dirtbox Posted November 9, 2008 Share Posted November 9, 2008 Hi there! I'm after some helpful advice regarding exhausts. I had a nightmare last friday trying to fix a leaky manifold/down pipe joint and whilst i was attempting the fix, i noticed how bad the rest of my exhaust was. Rather than spend £500 plus on a nice sporty stainless job, i thought i'd make a stainless sporty exhaust (from another project) fit. I'm running a 3.5 V8 on carbs (and gas), and in the future my plan was to fit a big Diesel conversion in place. The stainless pipe i had laying about was from a 110 and that was also where the exhaust originated from. As the exhaust would have eventually gone on anyway, i thought i'd see what it sounded like on the V8. The result was a testosterone boiling burble with a real mean roar when revved!!! Nice! Anyway, i have had my worries about possible problems this may cause. Can this cause any possible damage i.e. pinking due to the extra amount of air passing through the system or do i need to change my ignition timing etc to accommodate for the change? Exhausts seem to be a science all on their own and it would be great i someone could give the basics about them, like why you need back pressure etc. I have had a look through the search but cant really find much about how it all works. Many thanks in advance. Cheers, Paul Quote Link to comment Share on other sites More sharing options...
dirtbox Posted November 9, 2008 Author Share Posted November 9, 2008 OK. Sorry, didn't really ask a very clear question before! (Pretty hung over this morning!) What i need to know is- Should i need to adjust mixture now i have a larger bore exhaust? (Still got original cast manifolds and y pipe.) Does not running a rear silencer loose horses/torque? Why do you want some back pressure? I'm sure there was loads more i wanted to know. Been reading up a bit more about it but still not sure! Any helpful advice/tips would be greatly appreciated! Paul Quote Link to comment Share on other sites More sharing options...
Les Henson Posted November 10, 2008 Share Posted November 10, 2008 You need back pressure in order to prevent valve bounce at higher revs - usually having one silencer is enough. You can make your own exhaust (providing you can fabricate one of course). Bends need to be smooth and shallow. If you want a bigger improvement, then replacing the manifolds is needed. Les. Quote Link to comment Share on other sites More sharing options...
oakesy Posted November 10, 2008 Share Posted November 10, 2008 What is it with these v8 manifold. Like Dirtbox I am having trouble with the downpipe connection to the manifold passenger side. I have had the downpipe welded to the y pipe and the little sod goes on the manifold. Brand new pipes, yet would they stay on. Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted November 10, 2008 Share Posted November 10, 2008 If you read up about exhausts you'll probably go crazy - technically yes you should re-tune the engine, however the reality is that it's a wonky old Land Rover lump and hence it really doesn't matter that much. It's not a Ferrari. Quote Link to comment Share on other sites More sharing options...
Hybrid_From_Hell Posted November 10, 2008 Share Posted November 10, 2008 Should i need to adjust mixture now i have a larger bore exhaust? (Still got original cast manifolds and y pipe.) Doubt it, yes it will change the mixture but carbs are so far off being spot on anyway there is a big safety factor of mixture, so I would be very suprised if you ran too weak, on the Megasquirted VE Map yes it change the fuelling and quite a lot but no BY much = if that makes sese Does not running a rear silencer loose horses/torque? Running a pipe with no silencer will, or as the chavs do a 5" zost on a 1" Corsa pipe sounds 2Wikid" actaully there is less power its about balance and having the right size bore and a bit of back pressure and a siklencer in there somewhere Why do you want some back pressure? Yes you do need some, complex but also as Les H says Been reading up a bit more about it but still not sure!Any helpful advice/tips would be greatly appreciated! See my custom Exhuast Build thread in the tech archive, lots on info on zorsts in that Nige Quote Link to comment Share on other sites More sharing options...
dirtbox Posted November 10, 2008 Author Share Posted November 10, 2008 Thanks for the replies everyone. Been playing around again today and think i have finally sealed the downpipe blow. You need back pressure in order to prevent valve bounce at higher revs - usually having one silencer is enough. This has hit the problem then. I had been worried what the rattle/tapping/tick was and it only happens really at higher revs and gets louder the higher they go. Is this something i should worry about? Have fabricated the zorst from the Mid box back. Only has the mid box but its quite big. I'm presuming I don't have quite enough back pressure with this set up. I read your post HBFH and it was very interesting - and Ashford is not too far away from me! Wish i could afford to treat myself with a beaut like that! Mine is 2 1/2" and flows smoothly but i could just see through the mid box when looking what was inside- hence possible lack of back pressure! Back to the drawing board for now if I'm going to cause damage! Thanks again! Paul Quote Link to comment Share on other sites More sharing options...
