Discussion
What is the maximum safe RPM, to push the Cerb to?
The reason I ask is this,
Last weekend was he first run what you brung (RWYB) and my self and ASH gave it a go.
Now as you already know the strip was poor, so no real times to report.
I found my self having to hold off the accelerator at 7500 for fear of bending things.
The change into 4th was just as you approached the line, so a waste of time really.
While I would love to set a 12-, I do not want to blow anything. So what’s the deal? How far is it safe to go?
Yeah I know power is trailing off here, it’s just the extra gear change seems so wrong.
Before anyone suggests short shifting, I tried that. The Cerb likes being wrung out...unfortunatly you will find you are in third at 110 ish needing a new gear before you reach the line.
Incidentally I don’t remember any dash lights or buzzer.
Maybe a CR gear box would do the trick. Any ideas, don't get the wrong idea, the Cerb is a legendary car. Just doesn’t lend itself well to the 1/4 mile, the gearing leaves you on the edge of a change.
What I did notice was all my maximum speeds had increased, more HP defiantly, not easy to get a faster ET time though.
More HP does not mean faster times. What is does mean is, the driver must play more of a part. I found it far easier to floor the accelerator at last years bash, maybe as the conditions where far better. also 75 odd HP down
This time I had to feather the throttle as flooring it even in third would just light up the rear end.
must be the conditions, roll on the summer.
Nick.
>> Edited by Nickccc on Monday 30th January 00:19
The reason I ask is this,
Last weekend was he first run what you brung (RWYB) and my self and ASH gave it a go.
Now as you already know the strip was poor, so no real times to report.
I found my self having to hold off the accelerator at 7500 for fear of bending things.
The change into 4th was just as you approached the line, so a waste of time really.
While I would love to set a 12-, I do not want to blow anything. So what’s the deal? How far is it safe to go?
Yeah I know power is trailing off here, it’s just the extra gear change seems so wrong.
Before anyone suggests short shifting, I tried that. The Cerb likes being wrung out...unfortunatly you will find you are in third at 110 ish needing a new gear before you reach the line.
Incidentally I don’t remember any dash lights or buzzer.
Maybe a CR gear box would do the trick. Any ideas, don't get the wrong idea, the Cerb is a legendary car. Just doesn’t lend itself well to the 1/4 mile, the gearing leaves you on the edge of a change.
What I did notice was all my maximum speeds had increased, more HP defiantly, not easy to get a faster ET time though.
More HP does not mean faster times. What is does mean is, the driver must play more of a part. I found it far easier to floor the accelerator at last years bash, maybe as the conditions where far better. also 75 odd HP down
This time I had to feather the throttle as flooring it even in third would just light up the rear end.
must be the conditions, roll on the summer.
Nick.
>> Edited by Nickccc on Monday 30th January 00:19
Im 100% certain a TVR CR box would be extremely advantagous to a Cerbera 4.5 with remap/ 4.5RR - it has the kind of torque that the S6 lot can only dream of, so would be far better utilised than it is in a Sagaris (where most of them are atm!)
I would like to know what 3rd gear tops out at on the TVR CR box (which is a wide ratio in my mind, odd) Certainly 0-100 would be improved (it'll do it in second I think!) But as you have realised, 3rd gear to fourth is what does it.
I haev been told 7500rpm is fine and 8000rpm fine occaisionally (better with the "GT" crank) - we have the same problem as you except at 7200rpm our early air intake, without the supporting springs) crush and starve the engine of air (or atleast thats our best guess so far) We need Jules's (Cyclone) intake set up!
I would like to know what 3rd gear tops out at on the TVR CR box (which is a wide ratio in my mind, odd) Certainly 0-100 would be improved (it'll do it in second I think!) But as you have realised, 3rd gear to fourth is what does it.
I haev been told 7500rpm is fine and 8000rpm fine occaisionally (better with the "GT" crank) - we have the same problem as you except at 7200rpm our early air intake, without the supporting springs) crush and starve the engine of air (or atleast thats our best guess so far) We need Jules's (Cyclone) intake set up!
