VN heads on a 253

[T-Bone75]

Sorry I know similar questions have come up in the past, have done some reading but still uncertain.
I'm restoring a VC with a 253 in it. Moderate cam, putting an Edelbrock 2194 manifold on, Rochester Quad carb, extractors.
Bore is 60 over.

My question is, VN heads being 64cc, does this make them unusable in my scenario, due to reduced compression? Would appreciate advice.

(Please don't reply if all you're going to say is ditch the 253.)

 

[Reaper]

It will lower your CR. Carb heads are around 56cc's from memory so you will need to manage that. I'd start with a 5 litre block

 

[Freedon]

they will bolt up, but you will have valve issues being a smaller bore

 

[EYY]

No valve issues, it will work fine. It's only a problem when you run huge amounts of lift. If you try and up the compression, have the block decked or find some lumpy top Pistons.

Avoid having the heads machined as that will bring the valves closer to the block. As I'm sure you're aware, you'll need to use the efi cam. With vn heads they supposedly still make around the same power as a stock 5L, although they need to be revved hard to get it out of them. The bananas are almost too small for a 308 so would be better suited to a 253 anyway imo, if you're using the stock manifold. It doesn't look like you're going to be using the banana manifold anyway, and to me, the whole point of using the efi heads is to add efi.

The ports and valves are really too big and you'll lose lots of airspeed at low throttle openings so it'll be pretty gutless down low (in addition to the lower compression). The standard 253/308 heads flow well enough with minimal work for a 253 anyway with standard sized valves. Source some 253 head gaskets if you can too, in order to avoid losing even more compression.

I put one of these together, but I never ran it since I found a 308 at the right price and ended up using the old style heads instead.

 

[T-Bone75]

Thanks for the info guys, much appreciated. I did check the lift specs on the valves/heads vs cam and it seemed ok, although as noted skimming them to compensate for lost comp could be a mistake in terms of clearance.
I reckon I'll stick with the stock heads.