427-425hp w/GM 401 heads
 

what is the clarification as to what exhaust valve diameter is legal in the GM performance 401 replacement head, the head comes as a 1.88 diameter is this the legal valve size we can use in the 427-425hp engine, or do we have to use either the 1.84 or 1.72 valves? whats the answer?

Re: 427-425hp w/GM 401 heads
 

The correct answer is start working on a new 2013 Camaro. Or look in the guide for the spec. That head also comes with 11/32 guides which must be opened up to 3/8 so the valve size it comes with is also subject to change to meet the NHRA spec for a particular combo.

Re: 427-425hp w/GM 401 heads
 

Must use the 3/8 stem and 184 exhuast valve, also + 10hp when using this head.

Re: 427-425hp w/GM 401 heads
 

If the valve sizes have to remain stock factory spec then why is there 10 hp added to the combination? All aluminum heads in 1969 were either 1.84 closed chamber or 1.88 open chamber why would NHRA require a 1.72 valve and still penalize the engine10 hp or 80 pounds extra weight in A/SA?

Re: 427-425hp w/GM 401 heads
 

OK, I have 2 differint opinions now 1 for the 1.84 valve and 3/8 stems and another with 1.72 valve and 3/8 stems . Who is correct?

Re: 427-425hp w/GM 401 heads
 

I see in the NHRA blueprint specs that when you use the 401 the 1.84 exhaust valve is the legal valve to use ........Ruler you were right , thanks

Re: 427-425hp w/GM 401 heads
 

The iron head uses the 1.72 exh. and the 401 alum. uses the 1.84 exh and also you run at 435hp. with the alum. head 425hp with the iron head. Thanks

Re: 427-425hp w/GM 401 heads
 

I think the 401 alum head has a standard spec for all combinations it can be used on.

2195/1845 with a 103.3 chamber volume.

Again, check the guide as always.

Re: 427-425hp w/GM 401 heads
 

The 401 head can be used on the 1969 427/430 ZL1 or L88 with 2.195 1.885 valve and 114.8cc camber also.there is a different HP. rating for the ZL1 and the L88, The ZL1 gets a bigger cam. If you use an original head casting (aliuminum) then there is a HP reduction.

Re: 427-425hp w/GM 401 heads
 

Is there a horsepower penalty on the 396=375hp aluminum head engine if you use the original # 842 aluminum casting cylinder head or is the factored hp # for the 401 only ?