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Discussion Starter · #181 ·
An smaller pipe won't do that and it's not about pressure it's about exhaust scavenging and the sound. With them both separated completely with no x pipe it may end up sounding like two 3 cylinder engines running. Since the exhaust for each banls are completely separated. 2 inch piping will do just fine .
Well the old blow through a straw versus blowing through a toilet paper roll trick would disagree with pipe width equaling air pressure. But I get what you are saying.

Engine could be doomed however so I really need to focus on task at hand really last thing I need to worry about is how the exhaust will be ran that's my bad.

I envy you having a shop it appears to work on your stuff I'd be much further along in the process not having to inch worm below the car lol.
 

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I agree with rushking. You don't want back pressure. In fact it's a misnomer used by old hot rodders in the 40s and 50s that didn't understand fluid dynamics. (air acts like a fluid inside of a pipe) They just knew that a smaller pipe yielded better results in very specific low to mid RPM applications but couldn't explain why that was the case. What you want is exhaust velocity to help with scavenging where they meet at the collectors, merge and X pipes in the exhaust system.

Will the dual exhaust work? Sure it will. Is it the most efficient? Probably not. That depends entirely on the number of cylinders, the firing order, and how evenly the ignition events are per bank.

If you do opt for the dual exhaust you really want the X pipe because it helps a great deal when you have less than 4 cylinders on a single side of the exhaust. Our firing order is 1-2-3-4-5-6 with bank1 having 1-3-5 and bank2 having 2-4-6. This means you have one cylinder firing exactly every 120 degrees of crank rotation then if you divide the block by it's two banks for a true dual exhaust, you have an even spread of a cylinder firing exactly 240 degrees of crank rotation per bank. That's a big spread between ignition events on one bank which reduces the effectiveness of scavenging on a true dual exhaust. At least on a 4 cylinder (or a single bank of a V8) you have one ignition event every 180 degrees of crank rotation that is far better for scavenging than a single bank of 3 cylinders.

Our firing order, separation of banks and even spread of ignition events is also great because if we wanted to run a twin scroll turbo on the 2.7L it would work perfectly. We could separate bank1 and bank2 leading into the two halves of the twin scroll turbo without an overly complex header setup.

The 2.7L Delta sweet spot for primary tube sizing is between 1.63" and 1.75". The smaller 1.5" primaries of the ebay Chinese headers seem to work really good on a N/A car but falls on it's face up above 7000RPM because it's too restrictive. The rest of the catback after both banks merge together seems to range between 2.125" and 2.5" depending on the manufacturer. Larger isn't always better, but once you are past 18" after the last merge/collector it doesn't matter as much how big it becomes. However, if you have an X pipe on your dual exhaust, you need to maintain the same pipe diameter from the last merge/collector all the way through the X pipe and at least 18" after the X pipe.
 

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That's not good.....
 

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If it were me, I would look at the crank mains. Then decide if I do mains and rod bearings, or just rods. Likely no piston or rod issues.
But, it's your car.
 

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I would get all new bearings new main and rod bearings replace them.all since metal got in the motor and oil passages . Also when you take the rod baps off pay attention to how they come off the have to face the same direction they cam out.
 

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Discussion Starter · #193 ·
I would get all new bearings new main and rod bearings replace them.all since metal got in the motor and oil passages . Also when you take the rod baps off pay attention to how they come off the have to face the same direction they cam out.
Right, and just spin crank by pulley to gain access to each one. Very awesome if it works however I will post a pic of the journals see if you guys think it's toast or nah.
 

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Discussion Starter · #194 ·
Amazing news as well. I ubered a guy that owns the motorcycle shop down the street and he let me know they fab custom exhausts and bore manifolds plus heads for cars as well.

So basically possibilities are endless just depends on cash at this point lol
 

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That's awesome you met someone randomly like that. Just remember, DO NOT let anyone port your heads if they don't have a flow bench. A lot can go wrong if they aren't checking the consistency of their port work with flow numbers. You will lose power if consistency across all cylinders isn't there or if they destroy the port velocity by cutting too far into the short radius.