Hi Nick, Ben,
3rd should see you to about 118-120mph, the only problem is whether to hold 3rd or to shift up into 4th. With your extra power I think you'll be seeing 120mph+ at the finish line and this'll probably mean changing up to 4th
, I am going to have the same problem with mine now that it is around 30bhp up on last years power. I wouldn't worry too much about your times etc from your runs at SP a couple of weeks ago, anything less than perfect conditions and the Cerb will struggle to get proper traction. Last year the best conditions I encountered were at the end of March, I "only" had 375bhp running an unmapped Emerald but still managed consistent 12.7s, with a 12.5 thrown in. Thereafter (early May), I managed a 12.3 with 390bhp then the rain came. The next couple of events I went to both had rain at some stage and as I tried some slicks at one of them it proved pointless as the wheels spun even more at the start. A nice coolish day with a bit of sunshine and no sign of rain is what is needed.
3rd should see you to about 118-120mph, the only problem is whether to hold 3rd or to shift up into 4th. With your extra power I think you'll be seeing 120mph+ at the finish line and this'll probably mean changing up to 4th
, I am going to have the same problem with mine now that it is around 30bhp up on last years power. I wouldn't worry too much about your times etc from your runs at SP a couple of weeks ago, anything less than perfect conditions and the Cerb will struggle to get proper traction. Last year the best conditions I encountered were at the end of March, I "only" had 375bhp running an unmapped Emerald but still managed consistent 12.7s, with a 12.5 thrown in. Thereafter (early May), I managed a 12.3 with 390bhp then the rain came. The next couple of events I went to both had rain at some stage and as I tried some slicks at one of them it proved pointless as the wheels spun even more at the start. A nice coolish day with a bit of sunshine and no sign of rain is what is needed. Cyclone's hit the nail on the head .. traction is the santa pod problem so times will always suffer on anything but a good day .. but teh gearing on the cerbie doesn't help, and with more hp comes higher terminals and the gearing runs out even quicker..
i think you'll always struggle to get your run finished in 3rd gear, with 420bhp you're always going to have one of the fastest terminals of all the cerbies .. the best option to me would be to somehow make 3rd gear good enough for about 125mph at 7500rpm .. easiest route would be a change of diff ratio to something slightly higher, or chop the rear arches away to give the option of runing larger diamteter tyres for drag days.
i think you'll always struggle to get your run finished in 3rd gear, with 420bhp you're always going to have one of the fastest terminals of all the cerbies .. the best option to me would be to somehow make 3rd gear good enough for about 125mph at 7500rpm .. easiest route would be a change of diff ratio to something slightly higher, or chop the rear arches away to give the option of runing larger diamteter tyres for drag days.
BCA said:
Im 100% certain a TVR CR box would be extremely advantagous to a Cerbera 4.5 with remap/ 4.5RR - it has the kind of torque that the S6 lot can only dream of, so would be far better utilised than it is in a Sagaris (where most of them are atm!)
I would like to know what 3rd gear tops out at on the TVR CR box (which is a wide ratio in my mind, odd) Certainly 0-100 would be improved (it'll do it in second I think!) But as you have realised, 3rd gear to fourth is what does it.
I haev been told 7500rpm is fine and 8000rpm fine occaisionally (better with the "GT" crank) - we have the same problem as you except at 7200rpm our early air intake, without the supporting springs) crush and starve the engine of air (or atleast thats our best guess so far) We need Jules's (Cyclone) intake set up!
TVR CR box as fitted currently, would see comfortably over 120mph in 3rd. It will dispense with 100 in 2nd. A good launch with a 60+mph 1st gear takes a little practice however.
trackcar said:
the best option to me would be to somehow make 3rd gear good enough for about 125mph at 7500rpm ...
This is why I want to know the top of third gear in a CR fitted car, as daftlad says - 2nd is good for just over 100, so third on a Cerb must be 120+ surely? (revving to the same peaks as before of 8000rpm?
