Looking for advice on whether the parts I’m using will go well together and give an a decent increase in power over standard.
Motor is the original 308 for my trimatic HG. Keeping the original converter, intake and quadrajet, air cleaner, exhaust manifolds and distributor as I want to keep the stock appearance. Original style dual exhaust.
Block 0.040” over, decked -0.020”.
Original HQ type heads, machined face -0.010” L34 style valves, throated to suit bigger valves, hardened exhaust seats.
Later A9L rods.
Mild crow 5666 ski flat tappet hydraulic cam with springs to suit.
Flat top pistons come up 0.020” below deck height.
Using overpriced 0.027” stainless head gaskets to give 0.047” quench height.
A Google search suggest the HQ heads combustion chamber standard would be around 56cc. Hoping this is correct.
Using a compression calculator with all the info above, it should be around 10.8-1 compression ratio .
Have not rebuilt a Holden V8 since the 1983 and totally in the dark how much power this combination will produce. Feeling a bit unsure of myself and if these parts will work well together
Any tips appreciated.
Jim

Thanks
The cam was recommended by crow cams with all the info above.
I also have a 0.040” gasket which would give it 10.5-1 compression.
The advice I got was to reduce the top of the piston to head clearance from 0.060” to 0.047” by using the thinner head gasket.
He said something about quench and that 0.060” not being ideal. A lot of it went over my head but he did say 0.060” will be more prone to detonation and reduce potential power.
Not sure on all the technical side myself.

Edited by user Wednesday, 23 April 2025 7:47:51 PM(UTC)  | Reason: More information

Thanks
Yes the heads have been machine de-shrouded for the bigger valves.
I guess I should have a go at measuring the cc of the chambers myself and recalculate the static compression. I noticed today that the inlet valves taper down toward the middle around 0.100” which might increase the cc’s of the chambers a little.
As it is, if I’m doing it right, using ABDC close at 32 for this cam, the 55cc chamber, the dynamic compression comes out at 10.25:1 which I assume is too high.

Edited by user Thursday, 24 April 2025 3:50:58 PM(UTC)  | Reason: Wrong information

I think you’re right, had a look earlier and the de-shrouding has taken a fair bit of material out. I attempt to measure it tomorrow.
Using a dynamic compression calculator which is all new to me, it looks like I would have been better off with 12cc to 18cc dished pistons.
If the ideal is 8:5-1 dynamic, I need to get rid of at least 10cc off each chambers or the middle 2 1/2” of the pistons.

Thanks for the link. I will give it go.

Probably similar to mine except my block has been decked 0.020”.
Just got a different dynamic compression result at 8.3-1 and 10.3-1 static using the Port City calculator. It goes into a lot more detail, crown diameter, how far rings are down from the crown. It also has the 5666 crow cam specs on there to help.
Feeling a bit more confident but not still not 100% confident.