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421 Torque Monster

13K views 9 replies 8 participants last post by  CNC BLOCKS  
#1 ·
I tell people if your going to build a 400 or 406 bump up to the 421 for a street build its the way to go. Spent the morning on the dyno with Frank Carey. This is the 421 I built, Pump gas HYD roller he wanted a torque monster and that's what he got, I used the AFR 195 heads, Best Torque number 568 @4200 RPM Best HP number was 524 at 5500 RPM. This engine made the best HP & torque numbers with only 30 degrees of total timing. At 3400 RPM there was a dyno sheet that showed 550 Torque. Also a big shout out to Johnson Lifters the valve train was quiet as always, No need for the Snake oil and only needed a 1/4 turn down from zero lash. No need to break in lifters LOL.
Dart SHP block all machined in house
Mahle Flat top piston
3.875 stroke 4340 crank
Scat I Beam 6.0 - 7/16 bolts ARP 2000 series
195 AFR heads 75 cc chambers
Air Gap intake
GM Dist
Scott plug wires
Cam 238/242 on 108 lobe sep, .573 lift Step nose cam
750 Quick fuel carb
Timing set Cloyes Hex-A-Just
Lifters Johnson 2110-R
Champ 8 quart oil pan
Oil Pump 10552
Scorpion 1.5 rockers
326957
326958
326959
 
#7 ·
I looked up the price on a SHP block for an SBC, it's about $1600. A new GM block that needs way more work to use it is $1150. And the Dart block is undoubtedly better in all details. Price does not seem out of line.

The days of using a junkyard block to build a decent engine have been over for a long time. And really never existed for a big bore SBC.
 
#9 ·
CNC,

This is a very timely thread as I am considering a very similar engine for my 1966 Nova. It currently has a 406 with a spun main bearing. Turns out the screen broke off the end of the Milodon pick up tube. I had the motor built by a local performance shop, its runs pretty good but this is the second catastrophic failure...Needless to say it is getting expensive and I need to make a change.

I was researching crate motors using the Dart SHP block and noticed 421, 427 and 434 cubic inch engines being built. I have heard of issues with the 434 but that was in the 400 blocks. What is the pros and cons to these builds.

As mentioned, this engine would be for a 1966 nova that is 99% "spirited" street driven and very rarely taken to the track. I am looking for 550hp range. The car currently is a 4 speed but i will be making the change to an automatic at the same time. It has a factory 12 bolt (c-clips eliminated) with a 3.55 gear.

Any information you have would be appreciated

Thank you

Ron
 
#10 ·
CNC,

This is a very timely thread as I am considering a very similar engine for my 1966 Nova. It currently has a 406 with a spun main bearing. Turns out the screen broke off the end of the Milodon pick up tube. I had the motor built by a local performance shop, its runs pretty good but this is the second catastrophic failure...Needless to say it is getting expensive and I need to make a change.

I was researching crate motors using the Dart SHP block and noticed 421, 427 and 434 cubic inch engines being built. I have heard of issues with the 434 but that was in the 400 blocks. What is the pros and cons to these builds.

As mentioned, this engine would be for a 1966 nova that is 99% "spirited" street driven and very rarely taken to the track. I am looking for 550hp range. The car currently is a 4 speed but i will be making the change to an automatic at the same time. It has a factory 12 bolt (c-clips eliminated) with a 3.55 gear.

Any information you have would be appreciated

Thank you

Ron
Ron
The problem with 4.0 stroke is cam to rod clearance. When reducing to small base circle cam you increase lifter pressure angle which in not a good thing. That's why I stick to a 3.875 stroke, Even then you do have to run a reduced B/C cams. My 421's with a solid roller I can get away with a .990 B/C and use a .420 lobe, On the engine I posted I used a 1.050 B/C

You should be able to have your local shop look over one of these and have them build it for you.

Here is a 427 I build using a 3.875 stroke with a 4.185 bore custom pistons is the only draw back


421 solid roller 220 Heads

Good Luck which ever way you go.