Surely it cant be 1st = 65, 2nd 105, 3rd 115/120 again???
purpleheadedcerb said:
Most CR boxes have a tall first and the rest tightly bunched together. Sometimes the 4th and 5th gear will reduce the theoretical top speed. I can't understand why they would be spaced further apart than the standard ratios.
Close Ratios generally do have just that, closer ratios... The TVR close ratio box is infact a bo from what I can see. Presumeably this is to make better use of TVR's torque.
Toady1 said:
im a bit confused as to what you guys are saying??? usually a CR box will offer better acceleration but sacrifice the top speed, so if the std 2nd gear will do 60 then the cr 2nd gear will only do 50-55ish obviously depending on the actual number of teeth on the cog...
But the TVR one is the reverse, its a wide ratio gearbox, allowing 1st gear to top 60 and 2nd to top 100... not sure why they call it a close ratio one, but I understand why it works nicely with higher torque TVR's. A gear change takes a reasonable amount of time and in something as accelerative/ torquey as a modern TVR, its better to leave it accelerating in a wider gear and reduce the number of changes to 100mph.
I bet first and second get alot of wear on those boxes.
I understand the theory. It seems to me that the only reason you would make such an item would be to increase the 0-60/0-100 dash times. I know that the engines are torquey but I would still rather be making use of the 4000rpm and above band and staying in that. Does anyone know the gear ratios/diff ratio so that we can work it out?
I understand the theory. It seems to me that the only reason you would make such an item would be to increase the 0-60/0-100 dash times. I know that the engines are torquey but I would still rather be making use of the 4000rpm and above band and staying in that. Does anyone know the gear ratios/diff ratio so that we can work it out?
Gearing is one thing, the final ratio at the rear end is the other problem.
There are a good few drag-racing sites and online calculators which can help select the right ratios,
you will find it quite cheap to replace the T5 gears, your only problem is then fuel economy for road use. Once you start messing with the gearing simply for better 1/4 mile times then you're walking into another game. You need to draw the line somewhere, I'd say, get the traction sorted (try your best on a nice dry track) and you'll get there quicker and the right clutching and changing up would only sacrifice around .3 on your time at the 3rd to 4th change (in theory)....
another reason why those yanks rule the strip, its all 3 speed trannies with huge arse converters, but in a land where a gallon costs around a UK litre, no sweat...
Put it this way, the current world record fastest viper owner did a 8.9 on the quarter using a stock 6 speed and rear end, all on IRS, the only changes were the driveshafts which were custom built by the infamous Mark Williams to compensate for the fat stickies... the car was completely stock (all interior was there etc) bar the 1400bhp twin-turbo setup, so that was around 1700kg all the way...
Now, doing the maths, say a 1200kg cerbie with the right traction (stickies will work wanders, but I dont think the baby T5 and btr diff and shafts would hack it) and around 450bhp to boot, with 3 gear changes (not counting the first as that is ridden from the roll anyway), I calculate a 11.8 second pass, thats WITH everything done with perfection.... in the real world, traction problems, gear timing, I'd say 1 second to 1.5secs of losses can occur, so a time around 12.5 would be more realistic on a good day, and anything from 13 to 14 on a poor day....
There are a good few drag-racing sites and online calculators which can help select the right ratios,
you will find it quite cheap to replace the T5 gears, your only problem is then fuel economy for road use. Once you start messing with the gearing simply for better 1/4 mile times then you're walking into another game. You need to draw the line somewhere, I'd say, get the traction sorted (try your best on a nice dry track) and you'll get there quicker and the right clutching and changing up would only sacrifice around .3 on your time at the 3rd to 4th change (in theory)....
another reason why those yanks rule the strip, its all 3 speed trannies with huge arse converters, but in a land where a gallon costs around a UK litre, no sweat...
Put it this way, the current world record fastest viper owner did a 8.9 on the quarter using a stock 6 speed and rear end, all on IRS, the only changes were the driveshafts which were custom built by the infamous Mark Williams to compensate for the fat stickies... the car was completely stock (all interior was there etc) bar the 1400bhp twin-turbo setup, so that was around 1700kg all the way...
