[PyroManiacUSMC]

hey everyone i need some help and have some questions about an engine

i found a guy who has for sale what he says is a 400 out of a 1978 firebird, says it has 6x4 heads and the block # is 487934. now i have looked for hours through google with no luck. so dont say google it the question i have is this: would this be a good investment to take beyond 450hp? and if you fine a site with all the specs for this motor just paste the link and i can go through it, thanks in advance

[eloc431962]

I don't reconize that # exactly where on the engine did you take it from ?


Cole

[PyroManiacUSMC]

guy said he got it from behind the #8, right next to the distributor pad. same place as all the rest. i had to ask here becase i didnt recognise, nor could i find anything on it

[eloc431962]

It can be on the passeger side of the block or the distributer pad Or the rear of the block behind #8. This all depends on what yr it is on placement of the #s. He might have even read them wrong.JMO



Cole

[beertracker]

6x-4 is a 93cc chamber Pontiac head. Look on the head where the two center exhaust ports meet and you will find the casting number, 6X in this case. Look to the front of the head and you will see a boss which has 4 stamped in it. This head has 2.11" intake valves and 1.66" exhaust valves.

BT

[WDCreech]

I can't find any numbers for blocks cast after 1976, but I know there were some because the late '75 and '76 blocks were thin in the main saddles and they went to a new casting to alleviate the problems that were created. The inferior blocks were casting number 500557. Any other 400 block (400 will be cast on the right side) should be okay. Someone did post the casting # of the later blocks, but I don't know if it was on PY or one of the other Pontiac forums.

Bill

[cobalt327]

The following is from “Rick” of the tech staff on Hitman's Pontiac Trans Am Forum:

The original casting number for the early 400 CID Pontiac blocks was casting number 481988. It is a very strong casting and it has been successfully used for many high-power and stroker builds without any block problems at all.

The engineers in the drive train division looked at their engines, and decided that they could shave a few pounds out of the 400 block by redesigning it with thinner internal webs. The result of this was the 500557 block. It IS weaker than the 481988 block, but it's plenty strong for most street applications. In particular, it was WAY stronger than the factory needed for the 185 HP engine they were putting out in 75-76.

So... during the 1975 model year, Pontiac switched to the 500557 casting. They stuck with it through the end of the 76 model year. But as car production moved into the 77 model year, the painful memories of the gas lines of early 1974 faded. Pontiac had a few production problems with assembly of the 500557 block engines, and they wanted to emphasize performance a bit more with introduction of the higher-HP option package. Rather than sink the cost of engineering yet another revision to the 500557 block, they decided to simply revert to the 481988 block.

The use of the more robust block continued through the end of the Pontiac 400 CID engine production, during the 1978 model year. A set number of the 400 engines were stockpiled for the 79 model year, and then all the tooling was ditched because that was the end of the Pontiac 400, per corporate edict. The Olds 403 was use for the "big engine" production once the 400 engines were gone (all 400s were 4 speed, all 403s were autos), and for 1980 there were no more "big engines".

A 500557 block is fine for almost any streetable 400 engine you'd want to build, right up to 450-500 HP, and with RPMs under 5,000. It's not the BEST candidate for a stroker engine or a drag engine that's going to see 6,000+ RPM -- the 481988 block is much better for that. But given a choice, most people opt for the 481988 block if they can find one for the same or approximately the same money.