4.3 compression ratio.

4.3 compression ratio.

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Discussion

carsy

Original Poster:

3,018 posts

164 months

Wednesday 15th October 2014
quotequote all
I was always under the impression that the 4.3 was something a little special as it was offered as an upgrade on the pre cat Griffs and we hear such good things about this engine.

I know it is just a Land Rover low comp bottom end but having read the Bible and listening to folk on here i always thought that TVR must have made some changes somewhere to up the CR to around the 10:1 area. Maybe the block decked a bit and heads skimmed. Never really thought about it too hard just thought it was high CR, hence the ringed heads.

Well having pulled mine to bits and done a few very rough calcs it would appear not. Pretty sure the block has not been decked as it still has the Rover stamps on it saying 8.1:1 cr. Heads cc up to 36 as per standard 14 bolt heads so not skimmed. This is an extremely low comp engine folks. As said my calcs were very quick and approximate but do confirm low 8`s CR.

Ideal for anyone thinking of forced induction.

More to the point though, what could this engine do with some nice high comp pistons and a decent compression ratio. Problem is i`m not sure such pistons exist off the shelf, shame.




macdeb

8,492 posts

254 months

Wednesday 15th October 2014
quotequote all
yes
I don't think the CR is as stamped on most blocks. After measuring my 450 I was puzzled, then after some advice from some helpful folk on here [Rob, Spend] I realised my calcs were correct at around 8.9:1 and not 9.35:1 as stamped.
Your 4.3 sounds prime for FI bounce

carsy

Original Poster:

3,018 posts

164 months

Wednesday 15th October 2014
quotequote all
I`m just amazed they kept it so low compression. Like you say from what Rover put on the blocks, it may well be even less.

Looks like it would be ideal for FI and i very nearly went that route, but mines coming out for a 5 ltr transplant NA.

PeteGriff

1,262 posts

156 months

Wednesday 15th October 2014
quotequote all
carsy said:
I`m just amazed they kept it so low compression. Like you say from what Rover put on the blocks, it may well be even less.

Looks like it would be ideal for FI and i very nearly went that route, but mines coming out for a 5 ltr transplant NA.
yikes Oooh Ian, you are not getting rid of the lovely 4.3 engine are you? Don't forget it rev's smoother than the 500 and is a happier lump altogether. Why not sympathetically modify the 4.3 rather than spoil what is one of a very reducing few 430's now in existence? I have been playing around with updated ECU maps on my 4.3 recently and have realised what improvements can be made! Pete

stevesprint

1,114 posts

178 months

Wednesday 15th October 2014
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carsy said:
Well having pulled mine to bits and done a few very rough calcs it would appear not. Pretty sure the block has not been decked as it still has the Rover stamps on it saying 8.1:1 cr. Heads cc up to 36 as per standard 14 bolt heads so not skimmed. This is an extremely low comp engine folks. As said my calcs were very quick and approximate but do confirm low 8`s CR.
The compression test on my standard 4.3 averaged at 195 psi which is very similar to a standard Vitesse engine I had a few years ago (well actually more like a few decades ago). As Vitesse engines are 9.75:1 I’ve always considered the figures in the Steve Heaths book of 9.0 to 10.0 about right. Carsy, I trust your calculates more than TVR's over optimist figures but as I always thought TVR increased the CR from 8 it would be interesting to hear the view from someone like Precat.

I wouldn’t take any notice of the CR stamped on the block especially when you consider the original LR engine numbers were over stamped by TVR.

Please keep us posted on your rebuild as my rebuild is well overdue and it will be interesting to see what spec you go for.
Good Luck, Steve

spend

12,581 posts

250 months

Thursday 16th October 2014
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Don't overloook the head gasket thickness ~ & the originals are now unobtainable but I measured them being just less than 1mm when removed from mine. Thats why I developed a copper pattern so I could cut from 1mm thick sheet (to compress) as replacements.

cavebloke

640 posts

226 months

Thursday 16th October 2014
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spend said:
Don't overloook the head gasket thickness ~ & the originals are now unobtainable but I measured them being just less than 1mm when removed from mine. Thats why I developed a copper pattern so I could cut from 1mm thick sheet (to compress) as replacements.
Does this mean you have a method to reproduce the original gaskets? If so, I'm sure there's a market for them if you could do a run (I'll take 4). When I rebuilt mine I had to use the composite gaskets which was disappointing as it lowers compression even further. I still have the ringed heads though.

