Exhaust Header design and build for RV8

[rev-erend]

If I wanted to build a high flow exhaust manifold for the RV8 - what would be considered the best design.

My cam is a V8 dev 404 mechanical - so fairly hign lift / duration.

Is 4 into one best - this seems to be the method of choice for all TVR's .. or is 4-2-1 actually better for these 'high' torque engines.

What lenghts of primary and secondary (if 4-2-1) would be ideal ..

interested in the opinions of people who have dyno tuned these engines.

[jwb]

Use Google and search for David Vizard Exhaust and you will get a superb article that will expalin everything you need to know.

John

[topsparks]

On V8D's engine dyno my 5.5 put out 398 BHP,using Robs 4 into 2 into 1 but in the car the best I cold get using an ACT 4 into1 system was 370 BHP.My engine also had a 404m cam

[rev-erend]

JWB - Thanks..

James - thought that was the case .. did you get a picture of the engine on the dyno.

[topsparks]

I did ask Rob to take some pics but I think he forgot,did't get a print out either just the numbers.Rob did ring me to ask is anything was wrong with my tyres as he could't beleave how much the car was wheel spinning!,my car was the first TVR he had fitted a 5.5 to and I think he was impressed.

[stevieturbo]

Why didnt you dyno the engine with the exhaust you intended to use ?? or was it just an experiment ?

And are both power figures using the same equipment ?

[shpub]

The real question you should be asking is: What can I fit to the car in question as this will determine what options are available? With the wedge, the design is very much determined by the space available. The wedge manifolds are pretty good and to get much more would cost a lot more money. I have discussed this with John Eales on many occassions and it has always come back to the same conclusion. Yes it can be improved but not without chopping and cutting the body and chassis.

The Rover V8 engine is actually a strange beast in that it does seem to like a bit of back pressure. Removing it can actually reduce the engine power.

[knightly]

could a cross-over exhaust be used?.....with the un-even firing pattern of the cross-plane 90degree crankshaft in the rover - the exhaust pulses for each bank of cylinders will not be equal.....I'm looking at A.Graham Bells book at the mo, and for a cross-over system he is saying cylinders 1,4,6,7 should go into 4-1......then cylinders 2,3,5,8 should go 4-1......I dare say this is just how the original GT-40 pipes were done........but packaging might be a problem in a TVR :-(.......hence he is saying run a conventional V8 exhaust (4-1) but run a balance pipe between the two final diameters - close to the collectors......the balance pipe should be 1.5times the OD of the primary pipes.

From my personal experience of race exhausts, I would say dont fall into the "bigger is better" trap when sizing the primary OD - go too big and you will have no midrange drivability , and it will not pull out of corners, and you will be forever thrashing it - from experience I know 1-3/4" in 18 gauge wall thickness is quite OK on a 8500rpm 2.0 4cyl BTCC engine with between 270 to 280bhp .....therefore I would not go bigger than 1-3/4"

[rev-erend]

SH - fully agree.

Wedge engine bay is very tight for the headers - planning on making them myself out of stainless .. it's not the first set of headers I've made - so not too daunting.

Also - the heads will be off - so makes fabrication easier.

The available space does make a nonsence out of the 24 inch primary / 10 ~ 24 inch secondary idea's.. perhaps thats why TVR did a 4-2-1 with very short (6 inch) primarys..).

Been reading the Vizard stuff on V8 exhausts (interesting) and taken a look at the Burns Stainless site - real interesting stuff.

Knightly - think you are right about no having too large a diameter primary - I probably would be looking at 1 1/2 max for this or 1 3/4 if using stage 4 full race heads. Really depends on what I do with the heads. Also have an idea for the crossover - Burns use an xsection cross over - with a twin outlet system but the wedge has a single system - so will join the two manifolds as soon as possible - this should help the sonic scavaging effect that seens to work well on V8's.

