AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
- Jan 19, 2014
- Messages
- 24,967
- Reaction score
- 12,320
I'll jump in with a primer;
This combo is possible; heads 64, .012 deck is 2.4, .028 gasket is 6.5, and eyes are 5 for a total of 77.9cc. It doesn't matter how you get to the total of 77.9, let's just say you got there.
Then at 3.94 bore your swept is 662.32
The Scr then will be (662.32 + 77.9)/77.9=9.50
So let's say you get to that.
And the Q, if you use closed chamber heads comes in at .012+.028=.040
Then lets say you are at 800ft elevation.
Doing the math for this, to achieve 160psi so you can run pump-gas, Mr Wallace says that you need an ICA of 56*. You can find this ICA on lots of cams.
Here is one;
256/262/110/ Overlap of 39* so no headers required;doesn't mean you can't run them. Now the 256 is a small cam but the VP is pretty big at 129, so it will have low-rpm performance better than a stock 8/1- 360(116VP).Keep your eye on that 129 number.
You can go another size bigger, but you will have to tighten up the LSA. I get
262/270/107/52* overlap, so long-tubes still kindof optional, but they will make more power. This looks like;9.5/8.0/157psi@125VP, so we gave up 4 points of VP for 15ish Hp up top
I like this one for a stick with your gears.
If you want to run faster, you are outta compression headroom. From 56* on up, you will be trading low-rpm pull for hi-rpm charging, as the pressure will start falling. But with the Q already at .040, you don't have much room there either.
Max effort
Now,if you zero deck it, the Q will come in at gasket thickness, .028, and I have run that as well.This will get you up to 9.77, and now you can run the 268cam. And I get
9.77/7.9/153psi/ VP drops to 117, so the low-rpm goes mushy. But it's a stick car so you just rev it up a bit off the line.
Or you tighten up the LSA to 107 again and I get 268/276/107/58* overlap,and the numbers come in at 158psi/124VP, and you are back in action. This cam wants long-tubes for sure.
Alumunum heads
But now you are almost set up for aluminum heads,and if you run them, well, I have run 185psi and more with those, and others here have reported over 200psi. I run 175 on 87E10.
The teener will never get there without custom pistons.
So if you get inverted dome-flat tops, And adjust the total chamber size to 69.5 with a tight Q;(58heads,6.5gasket,5eyes=total 69.5)... Then the Scr comes in at 10.5.
Now you can run that 268* on the factory 110LSA and I get
10.5/8.5Dcr/172psi@132VP, and that is serious business now.
So now you know why nobody wants to say anything until the measuring has been done. The difference from dog to TopDog on a 318 is just 8 to 10cc of total chamber volume, and 6* of ICA.
And we haven't even talked about mechanical cams.......
Ok lets talk solids:
that 268HFT is about a [email protected], so that's pretty peppy.
As a solid it could be a 230*@.050 and that is a tic over one size bigger, so
still at 10.5Scr with those inverted domes, the pressure comes in at 172/ 134VP
So that looks like about 15 hp at the top , with 2 more points of VP. But it requires Aluminum heads to pull off.And is expensive to build.
OK, so what does it look like at the easy to achieve 9.5Scr and iron heads? And I get 151psi@118VP, so ouch.
How about at 9.77? I get 157psi@122VP, good for iron heads, so you are saving money.
How about we tighten the LSA up to 106, still good for your stick car. So now it's a 268/276/106/60* overlap and up comes; 159psi/126VP. This is 6 points short of the aluminum headed hydro-lifter engine, yet I think it will make similar to more power because of the extra 8* of intake duration.
But IMO this [email protected] is a bit much for the street. So lets go back one size, to the 262/268/108/49 overlap, mechanical, in the cheapest to build 9.5 engine. I get 9.5/7.9/154psi@121VP. So this is doable, but she's wanting more cylinder pressure, as you can see by the reduced VP.
At 9.77 then, BADABOOM; 8.14Dcr/159psi@126VP
So this is a pretty nice combo.
