The combustion chambers on my camel hump heads were 64CC the Combustion chambers on the new heads are 68cc so a slight increase.
The mechanic also said to get an extra thick Felpro head gasket because of the heads being aluminium. That will lower compression slightly too
But I have forged dome pistons still.
It should still have pretty decent compression and enough power for decent wheelspins...
Flat tappet springs
68cc combustion chambers
Springs - good up to 600 lift on flat tappet
* Intake: 196cc
* Exhaust: 74cc
* Chambers: 68cc
* Stud Base Thread Drilled: 7/16"
* Valve Guides: Bronze Manganese
* Suitable Valve Details
* Intake Valves: 2.02"
* Exhaust Valves: 1.60"
* Valve Stem Diameter: 11/32"
* Valves: Stainless Steel
* Height: Standard + .100
* Spring including dampener
* Spring Diameter: 1.450"
* Max lift: .600"
* Seat Pressure: 130lbs @ 1.800"
* Open Pressure: 335lbs @ .600"
* Lift Coil Bind: 1.060"
* Installed Height: 1.800"
Require longer pushrods to keep the valve train geometry correct
(currently running standard 7.8 pushrods)
Comp Cams XE268 Cam
Camshaft Part # 12-242-2 Designation XE268H-10
Duration @ 0.006": 268° / 280° Duration @ 0.050": 224° / 230°
Max Lift w/ 1.5RR: .477" / .480" Lobe Separation: 110°
Lobe ID#'s: 5443 / 5203 Intake Centerline: 106°
The old Camshaft that performed amazingly was:Old cashaft that was in the car:
Lunati 109 btd 00010 camshaft
Lunati 109 btd 00010 Cam
Camshaft Part # 00010 Grind # BM-II
Advertised Duration: 292° / 292° Duration @ 0.050": 230° / 230°
Max Lift w/ 1.5RR: .480" / .480" Lobe Separation: 109°
The mechanic said the spec on the new one he changed over to is practically the same.
The Current rocker arms I believe are standard pressed steel rocker arms so possibly swapping to 1.6 rockers might help too?
The pistons are the same, it has forged pistons: Pistons numbered 3942545
11 to 1 compression from a 1970 special edition corvette
Did your previous heads have 2.02 and 1.6" valves? Certainly the Camel hump heads were nowhere near the 196cc volume on the "new" intakes from the factory. Big valves and big ports only deliver more power at high revs, usually at the expense of power at low revs. You really want to avoid the situation where the cylinder head is starting to deliver at the revs where the camshaft is past it's powerband -and possibly where rods etc. are at, or past their safe rev limit.
Having spent so much money on these new parts I'm loathed to dump them and start again...
Is there a way of decreasing the combustion chamber on these heads so that they could go down to either 62cc or 64cc combustion chambers to raise my compression back up again?
is that a machine work job that could be done? What would that be likely to cost?
Clive @ probuild American has a good reputation and comes across as an approachable guy, have a look at his website and then have a discussion with him, I have only dealt with him on parts and used parts but would trust him
I get what your saying about being skint and being led down the garden path by someone else... unfortunately theres too many unscrupulous people in rodding now.
With regards to your heads - big valves COULD mean more power but its not as easy as that, there are lots of variables involved. the heads aren't just about valves they need to flow as well and be matched to the other parts you are using. Unfortunately I don't think there is an easy answer in getting the CC of them down - maybe go for a std gasket rather than a thicker one but I don't think that will make a huge difference. I think the heads would be fine for making top end power but the old heads were probably more suited for making low down power. I also think the cam you have used is a little small for the package you have, the next one up the 274 might have been a better choice. I think the cam you have now was suited to your old heads.
As I said before I think its the package you have which isn't really suited to work together which is causing your issues. I still think you would benefit from sitting down with someone and going through what you have and going through it to ensure everything is set up correctly given the issues you had with the previous mechanic. you might be chasing something which is a really simple fix but isn't obvious to you.