spend

12,581 posts

250 months

Thursday 16th October 2014
quotequote all
cavebloke said:
spend said:
Don't overloook the head gasket thickness ~ & the originals are now unobtainable but I measured them being just less than 1mm when removed from mine. Thats why I developed a copper pattern so I could cut from 1mm thick sheet (to compress) as replacements.
Does this mean you have a method to reproduce the original gaskets? If so, I'm sure there's a market for them if you could do a run (I'll take 4). When I rebuilt mine I had to use the composite gaskets which was disappointing as it lowers compression even further. I still have the ringed heads though.
I developed a pattern so that you can get solid copper gaskets made, having composite gaskets made & copper fire rings inserted would be extortionately expensive in comparison.

From the pattern I have any decent water jet cutting place can cut gaskets, you just need to cut from the sides so the chamfer points upwards (water jets don't cut square IYSWIM).

cavebloke

640 posts

226 months

Friday 17th October 2014
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spend said:
I developed a pattern...
Would you be happy to share the pattern? Is it a CAD-type file?

spend

12,581 posts

250 months

Friday 17th October 2014
quotequote all
cavebloke said:
spend said:
I developed a pattern...
Would you be happy to share the pattern? Is it a CAD-type file?
Yes a DXF, I can mail to you if you want.

I'm away for a while & the only version I have with me has the following features:
- In the waste from each bore an exhaust manifold gasket is cut (just delete under any CAD program)
- Both water passages are full size as I always bleed the rears from the inlet manifold, if you want to change this you need 2 dxfs mirrored in cutting to allow for the 'angled' cut that the jets make IYSWIM.

carsy

Original Poster:

3,018 posts

164 months

Friday 17th October 2014
quotequote all
This is mine showing how the rings have dug into a normal composite gasket. This gasket had done approx 5k miles with no problems.


carsy

Original Poster:

3,018 posts

164 months

Friday 17th October 2014
quotequote all
If anyone with a 4.3 was wondering what exactly they had head wise. Heres one of mine i cleaned up today.











davep

1,141 posts

283 months

Saturday 18th October 2014
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Great 'head' pics carsy. Just for comparison here's a chamber pic for a pre-cat 4.3 BV.


carsy

Original Poster:

3,018 posts

164 months

Saturday 18th October 2014
quotequote all
I take it the valves on yours BV are 37/43mm.

Sardonicus

18,928 posts

220 months

Saturday 18th October 2014
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carsy said:
I take it the valves on yours BV are 37/43mm.
certainly appear so, nice.

davep

1,141 posts

283 months

Saturday 18th October 2014
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carsy said:
I take it the valves on yours BV are 37/43mm.
They are and the inlet valve heads are recessed, which will have an impact on the compression figures I guess:



Are the valve heads recessed the same on your engine carsy?

carsy

Original Poster:

3,018 posts

164 months

Saturday 18th October 2014
quotequote all
Yep, both valves have a recess on mine. Only a small one on the exhaust and probably similar to yours on the intake.

I cc`d my heads the other day and they came bang on 36cc.


Dave, just out of interest what cam do you run on your BV motor and do you know what power its making.

Edited by carsy on Saturday 18th October 19:29

davep

1,141 posts

283 months

Sunday 19th October 2014
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I'm running a mild mannered V8D MC1, hence 280 bhp. This gives good all round drive-ability with no shunting around town and plenty of performance for my needs. Lately I've been running one of stevesprint's bespoke 14CUX tunes and the engine now runs even smoother, which is great for long distance journeys.

stevesprint

1,114 posts

178 months

Sunday 19th October 2014
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davep said:
Lately I've been running one of stevesprint's bespoke 14CUX tunes and the engine now runs even smoother, which is great for long distance journeys.
Dave Thanks, It was a team effort including yourself.

The 14cux fun will resume soon once I’ve finished fixing all parts that broke on my Griff during the summer. I’ve already got a 14CUX winter wish list in mind so let me know when you are ready.

Carsy, sorry if a little off topic.

Cheers, Steve

Edited by stevesprint on Sunday 19th October 20:20

davep

1,141 posts

283 months

Sunday 19th October 2014
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Carsy when you did your CR calculations what values did you use for the bore size and stroke length? Also are the piston crowns dished and eye browed on your engine?

If you have time, it'd be interesting to see what sort of CR figure you get when entering your engine values into this calculator:

http://www.csgnetwork.com/compcalc.html

Thanks.