Discussion
To be honest, I think there is a great deal of b******s talked about decatting. Had my 4.5 done about 6000 miles ago, and was already running sports pipes (from Peninsula). First off is an immediate noticeable power drop across the mid range revs (2000 to 5500). I'm surprised if you havent noticed it - 2 other owners I've talked to personally agree with me. This is caused by taking away nearly all the system back pressure - surely a good thing you might say? Well, not unless you want to spend your whole time up at way over 6000 rpm.The cam timing overlap on the AJP's is of pretty long duration and relies upon a degree of exhaust back pressure to stop the incoming mixture flowing out the exhaust valve on the overlap after it has helped to scavenge the exhaust gases. At low and medium revs a degree of back pressure is essential to keep as much mixture in the cylinder as possible whilst scavenging out the exhaust gases. At high revs however, back pressure usually becomes restrictive to the engines ultimate performance. In the case of the 4.5 Cerb, I found little noticeable improvement at the top end over 6500 rpm, certainly not enough to write home about, but the low and mid range performance, especially between 2500 and 5000 rpm to be seriously compromised - and lets face it, thats where we spend 95+% of our drive time. So, you pays your money, you takes your choice - if you want it to be loud, fine (although I think without cats it actually sounds terrible), but if you want it to go properly, leave them in.
As regards to the "so called" spitting of flames, mine never did, nor did the other two owners, so dont be swayed by thoughts of that either.
By the way, my cats are back in and the performance improvement was immediate!!!
Regards
John
As regards to the "so called" spitting of flames, mine never did, nor did the other two owners, so dont be swayed by thoughts of that either.
By the way, my cats are back in and the performance improvement was immediate!!!
Regards
John
Had my 4.5 two years and it had already had the cats removed and sports pipes fitted when I got it so I know no different. To me it sounds great and flames do come out of the exhaust pipes on over-run. It makes loud bangs which have sometimes been enough to set other car alarms off. I suppose that makes my car a menace, but its great fun!
However, I've got to get my MOT renewed next week and the garage say they are going to have to refit the cats to get it through the emissions. I have heard on a number of occasions that the performance is likely to improve with the back pressure being restored so I am very intrigued to see what the difference is like.
I expect the downside will be that the flames and bangs will be stopped. Hmmm, difficult choice perhaps....
However, I've got to get my MOT renewed next week and the garage say they are going to have to refit the cats to get it through the emissions. I have heard on a number of occasions that the performance is likely to improve with the back pressure being restored so I am very intrigued to see what the difference is like.
I expect the downside will be that the flames and bangs will be stopped. Hmmm, difficult choice perhaps....
intersting post john, and that's distinctly possible on your car, however you seem to be confusing the resons for torque changes on the cerbera.
the cats are relatively free flowing, they are not the primary reason for power loss in the exhaust system.
the cam runs a 106 degree lobe centreline angle and rapid valve acceleration, that means alot of lift on overlap and the possibilty for chamber scavenging HOWEVER ..
tvr have deiced to produce manifolds with port runner faces SMALLER than the exhaust port in the head, hence a step producing a neutral exhaust from the point of view of pulse reversion and scavenging.
there IS some momentum scavenging, but this is minimal and varies across the exhaust ports.
There IS some positive wave reflection back from the catalyst front face which can improve mid range torque, however back to back rolling road tests don't confirm this to any great degree .. you're talking less than 5% change on the best cars which CANNOT be felt seat of the pants style and can only be measured on accurate rolling roads.
In short, decatting does this:
It MAY reduce mid range torque, some cars being affected more than others, those with very bad mapping will be affected worse, since the change of airflow is small you would have to be running right on the edge of the mapping to be badly affected.
Decatting protects your catalysts for MOT time .. 100 pounds of cat pipes cheaper than 800 pounds of catalysts!
decatting and std back box sounds great, decatting and sports pipes sounds bad IMO.
Decatting has minimal effect on the performance of MOST cerberas since the cats are a minimal restriction and positive reflection point in the system.
Dcatting can release only tiny HP gains at the top end, not enough to be felt and can only just be measured on the rollers.
Hope that clears a few things up..
cheerz, joo
the cats are relatively free flowing, they are not the primary reason for power loss in the exhaust system.
the cam runs a 106 degree lobe centreline angle and rapid valve acceleration, that means alot of lift on overlap and the possibilty for chamber scavenging HOWEVER ..
tvr have deiced to produce manifolds with port runner faces SMALLER than the exhaust port in the head, hence a step producing a neutral exhaust from the point of view of pulse reversion and scavenging.
there IS some momentum scavenging, but this is minimal and varies across the exhaust ports.
