Page 1 of 2 12 LastLast
Results 1 to 15 of 28

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

  1. #1
    Fuel Injected! jim_in_dorris's Avatar
    Join Date
    Dec 2011
    Posts
    803

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

    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.
    Square body stepsides forever!!!

  2. #2
    Administrator
    Join Date
    May 2011
    Location
    Lakes Region, NH
    Age
    54
    Posts
    3,847
    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.
    Last edited by 1project2many; 09-09-2012 at 03:15 PM.

  3. #3
    Fuel Injected! gregs78cam's Avatar
    Join Date
    May 2011
    Location
    N. Idaho
    Posts
    767
    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.
    1978 Camaro Type LT, 383, Dual TBI, '7427, 4L80E
    1981 Camaro Z-28 Clone, T-Tops, 350/TH350
    1981 Camaro Berlinetta, V-6, 3spd
    1974 Chevy/GMC Truck, '90 TBI 350, '7427, TH350, NP203, 6" lift, 35s

  4. #4
    Fuel Injected! jim_in_dorris's Avatar
    Join Date
    Dec 2011
    Posts
    803
    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.
    Square body stepsides forever!!!

  5. #5
    RIP EagleMark's Avatar
    Join Date
    Feb 2011
    Location
    North Idaho
    Age
    63
    Posts
    10,477
    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!

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  6. #6
    Administrator
    Join Date
    May 2011
    Location
    Lakes Region, NH
    Age
    54
    Posts
    3,847
    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.

  7. #7
    Super Moderator
    Join Date
    Mar 2011
    Location
    Camden, MI
    Age
    35
    Posts
    3,026
    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.
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  8. #8
    Fuel Injected! jim_in_dorris's Avatar
    Join Date
    Dec 2011
    Posts
    803
    1project2many, I found this picture of the Dart SHP compbustion chamber on the Dart web site, I thought it looked pretty heart shaped?
    Dart SHP intake shape.jpg
    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?
    Square body stepsides forever!!!

  9. #9
    RIP EagleMark's Avatar
    Join Date
    Feb 2011
    Location
    North Idaho
    Age
    63
    Posts
    10,477
    You can adjust then MAP qualifying parameter. Can be done but not something I would recommend for towing.

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  10. #10
    Super Moderator
    Join Date
    Mar 2011
    Location
    Camden, MI
    Age
    35
    Posts
    3,026
    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.
    1995 Chevrolet Monte Carlo LS 3100 + 4T60E


  11. #11
    RIP EagleMark's Avatar
    Join Date
    Feb 2011
    Location
    North Idaho
    Age
    63
    Posts
    10,477
    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!

    1990 Chevy Suburban 5.7L Auto ECM 1227747 $42!
    1998 Chevy Silverado 5.7L Vortec 0411 Swap to RoadRunner!
    -= =-

  12. #12
    Administrator
    Join Date
    May 2011
    Location
    Lakes Region, NH
    Age
    54
    Posts
    3,847
    http://www.jegs.com/p/World-Products...46700/10002/-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.

  13. #13
    Fuel Injected! jim_in_dorris's Avatar
    Join Date
    Dec 2011
    Posts
    803
    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.
    Square body stepsides forever!!!

  14. #14
    Administrator
    Join Date
    May 2011
    Location
    Lakes Region, NH
    Age
    54
    Posts
    3,847
    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.

  15. #15
    Fuel Injected! gregs78cam's Avatar
    Join Date
    May 2011
    Location
    N. Idaho
    Posts
    767
    Quote Originally Posted by jim_in_dorris View Post
    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.
    1978 Camaro Type LT, 383, Dual TBI, '7427, 4L80E
    1981 Camaro Z-28 Clone, T-Tops, 350/TH350
    1981 Camaro Berlinetta, V-6, 3spd
    1974 Chevy/GMC Truck, '90 TBI 350, '7427, TH350, NP203, 6" lift, 35s

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •