7age blacktop..vvti possible??

[Mooro]

Actually thinking about that more, the increase in CR from the silvertop to blacktop 4age should stay the same with the 7age right...cos both the pistons and head are being used??

THe silver top 4age is 10.5:1 and blacktop 4age is 11:1 so would it stand to reason that if the silvertop 7age with 4a HG is 11.35:1 then the blacktop 7age with 4a HG should be in the vicinity of 11.85:1????

[johnny]

blacktop 7age with 4a HG should be in the vicinity of 11.85:1

Yep... I sent you some mail too.

[Mr Revhead]

With the BT the higher CR is achieved via the pistons right? as opposed to the silvertop where it is the combustion chamber,

pistons AND combustion chamber are different between the 2.
what thickness do you have for the 7afe gasket? your getting quite a lot of difference in compression there

[Mooro]

I think the 7a HG is 0.6mm vs 1.2mm for the 4a one, so quite a bit of difference. I'm just quoting what I have read in other threads though, so it is not gospel.

Thanks for the email Johnny, I get what you mean with the cam timing, in that you are basically lowering the dynamic compression even though the static compression is the same...but are there any other issues associated with altering the cam timing in this way or is it just the same as running the engine with a slightly lower static compression ratio?

[DX20VT]

Actually thinking about that more, the increase in CR from the silvertop to blacktop 4age should stay the same with the 7age right...cos both the pistons and head are being used??

THe silver top 4age is 10.5:1 and blacktop 4age is 11:1 so would it stand to reason that if the silvertop 7age with 4a HG is 11.35:1 then the blacktop 7age with 4a HG should be in the vicinity of 11.85:1????

What was the figure you used as the CC of a silvertop head?
I worked mine out on a BT, as I have one of them on the bench,
but dont want to pull the Silvertop head off my race car just to measure the CC.

I want to work out what the comp ratio is with 8.9 GZE pistons, a silvertop head, and a 1.2 mm gasket, and the ST head CC is the only number i'm missing.

[Billzilla]

What was the figure you used as the CC of a silvertop head?
I worked mine out on a BT, as I have one of them on the bench,
but dont want to pull the Silvertop head off my race car just to measure the CC.

I want to work out what the comp ratio is with 8.9 GZE pistons, a silvertop head, and a 1.2 mm gasket, and the ST head CC is the only number i'm missing.

I'm pretty sure it's 36cc's, though that'd need to be confirmed.

[johnny]

I'm pretty sure it's 36cc's, though that'd need to be confirmed.

We work on 36-37cc, Though when measured it was closer to 36cc, so your not far out Bill

[DX20VT]

We work on 36-37cc, Though when measured it was closer to 36cc, so your not far out Bill

I measured the BT to be 38cc, does that sound about right?

[Mooro]

So has anyone done the math to know the exact CR with blacktop 7age using 4age gasket?

I'm not exactly sure how to check it. I've found another potential BT halfcut but it's in Sydney !

[DX20VT]

So has anyone done the math to know the exact CR with blacktop 7age using 4age gasket?

I'm not exactly sure how to check it. I've found another potential BT halfcut but it's in Sydney !

From my own measurements and workings out,
( which may or may not be correct)

7A with AE101 8.9 GZE pistons, Std 20V 1.2mm head gasket and BT head is 9.07:1
7A with AE101 8.9 GZE pistons, Std 20V 1.2mm head gasket and ST head is 9.37:1

[Dimitri]

didnt see it noted anywhere here, but 2 things.

the chamber and piston crown is a different shape in the bt, with different squish areas (basically none on the bt)

the bt cam tooth profile is different to st. st profile the same as 16v.

so to use the camira/porsche/16v 4age belt, you need the correct pulleys on your bt.

[DX20VT]

Can't say I've noticed a difference,

I run a 20V Silvertop cam drive, and 20V Blacktop cam wheels and a 16V smallport cambelt.

[Dimitri]

well go look