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  • Help with my 383 Impala.

    I have a 383 sbc in my Impala. Here's the stats: 350 4 bolt block, cast turned down 400 crank, 5.7 rods, cast TRW pistons, 9.87:1 compression. Iron '186' heads, 64 cc, 2.02/1.60 valves, gasket matched both intake and exhaust, bowl blending, some exhaust port work and general casting cleanup. Comp Cams XE274, 487/490 lift, 230/236 dur. @ .050, 1.5 roller rockers, 'Z-28' valve springs. Edelbrock RPM intake, Quick Fuel 750 DP carb, HEI dist, MSD 6AL, MSD coil, Autolite 26 plugs, Taylor wires. Hedman 1 5/8 headers, 2 1/2 pipes, flowtech terminators muffs. 10 bolt posi 3.36 gears.

    The car ran a best of 14.61 at 95.29 mph at Sac Raceway about a month ago. I'm thinking something is missing. I'm pretty good at tuning for street driving. This car runs all day in the heat on 89 octane and near 10:1 compression, but I believe there should be more out this combo on the track. I believe that my heads are the weak point. 1970 LT1 double hump castings are a bit outdated. I have also been thinking that I need to put it on a chassis dyno to find more.

    What do you guys think?
    BS'er formally known as Rebeldryver

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  • #2

    Re: Help with my 383 Impala.

    Re: Help with my 383 Impala.

    Keep in mind you have an over-two ton car and not much gear. I'd say it is running just about right for the combination. Put in a 3.73 gear and/or better heads and you should see much better times.

    BTW, you should be shifting around 56-5800 for best et. Don't get sucked into the it-still-pulls-so-I'll-shift-higher syndrome.

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    • #3

      Re: Help with my 383 Impala.

      Re: Help with my 383 Impala.

      I don't know if I would run a 150 shot on a set of cast pistons without making sure there is a good fuel system for the spray. Go lean for a second and the cast pistons will pinch a ring or loose the top ring land where forged pistons are more forgiving. With a good fuel system, 150hp is about max for cast pistons anyways on a SBC. I would think it would really wake up the car however.

      I would look deeper into the tune - for a street car I like to maximize the midrange and let the top end fall where it may. This will give more power where you use it every day day and better gas milage since the engine is most efficent at maximum torque. And for this application, I would work to maximize the torque. I would think that this engine would be able to power a two ton car into the high 13's at around 100mph.

      I personally would keep the smaller tube headers that you have since they will promote better low end torque than larger ones, and torque is needed to get that heavy beast rolling. THe long reducer cones and extensions can give a big torque boost - as much as 40ft-lbs due to more efficent scavanging. A crossover tube is also a good idea if you can't easily fit an X pipe. Paint the extensions with normal paint and run the car hard. Where the paint stops burning off is about the right spot for the crossover tube.

      I think the timing and gear reccomdations are pretty close, if not right on, for a street/strip car.

      You never mentioned how the car hooks or the transmission either. What converter? Is there a shift kit? How tall are the rear tires?






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      • #4

        Re: Help with my 383 Impala.

        Re: Help with my 383 Impala.

        I'm running a four speed with a 3.06 first gear. I'm launching at about 1500 rpm to keep the Radial T/A's from going up in smoke. They are 28 inch diameter. My 60 foot times are in the 2.18 to 2.22 range when I do it right. The suspension is set up more for handling than drag racing. I might be able to get it to hook better by disconnecting the front sway bar. I found a spare pair of Cragar street stars that I am planning to get Drag Radials for track fun. The car weighs 3850 when I get all the crap out of the trunk. Which I did.

        I was shifting at 5500. I don't want to push it any harder than that.
        BS'er formally known as Rebeldryver

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        • #5

          Re: Help with my 383 Impala.

          Re: Help with my 383 Impala.

          I'd say for your combo that your running what you should be running. If you want more I'd look into swapping in some 3.73 gears in the rear. Along with getting some new heads like a set of Sportman II's or something comparable to those. Plus what kind of stall are you running.

