AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
- Jan 19, 2014
- Messages
- 24,929
- Reaction score
- 12,278
one point often overlooked is this;
My engine has over 100,000 miles on it now. I live at least 20 miles from the nearest town. So every time the car goes out, It will have to travel 40 hiway miles. And so, for me, fuel mileage is pretty important.
The towns are small, and the cops are merciless, so there will be a lot of second-gear cruising involved. So again, fuel useage is always on my mind. That is why the 292/292/110 cam came out before the first summer was over. But that cam, taught me why the fuel mileage was so bad.
I then went the other way, to see if I was right. I installed a 270/276/110, and the fuel consumption plummeted. So I knew I was on the right track.
Of course the power was way down, but I figured out how to work around that. And ultimately, the 292 was ridiculous anyway.
The point I want to make is this; the 270 cam, in the 4 years it was in there saved me thousands of gas dollars. Firstly it ran on 87E10 and
secondly, on the hiway it got double the mileage, that the 292 made, and
Thirdly, it was way more fun in the first 2 and 3 gears, and also used way less fuel in Part Throttle operation..
Do the math;
had I kept the 292 cam, and averaged 12 mpgUS (hiway plus city), 100,000 miles will take 8333 gallons.
With the 270 cam, she regularly averaged over 20 mpgUS so that is 5000USG.
The difference over the lifetime of 100,000 miles comes to 3333 gallonsUS.
How much is that in USd? IDK; would it be 3.50 a gallon? If it was, that would be $11,665.5USd
I drove most of those miles in the first 6 years, as she was my DD. I'll estimate 80,000miles in 6 years. That would come to 1555.33USd saved every year.
I cannot tell you how much of that might have been due to the Tight-Q and alloy heads at nearly 11/1 Scr.
But I can tell you that this was a ripper of a street engine, and I could never run 180psi with iron heads. I would still be driving that 270 cam today, if it had not dropped lobes right after an oilchange, which I traced to the disappearance of the ZDDP.
In about 2005, that forced me into a new cam, and I went just one size bigger; a 276/286/110 cam. I got greedy, for a lil more topend . The previous year, I had got me a GVod so I figured the MPGs would not suffer too bad. I was wrong.
Going from 276 exhaust degrees to 286 , dropped power extraction from 110 to 104, which killed hiway economy. and the overlap grew from 53 to 61 which killed the around town PT economy. And no amount of tuning could make it better.
But the top-end rush was back, which I loved; so I retired that combo from DD to weekend warrior. And then, since I had the GVod,I started playing with rear gears again. I ended up really liking 3.55s, but the car was a lil sluggish with the 2.66 low in first gear, and I couldn't drive it below about 6.5 mph. And so I called Jamie at Passon and he found me a 3.09/direct, Commando combo. And I bought his alloy box/sidecover right away too. Well, 3.09 over 2.66s is a 16% increase and I was back in action for first gear, and the bonus was that the new minimum roadspeed was 4.0 with the 3.55s, which previously had taken 4.88s ( yes I really ran 4.88s on the street). So now, parading was on the table.
So what's the point?
Thruout all this, I kept the cylinder pressure pretty much the same (in the range of 183 to 177), by decking and gasket selection. And more importantly, the Squish was kept in the range of .039/.040 , and currently is .034.
So all the changes could be directly compared and "blamed/credited" on/to the camshaft,
which translates to the Ica.
here it comes;
These three, pressure, ratio, and Ica, (and elevation) are intimately connected . And I learned right quick just how intimate that relationship is.
Op, I'm still wishing you nothing but success, whatever pistons you install, and whatever your pressure ends up being.. and I'll be here in the future with everyone else, to help you in any way I can, should you need help.
My engine has over 100,000 miles on it now. I live at least 20 miles from the nearest town. So every time the car goes out, It will have to travel 40 hiway miles. And so, for me, fuel mileage is pretty important.
The towns are small, and the cops are merciless, so there will be a lot of second-gear cruising involved. So again, fuel useage is always on my mind. That is why the 292/292/110 cam came out before the first summer was over. But that cam, taught me why the fuel mileage was so bad.
I then went the other way, to see if I was right. I installed a 270/276/110, and the fuel consumption plummeted. So I knew I was on the right track.
Of course the power was way down, but I figured out how to work around that. And ultimately, the 292 was ridiculous anyway.
The point I want to make is this; the 270 cam, in the 4 years it was in there saved me thousands of gas dollars. Firstly it ran on 87E10 and
secondly, on the hiway it got double the mileage, that the 292 made, and
Thirdly, it was way more fun in the first 2 and 3 gears, and also used way less fuel in Part Throttle operation..
Do the math;
had I kept the 292 cam, and averaged 12 mpgUS (hiway plus city), 100,000 miles will take 8333 gallons.
With the 270 cam, she regularly averaged over 20 mpgUS so that is 5000USG.
The difference over the lifetime of 100,000 miles comes to 3333 gallonsUS.
How much is that in USd? IDK; would it be 3.50 a gallon? If it was, that would be $11,665.5USd
I drove most of those miles in the first 6 years, as she was my DD. I'll estimate 80,000miles in 6 years. That would come to 1555.33USd saved every year.
I cannot tell you how much of that might have been due to the Tight-Q and alloy heads at nearly 11/1 Scr.
But I can tell you that this was a ripper of a street engine, and I could never run 180psi with iron heads. I would still be driving that 270 cam today, if it had not dropped lobes right after an oilchange, which I traced to the disappearance of the ZDDP.
In about 2005, that forced me into a new cam, and I went just one size bigger; a 276/286/110 cam. I got greedy, for a lil more topend . The previous year, I had got me a GVod so I figured the MPGs would not suffer too bad. I was wrong.
Going from 276 exhaust degrees to 286 , dropped power extraction from 110 to 104, which killed hiway economy. and the overlap grew from 53 to 61 which killed the around town PT economy. And no amount of tuning could make it better.
But the top-end rush was back, which I loved; so I retired that combo from DD to weekend warrior. And then, since I had the GVod,I started playing with rear gears again. I ended up really liking 3.55s, but the car was a lil sluggish with the 2.66 low in first gear, and I couldn't drive it below about 6.5 mph. And so I called Jamie at Passon and he found me a 3.09/direct, Commando combo. And I bought his alloy box/sidecover right away too. Well, 3.09 over 2.66s is a 16% increase and I was back in action for first gear, and the bonus was that the new minimum roadspeed was 4.0 with the 3.55s, which previously had taken 4.88s ( yes I really ran 4.88s on the street). So now, parading was on the table.
So what's the point?
Thruout all this, I kept the cylinder pressure pretty much the same (in the range of 183 to 177), by decking and gasket selection. And more importantly, the Squish was kept in the range of .039/.040 , and currently is .034.
So all the changes could be directly compared and "blamed/credited" on/to the camshaft,
which translates to the Ica.
here it comes;
These three, pressure, ratio, and Ica, (and elevation) are intimately connected . And I learned right quick just how intimate that relationship is.
Op, I'm still wishing you nothing but success, whatever pistons you install, and whatever your pressure ends up being.. and I'll be here in the future with everyone else, to help you in any way I can, should you need help.
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