Finished workshop. Now for a new engine.

[Dixie]

I have been toying with buying another engine for a winter project.  I have been offered a 4.0 ltr TVR engine from a Chim.  I know the heads and block are the same as a 4.6 RR engine, but will it be any better than my 3.5 Vitesse engine?

I could do a lot of head work and trick cam etc, but will it be worth it?

Mark

[chrislandy]

short answer... yes, a lot.

It's a massive leap from a 3.5 to 3.9 in terms of HP and torque so going TVR tuned as well with whatever trick stuff they did will be a huge improvement. The 4.0 TVR conversion is/was quite common in landy circles especially in racers, these guys would not do it unless it gave them something in return.

Didn't the TVR V8's have a flat plane crank? or was this just the 5L ?

[Moleman]

I know this ain't quite the same but I went from 2ltr duratec  to a 2ltr ungraded duratec with all the toys & extra bhp. Even then I had to make alot of changes with afew other unexpected issues to solve. I found it was also costing me more & more than I had originally ment too. but  Im I so glad I done it now!

[Dixie]

Dont know about the Flat plane crank, not even sure what one is?

I know the 4.0Ltr has a TVR cam so would make it go well.  But the 3.5 Vitesse motor has differant heads etc to a STD 3.5 out of a RR, so is already at 220BHP.

What I didnt want to do is go to the trouble of tricking up a 4.0Ltr when a bit more effort/cash and I could get a 4.6( even knowing the porus block issue, top hat liners will fix that)

Bloke wants 400 euros for it, so not the end of the world.  Could possible stoke it and make it a 4.4, would have heaps of torque.

M

[chrislandy]

a normal v8 crank has the big end journals at 90 degrees so you have a pair at 0, 90, 180 & 270 degrees, whereas the flat plane cranks are 0 and 180 aparently the torque curves are majorly improved.

From wikkithingy
4.0 TVR V8 = 240 BHP, 270lbft@4000
4.0 High Comp TVR V8 = 275BHP, 305lbft @ ?

[Hairy Santa]

a normal v8 crank has the big end journals at 90 degrees so you have a pair at 0, 90, 180 & 270 degrees, whereas the flat plane cranks are 0 and 180 aparently the torque curves are majorly improved.

From wikkithingy
4.0 TVR V8 = 240 BHP, 270lbft@4000
4.0 High Comp TVR V8 = 275BHP, 305lbft @ ?

what compression is standard and what is on the high comp, are these figures using the same cam and valve timing settings ?

[chrislandy]

I dunno, just re-iterating from wikipedia page on TVR V8's,

I'm pretty sure my 3.9 is a 9.75:1 which is considered HC in landy terms but I seem to remember they did a 10.5:1 in something.

[Hairy Santa]

just seems quite a rise in BHP and torque by raising the comp ratio

I wonder if anyone has worked out the amount that would be saved in having to increase the BHP by reducing the weight of the car say by starting with 1500 kg and reducing it to 1400kg - cant say I have ever seen anything on this

Speed = power over weight

[chrislandy]

The best money is spent when none is spent loose the weight first as it's a free way of getting a better power to weight ratio. If you can get the car less than 1000kg then the power to weight really starts moving as you are effectively getting more BHP/Ton than you actually have, hence why our lightweight toys are mentally quick. The Shelsley is around 350 BHP/Ton (circa 300 HP and 850kg)

So by simples maths:
1500kg, 200BHP = 133.33 BHP/Ton

reduce weight to XX => BHP needed to get same power to weight ratio
1400kg => 186.66
1300kg => 173.33
1200kg => 160.00
1100kg => 146.66
1000kg => 133.33
900kg   => 120.00
800kg   => 106.66
700kg   =>  93.33

[paintman]

The best money is spent when none is spent loose the weight first as it's a free way of getting a better power to weight ratio.

When are you starting the diet Mark?...... Lol..........   

['The Gaffer']

Don't forget the pleasure you will get from the project Mark. Is there a price on that if at the end of the day there is an an increase in power regardless? Go for it if you like a challenge.

[Bulldog Bri]

Have I missed something here. can someone actually put up the formula for this...

My car 750kg ish
My engine 83bhp (supposedly)
Power

[Lucky Ed]

It's power divided by weight so......................

   83 / .75(tonnes) = 110.666

Go steady Bri

[Bulldog Bri]

Ah... Got it now.  I think. Duh

[Hairy Santa]

just worked out my cars, and made a couple of graphs up to see how weight loss increases BHP/Tonne - quite interesting

the Spectre is now around 282 BHP/Tonne

the Daytona Cobra is now around 300 BHP/Tonne

and the Dax Busa is around 623 BHP/Tonne

def got to shave some more weight off, maybe even cut down to 1 breakfast as well 

[robp]

and the Dax Busa is around 623 BHP/Tonne

Ah, yes, that explains why it was the fast accelerating thing I've ever sat in. 