Edited by rev-erend on Wednesday 1st November 09:28

[wheeljack888]

There was a thread a while ago where some mad swiss guy went mental with a pipe bender. Here's the link:

www.kaeserfahrzeugbau.ch/auspuffanlagen.htm

Looks great but I wonder if the primary lengths are a little too long (guessing ~1.2m)

With V8's there is always the other exhaust grouping at 270deg firing. On a RV8 it'll be 1+5 2+4 3+7 6+8 but as always package is the killer.

[GreenV8S]

The clever guys do put a cross-over balance pipe between the two banks, but it makes the packaging much much harder so unless you're rear engined it's probably not worth the bother.

[knightly]

on a 4cyl motor 1-1/2" OD primary is good for no more than 180bhp, so on a V8 I would say no more than 360bhp on 1-1/2" primary OD.....which sounds about right for your V8's.....more than that and it restricts power.......jumping straight to 1-3/4" (from 1-1/2"actually might be too much of a jump!......

the next size up would be 1-5/8".......the problem is 1-5/8" bends are as rare as rocking horse 5hite in the UK!!!!.....but commonly available in the US and Australia.......Google Magnum exhausts for the US and google castle autos for Australia........I imported some mandrel 1-5/8" U-bends from Australia, including shipping for 4 was about £60......just something to bare in mind.

using 18gauge wall (1.2mm) the tube ID's cross sectional areas (CSA)look like this:-

1-1/2"= 1000mm squared

1-5/8" = 1188mm squared

1-3/4" = 1388mm squeared

so the difference in CSA between 1-1/2" and 1-3/4" is actually 28%.....thats too much of a jump......the difference between 1-1/2" and 1-5/8" is 16% which is much more sensible

1-5/8" is good for no more than about 230bhp on a full race 1600cc 4-pot at 9000rpm.......after that you need 1-3/4".....so for your 400bhp V8's I would go for 1-5/8".....hope that all helps

[chrisj]

knightly said:

the next size up would be 1-5/8".......the problem is 1-5/8" bends are as rare as rocking horse 5hite in the UK!!!!.....but commonly available in the US and Australia.......Google Magnum exhausts for the US and google castle autos for Australia........I imported some mandrel 1-5/8" U-bends from Australia, including shipping for 4 was about £60......just something to bare in mind

I agree they're not common, but they are available.
I got two different CLR (centre line radius) 1-5/8" bends in stainless 304 from JP Exhausts in Macclesfield.
If I remember rightly they were something like £6 or £8 each, the higher price being for the tighter CLR.
www.jpexhausts.co.uk

[rev-erend]

knightly said:

on a 4cyl motor 1-1/2" OD primary is good for no more than 180bhp, so on a V8 I would say no more than 360bhp on 1-1/2" primary OD.....which sounds about right for your V8's.....more than that and it restricts power.......jumping straight to 1-3/4" (from 1-1/2"actually might be too much of a jump!......

the next size up would be 1-5/8".......the problem is 1-5/8" bends are as rare as rocking horse 5hite in the UK!!!!.....but commonly available in the US and Australia.......Google Magnum exhausts for the US and google castle autos for Australia........I imported some mandrel 1-5/8" U-bends from Australia, including shipping for 4 was about £60......just something to bare in mind.

using 18gauge wall (1.2mm) the tube ID's cross sectional areas (CSA)look like this:-

1-1/2"= 1000mm squared

1-5/8" = 1188mm squared

1-3/4" = 1388mm squeared

so the difference in CSA between 1-1/2" and 1-3/4" is actually 28%.....thats too much of a jump......the difference between 1-1/2" and 1-5/8" is 16% which is much more sensible

1-5/8" is good for no more than about 230bhp on a full race 1600cc 4-pot at 9000rpm.......after that you need 1-3/4".....so for your 400bhp V8's I would go for 1-5/8".....hope that all helps

Many Thanks for that - I think that will come in handy over the winter

[rev-erend]

chrisj said:

knightly said:

the next size up would be 1-5/8".......the problem is 1-5/8" bends are as rare as rocking horse 5hite in the UK!!!!.....but commonly available in the US and Australia.......Google Magnum exhausts for the US and google castle autos for Australia........I imported some mandrel 1-5/8" U-bends from Australia, including shipping for 4 was about £60......just something to bare in mind

