Exhaust Dilema

kiwicar · Post by **kiwicar** » Wed Nov 25, 2009 11:15 am

If you copied that set up to get the 4 pipes under the car in the region of the bell housing, then join them with a y pipe and split them straight back out again you should have a pretty good set up, you will not have a "cross over " system by swapping the inner pair on each bank, or in fact any pair from one bank to the other.
For a cross over set up on a rover with the firing order of 18436572 you need to pair them 1&6, 8&5, 4&7,3&2 then pair the secondary from (1&6) to the secondary of (4&7) and like wise for 8&5 and 3&2 as you can see that is why they are difficult to do on a front engine set up

You could always try swapping the inner pair on etther side to the other side and joining and splitting the two pairs in an x pipe before re joining them on either side and splitting them again, should sound interesting and if you posted pictures up it should confuse the hell out of someone!

may work

, but I have no idea that it will do anything positive for the output.
Have fun
Mike

spend · Post by **spend** » Wed Nov 25, 2009 11:31 am

I think avoiding linking headers with 90deg firing separation is all you need to do. Just getting the pairings right to avoid traffic jams of exhaust gasses near to the head is the most significant factor IMHO.

topcatcustom · Post by **topcatcustom** » Wed Nov 25, 2009 2:12 pm

Ok- so assuming I cant cross over from each bank (and I doubt there is space to cross over any primaries on the l/h bank) would it be ok to pair 1&5, 3&7, 2&4, 6&8 ? I think thats the best I can do with my space available. Then they would go to 2 secondaries, then either a cross over and keep 4 small pipes or into a pair of 2 1/2" pipes to rear.

If I kept 4 pipes would I be able to get away with some nice bike cans or would they be too loud? Actually I could group them all together in the middle like Zonda or Murcialago style

kiwicar · Post by **kiwicar** » Wed Nov 25, 2009 2:32 pm

Hi Tom
pairing as you say is not a bad solution, it would be good to pair up either sida after though. This may sound counter intuitive but but it is thought best to 7 & 5 and 8 & 4 and 1 & 3 and 6 & 2 the exhaust system then join in the relevent secondaries on each side, the system then pulses as an almost even firing tripple but with one big cylinder and 2 little ones, this brings all the relevent harmonic resonences into play at 3/4 the revs they would come in otherwise so you get 33% more tuning peaks within the rev range. Realistically I wouldnt worry too much, concentrate on gettint it to fit and make the primaries and secondarys as big as you can get in, you are afterall supercharging this thing arnt you?
Mike

edit 1940 on 25th correction is bold and underlined[/b]

topcatcustom · Post by **topcatcustom** » Wed Nov 25, 2009 7:14 pm

Yep, its still preferable for as good exhaust tuning as poss though as the same principles apply- there is loads more gas to get rid with the blower! But thats in an ideal world. So you dont think it would be any benefit to pair 1&5, 3&7 instead of just neighbouring pairs (1&3, 5&7, 2&4, 6&8 easiest solution!) Its a bit of a bugger but I wont be crossing banks now though I may be able to fit a balance pipe, 1 1/2" maybe between sides.

Now the primaries (plan) is almost sorted, need to find mufflers! I think its pretty hard to make a V8 not sound nice- but TVR got it down to a T! Could I use cerbera or tuscan mufflers or is it a daft and expensive option? I want to finish the car as cheaply as possible now- and only spend the money I have to on important parts- which now the engine build is done is basically good oil pressure and water temp gauges!!!

kiwicar · Post by **kiwicar** » Wed Nov 25, 2009 8:03 pm

Hi Tom
If you can find the room to do them as 7 & 5 and 8 & 4 and 1 & 3 and 6 & 2 then you should get the best results, the 8&4 and 6&2 side may be tricky to fit, but they can be quite short pipes (about 1/2 the length of 4 into 1 primarys, 14" to 16") then joining to a secondary pipe probably above the chassis rail (again 14 to 16" or 21 to 24" or even 28 to 32") you want the secondarys about the same length as, 3/2X or 2X the length of the primarys. Then you then only have to drop the two secondarys down below the level of the rail and back to where you can join then easily.
I would use 1.5 or 1 and 5/8" primarys and 1 and 3/4 or 2" secondarys (depends what you are going to run the rest of the system in, if you are running them all into a single pipe each side and then splitting them straight out then use the same size pipe as you run the system in, also if you do this you will need less silencing than if you don't join them. bike cans are often use a closed baffel, they are not straight through, you really want a straight through silencer. a 1.5" cross pipe is plenty and will help further with silencing, bit wou will need to join it in where the pairs on each side join (you could always run 4 or 6" of larger diamiter pipe where they join before you split them again or run 2 cross pipes, just after the split in say 1" pipe

kiwicar · Post by **kiwicar** » Wed Nov 25, 2009 8:10 pm

TVR cerberas sound so good because they are a flat plane crank and the bank angle is 60 degrees and use exhaust tuning the same as two four cylinder engines, the result is a very crisp sounding exhaust, you get the same effect off a full crossover set up.
Mike

