SB

iTrader: (1)

I'm seeing a trend.

250ekelley is only using a 220/224 at .050" with 112LSA cam. Also Dual plane intake too,which cuts reversion tendencies .

Budman,on his BBC was fighting reversion issues too. Mild camshaft.

Common denominator - Lightning headers.

What the hell ?

SB

iTrader: (1)

What is the ID of the inner pipe on these stock Lightnings and what length ? I'm trying to get the "collector" length and ID.

And then add the length of the rest of the exhaust for a total length from beginning of collector to end of tailpipe. What is this length ?

corey331

Yeah, if I had it to do over again, I'm not 100% sure I would go with Lightning. The inner pipe is 3.5" O.D. 16 gauge stainless. I can get you a length later tonight when I get out to the shop.

SB

iTrader: (1)

Thanks ! If you have an angle finder , could you get rate of fall too ?

250ekelly

Yea there massive. I was thinking maybe the normal rules of reversion couldn't be applied to these engines because the heads flow so much better. Especially with these headers. It flows so good it could suck backwards better/eaiser. Just a thought. When I put the flappers on the inside of my tips that did help allot.

SB

iTrader: (1)

You are correct in that the better an exhaust port flows out, usually means they flow better in too.

As far as exhaust system sizing, collector length and diameter has a very big influence too. Just like most talk about cylinder head intake port sizing with velocity, same happens with exhaust 'sizing.'

SB

iTrader: (1)

Some more rambling.

During overlap, the piston ATDC going down has two sources for air, intake and exhaust.

On the intake side, you have throttle blades that are very close to being closed.

On the exhaust side, you have a 1.50-1.60" exhaust valve (sbc) as the only 'door.' The further this is opn and along with how good the port flows at this opening lift can be a lot easier for air to come in vs the throttle blades at the mostly closed position.

If the exhaust doesn't have enough momentum (and velocity) going towards the atmosphere, it can and will be easier for it to go back towards the exhaust valve and into the combustion chamber.

This is also why your exhaust flaps helped. Ie cutting off the air source on the exhaust side to run towards the combustion chamber. If the flapper sealed better and moved faster, it would help even more.

ezstriper

you also have to remember different engine will scavange the exhaust differently, with the LS stuff just coming on board little is known I'm thinking about how they act, them with your custom setup, you are the test mule.

SB

iTrader: (1)

^^^This is true^^^

As far as the OEM's using these motors, remember pretty much all of them use catalytic converters which I'm sure dampen exhaust pulses.

250ekelly

What if the exhaust is kind of acting like a expansion chamber on a two stroke exhaust. The primarys are big going into a big collector. Then getting reduced to about 3.5 inches I think. I can't remember it's been awhile since I put them in but I know it's smaller than 4 inches. The collector being so big going to 3.5 could be making a slight reverse wave. Even tho the water Is mixed in after the collector maybe there is slight pressure drop during the back pulse that bring a tiny bit of water into the collector.

I do know I only get water into a few ports. 5. 7. 4. 8. I think. So primary tube length is a factor