I recently got a great deal on a forged 383 LT1 shortblock and am looking for suggestions on which heads to run. The pistons are only -16cc dish, which would yield too high static compression ratio for FI. I calculated a cylinder chamber size of 65cc would put me at around 9.7:1, which would probably be decent to run 10-15 psi boost. The problem is that there are very few options for a chamber that size. Here are some options I can think of.

1) Un-ported AFR Eliminator heads with 65cc chamber. I want to know if real world performance matches the impressive flow numbers they publish on their site. I have been unable to find much information about real world performance.

2) Trickflow heads with chamber machined larger than standard 62cc. I asked AI about this, and they said it MAY be possible to get them to 65cc. I would also have them ported by AI if I go this route. This will be more expensive than the AFR's.

3) Switch to a larger dish piston. I don't want to do this because the rotating assembly has already been balanced, but it is an option. I could go with TFS or even ported stockers if I go this route.

Any other ideas?

 

The AFR heads (one before the eliminator series) had the option of 6x cc or 7x cc (I think it was 64cc or 74cc). would try and get the biggest chamber. There are always sets of used AFR's floating around if you look.

As far as the eliminators, they should perform well and have lots of meat left for serious porting. I am surprised they dont offer more than one chamber size... you may want to look into that.

 

afrs do not perform well untouched their numbers are overrated, theres been plenty of members throwing a set of stock afr heads on flowbench and seeing a much smaller number. Although they arent great out of the box, they have plenty of metal to work with so getting them worked over IMO is always a must to see a decent gain.

 

This seems to be the case with the old AFR's. I think the jury is still out on the "Eliminator" series AFR heads.

 

Exactly. I haven't found much solid data on real world performance for the Eliminators. Their published flow numbers for the 210cc SBC heads (not sure if the LT1's are available yet) are very impressive, especially for the price. I'm not really interested in the old AFR stuff.

 

I have no input about the heads. But if you are willing to pop in a set of new pistons, provided they are lighter than the old ones, you won't need to have the RA rebalanced. This is a quote from a prior post on this subject that I wrote.

I learned a lot more than I knew about balancing recently. Basically, the convention of balancing the whole piston/rings/pin weight and 50% the rod weight is somewhat arbitrary. Different shops have slightly different ways of balancing. If you don't specify exactly what you want, many (most) will deliberately "overbalance" by 1-2%. Overbalance means there is more counterweight than the traditional rod+50%. Some engine builders are convinced that overbalancing makes for smoother running at high rpm with a neglible increase in low rpm vibration.

When assembling my race motor this year this came up. After the shortblock was already assembled, I found a piston to valve clearance issue that necessitated new pistons. The new pistons were 36g lighter than the old ones. My machinist, engine building mentor, and JE all said "no problem, it might even be better". In spite of hearing this from three reliable sources I was skeptical but went ahead as the time and cost for rebalancing was prohibitive. And what do you know, it runs smooth as silk to 7,500rpm. Noticibly smoother above 5,000 than with a 50% balance and it is now ~3% overbalanced! I am going to take a look at a main bearing this weekend and will report any probems. But from the way it runs, I doubt there will be any.

Addendum: the mains are fine after ~50 passes.

Rich