Tubular MGRv8 exhausts versus block huggers. Worth it?

ppyvabw · Post by **ppyvabw** » Mon Feb 16, 2009 9:37 am

I am currently using the restrictive block huggers on my 3.5 MG Exhaust's dropped off this weekend though so whilst building a new exhaust I am considering replacing the manifolds with the much better ones that go through the wings.

This is in anticipation of the bigger engine I am about to start building, most likely now to be a 4.3 stroker conversion thanks to Kev's advice.

For 299 sheets, is it gonna be worth it? Don't want to choke the thing to death and now is the time to do it if at all.

What sort of gains can I expect. Are we talking an unnoticeable difference or will it yield significant gains, even on the current 3.5 which is likely to still be in there for the foreseeable future? It's a mildly worked over 3.5, and it's going into a 2.5 inch system at the end.

CastleMGBV8 · Post by **CastleMGBV8** » Mon Feb 16, 2009 11:12 am

Adam.

The RV8 style headers are a great improvement over the block huggers and said to gain 10-13 BHP on a 3.5.

It is even more important on a more seriously modified engine with a cam with more overlap where you need as much free flow in the exhaust as you can get.

Did you have a read of the article by Dan Jones I posted about a week ago, Cams in the Engine section.

The two bonuses with the RV8 headers are firstly the additional airflow through the engine bay through the holes in the inner wings, which considerably reduces under bonnet temps, and that the exhaust is much further away from the starter motor which reduces the possibility of the starter motor overheating and burning out.

Kevin.

ppyvabw · Post by **ppyvabw** » Mon Feb 16, 2009 11:38 am

The other alternative is to make my own. Just pricing up a few bends in 1.75" tube (bigger than the bought manifolds) and it comes to 200 sheets. Can make some nice stainless ones which will be great fun that pop out under the wings into a collector then run a mild steel system from under there to reduce costs. Carve the current flanges off, so that's another saving. Maybe open them out a bit.

I like welding stainless....

I have already had the starter motor problem

topcatcustom · Post by **topcatcustom** » Mon Feb 16, 2009 12:39 pm

I was going to use stainless for mine but I think I am going to use mild steel (price and easier to manipulate!) and ceramic coat them. Demon Tweeks do this stuff which looks excellent http://www.demon-tweeks.co.uk/products/ ... de=NIM1706

Also you can probably get prices down if you order half as many 180deg bends instead of 90's, then you can get the first bends closer to the engine as well.

p.s. I dont know what sort of power you are going for but 1 3/4 seems a bit big! I am going to use 1 5/8 and its a blown engine so the only concern I have is getting the gas out with no restriction- no interest in exhaust tuning like you N/A guys should have....

ppyvabw · Post by **ppyvabw** » Mon Feb 16, 2009 12:56 pm

Where are you getting tubing from? Jetex only do 1 3/4. Custom Chrome is a bloody site more expensive though.

CastleMGBV8 · Post by **CastleMGBV8** » Mon Feb 16, 2009 12:56 pm

Tom,

You do not want, especially with N/A the bend too close to the port as this cause back pressure and saps power, which is why the block huggers cost 10 - 13 BHP on a 3.5

With a supercharger with a restrictive cylinder head and poor exhaust system you need a high boost pressure to get effective cylinder filling, with decent head mods and free flowing exhaust you will get the same cylinder filling at a lower boost figure and with less heat which also costs power.

Kevin.

ppyvabw · Post by **ppyvabw** » Mon Feb 16, 2009 1:16 pm

just found another website.

1.5 inch tubing and doing what you suggested, getting 180 degree bends and cutting them in half for 90s, and some 90 bends for 45s. Will also have the ends of the bends for straights so will have plenty. That's a great idea Tom, cheers.

Got it down to 125 sheets now+whatever collectors are gonna cost

and that's with some 1.75 inch straight for after the collector. Need to find some collectors now. Making my own is deffo the way to go.

I'm only wanting 270 hp ish so maybe 1.5" is fine?

topcatcustom · Post by **topcatcustom** » Mon Feb 16, 2009 1:57 pm

CastleMGBV8 wrote:Tom,

You do not want, especially with N/A the bend too close to the port as this cause back pressure and saps power, which is why the block huggers cost 10 - 13 BHP on a 3.5

With a supercharger with a restrictive cylinder head and poor exhaust system you need a high boost pressure to get effective cylinder filling, with decent head mods and free flowing exhaust you will get the same cylinder filling at a lower boost figure and with less heat which also costs power.