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          • #6

            Re: Help with my 383 Impala.

            Re: Help with my 383 Impala.

            No stall. Clutch. Four speed manual.

            Another note. This car ran 14.10 at 101 mph with this motor, a TH350 with a stock converter (before the four speed change) and 2.56 peg leg rear.
            BS'er formally known as Rebeldryver

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            • #7

              Re: Help with my 383 Impala.

              Re: Help with my 383 Impala.

              101 MPH is enough power to go mid-13's so yes, I would agree that there is more to be had with the chassis.

              Better heads would make more power of course (I like the Dart Platinum 200 cc for your setup personally) but I think you have a solid .3 seconds to gain just in the first 60 feet. I would start with the chassis stuff and work on the power part later -- then you will be able to use the extra grunt.

              I like your Drag Radial idea -- that should help a lot right there. Disconnecting the sway bar is another good move IMO. I am not sure what kind of shocks you have but if you could loosen up the extension adjustment (especially in front) to let the front end lift quicker that would be another way to gain traction. A 3.73 gear set would help too (even with the 3.06 1st gear)

              I hope that helps.

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              • #8

                Re: Help with my 383 Impala.

                Re: Help with my 383 Impala.

                Thanks for everyone's input.

                I'm a fan of AFR's 210s, but at $1500 a pair. :-\

                I'm afraid the suspension is set-up for handling not straight line. I've got KYB's on all four corners, but changing the front ones out and installing drag shocks and disconnecting the sway bar would be helpful.

                Check out the difference in these two pics. Almost no diff in before and after launch.


                BS'er formally known as Rebeldryver

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                • #9

                  Re: Help with my 383 Impala.

                  Re: Help with my 383 Impala.

                  Yeah, even a cheap set of 90/10's in front would help a bit. FWIW I would stick with a 200 cc head with your combo -- mainly because of the weight of the car, and $$$ is why I suggetsed the Iron Eagles.

                  You know, Vortecs would work well too.

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                  • #10

                    Re: Help with my 383 Impala.

                    Re: Help with my 383 Impala.

                    So the Victor Jr's I just found are over kill?

                    I plan to bump up the cam with the new heads. Gotta be careful not to go overboard in order keep up enough vacuum for the brakes. I was thinking the Comp XE288HR or XE294HR.
                    BS'er formally known as Rebeldryver

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                    • #11

                      Re: Help with my 383 Impala.

                      Re: Help with my 383 Impala.

                      With your compression ratio being 10:1 I would stay with the smaller of the two cams you listed. Actually, I would consider one size smaller yet -- like the XE282HR.

                      I agree -- the Vic Jr is overkill, a Performer RPM would be my pick and a better match for your cam.

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                      • #12

                        Re: Help with my 383 Impala.

                        Re: Help with my 383 Impala.

                        I personally prefer the smaller heads for heavy cars with less gear. Dual purpose cars tend to run better when built to the mild side.

                        I like the AFR 195's better than the 210's for this car. I also would look at Brodix Race Rite 180's and the Dart Iron Eagle 180 Platinums personally. These heads all flow a ton with smaller ports for better velocity and will make more torque. With more gear, and a more radical cam where you are going to be spinning more RPM, the over 200cc heads would start to perform better.

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                        • #13

                          Re: Help with my 383 Impala.

                          Re: Help with my 383 Impala.

                          Ps. If you were referring to Vic Jr heads, yes, they are overkill IMO.

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                          • #14

                            Re: Help with my 383 Impala.

                            Re: Help with my 383 Impala.

                            I guess I went overkill. I just bought the Vic Jr's. They were such a deal that I couldn't pass on them even if I don't end up using them.



                            BS'er formally known as Rebeldryver

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                            • #15

                              Re: Help with my 383 Impala.

                              Re: Help with my 383 Impala.

                              Cool ;D dem dar are purdy . . .

                              What pistons do you have in it? If they are flat tops your compression will be a bit higher than 10:1 -- more like 11:1 with 64cc chambers. If that is the case then a bigger cam is in order and those heads will not be THAT big . . .

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