Landowner Posted November 10, 2008 Share Posted November 10, 2008 You need back pressure in order to prevent valve bounce at higher revs - Les. I would be very interested to know how back pressure stops valve bounce. I don't know much about modern engines so can't quite get my head round it Quote Link to comment Share on other sites More sharing options...
dirtbox Posted November 11, 2008 Author Share Posted November 11, 2008 Hi again. Just wanted to ask about the valve bounce idea as a fitter at work reckons this is very unlikely unless I'm over revving? I explained that i have advanced my ignition for my gas set up and he thinks it is probably detonation and that i should retard my ignition slightly to prevent this. I am only getting the suspect noise when under load and at med to high revs that is why i thought it probably wasn't pinking. To see if he is correct I am going to try to retard a degree or so to see if it makes any difference. I'm currently running at around 12 deg BTDC and will try 10 and see what happens. Will report back soon with the find! Thanks again! Paul Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted November 11, 2008 Share Posted November 11, 2008 I really doubt it's valve bounce, 1st check is has it got enough oil in it Quote Link to comment Share on other sites More sharing options...
Young bobtail Rhys Posted November 11, 2008 Share Posted November 11, 2008 I have janspeed manifolds, rimmer bros straight through stainless centre box, and a rear section of 2 1/4" stainless made by a14 exhausts. This systems flows very well. Very free revving, upto 5500rpm no problem, no bad noises, nothing. It is also pretty quite really, but does bark out a little when over 4000rpm. This whole system cost me just £185. A cheap system can be made by shopping around at second hand bits (although only my manifolds and y-piece was second hand) and look around at land rover shows and haggle with them. Very happy the way mine is now Quote Link to comment Share on other sites More sharing options...
dirtbox Posted November 11, 2008 Author Share Posted November 11, 2008 Did do that fridge freezer and at first I didn't! Topped up a while ago though and still not sorted! Don't suppose it could be the oil i am running? I have run it for well over a year with no problems and regular changes/ checks. Just been for a spin at 10 deg BTDC and doesn't really make any noticeable difference so will stay at that for now. Kinda out of ideas for now. If any good ideas to try pop in your heads I'd appreciate the info. Many thanks! Paul Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted November 12, 2008 Share Posted November 12, 2008 Don't suppose it could be the oil i am running? Could be (it'd help if you said what the oil was), then again could be lots of things. May be worth running some Forte engine flush through it at the next oil change. It's very difficult to diagnose strange noises over the internet. Quote Link to comment Share on other sites More sharing options...
dirtbox Posted November 12, 2008 Author Share Posted November 12, 2008 Could be (it'd help if you said what the oil was), then again could be lots of things. May be worth running some Forte engine flush through it at the next oil change. It's very difficult to diagnose strange noises over the internet. Its OMD 90 I'm running. Its an ex-military lump, and as I work with Royal Engineers/REME I'm aware that this is what many military engines are run on providing this is what they always have been used to. Might give the engine flush a go to ensure the oil is getting in all the right places! Been listening carefully to the noise (which i might add is slightly reduced today), and as hard as it is to diagnose a noise, its pretty hard to explain too! Thanks agin! Paul Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted November 12, 2008 Share Posted November 12, 2008 Googling OMD90 suggests it's really the wrong grade for a Rover V8: OMD90 can be a semi or fully synthetic, severe duty oil intended for use in Diesel engines. It has a 10W30 viscosity grade and must meet or exceed API grade SG/CF-4 or ACEA grade A3/B3. I'd run some Forte through, drain, and refill with Comma/Castrol or similar 20W50 or 15W40. Quote Link to comment Share on other sites More sharing options...
dirtbox Posted November 12, 2008 Author Share Posted November 12, 2008 Nice one, will do asap! Never thought about googling it! Oh well we live and learn eh! Quote Link to comment Share on other sites More sharing options...
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