Kevin.

Hi Kevin, I was looking at it with regards to the short straight bit you always get after a bend- I nearly get what you are saying in your 2nd paragraph- can you conclude it a bit more so I get it completely?! My heads should be a lot less restrictive than std, however I understand there is still a tight bend above the valve in every port so they will not be perfect...

TC

p.s. I have found that these guys seem to have most bits- was going to work out my order and haggle for a discount! http://stores.ebay.co.uk/Tube-Bending-Fabrications

ppyvabw · Post by **ppyvabw** » Mon Feb 16, 2009 2:12 pm

OOOOOooooo lovely, cheaper still!!!

sidecar · Post by **sidecar** » Mon Feb 16, 2009 2:16 pm

ppyvabw wrote:just found another website.

1.5 inch tubing and doing what you suggested, getting 180 degree bends and cutting them in half for 90s, and some 90 bends for 45s. Will also have the ends of the bends for straights so will have plenty. That's a great idea Tom, cheers.

Got it down to 125 sheets now+whatever collectors are gonna cost and that's with some 1.75 inch straight for after the collector. Need to find some collectors now. Making my own is deffo the way to go.

I'm only wanting 270 hp ish so maybe 1.5" is fine?

I built a set of headers in MS then had them camcoated, if I EVER get the sidepipes back from Powerspeed I could tell you if they're any good or not. My lump is a NA 4.6 stage III jobbie. The pipes are in 1.75"

(I did A LOT of head scratching before going for 1.75 rather than 1 5/8")

It's worth noting that the port does not come out of the head at 90 degrees to the flange, I whittled up a piece of wood that I pushed up the ports on my scrap engine to get an idea of the angle that is required.

A dremel with a proper tungsten carbide burr soon smooths out the flange to header join. (The swarf that come off it is nasty stuff, it floats about in the air then causes really horrible splinters when you lean on it)

I also made an anti reversion step at the top of each flange. Some people state that it should be at the bottom. It depends if you want top more top end or bottom end according to a book that I read.

You should also hammer the round tube into a square or rectangular section at the flange end, this helps the flow and gives you a bit more room to get the bolts or nuts for the studs in place.

You might not be able to form the right size rectangle in 1.75 so that it suits a standard exhaust port, the port is just too small! (you could cut a couple of triangle sections out on the long sides of the rectangle to reduce it's size a bit).

I warn you that making a set of headers must be one of the worst jobs ever devised by man!

Pete

CastleMGBV8 · Post by **CastleMGBV8** » Mon Feb 16, 2009 2:56 pm

Tom,

Just basic stuff, if you have a small pipe you will need more pressure to get a certain volume through it, which means a supercharger has to do more work and compress the gas at a higher pressure, which all generates more heat which expands the gas more which is to a certain extent self defeating, if that makes any sense. I f you then add extreme changes in direction it can only make matters worse.

I have never made a set of headers and have no intention of doing so. As Pete said they are a pain in the Ass.

The S/S RV8 exhaust I got from BHive was made beautifully with very high quality Tig welding, a young friend of mine who used to work for Pace Products welding stuff for F1 said it was about the best he'd seen, sadly I have heard of others who have recieved inferior quality ones.

Kevin.

ppyvabw · Post by **ppyvabw** » Mon Feb 16, 2009 4:24 pm

cant find 1 5/8 stainless tube and bends anywhere, not even on that ebay site, so it's gonna have to be 1 1/2 or 1 3/4

If I use my current flanges, I may enlarge them. What is the rule for doing this? Isn't there supposed to be some kind of step between the port and the flange or do I match it to the port/gasket?

kiwicar · Post by **kiwicar** » Mon Feb 16, 2009 5:07 pm

Try OJZ engineering http://www.ojzengineering.co.uk/
they do 1 5/8 stainless and were the cheepest I could find for any usefull quantity, also very good people to deal with, they also do all the collectors etc.
Mike

mgbv8 · Post by **mgbv8** » Mon Feb 16, 2009 9:10 pm

I just bought the RV8 style mani's from MGOC. Then cut the collector taper back so I could weld a S/S stub on at 2.5". Then I got some S/S pipe bent up for my outlets just behind the front wheels. Massive difference!!!
I use this setup on my 4.6 now. (now non road legal 1/4 mile MGB)

On my 3.5 I just disconnected all the exhaust system and the Y piece So I could run as close to open headers as I could. That made a big difference too.

The "off the shelf" RV8 mani's are a great improvement over the blockhuggers anyday.