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

[TA14]

Might be better in the Cerb forum.

AIUI the head can flow a lot so probably very limited scope for improvement.

Also AIUI the two garages offering 4.7 AJP V8s do so in different ways: one by increasing the bore and one by increasing the stroke.

Have you had a look at the spec of the 5.0?

[Byker28i]

TA14 said:

Might be better in the Cerb forum.

AIUI the head can flow a lot so probably very limited scope for improvement.

Also AIUI the two garages offering 4.7 AJP V8s do so in different ways: one by increasing the bore and one by increasing the stroke.

Have you had a look at the spec of the 5.0?

Stroked would be better for torque wouldn't it?

[KevinCamaroSS]

Byker28i said:

Stroked would be better for torque wouldn't it?

Better for torque, but can limit the rpms

[Jhonno]

1) Standard valves and ports are already big enough to support a 5.0

2) You will need custom liners to go bigger. I believe even 4.7 liners may be pushing it.

4) Carillo already supply AJP rods so no need to go custom.

[Kokkolanpoika]

Do you think that 1.81" valves make more power than 1.69" on Rover v8 engine??

My engine with 1.69" valve´s bush out 418hp. Theoritically mutch more, but port will limit flow too mutch..

Edited by Kokkolanpoika on Tuesday 18th April 17:58

[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?

[Kokkolanpoika]

DaviesDJ said:

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?

You will get same flow area with smaller valve if you want.. Go for bigger throat.. Why do you want to resist air flow with big valves allredy small port? You can get same amount of air if you use 1.69" valves with 90% throat vs 1.81" valves with 85% throat..Throat diameter is same.
Big valves usually need big port´s, Big valves is not magic word to power with Chevy engines.. Big port is..

[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

[Kokkolanpoika]

DaviesDJ said:

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

Very hard to explain another lanque what i mean..

Yes, big valves lead bigger curtain area, but i do not see any point to use big valves, because your port is too small for that size valves.. It wont make any more power..

Theoritically bigger throat lead´s knife edges, but it´s not allways a proplem. Those 85% throat diameter rule is very old school stuff.. You can customise your seat´s/throat by hand..

We can think those think´s on other way´s of valve area.. But it´s no allways the key to use big valves and hope it will give you more air at low lift. My skill´s to explain with technical English stop´s now..

Here is my current setup.. I´m not sure is this how special or some custom mod or everyday porting method in England..?



Inlet valve throat is offset ported to 90% diameter of 43mm valves. So there is no any 3 angle valve seat´s and angles are what they are.. It will flow what it will flow.. Bench tested bacause everyone want to know result´s, and it will flow approx 30cfm more that std 3 angle valve seat.. Also low lift flow is better vs 85% throat...

It´s not that simple, but it´s not science, it´s art.

Flow bench can shou somethink different what will work better on true life..