400 and purple cam
I've been thinking of throwing one (292) cam in my 360. However, i put kb 107 pistons and x heads but not sure of compression. 3.55s in rear but have 3.91's to go in. Now have a 280/474 but seems tame for my taste!
It's hard to build a 360 with too much compression for a 292; it wants 11.3 and the bottom is still soft. Mine wanted 4.30s with a 2.66low trans, for a starter gear of 11.44. If you have an automatic, it will want to be shifted at about 7000 for low ET, and a lotta stall. For the engine to live at those rpms,it means special build procedures need to be taken.For best results your X heads will need some work.You may have trouble escaping detonation with the lack of tightQ in this combo.
IMO, if the 280 isn't doing it for you, and you are a streeter, you'd be better off with a bigger engine, or a new combo.
I run a 276/286/110 in an Eddie headed 367 at 10.9, that goes 93 in the 1/8th which the Wallace calculator says can be an 11 second car. That car is always tame to me by midsummer. But the next spring, it is always a surprise, the tame is gone! This engine will spin 295s to waaaay past the speed limit, anywhere in Canada. This not to brag on my tuning skills, but to say what the combo can do. If your 280 cannot do it, then perhaps the combo, or the tune , is off.
1)I'm guessing your sitting at maybe 9.2 Scr, and if your ICA is 64*, then here's what your combo might be sitting at
Static compression ratio of 9.2:1.
Effective stroke is 2.79 inches.
Your dynamic compression ratio is 7.39:1 .
Your dynamic cranking pressure is
144.16 PSI.
V/P (Volume to Pressure Index) is 123........................................................
123
And that will certainly be tame to about 3500rpm, very tame indeed. And the 292 will only make it worse.
I get the Scr from a total chamber volume of 90.8cc, which is 72 in the heads, a gasket of 8.9, 5cc eyebrows and the pistons down about 4.9cc or .023 down.
The solution is to increase the compression and simultaneously bring the Q into the "tight" zone of .035 to .045. This will require some creative engineering on your part with the parts you have.Or swap out the heads, or the pistons.
2)This is what you might want
Static compression ratio of 10:1.
Effective stroke is 2.79 inches.
Your dynamic compression ratio is 8.01:1 .
Your dynamic cranking pressure is
160.14 PSI.
V/P (Volume to Pressure Index) is 136.......................................................
136
This would feel like an increase of nearly 11% on take-off, and diminishing somewhat up to 3000/3600. But the increased compression would still be felt all the way to the shift.
Bringing the Q into the zone with open-chamber heads is not possible with KB-107s tho, so something has got to go, or you will be stuck running premium grade gas forever.
3)If you swapped out to closed chamber heads and machined the decks down to zero, then your Q will equal your gasket thickness.So then you can run the .039 FelPros.
This will make a lot of compression,perhaps too much. It might look like this
Static compression ratio of 10.8:1.
Effective stroke is 2.79 inches.
Your dynamic compression ratio is 8.64:1 .
Your dynamic cranking pressure is
176.62 PSI.
V/P (Volume to Pressure Index) is 150.......................................................
150
Hyup you are committed to Premium grade, but it will be wicked out of the gate. 150 is a lotta VP.
So now, it makes sense to put that 292 in or to retard the 280
4) Say you put that 280 in at an ICA of 72*, this is what it could look like
Static compression ratio of 10.8:1.
Effective stroke is 2.58 inches.
Your dynamic compression ratio is 8.06:1 .
Your dynamic cranking pressure is
161.44 PSI.
V/P (Volume to Pressure Index) is 127.......................................................
127
Yep that will work, but the bottom went soft again
5) So let's try that zero-decker with 63cc aluminum heads,and put the cam back at say an ICA of 66*, and here it is; this is still the 280 cam
Static compression ratio of 10.7:1.
Effective stroke is 2.69 inches.
Your dynamic compression ratio is 8.29:1 .
Your dynamic cranking pressure is
167.44 PSI.
V/P (Volume to Pressure Index) is 137........................................................
137
Well that's looking better. this will run on pump gas
6) But say you wanted more at the top, and were ok to run a 3500TC, let's put the 292 into it with an ICA of 70*
Static compression ratio of 10.8:1.
Effective stroke is 2.64 inches.
Your dynamic compression ratio is 8.23:1 .