I agree they're not common, but they are available.
I got two different CLR (centre line radius) 1-5/8" bends in stainless 304 from JP Exhausts in Macclesfield.
If I remember rightly they were something like £6 or £8 each, the higher price being for the tighter CLR.
www.jpexhausts.co.uk

That's interesting - I had no idea that JP would sell bends .. thought they just did complete exhausts

[v8 racing]

There have been some very good coments on this thread so here's my penny's worth as it is rover related, you need to remember when you are working out header size, the first thing you need to consider is bhp per litre you are aiming at and revs, the rover is very poor on both, if you have an engine that is making 80 bhp a litre you have a stonking engine, however this still only needs 1.5 inch headers, 60 bhp litre needs 1.25 inch headers, i know your probably all laughing but this is from all the dyno testing i have done, all you end up doing by putting big headers on is robbing in the region of 25 ftlb in the low to mid range to gain 5 bhp at peak bhp, the cam also plays a massive part in header design, if you are running a long duration cam it massively helps if you put a good step on the flange to head face to stop the reversal, this alone will gain you a good 10-15 ftlb of torque below 4000 rpm, 4-1 is definetly the way to go, 4-2-1 or try y's only gain in the 2000-3000 rpm range but lose out bigtime at peak bhp, the most critical part of the headers is the first few inches, try and keep this to the same angle as the port itself, the main reason the griff headers are crap is because you have a 90 deg bend virtually at the flange, and a change of angle from the port, but there is not a lot they could do about this due to space!, any bend you have is also a restriction and the gasses asume the pipe is smaller than it is, (david vizards words not mine!) so if your engine which most tuned rovers only require 1.5 inch headers make the bends 1.5/8 and straights 1.5 inch, just out of interest i have seen over 400 bhp on 1.5 inch headers, this was on a 5.5 ltr engine which still only equated to 75 bhp per litre, so on a 4 pot 2 litre this is still only 150 bhp and today that is crap!!

[rev-erend]

Rob

Many thanks for your comments - always nice to have actual results to back up theory.

Looks like the exhaust size is not such a restriction as the immediate bend just after the gases leave the ex. port.

When you say put a step in the flange - I would not imaging that
there would be much if any of the flange showing on the inside of the pipe - if that is what you are suggesting - do you just create this step with a head porting drinding stone..

I did make some AR stub stacks that fitted inside the headers for a 4 cyl exhaust once - but don't think I could be bothered again..

[shpub]

The bend after the port is close to a 90 degree in a Wedge because of space. One other point which is easily forgotten: access to the manifold bolts and designing it so it can be fitted without removing engine/body. Oh that's two points: access to the manif.... There is also a third called the starter motor clearance.

Once saw a wonderfully artistic manifold that looked wonderful on an engine stand but couldn't be fitted into the car. If bolted to the engine and the engine dropped in, it fouled the chassis... If fitted afterwards, couldn't do up the manifold bolts because it was impossible to get a spanner on them.

Edited by shpub on Thursday 2nd November 06:24

[knightly]

some more helpful rules of thumb for the bends:-

1) ALWAYS buy mandrel bent tubing - this is where they insert a piece inside the tube while bending to ensure no "knecking" occurs - otherwise it will kneck and reduce the cross sectional area by about 10% - not good!

2) when sizing a tight bend - do NOT go below two times the tube OD as a minimum centre line bend radius - in order to not restrict flow and power......so for a 1.5" OD pipe - do not go below 3.0" centre line bend radius....

[leorest]

jwb said:

Use Google and search for David Vizard Exhaust and you will get a superb article that will expalin everything you need to know.

John

I managed to get most of that article but I cant get page 5 did anyone else manage? If so can you email me it?

www.geocities.com/motorcity/track/6992/vizard.html?200630