Gm performance 305 block
 

Does anyone know why the GM performance 305 block (10243878) has 10mm bell housing and motor mount threads instead of the standard 3/8 16? Is there anything else dimensionally odd about the block? With priority main oiling and .260" thick cylinder walls, it sure seems like an improvement over your "fathers 305" block... Thanks, Patrick.

Re: Gm performance 305 block
 

I am not sure as to why they would do that, unless it's just there weird way of introducing something metric to the block or maybe it was just a freak thing they did without realizing it. those things have happened,lol but if your looking for a great 305 replacement thats all standard threads check out the this. Dart#301-31151411 it's a beefy 305..

Re: Gm performance 305 block
 

I don't think the Dart 305 block is on the approved list. I would get a clarification before you invest.

Re: Gm performance 305 block
 

The 305's came out when GM was going to change everything to the Metric system....but never really did.

The stock 305 bore is an odd number and I believe it may have been a metric dimension....

Most other GM engines were based on std. fractional sizes....

Only other odd one I can think of is a 396 bore.....4.093 ?

Metric 200 transmissions were used with the 305's.....

In the mid to late 1970's GM started using metric body bolts in some cars.....It was a pain to have to buy metric tools back then when everything else was std....

Re: Gm performance 305 block
 

Started working on the rear suspension of a Grand National and things were going smooth. Got a few bolts off, (those with English/Metric "close enough" fit dimensions I guess) until I got to the other Metric fasteners and realized I'd been had. Not a happy camper! Luckily Sears was still in business then and it was just a ride to the store.

Re: Gm performance 305 block
 

Thanks for the feedback guys. They do list the dart block as an approved replacement. Why they didn't go with the SHP platform instead of the Little M I'm not sure; but it seems overkill for a 400 HP engine. I suppose if you're building a super stock engine that's a good thing. It's also about 70 LBS heaver than a stock block. I've been down the salvage yard block path only to be the proud owner of two cracked blocks. I thought maybe this block might be a little better than what came in the production vehicles. I guess the only way to find out is to buy one and try. :)

Re: Gm performance 305 block
 

All the approved replacement blocks for SBC by part number are for either 4" or 4.125" bore. I do not see one for 3.736" bore.

Re: Gm performance 305 block
 

Yes, i was not stating it for stock or super stock replacement. just saying it has more beef to the material. but I would recommend getting the NHRA approved list to be sure. and there are many blocks by World and Dart that are legal replacements.