Your dynamic cranking pressure is
165.87 PSI
V/P (Volume to Pressure Index) is 133.......................................................
133
See what happened there? we gave up a little on the bottom again,and got a little on the top, but to take advantage of it, she's gonna have to spin up to 7000 to find it ,on the 1-2 shift. Well hang on, how fast is that with 3.91s? That's about 56 mph. So then you bang it into second and the Rs drop to 4100 and you pull to the speed limit at 4800. See what I mean mine wanted 4.30s. It liked 4.88s even better.
IMO, if you are a streeter, it would be better to go the other way, the way of the smaller cam.
Take a look at the VPs here;they range from a possible current set-up of 123 to a high of 150.
To give you an idea of what these VPs mean;
A totally stock teener comes in at about 111VP, and a totally stock 360 comes in at about 120. So your bottom end performance currently might be feeling pretty much like a stocker. But it rips pretty good after 5000 right?
7) I tell you what, lets put a smaller cam in there for a sec, say a 268 fast rate in at 106, for an ICA of 60* and lets go back to the possible current Scr of 9.2. Here it is
Static compression ratio of 9.2:1.
Effective stroke is 2.88 inches.
Your dynamic compression ratio is 7.60:1 .
Your dynamic cranking pressure is
149.54 PSI.
V/P (Volume to Pressure Index) is 131......................................................
131
Wouldja look at that.This is already 8 points stronger than your current combo.
8) Lets pump it up a bit
Static compression ratio of 9.8:1.
Effective stroke is 2.88 inches.
Your dynamic compression ratio is 8.08:1 .
Your dynamic cranking pressure is
161.96 PSI.
V/P (Volume to Pressure Index) is 142...........................................................
142
Look at that! just a modest increase in Scr to 9.8 and with the Dcr at about the limit for iron heads and pump gas, we get a big fat bottom end, another 11 points higher. This will feel,perhaps, 142/123=15% more powerful at take off, than your current combo. This is like putting 15% more gear into it, or from 3.55s to 4.08s; isn't that nice. The power peak of a 268 cam in a 360 might be at about 5200. And the automatic will want to be shifted at 6400 on the 1-2 shift. This combo is now strong enough to run the 3.55s so outshifting at 6400 will get you 56 mph imagine that. And it will drop into second at about 3800. With any luck the 268 will be making more power at 3800 than your current 280 cam, so it will rocket to 60mph@4100. Certainly not ideal Rs, but that's 3.55s for you. Sometimes less is more.
9) But lets say you zero decked it and swapped to aluminum heads. Still the 268 cam Ica of 60* but now the Scr pumped up
Static compression ratio of 10.8:1.
Effective stroke is 2.88 inches.
Your dynamic compression ratio is 8.88:1 .
Your dynamic cranking pressure is
182.96 PSI.
V/P (Volume to Pressure Index) is 161...........................................................
161
Holy Smokers!!
This is again at about the upper limit for Dcr/psi with aluminum and tightQ, so you can't get much better than this. 161 is warmed up BB take off power, so basically it will bust any street tire loose at 35 mph with 3.55s, on the downshift.It might even do this all the way to 45/50mph
10) This is so much bottom end we can easily give some up.What happens if we retard the cam to an ICA of 62*
Static compression ratio of 10.8:1.
Effective stroke is 2.84 inches.
Your dynamic compression ratio is 8.77:1 .
Your dynamic cranking pressure is
180.05 PSI
V/P (Volume to Pressure Index) is 156...........................................................
156
There you go
11) by way of comparison,I currently run this; 276/286/110 in at 106, with OOTB Eddies, and ICA of 64*
Static compression ratio of 10.9:1.
Effective stroke is 2.79 inches.
Your dynamic compression ratio is 8.72:1 .
Your dynamic cranking pressure is
178.73 PSI.
V/P (Volume to Pressure Index) is 153........................................................
153
I run 3.55s and it busts the 295s loose at up to 50/55 in second gear (M/T), and It's a dump it and go deal from the stoplight. (3.09 low gear), and best of all?
It burns 87E10
So there are some ideas. Always be aware of the Q; for best results, it needs to be in the .035 to .050 zone
Also keep in mind that the VP numbers are just tool to help you understand why your bottom end is so soft..................or not soft,lol. Read about it here
Cam Timing vs. Compression Analysis
