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Everything else on the blower setup was the same. 21 psi boost and ~16-18 deg of timing, 11:1 A/F. Did a meth-off run to see the before/after.
Top end swap was worth about 67 HP, or about 8% improvement in power. Cathedral made 2% more between 4,500 and 5,500, but notably less above 5,700.
Left the car at 975 HP until I put the stiffer valve springs on and make some adjustments to the meth system - will then be turning it up to 1000+ or so (we'll see).
I'm not sure, but I suspect the duration difference isn't doing a lot of work here. Others may have some other insight.
I suspect the lift notably contributed. However, the lift is bigger because the flow sheet of the square port heads. The square ports have a broader flow range at the higher lift. If I left the cathedral cam in on the square ports it would have just been a bad lift range for the head.
Very nice!
It's interesting that your boost pressure didn't change, usually it drops a bit when flow is improved.
Boy at 5,700rpm you can really see where the square ports leave the cathedrals in the dust.
What rpm are you shifting at?
Pretty sure I'm loosing the valvtrain. Both setups used 160/400 lb in thevalves and I dont think that is cutting it for the 20+ psi of boost. So, similar issue on both setups, but I'll fix it this time around (hopefully).
You might be able to just shim them up if you have the clearance to coil bind
Agreed. The right shim I think is 0.130/0.140 which shrinks my bind clearance to 0.01-0.02....so I'll probably just get a stiffer spring - and will still need to shim a little.
What opening/seat pressure are folks running for this kind of boost and having good luck?
Very nice!
It's interesting that your boost pressure didn't change, usually it drops a bit when flow is improved.
Boy at 5,700rpm you can really see where the square ports leave the cathedrals in the dust.
What rpm are you shifting at?
I thought that was odd on the boost as well.
I set the limiter to 6,600. Will shift in 6200-ish for now. However, I think once i get the spring issue resolve, I'll get it up to something normal with a 6,500-ish shift point.
Agreed. The right shim I think is 0.130/0.140 which shrinks my bind clearance to 0.01-0.02....so I'll probably just get a stiffer spring - and will still need to shim a little.
What opening/seat pressure are folks running for this kind of boost and having good luck?
Well you want at least 0.050" from coil bind so I don't know if you have that much left or not. I'd try to add 20-30lbs on the seat and test a spring pack to see what you need for shims to get there, it all depends on your spring rate. I'd guess you need about 0.060" shims at least, but best to check over every spring install height apart. It does seem weird that the boost pressure curve tracks with both sets of heads/cam as you would guess the pressure would decay up top on the higher flowing units unless valve float was an issue sooner idk.
Pretty sure I'm loosing the valvtrain. Both setups used 160/400 lb in thevalves and I dont think that is cutting it for the 20+ psi of boost. So, similar issue on both setups, but I'll fix it this time around (hopefully).
I'm surprised, normally I don't see that type of issue on blower setups even at 20 psi. Hopefully that's all it is though and you can either shim or replace.
Agreed. The right shim I think is 0.130/0.140 which shrinks my bind clearance to 0.01-0.02....so I'll probably just get a stiffer spring - and will still need to shim a little.
What opening/seat pressure are folks running for this kind of boost and having good luck?
I'm using the BTR .660 drop in springs and they are excellent.
21 lbs. of boost and 7,000rpm without issue.
I'm surprised, normally I don't see that type of issue on blower setups even at 20 psi. Hopefully that's all it is though and you can either shim or replace.
Me too - I've thrown the kitchen sink at everything else. Blower boost keeps rising consistently (ie. belt seems okay), ignition system upgraded to 510C (and car wasn't blowing chow during run), timing was okay, A/F was a smidge rich but on target.
Also, the boost takes an odd uptick when the torque plummets - and boost higher for the same RPM (in my experience) can be a tell-tale for loosing the valvetrain. Open to other suggestions though - getting this turd to a reliable 1k has been obnoxious.
Me too - I've thrown the kitchen sink at everything else. Blower boost keeps rising consistently (ie. belt seems okay), ignition system upgraded to 510C (and car wasn't blowing chow during run), timing was okay, A/F was a smidge rich but on target.
Also, the boost takes an odd uptick when the torque plummets - and boost higher for the same RPM (in my experience) can be a tell-tale for loosing the valvetrain. Open to other suggestions though - getting this turd to a reliable 1k has been obnoxious.
I'd be looking at the BTR Shaft rocker kit if possible and better springs as you mentioned.
The shaft kit is definitely on my to-do list now.
Me too - I've thrown the kitchen sink at everything else. Blower boost keeps rising consistently (ie. belt seems okay), ignition system upgraded to 510C (and car wasn't blowing chow during run), timing was okay, A/F was a smidge rich but on target.
Also, the boost takes an odd uptick when the torque plummets - and boost higher for the same RPM (in my experience) can be a tell-tale for loosing the valvetrain. Open to other suggestions though - getting this turd to a reliable 1k has been obnoxious.
Hmm, yeah that is strange with the boost jumping a bit. Does the exhaust note change at all when it happens up top? I normally can hear valve float starting to occur on most combos on the dyno.
I would be measuring installed height and seeing if you can shim them at all, pretty sure 0.060" is the typical safety margin to not go past for coil bind.
Hmm, yeah that is strange with the boost jumping a bit. Does the exhaust note change at all when it happens up top? I normally can hear valve float starting to occur on most combos on the dyno.
I would be measuring installed height and seeing if you can shim them at all, pretty sure 0.060" is the typical safety margin to not go past for coil bind.
I didnt notice a pitch shift, but the 4" boost activated dump on the exhaust makes it already pitchy and tough to tell.
Looking for a 15% increase in seat pressure - 185 seated, 450 open. I can shim to the seated (0.060 does it), but will need a different spring for the open.
So, in the theme of throwing the kitchen sink, I'll try the stiffer spring first and posibly back to something softer with a shim if it works.
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