4.3 compression ratio.
Discussion
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.
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.
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.
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
Hi Steve. Unfortunately my 4.3 block is all greased and wrapped up in storage at my sisters should i ever need it again. ( i`ve gone to 5ltrs ). So struggling with pics.
Anyway the 4.3 pistons are just Rover 4.2 items. I think TVR preferred calling it a 4.3 as againt a 4.2. All they have different is the valve cut outs added. Thats it nothing else touched, the skirts arent touched.
The TVR 5ltr pistons are the same. Just Rover 4.2 pistons. These also have the valve cut outs but also have some of the skirt machined away to clear the crank.
The 3.9 piston is different but can be made to fit by machining the top of the piston slightly. This would help to raise the CR. This thread shows the difference between 3.9 and 4.3. The 3.9`s are also available oversized.
http://www.v8forum.co.uk/forum/viewtopic.php?t=847...
Anyway the 4.3 pistons are just Rover 4.2 items. I think TVR preferred calling it a 4.3 as againt a 4.2. All they have different is the valve cut outs added. Thats it nothing else touched, the skirts arent touched.
The TVR 5ltr pistons are the same. Just Rover 4.2 pistons. These also have the valve cut outs but also have some of the skirt machined away to clear the crank.
The 3.9 piston is different but can be made to fit by machining the top of the piston slightly. This would help to raise the CR. This thread shows the difference between 3.9 and 4.3. The 3.9`s are also available oversized.
http://www.v8forum.co.uk/forum/viewtopic.php?t=847...
Edited by carsy on Wednesday 4th November 09:42
Using 28cc heads will obviously up the CR and which from what i can see will be beneficial on the 4.3
What it will take it to i`m not sure you would have to do your checks sums when rebuilding.
Re head gaskets you dont need the copper ones. Just use normal composites such as Elring. These are the same thickness as the copper ones TVR used. The wire rings in the 4.3 heads will still dig into the composite just fine.
What it will take it to i`m not sure you would have to do your checks sums when rebuilding.
Re head gaskets you dont need the copper ones. Just use normal composites such as Elring. These are the same thickness as the copper ones TVR used. The wire rings in the 4.3 heads will still dig into the composite just fine.
Very interesting Steve. In that case I stand corrected and apologise for any confusion.
Im intrigued now as to what I had. I will try and get to my 4.3 block and measure the piston dish depth in mm. I wont really be able to accurately cc it.
Is your engine in bits steve to compare. Mine was 265 bhp running an Emerald ecu.
Im intrigued now as to what I had. I will try and get to my 4.3 block and measure the piston dish depth in mm. I wont really be able to accurately cc it.
Is your engine in bits steve to compare. Mine was 265 bhp running an Emerald ecu.
Just thought this may be of interest to some. Did some accurate cc'ing of my 4.3 pistons yesterday.
I think it was Stevesprint who said he thought the 4.3 pistons were actually 3.9 items that had the crowns machined down to bring them to the same height as original 4.2 pistons. Hence in doing so raised the compression ratio slightly.
Well i can confirm my pistons have had the crowns machined down so suspect Steve is right that tvr changed the original ones for 3.9 items. They are Hepolite items. Mine measure up to 23cc even after this machining, so presume they are low comp 3.9' pistons as against the high comp ones.
A quick go on summit racings online cr calculator shows the engine will be approx 9.1. So still not overly high. Maybe tvr should have used high comp 3.9 pistons to give us a bit more.
I think it was Stevesprint who said he thought the 4.3 pistons were actually 3.9 items that had the crowns machined down to bring them to the same height as original 4.2 pistons. Hence in doing so raised the compression ratio slightly.
Well i can confirm my pistons have had the crowns machined down so suspect Steve is right that tvr changed the original ones for 3.9 items. They are Hepolite items. Mine measure up to 23cc even after this machining, so presume they are low comp 3.9' pistons as against the high comp ones.
A quick go on summit racings online cr calculator shows the engine will be approx 9.1. So still not overly high. Maybe tvr should have used high comp 3.9 pistons to give us a bit more.
Sardonicus said:
If that's the case I have a brand new old stock set of genuine 3.9/4.0 pre serp/int serp pistons to compare for you guys, I was always under the impression the 4.2/4.3 had different Pistons i.e piston wrist pins in a different position than the 3.9 Pistons but of the same design
I think you are correct Simon. If both pistons were fitted onto the same rod so to speak, the 3.9 piston crown would be a few mm higher than the 4.2 one taking it out the top of the block. Hence why tvr had to take a few mm off the top of the 3.9 piston.Sorry but i stupidly didnt take any pics.
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