Need some help with a 426 hemi street build

Engine, Trans & Driveline

  1. Beekeeper

    Beekeeper FBBO Gold Member FBBO Gold Member

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    This is my very first 426 hemi build and I really need some guidance from the guys here that
    have built one or more and here’s what I have to build on. 1970 block 4.310 bore that has a deck height of 10.612 with a 4.250 stroke crank with 7.1 rods and diamond 108 cc dome pistons. So to bring the compression down and get the heads back up to be able to use a factory type intake I thought of using a cometic MLS .140 head gasket. I ran all my numbers
    in the diamond compression calculator and come up with 11.1 : 1 ratio with a 4.310 bore gasket and 170 cc combustion chamber. I would like to use the standard Stage V heads with some port work and a 2x4 inline mopar performance intake with 600 cfm carbs and a mechanical roller cam of which I have no idea of which would be best for the combo in mind.
    The car is a 69’ bee with a hemi 4 speed and 3.91 gear I hope to make around 600 to 650 HP
    and equal amount of torque. Please keep in mind these things are only my idea so I would like to know if this seems like a good combo or if not please school me on what would work best
    together with the short block I have and will run on 93 pump.
     
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    • Jerry Hall

      Jerry Hall FBBO Gold Member FBBO Gold Member

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      I think your 600-650 HP & torque is easily attainable with what you have, but I wouldn't expect it to run without detonation on 93 pump gas at 11.1 compression. Just my thoughts. My basically stock 10.25 compression Hemi's can run on 93 octane and not ping by dialing the timing back a few degrees. They really come to life with 100 octane and the timing back to where it should be.
       
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      • Darter6

        Darter6 FBBO Gold Member FBBO Gold Member

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        I'm with Jerry. I lowered my compression from 11.1 to 9.6 mainly because all we have is 91 at the pump.
        FYI, Some stations around here sell 100 for boats,but I was told that the only bring in less than 2,000 gallons once a year and the tanks may or may not be filled at all until they have sold a minimum of 1000 gallons.So it can be very old.I stay away.
         
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        • moparsquid

          moparsquid FBBO Gold Member FBBO Gold Member

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          have you tried recurving the dizzy was told by several people you can run the high numbers on the street as long as you recurve the distributor
           
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          • hsorman

            hsorman FBBO Gold Member FBBO Gold Member

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            I do not suggest building higher compression and then turning the timing back - build in the pump tolerant compression.

            I did that years ago with a 340 that had very close to 11:1 compression. It pinged on premium gas so I had to turn back the timing to get it to run without pinging. But it never ran great. So my father-in-law then cut down the pistons to 9.33:1 (using a special cut to improve quench). We reassembled the engine with no other changes and when the timing was set, it ran like a scared ape - much better than it ran in it's 11:1 configuration.
             
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            • moparsquid

              moparsquid FBBO Gold Member FBBO Gold Member

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              I agree to the lower compression im cutting my 11-1 pistons on a 383 build im doing but I think dulcich or another mopar guy did a build recurving the spark advance so it comes in slower to a max at 3000 rpm that makes high comp livable I been looking for the video but cant find it
               
            • 68 HEMI GTS

              68 HEMI GTS Well-Known Member

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              Hemi should handle 11.1 on pump fuel with aluminum heads. And don’t compare them to wedge engines as they act different. They also require compression to make any power. I wouldn’t go less than 10.5:1. Run a solid roller, 250’s @ .050 range. Target low to mid .600 lift. They usually don’t require timing like a wedge either . Usually 32 total is about right. I’m building a 548 right now at 11.1 as a street engine. Shooting for a bit more power though...
               
              Last edited: Nov 30, 2020
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              • Challenger340

                Challenger340 Well-Known Member

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                I don't like Roller Cams that require 500#-550# V/Spring rates for Street usage ?
                It's not IF but rather WHEN a V/Spring goes away and Lifters start bouncing on the Cam in a street environment in our experience ?
                If you gotta have a Mechanical Roller ?
                and,
                you plan on sustained Street Duties ?
                you may wish to investigate a Street Mechanical Roller profile ?

                That said....
                and seeing as how you are NOT trying to make much power at all ?
                Just me..... but for sustained street duties we prefer Solid Flat Tappets, and Ray Barton has some proven very good Flat Tappet Cams that are easy 700 HP capable on 91 Octane friendly Compression Ratios.
                The last .030" 426 we did using Eddy Heads spanked 700hp easily right around 7,000 I believe ? But I'd have to go pull the Dyno Sheet for certain.
                 
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                • Dragon Slayer

                  Dragon Slayer Well-Known Member

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                  You would be ok at 11 to 1 and of course you can use gasket to lower compression if desired. But bigger issues are clearance on a hemi. Are you using Chevy journal crank, what rods. 4.25 stroke with Nascar rods as an example will require a lot of grinding of block for clearance. What CD on the piston? You also will find those calculators and even some of the piston info misleading. You need to measure Compressed CC against your uncompressed value to determine a more accurate static compression. Valve pockets on the pistons, wrt clearance etc... 108cc dome is towards the higher compression. 112cc was the 12 to 1 in stock form.
                   
