Anyone built a 4.2 overbore?

[MrChips]

Just amusing myself with a few thoughts planning out the next few weeks as I try to get my car back on the road by early March. The engine is currently up with Jason at str8six so he'll be doing the build for me.

I've decided against the 4.3 kits as I want to make sure I keep the manic bike-reviness of the engine, and I don't really want much more torque. However looking at the work that Dom does to get to the 4.5, then is it not entirely feasible to build a high revving, 4.2 using an overbore, and the 4.5 pistons?

Would the slight increase in piston size mean you need new rods and crankshaft? (in which case you could argue that you might as well go for the 4.5?)

At the moment my build spec plan (not including the change in bore). Please feel free to critique/advise if you have any specific experience you'd like to share!

New block including coolant and oil pathways
New pistons
Full rebuild including all normal stuff (cams, valves, followers)
Higher flow injectors
Lightened flywheel
ACT Trumpets in std airbox
High volume/pressure oil pump
Full remap (still using the std MBE Ecu)
Small additional oil pressure warning light (not sure where i'll put this yet)

From speaking to Jason, he didn't seem to think that any additional porting on the head would be necessary (if I stay at 4.0litres) as the returns are minimal?

P.S. Anyone know of any good credit cards around at the mo?

[Night Rider]

Mister Chips, I'm doing the same to mine atm but staying with the 4.0. You mention a high volume/high pressure oil pump, where is that coming from? Is it Jason’s mod or are you supplying it?

It's something I should consider when rebuilding mine.

Cheers

[blueg33]

Apart from the Trumpets and oil pump (I think), that is pretty much the spec of mine, I have high flow injectors etc. Rebuild was by Dom and I get 363bhp on the dyno, but he wants to map it again as he thinks there is a bit more to be had. So no real gains over TVR's published figures.

[Robertjp]

blueg33 said:

Apart from the Trumpets and oil pump (I think), that is pretty much the spec of mine, I have high flow injectors etc. Rebuild was by Dom and I get 363bhp on the dyno, but he wants to map it again as he thinks there is a bit more to be had. So no real gains over TVR's published figures.

High flow injectors on a standard rebuild or did you go for s / red rose spec? what benefit over standard? I left pistons standard on mine - they were the later coated type in good condition.

for the OP i think Jason may steer you away from the high pressure oil pump (he did with me) - its really not necessary and the effects are a bit of an unknown. I went for the new block and my oil pump needed replacing anyway, i now get good oil pressure through the whole rev range using 5w 40 oil.

I also think if you go for something that isnt currently offered as a package you will pay more will you not? I think you can still achieve a 'revvier' engine with a lightened flywheel and simplex chain set?

[jcpgasoline]

MrChips said:

Just amusing myself with a few thoughts planning out the next few weeks as I try to get my car back on the road by early March. The engine is currently up with Jason at str8six so he'll be doing the build for me.

I've decided against the 4.3 kits as I want to make sure I keep the manic bike-reviness of the engine, and I don't really want much more torque. However looking at the work that Dom does to get to the 4.5, then is it not entirely feasible to build a high revving, 4.2 using an overbore, and the 4.5 pistons?

Would the slight increase in piston size mean you need new rods and crankshaft? (in which case you could argue that you might as well go for the 4.5?)

At the moment my build spec plan (not including the change in bore). Please feel free to critique/advise if you have any specific experience you'd like to share!

New block including coolant and oil pathways
New pistons
Full rebuild including all normal stuff (cams, valves, followers)
Higher flow injectors
Lightened flywheel
ACT Trumpets in std airbox
High volume/pressure oil pump
Full remap (still using the std MBE Ecu)
Small additional oil pressure warning light (not sure where i'll put this yet)

From speaking to Jason, he didn't seem to think that any additional porting on the head would be necessary (if I stay at 4.0litres) as the returns are minimal?

P.S. Anyone know of any good credit cards around at the mo?

Interesting idea! You may well need new rods + crank because, assuming cylinder pressures remain the same or similar, the bigger bore will result in more force from the pistons, so more stress in the conrods and more torque at the crankshaft. And bigger pistons probably mean more mass so again that's more stress on the rods. I don't know if the existing rods & crank would be up to the job or not. I would be really interested to follow the development if you go down this route. Good luck!

Edited by jcpgasoline on Tuesday 10th January 12:29

[blueg33]

Robertjp said:

High flow injectors on a standard rebuild or did you go for s / red rose spec? what benefit over standard? I left pistons standard on mine - they were the later coated type in good condition.

for the OP i think Jason may steer you away from the high pressure oil pump (he did with me) - its really not necessary and the effects are a bit of an unknown. I went for the new block and my oil pump needed replacing anyway, i now get good oil pressure through the whole rev range using 5w 40 oil.

