I am ordering my block today. Machine shop talked me out of using my production 400 small block and going aftermarket instead. Whick block to go with? 3.990" bore or 4.115" bore. This will have the 350 main bearing size. I will be going 427ci. What crank size do I need to get the displacement? They are porting and polishing my brodix heads in the mean time.

 

You need the larger bore, bored/honed to 4.125" to make a 427, along with a 4.0" stroke crank. I'd go with the 400 main size, it's the same price, and the larger main journals increase the cranks strength. But if you've already got the 350 mains, I wouldn't worry about it.

 

So order the motown race w/400 main bearings and 4.115" bore? Cost is $1895.99 through jegs.

 

I understand the Motown block would take a 4.200" bore and the block comes clearanced for a 3.875 stroke. So a 4.185" bore and 3.875" stroke gives 426.2 cubes. Close enough to a 427. What is the general opinion on this bore/stroke combo?

 

I went with the Dart Iron Eagle/GM Rocket Block - Part Number: 31122222
Price: $1,850.00, you can get it through Jeg's also. It's the same price, but it has features not found in the Motown's. Not everyone needs some of them, but they are at least worth considering.

You can get the Dart/GM blocks with a 9.325" raised deck, which gives you the room to run 6.125" rods with the 4.0" stroke crank. This will result in a 1.53 rod/stroke ratio which is not too bad, comparable to the 1.52 r/s ratio of the common 5.7" rodded 383. Also, you can get 350 or 400 mains; cam bearings in SBC, BBC, or 50 mm roller bearing journal diameters: and it comes with .800" spread pan rails and a .391" raised cam. Contrary to what World Products implies in their ad's, these features do not require you to run 'expensive, race parts.'

You can get a a good Moroso oil pan from Summit for $250, or a custom aluminum sheetmetal oil pan from Stef's for $300 with all the tricks. A Cloyes Tru-roller timing chain is about $95, and a standard timing covers works just fine. With the spread pan rails and raised cam, you can run a 4.0" stroke crank without touching the pan rails or grinding the rods, and you can run a stronger, standard base-circle cam. You can go up to 4.125" with some minor clearancing of the block - about the same as what you would need to do to make a 383 out of a 350 block.

Certainly, you could go with the larger 4.185" bore and 3.875" stroke, but you would be sacrificing future rebuild potential of the block. These blocks can be bored to 4.200" (max recommended) and still have over .300" cylinder wall thickness. So realistically, you could go even farther, but I don't see the need to bore it out right away. The cost of a 3.875" or a 4.00" crank are the same, and the clearancing difference is minimal. I've taken my 4.0" stroke SBC 427 up to 7500 on the dyno, so it is fully capable of all the rpms you need, depending on the parts you select. The engine also accelerates very quickly - causing the dyno operator to comment on how 'frisky' it was, and considering the engine's Fast Times is famous for building, that's pretty significant.


[Modified by Monty, 6:57 PM 1/2/2002]

 

I am not sure if others are running this special but I just got a Dart 4.5" bore Big M block ( I am building a 540 ci stroker) from Flatlander Racing and the shipping was only $1. I just checked their website and they are still running the promotion for any Dart Iron Block. It looks like their price is the same as the others. $1899 for Part # 31122222. It might be worth checking into if you can save $100+ on freight. http://www.flatlanderracing.com/

John.

 

Between the two blocks, which one is stronger? I think I remember that the rocket block was the stronger but that it use to cost more. Something like $2200. If the Dart block is better and it costs about the same why would I want to go with the motown?

 

If I don't hear anything to change my mind, I will be ordering the Dart block tomorrow?

 

The Dart Iron Eagle and the GM Rocket Block are identical. Dart actually makes the rocket block for GM - same casting, same material, same machining etc. The only difference is that Dart offers the wet or dry sump option under the same part number - the block can be configured either way depending on whether you plug the main cap or not. Whereas the Rocket block is offered as wet or dry sump under two separate part numbered blocks.

The Dart, GM Rocket, and Motown all feature thicker decks, bulkheads, main webs, etc. AS I mentioned before, the Dart/Rocket blocks have options that are desirable if you're building a high-output stroker, but otherwise they're probably equal. Some NMCA/NSCA racers have experienced cracked main webs on the Motown blocks due to the thin main webs surrounding the 1/2" main studs/bolts. It appears that the larger stud/bolt holes have resulted in thin main webs and have cracked under high output, racing conditions. I don't know if this is anything to be concerned about under typical street level applications. I have heard that World has addressed this by going back to the standard 7/16" main stud/bolt diameter. I do not have first hand knowledge of this, but this is what I have heard directly from NMCA/NSCA racers and have read it on the NMCA/NSCA racer forum, Headsupreveiw.com.

 

P.S.

One thing I learned is that none of the cam companies offer a samll block cam, with big block cam bearing journals, with a cast iron cam gear. This means that if you order the same aprt number Dart block I did, that features Big Block cam bearing journals, you will have to run a bronze distributor gear. This is not a big deal, but you will need to replace the distributor gear every 10,000 miles or so at about $35 a pop. The larger cam bearings offer a minimal amount of cam strength, but if I had to do it over again, I'd go with the SBC cam bearings. However, the reason I went with the larger BBC cam bearing jouranl is that it allows you to run a larger lift cam. The camshaft I am running now would not fit easily fit in a block with SBC cam bearing journals since the radius of the cam lobe (lobe lift) is larger than the radius of a SBC cam bearing . So if you want to run a .650" or so cam (depending on rocker ratio), go with the BBC cam bearings.