Discussion
hi, just a quickie.
i have been porting my own cylinder head and have gone into the valve seats on the exhausts (oops!). the head is leaded so would getting an engineering firm to put unleaded seats in and blending them in solve the problem?
im going to run stainless steel valves, the seat at the moment is about 0.30" thick, not thick enough so i gather...
any ideas?
i have been porting my own cylinder head and have gone into the valve seats on the exhausts (oops!). the head is leaded so would getting an engineering firm to put unleaded seats in and blending them in solve the problem?
im going to run stainless steel valves, the seat at the moment is about 0.30" thick, not thick enough so i gather...
any ideas?
We've all done that, Rob. Well, all of us who do our own competition heads, that is.
I would go for unleaded hardened seats and use 35.5 mm inlet valves as a complete cure for this and then just blend the new seats in very, very carefully.
Alternatively, you could go to 37mm inlets and have the seats re-cut to take these which should take out your, er, slight indiscretion with the grinder.
It depends on the use you intend.
On my 1310 cc 1964 'S' Historic Rally Car I use the bigger valves with leaded fuel (lead additive of course - Castrol Valvemaster Plus) and this works fine giving about 115 bhp at the (lightened) flywheel. However, I do take the head off and check/lightly lap the valves after every or 7 rallies, stripping the engine and fitting new big ends and mains at the same time, plus timing chain, oil pump and thrust bearings. Doing this means I get reliability and minimum crank wearwhilst keeping the power at the best level possible.
I would go for unleaded hardened seats and use 35.5 mm inlet valves as a complete cure for this and then just blend the new seats in very, very carefully.
Alternatively, you could go to 37mm inlets and have the seats re-cut to take these which should take out your, er, slight indiscretion with the grinder.
It depends on the use you intend.
On my 1310 cc 1964 'S' Historic Rally Car I use the bigger valves with leaded fuel (lead additive of course - Castrol Valvemaster Plus) and this works fine giving about 115 bhp at the (lightened) flywheel. However, I do take the head off and check/lightly lap the valves after every or 7 rallies, stripping the engine and fitting new big ends and mains at the same time, plus timing chain, oil pump and thrust bearings. Doing this means I get reliability and minimum crank wearwhilst keeping the power at the best level possible.
hi, thanks for the advice. i was thinkning ov unleaded seats for longevity cous its going to be a road and track burner. i think that its pushed me over the edge!!
just another query while im at it. for a 998 with a 12g940 (hopefully if the seats are sorted!!)which cam would you recomend? i have a mew kent md286 and a piper 270 still in good nick. just wanting to kno cous the engines going in soon and i dont wanna hoik it out again to change it!!
Any ideas?
(sorry for the different subject in the same thread!)
just another query while im at it. for a 998 with a 12g940 (hopefully if the seats are sorted!!)which cam would you recomend? i have a mew kent md286 and a piper 270 still in good nick. just wanting to kno cous the engines going in soon and i dont wanna hoik it out again to change it!!
Any ideas?
(sorry for the different subject in the same thread!)
Hi again Rob,
Remember that to fit a 12G940 onto a 998 you need to 'pocket' the block to give clearance for the valves at full lift.
As to the cam, the 270 will be smoother but the Kent 286 should give a few more bhp at the top end. However, the advantages of the 286 power-wise will be offset by the fact that it will be a 'cammy' beast below about 3500 rpm in a 998. I would go for the 270 cam. If you want a bit more you can always fit 1.5:1 roller rockers.
For a 998 cc lump 33.5 mm inlet valves are quite big enough and if you de-shroud aroung the valves in the combustion chamber you'll have a head which breathes very well.
I'm just building an 1118 cc A-H Sprite Mk 1 engine for a Historic Rally Car and I'm using 33.5 mm inlets with 27 mm exhausts, 10.5:1 c.r., a 266 cam and a well ported and shaped 12G295 head, which is also a great head for a 998 if you can find one. With twin 1.5 SU's I'm aiming for about 80 bhp to feed into the straight cut box. It should be quicker than a 1275 'S' as it's 100 kg lighter.
Remember that to fit a 12G940 onto a 998 you need to 'pocket' the block to give clearance for the valves at full lift.
As to the cam, the 270 will be smoother but the Kent 286 should give a few more bhp at the top end. However, the advantages of the 286 power-wise will be offset by the fact that it will be a 'cammy' beast below about 3500 rpm in a 998. I would go for the 270 cam. If you want a bit more you can always fit 1.5:1 roller rockers.
For a 998 cc lump 33.5 mm inlet valves are quite big enough and if you de-shroud aroung the valves in the combustion chamber you'll have a head which breathes very well.
I'm just building an 1118 cc A-H Sprite Mk 1 engine for a Historic Rally Car and I'm using 33.5 mm inlets with 27 mm exhausts, 10.5:1 c.r., a 266 cam and a well ported and shaped 12G295 head, which is also a great head for a 998 if you can find one. With twin 1.5 SU's I'm aiming for about 80 bhp to feed into the straight cut box. It should be quicker than a 1275 'S' as it's 100 kg lighter.
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