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5.0 TVR Engine recommendation
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gilps
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PostPosted: Thu Aug 10, 2017 8:44 pm    Post subject: 5.0 TVR Engine recommendation Reply with quote

Well after finally getting the car running perfectly 422bhp and 430FTLB Torque on the RR a piston has decided to let go part of the piston top where the valve cut outs are broke away so need something a bit stronger.
Would like to retain the TVR engine but only if it can be made reliable.
Any recommendations of pistons cranks rods etc etc would be great.
Just to add there was no detonation and no visible signs of detonation on the piston tops in fact they were immaculate no carbon build up you can see very clearly the casting marks and and writing you would think they were 10 miles old not 60,000
Chris
Just to mention the car has a Rotrex supercharger with intercooler running 6psi of boost
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Rossco
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PostPosted: Fri Aug 11, 2017 8:10 pm    Post subject: Reply with quote

Sounds like exactly the same issue Coops had.
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stevieturbo
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PostPosted: Fri Aug 11, 2017 9:45 pm    Post subject: Reply with quote

pics of damage ? Pistons rarely just fall apart for no reason

Exactly what pistons where they ?

If you cant get any off the shelf, it would be very easy to get some custom made.

Although I boosted the crap out of standard 4.6 pistons for years without issue ( other than my own fault lol )
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gilps
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PostPosted: Fri Aug 11, 2017 9:57 pm    Post subject: Reply with quote

The piston broke a chunk awaywhere the valve cut outs are. They were a standard Tvr 5.0 piston which are a week piston anyway. Having spoken to John Eales today the best way forward is to either return it to NA or build a better short engine using a 4.6 crank, low compression forged pistons, steel rods etc.
Chrisn
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stevieturbo
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PostPosted: Fri Aug 11, 2017 10:12 pm    Post subject: Reply with quote

gilps wrote:
The piston broke a chunk awaywhere the valve cut outs are. They were a standard Tvr 5.0 piston which are a week piston anyway. Having spoken to John Eales today the best way forward is to either return it to NA or build a better short engine using a 4.6 crank, low compression forged pistons, steel rods etc.
Chrisn


Or seeing as the only thing that broke was the pistons.....just rebuild it with better pistons.

It's only 6psi boost....not a monster.

Is he saying the crank/rods also fail on very mildly tuned or standard engines ?
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gilps
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PostPosted: Fri Aug 11, 2017 10:21 pm    Post subject: Reply with quote

Yes week crank and crap pistons says he has seen loads of 5.0 tvr cranks break on standard engines with 280bhp and it was only a matter of time before mine would probably go as well along with other pistons. TBH I actually know two people who have broken on a 5.0 crank on only Mildly tuned 300bhp
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stevieturbo
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PostPosted: Fri Aug 11, 2017 10:45 pm    Post subject: Reply with quote

Wow...that's shocking.

When I turbo'd the 4.6, it was just standard crank, rods and pistons. Other than melting a piston after a year or two ( my fault ) the engine held up to dogs abuse.
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Coops
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PostPosted: Sat Aug 12, 2017 10:11 am    Post subject: Reply with quote

As Rossco said,
I had the side of my piston fall away between two ring lands,
no sign of detonation to the crown or head face, no pinking just a sudden heavy venting of oil vapour while driving it one day,
Only found the broken piston after strip down of the engine and it fell away after we removed the offending piston from the block,
after talking to a few people it was put down to shock compression causing the stock cast piston to fail, I was running nearly 14psi of boost and quite a high CR engine though so my own fault I pushed it too far,

Now have built this engine with parts from v8performance parts,
same 4.6 block but stroked to 4.8ltrs now, diamond forged slipper pistons and lunati 6" chevy H beam rods,
started out with a bigger pulley on the charger to allow the charger to match the engine red line of 7000rpm without damaging it, but it only gave 3psi of boost,
so the original pulley is back on and we are back up to 10psi again, but now limited to engine revs due to the risk of over revving the rotrex,
So pahse3 of the engine, in the process of fitting a procharger with a bigger cfm than the rotrex , which we can run in the same rev range of the engine without fear of over revving it like the rotrex and control the boost via the ecu and an electronic boost controller, to bring it back down to where we want it






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gilps
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PostPosted: Sun Aug 13, 2017 8:46 am    Post subject: Reply with quote