Here is an archaic flow bench diagram of a DIYer that is more than sufficient for flow testing:

Microphone Laptop Personal computer Computer Gas


This is what NGM flowed one of his first sets of heads at. Highlighted in yellow are the OEM flow numbers at a given lift then green were the final numbers. Just remember that the OEM cams only have .315" lift and most regrinds only have .350" lift so take that into account and ignore anything .375" and higher. NGM supposedly had some custom .400" + lift cams made for one of his motors because the heads were still flowing that high up there.

Rectangle Font Parallel Software Number


I went down a rabbit hole several years ago in my research and found a Finnish car that had a whole lot of custom work done to it in the very early days. This guy "Coupetuner" had custom regrinds and ported heads done by a local speed shop with great results. The wording on this is really weird because it was translated from Finnish to English so words like "covers" means cylinder heads or "cam pecked polished" translates to a "cam regrind and polished" cam lobe etc. The term "300HP" is a weird measurement but it translates to about 210CFM according to an online calculator. I am assuming that's at his listed lift of .356" on the cam regrinds.

Font Screenshot Rectangle Parallel Number
 

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Discussion Starter · #196 ·
Been looking into the dimensions of the ngm manifolds as well. They were just short of 40mm I think for stage 3?

I think the heads are 49mm so really as long as from the upper to lower to heads there isn't a STEP DOWN the airflow would increase?
 

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NGM stage 3 ported OEM upper was around 39mm or possibly closer to 40 at around 39.5mm. I don't know but I did port my OEM upper to 39.5mm to mimic the stage 3 ported NGM manifolds.

The NGM stage 4 lowers were 40mm or just shy of it like 39.8mm. Then the lower to head port was gasket matched in the lower manifold. Be careful if you port the floor of the port because it can be deceiving and it's easy to accidentally port too much creating a ledge down into the head the wrong way.

The heads intake port is an oval shape so if it's 49mm wide, it's more like 32mm tall. The cross sectional area of that oval shape is equivalent to a 42mm circle. I proved this in my last couple of posts to my build thread using a CAD model. As long as the ports are the same size OR you have a small step out by .5mm or so, it won't decrease flow or generate major turbulence.
 
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Discussion Starter · #198 ·
Rockauto mass order:

-New rod bearings
-Main bearings
-Starter
-Alternator
-Lower oil pan+gasket+upper silicone
-Valve cover gaskets
-2x Rear hubs + bearings
-Ruthium ngk spark plugs
-Ngk 02 sensors
-Ngk spark plug wires
-Dayco serp belt no a/c
 

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My advice, for what its worth, at the very least, take your bottom end to a professional engine rebuilder. Having proper clearances is very important for longevity of the motor. Do not use cheap bearings. In fact, use the bearings that the builder wants to use. They may also be able to save the crank by polishing it, they may also need to line bore the rods or main bearing caps. Theres so many variables that go into doing that correctly... IF you dont want to spend your money twice. FYI I have an amazing rebuilder local to me if you cant find anybody you trust.
 

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Discussion Starter · #200 ·
If the journals look messed up I might have to. I haven't touched it as I'm waiting for the parts and want to replace as I go since like rushking said the bearings have specific ways they have to go and it's easier to keep track of that to do it as they are removed.

I will take the gamble if the journals are clean. None of the rock auto parts I bought are cheap. I'm even replacing parts that were not broken just do to them looking extremely worn.

I'm making this worthwhile. Worst case scenario the crank is still messed up and like you said I'll need a pro on it. But at least if the car Does hold up I won't have a starter, alternator, or other failures weeks after.

The wheel bearings were already sounding rough so those need to be done.

I inquired on the cams. Crower does the regrind for the cams for 600 bucks.
 
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