Cylinder head query

[sidecar]

Unless you are going to spend a lot of money on parts that are going to withstand the revs that your cam is going to want to run the motor to you will end up with a real mis-match of components in my humble. That cam will want to push the motor to 7.5k RPM. The pistons, rods, rockershafts, valves spring retainers, valve springs and probably other stuff won't hold together for long at that RPM.

On top of that you will need an inlet system that will support the required air flow and an ignition system that can supply decent sparks at high RPM.

One last thing....two bolt mains....

EDIT..Just read that you are fitting 45mm throttle bodies, I guess they will flow enough air, the heads will need some flowing though!

[CastleMGBV8]

Plus race prepped crank, aftermarket conrods, race flywheel and clutch, full balance, and a race oil system to provide 10psi per 1000 RPM.

Sidecar mentions the two bolt mains on your engine which will not withstand the sustained high rpm of circuit racing, and will require substancial work to make the engine stay together if revved to 7500 RPM.

What sort of use is this engine going to have? if drag racing you can get away with less bottom end work as the engine is only at peak RPM for very short periods, whereas a circuit engine will be held a max RPM for much longer.

Kevin.

[Sunbmw]

Hi fellas, I have mentioned my spec in another post, but here goes..........

The crank will be Knife edged and balanced, or if I can find on at the right price, a steel crank, Arrow steel rods, Ross or Cosworth Intruder pistons, my block is X-bolted, I have a dry sump system, the heads are very nicely ported. To top that off, I will be using, as said, either some 45mm throttles or quad Webers/Dell'ortos.

The car is to be a stage rally car, so will spend quite a bit of time at full chat, but will be doing a lot of up and down the box too.

Any more advice is always appreciated, as I have said before, I have built Dozens of good BD Fords, and XE Vauxhall engines, but I am learing the ropes with the V8.

[CastleMGBV8]

Sounds like you have a sound basis for a high rev 3.5.

Re the cam I still think that it may be a little wild for a rally car with virtually nothing under 3000 RPM also it's a mechanical cam and with need solid lifters (cam followers in english) adjustable rockers, adjustable roller rockers would be nice and handle the RPM as long as you fit rocker shaft end support pillars available for around £80.00

If you use roller rockers you will need to restrict the oiling to the rockers shafts by reducing the size of the oil feeds in the heads otherwise you will pump far too much oil into the rocker area.

Don't consider adjustable push rods, they are far too heavy for a 7500 RPM engine and probably will not sustain that usage.

kevin.

[Sunbmw]

Sounds like you have a sound basis for a high rev 3.5.

Re the cam I still think that it may be a little wild for a rally car with virtually nothing under 3000 RPM also it's a mechanical cam and with need solid lifters (cam followers in english) adjustable rockers, adjustable roller rockers would be nice and handle the RPM as long as you fit rocker shaft end support pillars available for around £80.00

If you use roller rockers you will need to restrict the oiling to the rockers shafts by reducing the size of the oil feeds in the heads otherwise you will pump far too much oil into the rocker area.

Don't consider adjustable push rods, they are far too heavy for a 7500 RPM engine and probably will not sustain that usage.

kevin.

Hi Kevin, we have traded a few PM's before on this subject............

Here are my heads/ Rockers..........



They have fairly large valves, very nice ports, double springs and lightweight retainers. Not sure on the oiling side, but I can investigate this.

Dry sump pan............



Modified cover..............



And also, rightly or wrongly, I am intending to use these Headers, as I have moved the engine way back and down, this will give me lots of room for the dry sump pump etc.



We may speak again...........................

[spend]

I think with those roller rockers you just have to use plain 3/8"UNC bolts to restrict flow in the pedestals. I have a set on the shelf like that, just run a bolt down the pedestal and it will be pretty obvious to the eye (the std Rover bolts are waisted for the oil flow up the pedestal).

Those rockers have no offset (ie not LH + RH pairs) so be very careful with alignment, I would advise making spacers + wavy spring washers and dumping the springs..

[CastleMGBV8]

Sunbmw

Name?

I remember names better than logins, must be an age thing!

The rockers look great but I would certainly ditch the springs for spacers, you can make your own from some tubing.

Don't know if spends fix will reduce the flow enough, it's normally done by reducing the oil holes in the heads by as much as 50%

I may have already said this but do double check that the oilways to the rockers are clear, they do get gunged up especially the redundant ones which are there so the heads can go on either bank and if you fit the heads so they are reversed to the way they were originally fitted on an engine you could have no oil supply at all.

Kevin.

[ged]

Hi Sunbmw

This is what I did to adjust oil flow.



Regards Ged

[Sunbmw]

Thanks Gents, i'm Lee by the way.

I am very interested in all the points that you make, and will be taking them all on board, but whan I have got all the bits together and start the build proper, I will be calling on you guys for some more tips and advice.

Thanks again.

[CastleMGBV8]

Lee,

If the rockers are plain bearing as opposed to roller bearing then the oiling is less critical however at high RPM and with increased oil pressure you will still pump too much oil up to the top of the engine, restricting the flow partially will assist in maintaining good pressure in the important main and big end bearing areas.

Kevin.