I also think if you go for something that isnt currently offered as a package you will pay more will you not? I think you can still achieve a 'revvier' engine with a lightened flywheel and simplex chain set?

The injectors dealt with some lean spots. Pretty sure its not the red rose spec, but at high revs it was leaning off too much. (well thats my interpretation of what Dom said)

[Tuscanuwe]

I have choosen to the 4.3 from Dom(TVR Power), i wanted also the old reviness, the 4.3 does same as 4.0, but a lot power more at low and middle revs!
Ask Dom for test drive!!!!!!!
So i got a new forged crank and new better con rods due to more stress from bigger pistons. Be aware for lightened flywheel, Dom said to me he has had trouble already with this flywheels! If flywheel get broken you will have a very big damage.
For the 4.5 max revs are reduced!
Also uprated injektors are required and a correct fuel/air mixture setup.
Ask dom for all your specials, he will also install NOS for you,which is also covered in his 5 years guarantee.

You only need a pocket full of money and nearly everything(k) is possible

Uwe

[jcpgasoline]

Tuscanuwe said:

I have choosen to the 4.3 from Dom(TVR Power), i wanted also the old reviness, the 4.3 does same as 4.0, but a lot power more at low and middle revs!
Ask Dom for test drive!!!!!!!
So i got a new forged crank and new better con rods due to more stress from bigger pistons. Be aware for lightened flywheel, Dom said to me he has had trouble already with this flywheels! If flywheel get broken you will have a very big damage.
For the 4.5 max revs are reduced!
Also uprated injektors are required and a correct fuel/air mixture setup.
Ask dom for all your specials, he will also install NOS for you,which is also covered in his 5 years guarantee.

You only need a pocket full of money and nearly everything(k) is possible

Uwe

The 4.3 is a stroker, no?

[Tuscanuwe]

http://www.enginebuildermag.com/Article/92119/raci...

---Something to read----

So you need a very good engine builder for your experimental engine

Uwe

[MrChips]

jcpgasoline said:

Tuscanuwe said:

I have choosen to the 4.3 from Dom(TVR Power), i wanted also the old reviness, the 4.3 does same as 4.0, but a lot power more at low and middle revs!
Ask Dom for test drive!!!!!!!
So i got a new forged crank and new better con rods due to more stress from bigger pistons. Be aware for lightened flywheel, Dom said to me he has had trouble already with this flywheels! If flywheel get broken you will have a very big damage.
For the 4.5 max revs are reduced!
Also uprated injektors are required and a correct fuel/air mixture setup.
Ask dom for all your specials, he will also install NOS for you,which is also covered in his 5 years guarantee.

You only need a pocket full of money and nearly everything(k) is possible

Uwe

The 4.3 is a stroker, no?

Yep! Longer stroke crank, new pistons and rods, presuming then that the rods themselves are longer and utlise shorter pistons?

I'll see if I can have a chat with Dom over the next day or so as he has emailed me with some initial thoughts.
I do now recall a conversation with Jason as to why he doesn't go bigger than 4.3 so it might be that there are concerns over the cooling between the cylinders once you start boring out to wider dimensions? From what I understand, the new blocks have both improved oilways and also coolant pathways between the cylinders to aid cooling?

My engine was suffering with bad detonation, and also must have been running v.lean at WOT as a couple of pistons looked like this



Does anyone know why is it that the 4.5's have had to curb their top end speeds? Is it a balancing issue in keeping things in check above 7000rpm? Or something to do with the wider piston sizes?

[BCA]

See 'Tail slide' on here. I can confirm his car is ridiculously quick.


Faster than an F458 up Loton...

Edited by BCA on Tuesday 10th January 23:17

[jcpgasoline]

MrChips said:

jcpgasoline said:

Tuscanuwe said:

I have choosen to the 4.3 from Dom(TVR Power), i wanted also the old reviness, the 4.3 does same as 4.0, but a lot power more at low and middle revs!
Ask Dom for test drive!!!!!!!
So i got a new forged crank and new better con rods due to more stress from bigger pistons. Be aware for lightened flywheel, Dom said to me he has had trouble already with this flywheels! If flywheel get broken you will have a very big damage.
For the 4.5 max revs are reduced!
Also uprated injektors are required and a correct fuel/air mixture setup.
Ask dom for all your specials, he will also install NOS for you,which is also covered in his 5 years guarantee.

You only need a pocket full of money and nearly everything(k) is possible

Uwe

The 4.3 is a stroker, no?

Yep! Longer stroke crank, new pistons and rods, presuming then that the rods themselves are longer and utlise shorter pistons?

