4.7 build tech notes

[DaviesDJ]

Hi guys - am an amateur engine builder used to Chevy / rover etc trying my hand at my 4.5 cerbera rebuild as a 4.7 when the engine comes it for the chassis replacement this summer.

Do a lot of the work myself as I have a good freind and mentor who owns a large engineering shop. I am not an engineer but a keen amateur

Have a few ideas to make a fast engine to compete with newer cars. Now wanted to ask if anybody has tried the following before I waste my time - as have yet to inspect my particular engine but want to do a few of the following

1) larger inlet valves with the larger bore (1.81 custom valves - have the drawings for custom make - but wandered if this had bee tried on a 93mm bore)

2) to optimise this wanted to go 93.5mm on the liner - or maybe 94mm (to 4.8 I think) - can this be done - should it be done - any real world experience - happy to leave at 4.7 but wanted to give the new valve the best shot at de-shroud

3) quench / squish band - the base engine seems to want a lot of timing! So wanted to increase combustion efficiency - a dome is needed I know - I am having custom Pistons made and the original C&C drawings are available - but thought is there any scope to take 10 thou off the quench?? What is the normal deck clearance/gasket thickness / quench band on an average engine?? I wanted to aim for about 26 thou. So if it's near 40 I will add 10 thou Ronny piston spec - I will measure at build obviously and alter CHG if required - but if it's usually optimum I won't bother

4)anybody have any thoughts on standard con - rods - was hoping to save a little and keep them? If not anybody have and improved forged items for sale or know where they can be sourced - have all the dimensions of items ordered by a kind chap on another forum (FB) but Carrillo are an expensive custom make!

Best wishes

Dave

[DaviesDJ]

I could be swayed to drop the valve upgrade - however, having massed about with this size valve in a BUIC 300 head on a rover (1.77) I can't help but get the feeling a valve upgrade will not guarantee higher power - but may make the headline 4.7 figures we see come up easier to achieve without long primary exhausts and ridiculous compression????

Any discussion welcome

[DaviesDJ]

It's not that a bigger valve will offer more overall flow - but more area under the curve at low lift

Increasing stroke pretty difficult without deck extension plates - mores increased in capacity come from bore in this engine so I gather

Timo - I know that theoretically the valve is not in itself an issue - however as we see in Chevy engines, it makes achieving figures easier. It's just development. I am more interested in optimising the combustion character when it comes to capacity - hence getting the quench band right

G&S valves say TVR themselves put a 2 inch valve in 1995 (made by them) - so this option has clearly Ben explored - but to what end I wonder??

Carrillo wound be pricey but good quality - wonder if anybody has any for sale?

[DaviesDJ]

Big valves lead to a larger curtain area - granted you need to combine this with greater lift.

Hogging out a throaty eventually leads to a knife edges seat situation - a longer radium is better for flow - especially in a flat rapper cam.

Timo what you are saying is incorrect - valve area is of real importance - hence the advantage of a 4 valve head. THe port max have a maximum flow, but with a larger valve it can utilise more of that at low lift, its low lift flow that's the key.

I agree - high lift flow will be almost identical. But on this type of cam profile and duration then low lift is key