[Daley Down Under]

and the Dax Busa is around 623 BHP/Tonne

Pete - I remember Llandow. You sure its only 623? 

Cheers Adrian

[Dixie]

You gotta remember that's 600 bhp/t kerb weight.  When Pete sits in it, its somewhere nearer 300 bhp/t.

Sorry Pete, just couldn't resist.

[Hairy Santa]

my turn will come 

[chrislandy]

Been thinking about this yesterday, it's a direct corrolation between the ability to accelerate and the power/weight (given all else remains constant - obviously they don't as the gear ratios will be different, power delevoped at different RPM's etc...)

From GCSE Physics: Force = Mass x acceleration, so Force = Power, Mass = Weight

Force and power are different things with differnt units but if you assume all else is constant then you can take them as being equal

[Hairy Santa]

 Chris your just trying to confuse us 

plus its too early in the morning for this sort of thing

[Bulldog Bri]

So, does this mean, Pete's Dax will be slower on the way back from a run out after breakfast then? Lol

[chrislandy]

So, does this mean, Pete's Dax will be slower on the way back from a run out after breakfast then? Lol

Signifiantly Just think if you drove a 400kg, 300hp car, adding 2kg of breakfast would "loose" you 4 HP/Ton (0.5%)

Chris your just trying to confuse us 

plus its too early in the morning for this sort of thing

Bit of engineering first thing in the morning never hurt anyone

[Hairy Santa]

brill answers  - chuckling to myself 

But I think we have nicked Dixie's thread so we better back off I think 

Sorry Mark, we were chatting about your new engine !!!!!

[Dixie]

No worries Pete, didn't even notice.

M

[Iancider]

Dixie,

I have nothing really informed to say but generally agree that adding power alone isn't everything and there is an argument for losing weight BUT then you'll be anorexic, wont have any passengers and will be running on empy all of the time. 

But something does occur to me.  How will it sound?  It is the music they make that really excites me.  Perhaps we shoud be talking HiFi here with big bass bins! 

[Dixie]

Well I didn't go for the 4.0ltr motor.  I have brought a 4.6 motor c/w all ancillaries.

Should be a good base for a stage 3 tricked up motor.

Mark

['The Gaffer']

Dixie,
But something does occur to me.  How will it sound?  It is the music they make that really excites me.  Perhaps we shoud be talking HiFi here with big bass bins! 

Agreed

Well I didn't go for the 4.0ltr motor.  I have brought a 4.6 motor c/w all ancillaries.

Should be a good base for a stage 3 tricked up motor.

Mark

The louder you scream, the faster we go

[bluehornetrider]

One of my clients has a tvr chrimea and swapped the 4.0 for the 4.6 and says it made a huge difference, you will never notice the top end difference unless your a regular on the autobahn but the acceleration is great.  So if you have a huge horsepower engine but its all geared too high and isn't driveable you wont be as fast.  Concentrate on driveability and reliability the rest is left to racing teams.

[Hairy Santa]

4.6 -  oh yes that will do 

[paintman]

Might be able to keep up with me up to 70 now Dixie!!

[Pilgrim Anna]

Looking brill!

[Moleman]

You will have to test it on one of our trackdays to see how it really goes. 

[Dixie]

Going to build it for street use.  More interested in torque than out right BHP, so will choose the CAM very carefully.  Luckily there are several people on the Cobra site that have done this conversion.

Mark

['Mendip Wurzel']

I expect you have this book already Mark, but 'How to Power Tune a Rover V8' by Des Hammill taught me more about tuning an RV8 than everything else I had ever purchased.... just a brilliant book which I used to tune my engine as much as a reasonably could without it costing me a fortune. Like you I wanted to keep acceptable torque and steady tickover, because as we all know what you gain on the top end you tend to loose low down.
Kevin   

[Dixie]

Kev.

I know the book, but you cant buy it now for under £70.  Its a rare beast.

Would love to copy it or borrow it?

thanks Mark

[Hairy Santa]

been told its a very good book, and would also love to have a copy of it

would it please be possible for Dixie and myself to borrow it to see If its possible to copy at all for our own use

many thank if you could Kev 

[Dixie]

Motor landed.  Blooming heavy.

Got a few fitters taking off the heavy bits to make easier to lift into my shed.

[Hairy Santa]

Motor landed.  Blooming heavy.

Got a few fitters taking off the heavy bits to make easier to lift into my shed.

should keep you quiet for a while 

[Moleman]

Nice winter project mate.