There IS some positive wave reflection back from the catalyst front face which can improve mid range torque, however back to back rolling road tests don't confirm this to any great degree .. you're talking less than 5% change on the best cars which CANNOT be felt seat of the pants style and can only be measured on accurate rolling roads.
In short, decatting does this:
It MAY reduce mid range torque, some cars being affected more than others, those with very bad mapping will be affected worse, since the change of airflow is small you would have to be running right on the edge of the mapping to be badly affected.
Decatting protects your catalysts for MOT time .. 100 pounds of cat pipes cheaper than 800 pounds of catalysts!
decatting and std back box sounds great, decatting and sports pipes sounds bad IMO.
Decatting has minimal effect on the performance of MOST cerberas since the cats are a minimal restriction and positive reflection point in the system.
Dcatting can release only tiny HP gains at the top end, not enough to be felt and can only just be measured on the rollers.
Hope that clears a few things up..
cheerz, joo
Ive had a 4.2 for 3.5 yrs now. I also have had the cats removed and sports pipes fitted. As for the loss of power I must say I have never really noticed, I have a very early 96 car with the original clatter cams in, this might make a difference. Its very loud and does spit flames but only when driving Very hard and yes car alarms are set off on a regular basis. If your going to use the car every day then it may get a bit tireing however I love it. Have a go in one thats had it done and make up your own mind, dont be put off by one persons opinion.
Joolz,
Thanks for your, as ever, informative, reply. Its nice to get a proper engineering viewpoint. I agree with pretty much all you say (I even understand it being an ex Ford engineer myself, lol). I'm interested in your comments on mapping. If I am at the "ragged edge" of the map, is their anything that can be done to remap for my specific engines needs. By the way, every dealer that has had my car in have said its a real flyer of a 4.5 - one of the very best, so maybeit is very sensitive to chasnges.
Without doubt the power loss I encountered was significant and could easily be felt - that means it had to be in the 20 - 30 bhp range at least. The major area of loss I would say was in 2 rev bands - 1700-2200 rpm and 3400-3800 rpm. In addition, the throttle response was noticeably less crisp at all revs. Those rev bands may be significant. I have noticed that the 4.5 AJP sets up exhaust resonances in the car at well defined points - 1800, 3600, 5400 and on the limit at 7200, i.e at 1800 rpm multiples. There are also half wave effects causing minor resonances at the mid points, i.e. 2700, 4500 and 6300 rpm. Now I am presuming that some sort of shock wave is being set up due to the firing characteristics of the AJP. Are the power drops in those bands purely co-incidental? I would doubt it myself. I would appreciate any comments you may have to enlighten me. Hope you get to read this.
Regards
john
Thanks for your, as ever, informative, reply. Its nice to get a proper engineering viewpoint. I agree with pretty much all you say (I even understand it being an ex Ford engineer myself, lol). I'm interested in your comments on mapping. If I am at the "ragged edge" of the map, is their anything that can be done to remap for my specific engines needs. By the way, every dealer that has had my car in have said its a real flyer of a 4.5 - one of the very best, so maybeit is very sensitive to chasnges.
Without doubt the power loss I encountered was significant and could easily be felt - that means it had to be in the 20 - 30 bhp range at least. The major area of loss I would say was in 2 rev bands - 1700-2200 rpm and 3400-3800 rpm. In addition, the throttle response was noticeably less crisp at all revs. Those rev bands may be significant. I have noticed that the 4.5 AJP sets up exhaust resonances in the car at well defined points - 1800, 3600, 5400 and on the limit at 7200, i.e at 1800 rpm multiples. There are also half wave effects causing minor resonances at the mid points, i.e. 2700, 4500 and 6300 rpm. Now I am presuming that some sort of shock wave is being set up due to the firing characteristics of the AJP. Are the power drops in those bands purely co-incidental? I would doubt it myself. I would appreciate any comments you may have to enlighten me. Hope you get to read this.
Regards
john
Great post.
I had mine de-catted at the end of October 2003.
It certainly runs better but I think that is because of a blocked cat and the engine air and fuel intakes being reset.
Since de-cat it does seem to pop a little more (although it did pop a lot with the cats too) and it has a slightly deeper engine note (I have the standard exhaust).
