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large cubic inch small blocks....420 etc.... GURU'S Please ?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by twenty_below0, Mar 31, 2003.

  1. twenty_below0

    twenty_below0 1/2 ton status

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    large cubic inch small blocks....420 etc.... GURU\'S Please ?

    Planning to start the build up of a 400 in the next few weeks . So I'm wondering who has a large cubic inch small block in there rigs and how they went about the build . I have found a Scat 4.00 stroke crank on Ebay for 600.00 which is a Quality Crank and it says no block clearancing needed ? So with this crank and a decent set of rods I'm looking at 1000.00 . What should I go with the 4.00 crank or a 3.875 crank and then the rod length , would 6.00 or 5.7 be the way to go ? I'm not a stroker expert and I know there are reasons for going with either one of these and rod lengths . I have the 400 standard block and crank waiting for instructions at the machine shop /forums/images/graemlins/grin.gif Also it is a 4 bolt so should I buy a set of splayed caps for it or just run the factory caps . The motor will be a ripper and twisted up to 7,500 regularly in the sand and mud . I know in the dirt track cars alot of people run 2 bolts for less rigidity and have less bottom end bearing problems them the 4 bolt motors . So coach me on this one guys what should I do to make a monster small block ? /forums/images/graemlins/1zhelp.gif
     
  2. Lonnie

    Lonnie 1/2 ton status

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    Re: large cubic inch small blocks....420 etc.... GURU\'S Please ?

    Here are a few suggestions.

    Big inch small blocks are nice, but not the economical way to go as far as $$ per HP.

    The 4" stroke crank will require some work in a 400SB. The low deck height of a small block will limit rod length.

    The longest practical rod length for a 3.875 crank is 5.85" & approx 5.7" for a 4" stroke. Rod to stroke ratio will be very poor. You can go longer, but the piston will be very short & the rings packed close together... not good for long term use. The long stroke will also net very high compression, since a long rod will not allow room for a dished piston. Compression will likely be well over 11:1 minimum (race fuel). In order to feed this engine, you will need very large heads to make any power.

    As far as a 7500rpm motor, with long stroke, plan on frequent breakage or spend some major $$ on the best available bottom end parts. Decent rods & crank can live in a 350 at 7500, but you are in billet crank/rod territory for a 7500rpm stroker. (remember this is an equivalent piston speed to a 350 at 8600 rpm) Plan to spend close to $10K to make it all work. Not to bear bad news, but this could be a disaster waiting to happen.

    The 400 block is not recommended for this type of power level. The 4 bolt block is known to crack in the outer main bolt holes under high power output. The 2 bolt block converted to splayed caps is much better in this application but still marginal. Aftermarket blocks are almost a necessity at this modification level.

    All in all, you would be better off building a nice .030 over 400 with some decent quality parts, spin to to 6000 max & make approx 450hp or start from scratch on a purpose built motor.

    For short term usage under class rules requiring a small block, this may be the way to go. Unless you are dead set on a small block, a big block will make more usable power with a driveable combination for less money.
     
  3. crazyrc

    crazyrc 1/2 ton status

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    Re: large cubic inch small blocks....420 etc.... GURU\'S Please ?

    I'm no guru, but I like what I have.
    460 HP and 540lbs torque.
    Comp Cam Roller extreme 4x4
    Dart heads with a ton of work, including 2.05 intake valves.
    Edelbrock RPM intake
    9.8:1 Comp.
    I have the two bolt and I kind of regret not going with splayed caps, because this engine may see short blasts of nitrous several times a year. They say I'm safe up around 550HP. After that I'm pushing it. By the way this thing idles at 750 RPM and makes good vacuum. I'm running the biggest lift /duration 4x4 roller cam available. Don't know specs off hand.
     
  4. twenty_below0

    twenty_below0 1/2 ton status

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    Re: large cubic inch small blocks....420 etc.... GURU\'S Please ?

