06 1st gear ratio = 2754 ft/lbs of torque produced at the driveshaft. Yep, 2754. Hang on, baby. :)

[1project2many]

Jim... I just wanted to mention this. I was talking to a very good transmission man the other day who mentioned that for a short time you could get dual stator torque converters for 700R4 applications. Where typical torque multiplication is around 2 - 2.5:1 these were good for 3 to 3.5X. The problem is that they worked. 4.3L engines making 250 ft/lbs at the flywheel were destroying the cases of stock trannies as they'd produce nearly 900 ft/lbs at the input shaft of the trans. Now I don't know if this is is a warning or if it means you should try and locate such a beast for your own application, but I do know that I'm considering a 4L80E swap.

[jim_in_dorris]

Holy Cr@p if I make 420 FT/LBS with a 3.5 multiplier Torque converter I would be hitting the input shaft with 1470 Ft/Lbs. That will break stuff. I guess I could go all billet. There goes a years budget.

[RobertISaar]

be great for us small 6 guys though. :D