topcatcustom · Post by **topcatcustom** » Wed Nov 25, 2009 8:51 pm

I thought the first cerberas used RV8's! Anyway tuscans etc all sound the nuts so no bad! Never realised TVR used single plane cranks too, what engines were they in as as mentioned, I thought they went from rover V8's to their own S6 lumps? I will soon have aquired some 1 5/8" headers to cut n shut, will try to get 2&6 4&8 paired but it may not be practical in which case I'll just get on and enjoy the final straight on the build

kiwicar · Post by **kiwicar** » Wed Nov 25, 2009 9:29 pm

Hi Tom
I am pretty sure the cerbera only had the TVR lump in them, they were based on the Judd racing engine but with 2 valve single over head cam heads, the rest of the TVRs were rover based twin plane crank engines.
Mike

topcatcustom · Post by **topcatcustom** » Sun Nov 29, 2009 8:57 pm

Just had another read and still trying to work out why it is best to put 5&7 together and 8&4, if they were seperated you would get 180deg seperation (ish)- with them firing consecutively does it have the effect of increasing velocity and help draw more gas out or is it a completely different reason?! Sorry I must be giving you a headache now Mike!

Secondly, I have taken the engine back out to finish some work in the bay, I think I have made some more room so should be able to get either a single 2 1/2" pipe through beside the bell housing or 2 smaller secondaries (on each side of course). So 3 more small questions!
1. If I can fit it, would I be better using a 4-1 system or 4-2-1?
2. Not that I have much choice but how much difference does it make having short primaries of about 10"?
3. How close should the crossover be to the engine? The best place for it to fit is right behing the gearbox...

kiwicar · Post by **kiwicar** » Mon Nov 30, 2009 10:55 am

Hi Tom
Joining 5&7 and 8&4 makes the exhaust behave as if it is two banks of even(ish) fire 3 cylinder engines (with 1 big cylinder) which is resonating at 3/4 engine revs, you are not using the fundimental frequancy to tune the system but the 3rd harmonic, 4th harmonic, and if you run this type of system the 5th harmonic (on a flatplane or cross over system this would be too high in the rev range to use, but as it looks to the axhaust as if it is running at 3/4 revs it is usable).

1/ 421 system makes more resonent combuinations available to the engine, however each one has about 2/3 the effect of a 4into1 set up, 421 set up tends to flow better and scavenge more at low revs, 4 into 1 system tends to flow better at high revs. probably best to see what fits!
2/ shortening the primarys to 10" will probably shift any scavenging to very high revs and beyond where it is of benifit to the engine, but it depends a bit on the secondarys and the collector (use a 20" secondary may gain somthing back) this I can't tell from the theory I've read up on as it isn't normally done.
3/ as close to the engine as you can get it.
personally I would be inclined to fit in the biggest bore primary and secondary pipes you can fit, make the primarys as long as you can fit in and join them in as described above if you can but don't worry about it otherwise, do a 421 if it makes fitting easier but a 4:1 if that is easier.
Best regards
Mike

topcatcustom · Post by **topcatcustom** » Mon Nov 30, 2009 12:06 pm

Cheers Mike, not looking great from a performance exhaust point of view then! But I'm still going to be able to get 1 5/8" primaries in which isn't so bad, main system will be 2 1/2" all the way from front to back, if I manage to get a 4-2-1 system in what diameter secondaries am I best with?

I'm cutting the spot welded seam off all along the inside of the inner wings to chassis rails join and going to seam weld it instead- this will give me a good 15mm extra room to get the things in and out! Have also plasma cut a lump out of the front subframe beside the starter motor- will plate it back up but concave instead of convex to allow room for the pipes to pass through the transmission tunnel so I can use the X pipe instead of having 2 single pipes along the sills.

kiwicar · Post by **kiwicar** » Mon Nov 30, 2009 1:51 pm

Hi tom
from my posting of 25th, 2" if you can get it to fit (especially with the pairs at 90 degree firing) or 1 3/4 otherwise for the secondaries, I think if you are folowing up with 2.5" you will be ok with one pipe either side, especially if you can get the ballance pipe in, if you are still planning to run 4 pipes to the back of the car, split out after a collector then I would run 4 X 2" and make life easy for yourself. with the supercharger I would just worry about getting unrestricted flow through the manifolds and system.
Best regards
Mike

topcatcustom · Post by **topcatcustom** » Mon Nov 30, 2009 2:07 pm

Oops sorry I forgot about that! Well I have the X pipe and it has to be better to use it- will be neater under the car as well. So it will be 1 5/8" primaries, 2" secondaries and 2 1/2" twin pipes

Mufflers- would the DAYTONA BUDGET TURBO SILENCERs be ok? 1 on each side under the boot? They are on page S9/14 here http://www.realsteel.co.uk/section9.pdf second down in the exhaust section on the left. They aren't straight through so it should easily pass a sound test and be less likely for a pull- how many horses would they lose compared to straight through mufflers?

Ian Anderson · Post by **Ian Anderson** » Mon Nov 30, 2009 3:07 pm

The GT40 crowd have had reasonable success using the rear box from a Vauxhall Cavalier 2l

These are using 5l enginses and running 2 such silencers - reasonably short and reasonably quiet and reasonably priced!

Ian