    WOW , I'm glad I asked , I checked with Eagle rotating assemblies and they sell rotating assemblies with both cranks , and 6" rods for both , with cr. ratio's at 10.5.1 and 11.1 with 76cc heads . So how is this , they say nothing about using a "tall deck" block , am I missing something , I assumed that a 3.875 crank with 6" rods would be a comparible r/s ratio to a stock 3.75 crank with 5.65 rods . If they are comparible then I think it would be a do able build , I was hoping to get a 450/450 motor with this (or even more torque) and if I need to set the rev limiter at 6,000 then I will but they rate these cranks to turn 8,500 and up to 1000 h.p. Now I will never do that but I would hope they could handle it , they quote a rotating assembly at $1569.00 for the 3.875 and 6" rods rated @ 7500 rpms and 700 horse ,this is with pistons,rings and bearings so is this bull or actual figures....I assumed Eagle was reputable company but as you can tell I have no real experience with strokers....LOL I appreciate the info GREATLY /forums/images/graemlins/thumb.gif
     
  5. b454rat

    b454rat 1/2 ton status Premium Member

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    Re: large cubic inch small blocks....420 etc.... GURU\'S Please ?

    Like the other guys said, it will take alot of money to do that to a motor. Iknow a guy that used to build motors, we called it Millenium Motors, cause that's how long it took to build them. Anyway, he had a 433 motor that he built for the roundy rounders that made 750 horses. Don't know the rpms, but was pretty high, guessing 7000 an above. Dont know the manufactors of the parts, but used a 4" crank, 6" rods, and a hellofa piston. The block needed to be cleared in alot of places, and needed block filler to keep it from cracking. The motor got hot or low on oil, and had small cracks in the journels, so he parted it out. I could have gotten the crank and rods, but at the time didn't have a use for them. Friend of mine is using the block in his car, but now it's just a 406. If you want something that wild, go big block. It won't cost you as much, and won't be at the motor's limits, have room to make more power if needed. Get a ZZ502, over 500 horses, want more?? Put a stroker crank, bigger cam, some work on the heads and have 600+ horses, all naturally aspirated.
     
  6. BigBurban350

    BigBurban350 1/2 ton status

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    Re: large cubic inch small blocks....420 etc.... GURU\'S Please ?

    With a 4" stroke you aint gonna be runnin 7500 rpms because it will fly apart(unless you buy really expensive parts). Shorter the stroke higher the RPM capabilities. What you got there is a low RPM torque monster. /forums/images/graemlins/usaflag.gif /forums/images/graemlins/burb.gif /forums/images/graemlins/usaflag.gif
     
  7. b454rat

    b454rat 1/2 ton status Premium Member

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    Re: large cubic inch small blocks....420 etc.... GURU\'S Please ?

    Everything in this motor was high dollar. Some of the guys out here get pretty serious in racing, and spend ungodly amounts of money on motors, that will get smoked in a nite because the air cleaner came off and sucked in a dust cloud.
     
  8. twenty_below0

    twenty_below0 1/2 ton status

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    Re: large cubic inch small blocks....420 etc.... GURU\'S Please ?

    Did you read my last response ?? According to Eagle there 1600.00 rotating assembly is rated for 1000 h.p. and 7500 rpms so I just figured this is what it could handle....maybe not . I also said to solve that , just set the rev limiter at a lower limit . But I agree with the block problem associated with the 4.00 stroke but the 3.875" crank and 6.00" rods looks a little more do able and I think the torque would be worth it and the R/S shouldn't be hardly any worse than a stock crank and 5.565 rods . So I think that will probably be the better choice ? What do you think , 450 h.p. and 500 torque or close to it would be NICE . I think I could do the short block for about 2500.00 with all machine work and cam , gear drive . I think I will try it , I mean I could go with a big block but why not be different...make a sleeper /forums/images/graemlins/eek.gif /forums/images/graemlins/grin.gif
     

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