Difference between 45 degree seats and 3 angle
Discussion
People often ask what is the difference between 45 seats and 3 angle and are they really needed? I have always thought the 3 angle seats are the first 10-15% increase in power.
Today we had a restricted class MG Midget in. Restricted to the small standard inlet valves 1.33" (1.401" Cooper S /MG Metro inlets always seem to be worth 10 or so more bhp but we can't use them in this class), a pair of 1 1/4" SUs, air filter free and cam free.
The one today showed 92 at the wheels and sounded soft. It was running a Swiftune SW23T cam. The last similar car we ran up was on our old rollers and showed 103 bhp at the wheels.
I asked the owner and he had done the head himself but had not had three angle seats cut. He had also left a small lip in the inlet ports on the short side as he had inserts fitted to save valve seat sinkage,
The pic shows a standard seat alongside the three angle seat I cut ( 1mm 45degree). I blended the throats and improved the back of the valves as we put more blended 30 degree back cut on.
Today we had a restricted class MG Midget in. Restricted to the small standard inlet valves 1.33" (1.401" Cooper S /MG Metro inlets always seem to be worth 10 or so more bhp but we can't use them in this class), a pair of 1 1/4" SUs, air filter free and cam free.
The one today showed 92 at the wheels and sounded soft. It was running a Swiftune SW23T cam. The last similar car we ran up was on our old rollers and showed 103 bhp at the wheels.
I asked the owner and he had done the head himself but had not had three angle seats cut. He had also left a small lip in the inlet ports on the short side as he had inserts fitted to save valve seat sinkage,
The pic shows a standard seat alongside the three angle seat I cut ( 1mm 45degree). I blended the throats and improved the back of the valves as we put more blended 30 degree back cut on.
With the head back on we re ran the tuning, having optimised fuelling and ignition as was.
We had to retard the ignition about 2 degrees to get the best from the re done head, fuelling remained the same. We ended up with 99 bhp at the wheels. Customer happy and we were happy to test before and after. I was feeling kind today and the customer did all the work removing. stripping, rebuilding and refitting the head.
We had to retard the ignition about 2 degrees to get the best from the re done head, fuelling remained the same. We ended up with 99 bhp at the wheels. Customer happy and we were happy to test before and after. I was feeling kind today and the customer did all the work removing. stripping, rebuilding and refitting the head.
I usually work the 3 angle to a complete radius by hand both on the valve and the seat form. There appears to be a little seat recession in the chambers there, be interesting to see what difference there would be from removing it.
I once spent around 6 hours working the seats to a good radius on a Xflow head, only for the owners friend to recut the seats to a single angle and ruin all the hard work (and the airflow).
Dave
I once spent around 6 hours working the seats to a good radius on a Xflow head, only for the owners friend to recut the seats to a single angle and ruin all the hard work (and the airflow).
Dave
Over 40 mm valve and we cut 4 angle seats 25/30,45,60 then 70/75. We are gaining power everywhere this way. We do hand blend top and bottom cuts anyway, as you say, no such thing as a 3 angle seat if blended.
What I do notice, if we get a race B head in which needs the seats tweaking, when we recut then a quick top and bottom cut to make sure we have three/four angle seats we find no difference in power if the 45 is say 1.5 mm or 2 mm with correspondingly larger/smaller top and bottom cuts.
What I do notice, if we get a race B head in which needs the seats tweaking, when we recut then a quick top and bottom cut to make sure we have three/four angle seats we find no difference in power if the 45 is say 1.5 mm or 2 mm with correspondingly larger/smaller top and bottom cuts.
DVandrews said:
I usually work the 3 angle to a complete radius by hand both on the valve and the seat form. There appears to be a little seat recession in the chambers there, be interesting to see what difference there would be from removing it.
I once spent around 6 hours working the seats to a good radius on a Xflow head, only for the owners friend to recut the seats to a single angle and ruin all the hard work (and the airflow).
Dave
How much difference did that make ?I once spent around 6 hours working the seats to a good radius on a Xflow head, only for the owners friend to recut the seats to a single angle and ruin all the hard work (and the airflow).
Dave
A friend had a pair of heads done a few years ago...then after needing some remedial work a time later, we had a local "shop" recut the seats.
What a complete and utter f
k up they made of that, re-cutting far too deep, pushing depth beyond where the bucket could work for lifter clearance etc etc.But we simply had no choice at the time to re-use them despite the major flaws and hassle so had to rebuild around this poor work. Very frustrating.
DVandrews said:
I usually work the 3 angle to a complete radius by hand both on the valve and the seat form. There appears to be a little seat recession in the chambers there, be interesting to see what difference there would be from removing it.
I once spent around 6 hours working the seats to a good radius on a Xflow head, only for the owners friend to recut the seats to a single angle and ruin all the hard work (and the airflow).
Dave
FFS I once spent around 6 hours working the seats to a good radius on a Xflow head, only for the owners friend to recut the seats to a single angle and ruin all the hard work (and the airflow).
Dave
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