4.3 compression ratio.
Discussion
carsy said:
I used the cr calculator on the summit racing site.
Bore 94. Stroke 77. Head 36cc. Pistons are the same as in the 5 ltr. Dished with valve cutouts. I got the piston dish to 26cc. Composite Head gasket 1.2mm. My pistons come out the top of the bore slightly, roughly 5 thow.
CarsyBore 94. Stroke 77. Head 36cc. Pistons are the same as in the 5 ltr. Dished with valve cutouts. I got the piston dish to 26cc. Composite Head gasket 1.2mm. My pistons come out the top of the bore slightly, roughly 5 thow.
I hope you don't mind me resurfacing your old thread.
Does the above mean you believe precat 4.3 pistons are Griff 500 pistons? Does anyone know the cc volume of a standard 500 piston? Carsy, if possible would you be kind enough to post a picture of your 4.3 pistons, thanks.
carsy said:
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.
I would of thought Precat 4.3 are high compression to produce 260-280 bhp and have a compression test of 195psi plus your 4.3 pistons coming out 4 thou would help.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.
I always assumed the 4.3 pistons are standard 3.9 pistons but with the tops and possibly skirts machined as the tops of a few 4.3 pistons have been known to break.
Steve
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
davep said:
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?
Well…Are the valve heads recessed the same on your engine carsy?
Very Nice! And a proud owner too :-)
My heads have never been removed so not really sure what I have.
However, after using a bore scope, I can say they need a dam good clean…
I wouldn’t mind having a set of copper gaskets in readiness…
If anyone is getting any made up let me know and I will chip in towards the cost :-)
MPO
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.
stevesprint said:
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
Looking forward to that Steve!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
Carsy, do keep the updates coming!
Regards, Pete
Carsy
Today I asked John Eales what pistons TVR used in 4.3 Griffs and with John’s permission I quote his reply:-
“MOST TVR 4.3s had Land Rover 3.9 (9.35:1) pistons with 22.5 cc at TDC with 2mm removed resulting with 12cc APPROX and giving 10+:1, the pistons should be level with the deck. However, SOME TVR 4.3s had Land Rover 4.2 (8.94:1) pistons with skimmed heads giving 9.5:1”.
This means we are both correct and explains the variations, what bhp was your 4.3?
Steve
Today I asked John Eales what pistons TVR used in 4.3 Griffs and with John’s permission I quote his reply:-
“MOST TVR 4.3s had Land Rover 3.9 (9.35:1) pistons with 22.5 cc at TDC with 2mm removed resulting with 12cc APPROX and giving 10+:1, the pistons should be level with the deck. However, SOME TVR 4.3s had Land Rover 4.2 (8.94:1) pistons with skimmed heads giving 9.5:1”.
This means we are both correct and explains the variations, what bhp was your 4.3?
Steve
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.
carsy said:
Is your engine in bits Steve to compare. Mine was 265 bhp running an Emerald ecu.
Sadly not. I’m trying to solve the 430 mysteries as mine is overdue a refresh/rebuild but I’m loathed to disturb it while its still reliable, smooth & going strong.Mine’s very similar with 264 bhp running 14CUX (Growl 2014) and 269bhp on Surrey rolling road in the same week.
Cheers, Steve
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.
carsy said:
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.
CarsyI 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.
What part number is stamped into the pistons?
Cheers
MPO
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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