390se head gaskets

[ed_crouch]

What headgaskets do people use on 390SEs?

Dont need 'em, but all that jazz about the dodgy 3rd row of bolts on all but the latest RV8s makes me think I might have the heads off and stick new gaskets in at some point.

The tin ones are cheap and dont reduce the compression ratio cos theyre dead thin, but the composite ones are better, albeit at the cost of some compression.

Would the engine lose power with the composite ones?

Ta.

Ed.

[Boosted LS1]

Composite ones are nice, I like them and they seal well. Tin ones are ok if your head/deck are nice and clean plus smooth and flat.

[deetes]

ed_crouch said:

What headgaskets do people use on 390SEs?

Dont need 'em, but all that jazz about the dodgy 3rd row of bolts on all but the latest RV8s makes me think I might have the heads off and stick new gaskets in at some point.

Are the gaskets blown? If not, why would you want to do this?

[ed_crouch]

Cause people tell me they do leak a smidge due the the stoopid 3rd row of bolts jacking one edge of the head off the block slightly. The 3rd row of bolts were omitted altogether in late 4.6 heads. I believe in preventative maintenance.

Thanks for the replies, I shall go with composite jobbies when I get around to it!



Ed.

[Boosted LS1]

^ If they don't leak then I'd leave them alone. Why disturb the engine? Head jacking isn't very common, well I've never seen it and there were thousands of engines built using the outer row of bolts.

[grahamw48]

Mine already has them.

[GRIFFONMARK]

I met a guy the other day who races old Rover V8's (in MGBs)up and down santa pod and he reckons he has always used the thin metal gaskets, the only problem being the 260hp (wild cam + nitrous) he gets from a 3.5 melting pistons. I'm going to rebuild my Griffon 3.5 with the thin gaskets as I don't want low comp ratio. If they blow I'll let you know!

[grahamw48]

According to Brummmie (PH nic) who had my engine apart to put in the new cam,
it had smaller 28cc combustion chambers rather than the 36cc previously used, presumably to retain the higher CR while using the composite gaskets ?

He's since built a 600bhp LS powered Cerby.

Edited by grahamw48 on Thursday 23 October 22:33

[Roger McLittriss]

grahamw48 said:

According to Brummmie (PH nic) who had my engine apart to put in the new cam,
it had smaller 28cc combustion chambers rather than the 36cc previously used, presumably to retain the higher CR while using the composite gaskets ?

That makes sense: assuming a 94mm bore (standard 4L engine) the surface area of the piston would be 6936mm sq.
So a copper gasket 0.1mm thick (say 4 thousandths of an inch) would contribute 0.693cc to the cahmber.
Going up to a composite gasket (at a guess) 1mm thick (40 thous) would give a 10-fold increase in chamber volume, ie 6.936cc.
So lopping 8cc off the head part of the chamber would be about right

[GRIFFONMARK]

I'm not so sure that the difference in thickness between the 2 gaskets is so great. I don't know the thickness of a composite gasket but I seem to remember someone once telling me it was 40 thou which is about 1mm. I've just checked my steel gaskets and they are 0.42mm thick. That would mean a slight increase in combustion chamber volume of only 1.73cc going from steel to composite.

I don't know a great deal about these engines but a 3905cc engine would need a combustion chamber (including the volume above the dished piston) of 50cc to produce a comp ratio of 9.75:1. Decreasing this by 8cc would increase the comp ratio to 11.6:1.

I have a stripped down MGB 3.5V8 race engine to fit in my Griffon which should have a comp ratio of 8.25:1. However, the heads have been skimmed by 10thou which means I should have a comp ratio of 8.5:1. The engine came with steel gaskets to fit, but I don't know whether the original 8.25:1 was with steel or composite gaskets. Oh dear! I've checked the combustion chambers and on my old 8.25:1 they are 38cc (making a total of 53.5cc inc piston gap). So if I fitted 28cc heads I'd get a comp ratio of 9.7:1 using standard gaskets, whatever they are!

It's all very interesting this, but am I right?

Regards, Mark

[grahamw48]

The V8S, 400SE and Chim and Griff 400s had the 3947 cc engine rather than 3905. Not sure how much difference that will make (apart from 42cc).

[rev-erend]

Roger McLittriss said:

grahamw48 said:

According to Brummmie (PH nic) who had my engine apart to put in the new cam,
it had smaller 28cc combustion chambers rather than the 36cc previously used, presumably to retain the higher CR while using the composite gaskets ?

That makes sense: assuming a 94mm bore (standard 4L engine) the surface area of the piston would be 6936mm sq.
So a copper gasket 0.1mm thick (say 4 thousandths of an inch) would contribute 0.693cc to the cahmber.
Going up to a composite gasket (at a guess) 1mm thick (40 thous) would give a 10-fold increase in chamber volume, ie 6.936cc.
So lopping 8cc off the head part of the chamber would be about right

I just measured the thickness of my tin gaskets..