Now, doing the maths, say a 1200kg cerbie with the right traction (stickies will work wanders, but I dont think the baby T5 and btr diff and shafts would hack it) and around 450bhp to boot, with 3 gear changes (not counting the first as that is ridden from the roll anyway), I calculate a 11.8 second pass, thats WITH everything done with perfection.... in the real world, traction problems, gear timing, I'd say 1 second to 1.5secs of losses can occur, so a time around 12.5 would be more realistic on a good day, and anything from 13 to 14 on a poor day....
Nickccc said:
What is the maximum safe RPM, to push the Cerb to?
...................
Nick.
>> Edited by Nickccc on Monday 30th January 00:19
I talked to someone in AJP8 race engine prep at the factory a couple or three years ago re possibility of upping the revs. I had a good long chat and the guy was open and honest - unfortunately I didn't keep his name. I was told that there is a reciprocating balance problem that the factory couldn't fix (bottom-end design problem)that means 7,500 is the absolute maximum safe revs, and they often set rev limit to 7,250 to prevent rods popping out the crankcase if a particular engine was a bit rougher (good'ole TVR production tolerances
), something that happened 'quite a lot' in the early days before they figured out what was going on. Morning,
Ok thanks for the replies; I will not be messing around with anything just yet.
Once the better whether shows up I will try some ¼ mileing then.
If I can get the traction and get the power down in 2nd and 3rd then I will surely beat 13 seconds.
Maybe will get one of those V Boxes, and have a bit of practice elsewhere.
Regards the max revs, my crank is almost certainly steel so should be ok for 7500ish, just not to often.
This raises another question, how accurate is the rev counter?
I will plug the laptop up get it up to 5000 and then check the trace.
The ECU works from a trigger wheel so should be accurate than the dial, not that the rev counter may be reading this pulse also, bet it’s not accurate.
Nick.
Ok thanks for the replies; I will not be messing around with anything just yet.
Once the better whether shows up I will try some ¼ mileing then.
If I can get the traction and get the power down in 2nd and 3rd then I will surely beat 13 seconds.
Maybe will get one of those V Boxes, and have a bit of practice elsewhere.
Regards the max revs, my crank is almost certainly steel so should be ok for 7500ish, just not to often.
This raises another question, how accurate is the rev counter?
I will plug the laptop up get it up to 5000 and then check the trace.
The ECU works from a trigger wheel so should be accurate than the dial, not that the rev counter may be reading this pulse also, bet it’s not accurate.
Nick.
Forgive my ignorance here but do any of the engines (red rose or otherwise) have freudenberg dampers fitted to them? I know that with harmonic balancing they shouldn't really be needed but I know of people who still use them on engines I'm more familiar with due to a particular 'inbalance' at certain revs that tends to result in rods being thrown out the side of the block!
As far as the revs are concerned, its simple. NO!
The reason being is the stroke is too long as it is and the total piston/rod mass is too great, going titanium on rods would help yup, but there is one problem that always gets in the way of a flat-crank engine =
SECOND ORDER VIBRATION!
Now, as far as first order is concerned, this not a that much of a problem, normally on crossover-crank engines, the counterweights are oversized to compensate/correct inbalance issues, or a mechanical/fluid damper, balancer shaft is used. But with a flat-crank, the second bank cancels out the first bank in simple lamers terms (although a little more complex than that).
Now in a flat-crank engine, on EVERY full 2 turns of the crank, a vibration is produced, this vibration is known as "second order", these unwanted vibrations/harmonics are extremely hard to contain, whence F1's/Ferrari's run very small strokes and normally compensate by running an increased bore size but also keep the rotating mass down by employing the use of exotic material such as G1 titanium.
