Carb / itb advice pinto with BV head and ht1 cam

[redhf]

Thanks for this, I have seen a previous post from graham when he flown tested one, I will get some pictures and post them

Yes that head was mine .

[Warrior]

I'm having trouble with uploading phots for some reason,

having measured the head I have 6mm from valve to head face when full closed both inlet an exhaust, this would suggest that theres a fir bit of meat I could remove to increase the compression??? not for the ht1 cam cause as has been said I would blow the bottom end to bits,

[Warrior]

[Graham]

run your finger over the short turn, if its like the other head i saw it will be a near 90 degree sharp edge, with no blending between the throat and port, if so it will flow WORSE than a standard head

[Forest_rallying]

In defence of JEMS it does say in their advert that their big valve heads are left UN ported and up to the customer to do their own porting to their own requirements.

You can't get an accurate measurement from valve closed to cylinder face. You need the cam in and set on overlap where your piston would be at TDC when in the correct timed position.

You need to accurately measure the CC in the chambers instead of blinding on skimming too much off the head face and knackering a perfectly good casting.

[Dyno]

Hold on before you get into troubles, you need to fit the camshaft and head must be on block. Time the cam correct and measure the play between the valve and piston by pushing the valve with your finger until it touches the piston. This can best been done with the inner valve springs from a double valve spring set. Do this at TDC, but also 5, 10 and 15 before and after TDC. These numbers are a lot more important. If you go a camshaft lifting 5,33 mm it whole time out of his starting ramp. It's in his faster acc. periode and will open the valve a LOT faster as the piston will be moving from top. Usual between 5 and 10° is most critical.

[Warrior]

run your finger over the short turn, if its like the other head i saw it will be a near 90 degree sharp edge, with no blending between the throat and port, if so it will flow WORSE than a standard head

I have done that and it feels very smooth and rounded, the head was built for a classic hot rod race car apparently.

His engine parts where machine by jems and built by jems from what he said, the full engine and thisbhead was built up as a spair and never used.

[Warrior]

I also have another short engine that’s at a mates that I’ve not a look at, this was removed from a mk1 rally car, the head was used on another engine,

Thinking it may be worth pulling it apart and having a good look at it to see what’s what and if it’s not bad then a refresh and build back up with this head and just leave my current engine complete.

[Dyno]

OK, perfect if it was build for the purpose but be aware, you will see numbers of at least 6 up to 7mm between 5 and 10°. Also, despite it should be correct build, not checking at the correct engine is the first stupid mistake you can do. You ALWAYS have to double check. If the block has been decked to bring the piston in the right position you probably already loose almost 1 mm.

[Warrior]

OK, perfect if it was build for the purpose but be aware, you will see numbers of at least 6 up to 7mm between 5 and 10°. Also, despite it should be correct build, not checking at the correct engine is the first stupid mistake you can do. You ALWAYS have to double check. If the block has been decked to bring the piston in the right position you probably already loose almost 1 mm.

I will post up when I have got it apart