Lets recap it
3.94 bore. KB 167s in at zero-deck. 58cc iron heads,6.5 gasket,5cc eyes,.028Q, and total chamber volume of 69.5, for an Scr of 9.77 , which will net to 8.14Dcr/159psi@126VP with an ICA of 58* on a mechanical 262/268/108/49 overlap cam. This solid lifter cam might net to 224/[email protected]. And it burns probably 89 under WOT, 87 while cruising....I like it.
You might be able to run a lil less gear if you wanted to, especially if you have the 3.09low in your trans.
BTW, this cam has compression/power duration numbers just 9* total less than the 240/248/112/16overlap factory cam. This means that in steady state hi-way cruising it has the potential to attain greater fuel economy than the stocker.
I know whatcherthinkin, what about at 10.5Scr?
Static compression ratio of 10.5:1.
Effective stroke is 2.74 inches.
Your dynamic compression ratio is 8.85:1 .
Your dynamic cranking pressure is 177.94 PSI.
V/P (Volume to Pressure Index) is 143
Of course 178psi requires aluminum heads, but the win is that it will burn 87E10, all the time
This is a dynomite street teener!
This is now a pretty expensive build, what with the aluminum heads the reverse-dome pistons and various machinings required, custom balancing, etc. You'd have to be pretty dedicated to the teener.
Probably for a little less money, you could run a 3.58 crank, your 64cc heads,an .039 gasket, get a total chamber volume of about 77.9cc, for an Scr of 10.2. and then you could run that 268/276/110 hydro cam, and I get
Static compression ratio of 10.2:1.
Effective stroke is 2.84 inches.
Your dynamic compression ratio is 8.30:1 .
Your dynamic cranking pressure is 163.52 PSI.
V/P (Volume to Pressure Index) is 136
It wouldn't take much to tweek that for pumpgas.
And the only extra expense here is the 3.58 crank, and maybe a little more for the right cd height pistons.
BTW, this is now a 349 cuber, and a pretty sweeet powerhouse
Happy HotRodding
This combo is possible; heads 64, .012 deck is 2.4, .028 gasket is 6.5, and eyes are 5 for a total of 77.9cc. It doesn't matter how you get to the total of 77.9, let's just say you got there.
Then at 3.94 bore your swept is 662.32
The Scr then will be (662.32 + 77.9)/77.9=9.50
So let's say you get to that.
And the Q, if you use closed chamber heads comes in at .012+.028=.040
Then lets say you are at 800ft elevation.
Doing the math for this, to achieve 160psi so you can run pump-gas, Mr Wallace says that you need an ICA of 56*. You can find this ICA on lots of cams.
Here is one;
256/262/110/ Overlap of 39* so no headers required;doesn't mean you can't run them. Now the 256 is a small cam but the VP is pretty big at 129, so it will have low-rpm performance better than a stock 8/1- 360(116VP).Keep your eye on that 129 number.
You can go another size bigger, but you will have to tighten up the LSA. I get
262/270/107/52* overlap, so long-tubes still kindof optional, but they will make more power. This looks like;9.5/8.0/157psi@125VP, so we gave up 4 points of VP for 15ish Hp up top
I like this one for a stick with your gears.
If you want to run faster, you are outta compression headroom. From 56* on up, you will be trading low-rpm pull for hi-rpm charging, as the pressure will start falling. But with the Q already at .040, you don't have much room there either.
Max effort
Now,if you zero deck it, the Q will come in at gasket thickness, .028, and I have run that as well.This will get you up to 9.77, and now you can run the 268cam. And I get
9.77/7.9/153psi/ VP drops to 117, so the low-rpm goes mushy. But it's a stick car so you just rev it up a bit off the line.
Or you tighten up the LSA to 107 again and I get 268/276/107/58* overlap,and the numbers come in at 158psi/124VP, and you are back in action. This cam wants long-tubes for sure.