The cerbera engine, at 7200 starts exponentially producing second-order vibrations, once you get to the 7800 mark, you are running the risk of all kinds of mechanical fun/disasters, from bearing wear n tear/piston-slapping to liners wearing quicker, bores deforming, ring seal worsening, bent valves, snapped crank, rods snapping etc etc.... in general, as far as the dynamics of the AJP are concerned, you should stop at 7000, its not worth running higher as the risks far outweigh the gains.
Lol, you can only imagine what my engine will be going through with a 6 litre stroke!!!!
Oh and also, just because you have a billet crank, doesnt mean you are automatically invunerable, if you've seen the quality of a AJPV8 TVR billet crank up close you'll know what I mean.
Also, the pistons are shite, the rods are sorry excuses and the liners are just plain ordinary used condomns, oh and also dont forget, the outercap is a 2 bolt main! ferkin pathetic! I wont go on, because its feckin depressing, but keep to 7000 and a good eye on your oil level+pressure and your engines will run rings around any ferrari, literally
The reason being is the stroke is too long as it is and the total piston/rod mass is too great, going titanium on rods would help yup, but there is one problem that always gets in the way of a flat-crank engine =
SECOND ORDER VIBRATION!
Now, as far as first order is concerned, this not a that much of a problem, normally on crossover-crank engines, the counterweights are oversized to compensate/correct inbalance issues, or a mechanical/fluid damper, balancer shaft is used. But with a flat-crank, the second bank cancels out the first bank in simple lamers terms (although a little more complex than that).
Now in a flat-crank engine, on EVERY full 2 turns of the crank, a vibration is produced, this vibration is known as "second order", these unwanted vibrations/harmonics are extremely hard to contain, whence F1's/Ferrari's run very small strokes and normally compensate by running an increased bore size but also keep the rotating mass down by employing the use of exotic material such as G1 titanium.
The cerbera engine, at 7200 starts exponentially producing second-order vibrations, once you get to the 7800 mark, you are running the risk of all kinds of mechanical fun/disasters, from bearing wear n tear/piston-slapping to liners wearing quicker, bores deforming, ring seal worsening, bent valves, snapped crank, rods snapping etc etc.... in general, as far as the dynamics of the AJP are concerned, you should stop at 7000, its not worth running higher as the risks far outweigh the gains.
Lol, you can only imagine what my engine will be going through with a 6 litre stroke!!!!
Oh and also, just because you have a billet crank, doesnt mean you are automatically invunerable, if you've seen the quality of a AJPV8 TVR billet crank up close you'll know what I mean.
Also, the pistons are shite, the rods are sorry excuses and the liners are just plain ordinary used condomns, oh and also dont forget, the outercap is a 2 bolt main! ferkin pathetic! I wont go on, because its feckin depressing, but keep to 7000 and a good eye on your oil level+pressure and your engines will run rings around any ferrari, literally
SXS said:
another reason why those yanks rule the strip, its all 3 speed trannies with huge arse converters, but in a land where a gallon costs around a UK litre, no sweat...
actually, the more powerful the engine, the smaller the converter... the bigger cam, larger intage ports and carbs tend to move the peak torque towards the higher revs. the smaller the converter, the higher the 'stall speed'. basic idea is to have the stall speed of the converter very close to the peak torque rpm, helps in getting a nice sick launch
and once that starts happening, they move to 2 speed chevy powerglide trannies as they have a planetary setup that can handle it all the power
methodwares said:
another reason why those yanks rule the strip, its all 3 speed trannies with huge arse converters, but in a land where a gallon costs around a UK litre, no sweat...
actually, the more powerful the engine, the smaller the converter... the bigger cam, larger intage ports and carbs tend to move the peak torque towards the higher revs. the smaller the converter, the higher the 'stall speed'. basic idea is to have the stall speed of the converter very close to the peak torque rpm, helps in getting a nice sick launch
and once that starts happening, they move to 2 speed chevy powerglide trannies as they have a planetary setup that can handle it all the power
That goes without saying bud, I was comparing like for like, dual purpose road/strip users like the auto TH350/400 and C4/C6 muscle runners.... (which is why I mentioned the fuel pun!)
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