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                  • PolyJon

                    PolyJon Active Member

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                    Hi beekeepa,
                    Wonderful car and a perfect colour too!
                    I’m in the same boat wth a hemi build too.
                    What’s a good comp for pump gas?
                    Both engines I bought had 12 to 1 pistons in and were on the street.
                    One was 4.250 and 7.100 rods and the other stock crank with Ali rods.
                    They both had massive cams, the stroker engine being a roller with a four speed Transmission.
                    It ran and drove ok but not for grocery getting, just ‘all or nothing’ kinda deal.
                    Unfortunately the stroker crank is shot so I’m going for a stock build, maybe 9.5 to one is best for me, all said and done?:moparsmiley:
                     
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                    • Dragon Slayer

                      Dragon Slayer Well-Known Member

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                      Your car so you can do it, but why build a hemi at the extra cost and weight and make it 9.5? Hemi's like compression and you would not have issues with static at 10.25 or 10.5. Any sort of cam, which you would want, will help reduce dynamic compression anyway.
                       
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                      • RJRENTON

                        RJRENTON FBBO Gold Member FBBO Gold Member

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                        IMO....
                        B4 spending any serious $$$, have you had the block's bores inspected for wall thickness, especially on the thrust side half way down the hole? As your block has been machined to 0.060" over the standard 4.250" diameter, I would be concerned about wall thickness and the block's core revisions, as usually higher number cores or later core revisions MAY have thinner walls. Usually thinner bore walls result in higher operating temps and can possibly result in detonation issues, especially with high compression ratios. Just my opinion of course.
                        BOB RENTON
                         
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                        • Beekeeper

                          Beekeeper FBBO Gold Member FBBO Gold Member

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                          This was a running short block in it’s configuration and at a way higher compression than I’m gonna run I got all the specs on the pistons from diamond. This block has had .108 taken off the deck so to get the heads back up so an off the shelf intake will fit and get the compression down
                          I have chosen the .140 gasket thickness.
                           
                        • Beekeeper

                          Beekeeper FBBO Gold Member FBBO Gold Member

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                          I finally just called Ray Barton and gave him the specs on the short block and the car and asked him to put together all the components that work well together for a street driven car.
                           
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                          • 70chall440

                            70chall440 FBBO Gold Member FBBO Gold Member

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                            This sounds a lot like the Hemi I have for my Roadrunner, I am going to be running something like .120 MLS head gaskets to get to 10.5 (ish). I haven't decided on a cam but I am thinking hydraulic at this point. I am not looking for big power, more reliability.
                             
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                            • Beekeeper

                              Beekeeper FBBO Gold Member FBBO Gold Member

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                              Ray Barton informed me of two things when we spoke on the phone. dual plane intakes are for 318s and hydraulic cams are for 350 chevys:lol: or something like that anyway.
                               
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                              • 70chall440

                                70chall440 FBBO Gold Member FBBO Gold Member

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                                LOL well when you have a building full of hemi's that easy enough to say.... I am sure they would not like my build, going to run a single EFI (4BBL) TB as well. Like I said, I am looking for reliability first and foremost, the engine has enough appeal naturally and I will never race the car.
                                 
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                                • Beekeeper

                                  Beekeeper FBBO Gold Member FBBO Gold Member

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                                  I totally agree these builders all have some type of components they like to use. I like your thought and direction on your build I hope to see it when you get it completed. Mine is the first
                                  Hemi I will have built and the reason I have it was I came across a deal for two of them and I couldn’t pass them up. I recently sold one for what I paid for both otherwise I probably wouldn’t have ever had the chance or the funds to own one.
                                   
                                  Last edited: Dec 6, 2020
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                                  • 70chall440

                                    70chall440 FBBO Gold Member FBBO Gold Member

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                                    I pretty fell into my engine and got a smoking deal on it. My engine is far from pristine, it was an old race motor that was windowed at some point but repaired and continued to be raced. I had it sonic tested and magnafluxed and it is good but it doesn't have a dip stick tube because it got welded up during the repair. It was never bored badly or decked hard. My initial plan was to use all of the parts i got with the motor which includes some 12.5:1 pistons which are currently in the short black and the head gaskets will help me get the compression down to where I can run it on pump gas. My intake is a crate 426 take off I got off eBay; I have been told that all 426 Hemi's need dual 4's but I don't really want to go that route.

                                    This is my 426 build as well and they definitely have a steep learning curve. I did get a Mopar Performance solid cam with the engine, kind of a mid range cam but I think I am going to use hydraulic as I mentioned. The car this engine will be going into is a 70 Roadrunner that has been pretty chopped up, has a tilt front end currently (was a 383 AT MS MB car). I was building the car but then fell into a smoking deal on my 71 which will have a 5.7 and 4 speed in it.
                                     
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                                    • PolyJon

                                      PolyJon Active Member

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                                      Now that’s a worry because my Moparmate is rebuilding his ex-Barton 572 with a 4.150 crank and and 9.5’s to keep the costs down after it went ‘bang’...
                                      The dragon-slayer 4.500 crank broke into three pieces...
                                      Some folks think it was running too much comp on cheap race gas!
                                      Oops:nutkick:
                                       
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