0.4 mm

[Roger McLittriss]

rev-erend said:

Roger McLittriss said:

grahamw48 said:

According to Brummmie (PH nic) who had my engine apart to put in the new cam,
it had smaller 28cc combustion chambers rather than the 36cc previously used, presumably to retain the higher CR while using the composite gaskets ?

That makes sense: assuming a 94mm bore (standard 4L engine) the surface area of the piston would be 6936mm sq.
So a copper gasket 0.1mm thick (say 4 thousandths of an inch) would contribute 0.693cc to the cahmber.
Going up to a composite gasket (at a guess) 1mm thick (40 thous) would give a 10-fold increase in chamber volume, ie 6.936cc.
So lopping 8cc off the head part of the chamber would be about right

I just measured the thickness of my tin gaskets..

0.4 mm

Ah, the plot thickens! Unless the composites are a lot thicker than 1mm of course, otherwise the chamber difference won't affect the c.r. anything like as much.

[Roger McLittriss]

GRIFFONMARK said:

I don't know a great deal about these engines but a 3905cc engine would need a combustion chamber (including the volume above the dished piston) of 50cc to produce a comp ratio of 9.75:1. Decreasing this by 8cc would increase the comp ratio to 11.6:1.

Regards, Mark

The 3905cc ran 93.5mm flat-topped pistons with valve pockets and a 10.5:1 c.r. (or so they claimed). Great on 100RON 4-star, maybe not so on 95RON Tescotrol.
The 3948 ran dished pistons with or without pockets depending on how hot the cam was (standard Range Rover cast pistons mind, not forged like the 3905's were) and a c.r. of about 9.35:1 (I suppose the pockets would actually lower it a bit as well).
If you bore a 3905 out by 10 thou or so (on the radius) you get a 94mm bore and 3948cc. However flat-topped 94mm pistons (to keep the c.r. up around 10:1) will cost you limbs. Places like JE Developments do them.

[grahamw48]

Here's something to mull over:

http://www.mez.co.uk/TuningTheRoverV8-pt11.html

[GRIFFONMARK]

Well I've learnt a lot so far. However, I don't care what Graham's link says, my 3.5 gasket is 0.42mm thick! From my calcs I don't believe that the smaller combustion chamber is due to the difference between the gasket thicknesses, this is minimal. It must have been used to raise cr. If a 3905 started life as a vitesse 3.5 then its cr should have been 9.75:1. Losing 6.5cc (assuming 1.5cc lost by using thicker gasket) would produce a cr of 11.2:1. Maybe the flat top pistons were shorter and the smaller combustion chamber was required to compensate? Maybe I'll get my file out and smooth the tops of my pistons, then machine half an inch of my heads......

[grahamw48]

OMG!

Careful with that file Eugene !

[rev-erend]

GRIFFONMARK said:

Well I've learnt a lot so far. However, I don't care what Graham's link says, my 3.5 gasket is 0.42mm thick! From my calcs I don't believe that the smaller combustion chamber is due to the difference between the gasket thicknesses, this is minimal. It must have been used to raise cr. If a 3905 started life as a vitesse 3.5 then its cr should have been 9.75:1. Losing 6.5cc (assuming 1.5cc lost by using thicker gasket) would produce a cr of 11.2:1. Maybe the flat top pistons were shorter and the smaller combustion chamber was required to compensate? Maybe I'll get my file out and smooth the tops of my pistons, then machine half an inch of my heads......

11.2 would be just too high..

You would have to use optimax at every fill and even then probably retard ignition (big, big, compromise) to stop the detonation.

I've been there, done that .. it's just not worth it.

My current engine is going to use 10.5 cr with fully mapable ecu (no dizzy) and different heads which have less issues with cr and det..

Always err or the side of caution with the cr.

[rev-erend]

I've measured my composite gaskets and they are 1mm exactly ..

[TVRleigh_BBWR]

GRIFFONMARK said:

Well I've learnt a lot so far. However, I don't care what Graham's link says, my 3.5 gasket is 0.42mm thick! From my calcs I don't believe that the smaller combustion chamber is due to the difference between the gasket thicknesses, this is minimal. It must have been used to raise cr. If a 3905 started life as a vitesse 3.5 then its cr should have been 9.75:1. Losing 6.5cc (assuming 1.5cc lost by using thicker gasket) would produce a cr of 11.2:1. Maybe the flat top pistons were shorter and the smaller combustion chamber was required to compensate? Maybe I'll get my file out and smooth the tops of my pistons, then machine half an inch of my heads......

AFAIK my 400SE was high compression and has flat cosworth piston. I think it was 11 or 11.5:1 it did suffer from pinking now and then, which has now gone after fitting compersit gaskets. it did have the strange copper ring gaskets originally.