Overall I would recommend it because cats cost about £400 each and as Joolz said straight through pipes are £100 a pair. Due to the nature of the TVR engine, e.g. popping on over-run, cats are not going to last that long, so you may as well save them.
The only downside being no cats = illegal and they need to be swapped in and out again come MOT time.
I had mine de-catted at the end of October 2003.
It certainly runs better but I think that is because of a blocked cat and the engine air and fuel intakes being reset.
Since de-cat it does seem to pop a little more (although it did pop a lot with the cats too) and it has a slightly deeper engine note (I have the standard exhaust).
Overall I would recommend it because cats cost about £400 each and as Joolz said straight through pipes are £100 a pair. Due to the nature of the TVR engine, e.g. popping on over-run, cats are not going to last that long, so you may as well save them.
The only downside being no cats = illegal and they need to be swapped in and out again come MOT time.
john .. interesting you should mention those rev points 18 / 36 / 5400 revs .. that's where the engine mapping is running weaker, inbetween there's ricj running that costs significant torque, so it's quite possible your car is right on the weak mixture limit and costs significant torque loss there also, but not enoughto compensate for the over rich mixture in between.
remapping sounds the only option to sort, but progress is a little slow on that, but will know from two independant sources after autosport show about the benefits of remapping ..
cheerz.
Joo
remapping sounds the only option to sort, but progress is a little slow on that, but will know from two independant sources after autosport show about the benefits of remapping ..
cheerz.
Joo
Must say, very intrigued about this re-mapping idea since reading that article about someone's TVR S that they had remapped in the South of England for (I think) about £575 - can't remember the name of the garage off the top of my head (sorry, bad memory!).
The results sounded quite spectacular, I seem to remember in that particular example the power increase was 20-25% after a few hours tinkering, and the general running was much better, I think the mixture was too lean. Perhaps if that could be achieved on other cars they might get closer to the quoted BHP?! I'd definitely have a go with the Cerb.
Anyone know if its being done yet?
The results sounded quite spectacular, I seem to remember in that particular example the power increase was 20-25% after a few hours tinkering, and the general running was much better, I think the mixture was too lean. Perhaps if that could be achieved on other cars they might get closer to the quoted BHP?! I'd definitely have a go with the Cerb.
Anyone know if its being done yet?
joospeed said:
remapping sounds the only option to sort, but progress is a little slow on that, but will know from two independant sources after autosport show about the benefits of remapping ..
Joo
Well, then, Joolz, any news?
The autosport show must have finished, as we watched a report on it on Motors TV last night...
Do those of us without the "top of the range" 4.5 or the "almost-equally-fast-in-the-real-world" SP6
have the ability to reduce overfuelling at random points on the map yet, for our Ford Escort soundalikes? Is an article appearing in Sprint? Tam Lin said:
[quote=joospeed]
Do those of us without the "top of the range" 4.5 or the "almost-equally-fast-in-the-real-world" SP6
lol Tam we are the poor relations
Did Santa bring you anything nice? D.
PS I noticed no change in performance when I decatted mine, it really does spit fire though, ask Bonce
Tatlow said:
Must say, very intrigued about this re-mapping idea since reading that article about someone's TVR S that they had remapped in the South of England for (I think) about £575 - can't remember the name of the garage off the top of my head (sorry, bad memory!).
The results sounded quite spectacular, I seem to remember in that particular example the power increase was 20-25% after a few hours tinkering, and the general running was much better, I think the mixture was too lean. Perhaps if that could be achieved on other cars they might get closer to the quoted BHP?! I'd definitely have a go with the Cerb.
Anyone know if its being done yet?
The person concerned was 'Podie' who used Austec near Gatwick IIRC. They did various remapping to his S3 and made what he described as significant improvements.
davidd said:
lol Tam we are the poor relations
Hi David
I do worry what will pull up next to the Cerb at the lights, with a mere 4.2 to pull us along.
Generally only get beaten if they have nice shiny blue lights, though
davidd said:
Did Santa bring you anything nice?
D.
Silly, I'm 38, and thus too old to believe in Santa. Sgirl says I can have Nitrons if I'm good for my birthday, so I'm being very good...
Re. PS: Spitting fire eh, that ties up with the colloquial Italian "Cerbera", meaning a fiery wench, or some such (can one still say wench on here?). Me I'm going the other way, quietening the thing down, ready for some gentle action on track days.
Gassing Station | Cerbera | Top of Page | What's New | My Stuff