Alumunum heads
But now you are almost set up for aluminum heads,and if you run them, well, I have run 185psi and more with those, and others here have reported over 200psi. I run 175 on 87E10.
The teener will never get there without custom pistons.
So if you get inverted dome-flat tops, And adjust the total chamber size to 69.5 with a tight Q;(58heads,6.5gasket,5eyes=total 69.5)... Then the Scr comes in at 10.5.
Now you can run that 268* on the factory 110LSA and I get
10.5/8.5Dcr/172psi@132VP, and that is serious business now.
So now you know why nobody wants to say anything until the measuring has been done. The difference from dog to TopDog on a 318 is just 8 to 10cc of total chamber volume, and 6* of ICA.
And we haven't even talked about mechanical cams.......
Ok lets talk solids:
that 268HFT is about a [email protected], so that's pretty peppy.
As a solid it could be a 230*@.050 and that is a tic over one size bigger, so
still at 10.5Scr with those inverted domes, the pressure comes in at 172/ 134VP
So that looks like about 15 hp at the top , with 2 more points of VP. But it requires Aluminum heads to pull off.And is expensive to build.
OK, so what does it look like at the easy to achieve 9.5Scr and iron heads? And I get 151psi@118VP, so ouch.
How about at 9.77? I get 157psi@122VP, good for iron heads, so you are saving money.
How about we tighten the LSA up to 106, still good for your stick car. So now it's a 268/276/106/60* overlap and up comes; 159psi/126VP. This is 6 points short of the aluminum headed hydro-lifter engine, yet I think it will make similar to more power because of the extra 8* of intake duration.
But IMO this [email protected] is a bit much for the street. So lets go back one size, to the 262/268/108/49 overlap, mechanical, in the cheapest to build 9.5 engine. I get 9.5/7.9/154psi@121VP. So this is doable, but she's wanting more cylinder pressure, as you can see by the reduced VP.
At 9.77 then, BADABOOM; 8.14Dcr/159psi@126VP
So this is a pretty nice combo.
Lets recap it
3.94 bore. KB 167s in at zero-deck. 58cc iron heads,6.5 gasket,5cc eyes,.028Q, and total chamber volume of 69.5, for an Scr of 9.77 , which will net to 8.14Dcr/159psi@126VP with an ICA of 58* on a mechanical 262/268/108/49 overlap cam. This solid lifter cam might net to 224/[email protected]. And it burns probably 89 under WOT, 87 while cruising....I like it.
You might be able to run a lil less gear if you wanted to, especially if you have the 3.09low in your trans.
BTW, this cam has compression/power duration numbers just 9* total less than the 240/248/112/16overlap factory cam. This means that in steady state hi-way cruising it has the potential to attain greater fuel economy than the stocker.
I know whatcherthinkin, what about at 10.5Scr?
Static compression ratio of 10.5:1.
Effective stroke is 2.74 inches.
Your dynamic compression ratio is 8.85:1 .
Your dynamic cranking pressure is 177.94 PSI.
V/P (Volume to Pressure Index) is 143
Of course 178psi requires aluminum heads, but the win is that it will burn 87E10, all the time
This is a dynomite street teener!
This is now a pretty expensive build, what with the aluminum heads the reverse-dome pistons and various machinings required, custom balancing, etc. You'd have to be pretty dedicated to the teener.
Probably for a little less money, you could run a 3.58 crank, your 64cc heads,an .039 gasket, get a total chamber volume of about 77.9cc, for an Scr of 10.2. and then you could run that 268/276/110 hydro cam, and I get
Static compression ratio of 10.2:1.
Effective stroke is 2.84 inches.
Your dynamic compression ratio is 8.30:1 .
Your dynamic cranking pressure is 163.52 PSI.
V/P (Volume to Pressure Index) is 136
It wouldn't take much to tweek that for pumpgas.
And the only extra expense here is the 3.58 crank, and maybe a little more for the right cd height pistons.
BTW, this is now a 349 cuber, and a pretty sweeet powerhouse
Happy HotRodding
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