That certainly looks the way to go I am really torn with putting it back to normally aspirated and spending a fortune getting it to accept the extra power of the charger. I've only had the car for just over a year and it's cost me a fortune getting it all working right only to end up having the major failure I was trying to avoid. It's just a road weekend car probably does about 3,000 miles a year but I did like the extra power and kick in your back.
There is the cost to take into consideration as well putting it back to NA won't cost much just a set of pistons a light hone to accept the new rings balancing and possibly cross bolting, selling the SC kit will more than pay for that. Sorting the engine to run safely with the SC will cost me 4K plus.
Still very undecided what to do.
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Blown v8
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PostPosted: Sun Aug 13, 2017 10:57 am    Post subject: Reply with quote

Once you've used forced induction,it's hard to go back
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SuperV8
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PostPosted: Thu Aug 17, 2017 7:52 am    Post subject: Reply with quote

Sorry to hear about your broken piston, can you share some photos?

To cut a long story short my Procharger supercharger high speed bearing failed (detailed in another thread), so I took the sc belt off and drove home, the difference was amazing, 4.6 in a 650kg car should still be quick but it felt sooo slow compared to with the sc! even though the sc was only adding 6 odd psi it made a big difference.

You would need to spend a fortune to get the same power NA, you'd need to rev it more and would still need a stronger bottom end to hold together at the higher rpm, but you'd also need heads/valve train which will support 400hp which on a rover with be rather special - read expensive!

You already have a supercharger, I think I would just get a set of good pistons, or if you have doubts about the 5L cranks fit a smaller crank, you don't need the CC anyway as you are forcing the air in.
The standard 4.6 bottom end is strong and will easily cope with 6psi (tunned correctly!), my 4.6 is running at 7.5psi with intercooler and coil packs, although that's at 3/4 throttle and 4500rpm so probably more if I grow some bigger balls Shocked
I don't know what size main bearings your 5L has vs the 4.0/4.6? Think they are a stroked 3.9? so maybe use 3.9 rotating assembly If it will bolt in and will be very cheap.

Tom.
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gilps
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PostPosted: Fri Aug 18, 2017 1:57 pm    Post subject: Reply with quote

Thanks again guys I am taking the short engine to john Eales tomorrow to hopefully get sorted. At the very least it will be dynamically balanced, cross bolted, new Omega pistons and rebuilt as a short engine. How far I go above this is down to cost and what will be gained. Although the crank is a weak spot I think that the cross bolting and balancing sorts this problem out but will have a good chat with John tomorrow.
Chris
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gilps
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PostPosted: Fri Aug 18, 2017 2:31 pm    Post subject: Reply with quote





Pictures of the broken piston and one of the others. Not sure why the pistons are so clean. They are all the same and have all done over 60,000 miles over 10,000 with the Supercharger fitted. If you zoom in on the "good" piston you can see a crack developing on the right valve cut out
Chris
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stevieturbo
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PostPosted: Fri Aug 18, 2017 5:27 pm    Post subject: Reply with quote

It does look like the crown could be extremely thing where the cutout is...cutout in towards the top ring groove.

There are a few small dots, which may be indicative of some detonation, but the photo might be misleading.

Clean is often an indication of water getting in there, but if not the case I wouldnt be worried about them being clean

Definitely more suitable pistons required though.
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DEVONMAN
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PostPosted: Sun Aug 20, 2017 6:44 pm    Post subject: Reply with quote

I have heard of cases where the TVR 5.0 crank has snapped. I put this down to the high revs people push these engines to to achieve the maker's high BHP claims together with the fact that the crank is externally balanced with loaded flywheel and front pulley. The snapped one I have personally seen was broken at the rear main journal.
I have Turboed two of these engines to about 12 psi without trouble and performance is way sufficient without screaming the nuts off it.
The TVR Pistons are just Rover 4.2 pistons with their skirts shortened to clear the crank counterweights and are the weak link when it comes to FI and the higher thermal stresses likely. Compression ratio using these pistons and the 90mm stroke crank is a tad high for FI. I use Low compression forged pistons and had the crank internally balanced. I also cross bolted the block (which is just a late Rover 3.9 modified to clear the TVR crank like TVR do) but I'm not sure it's necessary if you are working with revs under 5000.
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