I'll see if I can have a chat with Dom over the next day or so as he has emailed me with some initial thoughts.
I do now recall a conversation with Jason as to why he doesn't go bigger than 4.3 so it might be that there are concerns over the cooling between the cylinders once you start boring out to wider dimensions? From what I understand, the new blocks have both improved oilways and also coolant pathways between the cylinders to aid cooling?

My engine was suffering with bad detonation, and also must have been running v.lean at WOT as a couple of pistons looked like this



Does anyone know why is it that the 4.5's have had to curb their top end speeds? Is it a balancing issue in keeping things in check above 7000rpm? Or something to do with the wider piston sizes?

Don't know, although I think the 4.5's stroke is the same as the 4.3's even though the bore is bigger. If I'm right then the piston speed should be the same if the rod length is the same, which it should be, so that shouldn't be the reason. Maybe its to do with having more piston mass hence more stress on the rods? I would like to know!

[PipeNslippers]

jcpgasoline said:

Don't know, although I think the 4.5's stroke is the same as the 4.3's even though the bore is bigger. If I'm right then the piston speed should be the same if the rod length is the same, which it should be, so that shouldn't be the reason. Maybe its to do with having more piston mass hence more stress on the rods? I would like to know!

How about putting these in:

Dom has some early (used) Red Rose cranks which were made out of billet steel (the same material as Dom's 4.3 / 4.5 cranks for strength


made by http://www.farndon.com/index.htm and I went for some Carrillo H-section rods

This will give the extra strength and smoothness that you would like.

I assume the 4.5 pistons are heavier than the standard 4.0 pistons (thus requiring the stronger bottom end), but you can confirm with Dom.

[MrChips]

Had a good chat with Dom a little while ago and it's certainly possible to overbore to 4.2 so long as the right liners are used (as per his 4.5). It's also a good idea (essential really) to change the crank and rods for stronger items as per those above. Trouble is, if you're getting new crank, rods, and pistons, why wouldn't you go the full 4.5 route, and choose something that is more of an unknown!

From what I can gather, there's no one specific reason why the rev limits of the 4.5 are lower than others, but it appears to be a combination of slightly higher piston weight, but moreso simply because the engine is doing its best work just below 7k, and so there's simply no point in revving higher and higher, in an engine which is already running close to the natural limitations of parts of its design.

So... what's happening with mine then. Well it looks most likely i'm going to go for a 4.3 kit, put together by Jason, with some minor extras (ACT trumpets, flywheel, decats etc). Whilst in an ideal world i'd quite fancy doing something different, money is a big factor, and sticking with the tried and tested will help the cars residual in the longer term. Boring I know!!

[Flyin Banana]

I'm pretty sure that one of the guys in the TVR speed championship runs a 4.2 straight six t350 thats had a bit of work done to it, seems to go very well

Rob

[Geoff Ashcroft]

MrChips said:

From what I can gather, there's no one specific reason why the rev limits of the 4.5 are lower than others, but it appears to be a combination of slightly higher piston weight, but moreso simply because the engine is doing its best work just below 7k, and so there's simply no point in revving higher and higher, in an engine which is already running close to the natural limitations of parts of its design.

You've answered your own question there Chips - it's all to do with weight. The forces applied to crank, big end and small end bearings increase dramatically as revs climb when using bigger, heavier components. Reciprocating parts need to be so much stronger to withstand the constant stop/start process at either end of the stroke, otherwise they'll come out. So limiting rpm quite simply prolongs life

[Mattt]

What's the difference between an engine built by TVR Power with components supplied by them, and an engine built by Str8six with components supplied by TVR Power?

Just personal preference?

[crimbo]

BCA said:

See 'Tail slide' on here. I can confirm his car is ridiculously quick.


Faster than an F458 up Loton...

Edited by BCA on Tuesday 10th January 23:17

So its not just me then, This car feels very nice indeed when you are in it (His is the 4.2 that races and holds records in the hillclimbs)

From what I remember his is a stroked 4.2 with A CUSTOM CRANK. Its so smooth and revs like crazy, left a very big impresion on me!

[BCA]

crimbo said:

So its not just me then, This car feels very nice indeed when you are in it (His is the 4.2 that races and holds records in the hillclimbs)

From what I remember his is a stroked 4.2 with A CUSTOM CRANK. Its so smooth and revs like crazy, left a very big impresion on me!

IIRC he has the 'Le Mans' crank. It is fantastic though, really really impressive!

[Betz74]

The 4.2 intrigues me as oversquare engines traditionally rev harder,

IIRC the S6 4.0L has 2 different rod lengths, RND engineering explain important piston speed and rod length info which is worth knowing about if a stroker assembly ends up killing the rev thrill.

I think it is worth considering these engines are already stroked out as the OEM design was 3.0L and 3.5L

Strait six engines of 4.0L or more worth talking about are few and far between and alot of them cannot be considered 'performance' at all.