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Port matching

Chewy1576

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Hey yall,

Thanks to @WarWagon, I have new heads ready to go on in place of my more than likely warped original heads. Mahle gaskets and ARP studs will accompany them. While I have it all blown apart (no pun intended), would it be worth taking some extra time and doing some port matching on the intake and exhaust? Can it be done with the valve installed, or should I not bother and just get them swapped out?
 

Will L.

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Take the time and port them. Practice a little on your old head. Port match aka gasket match doesn’t hurt, but also does not help much. Doing bowl work and unshrouding make the biggest difference.

Pop old valve from other head inplace for unshrouding is good trick to not do damage.

Just number new valve and matching locations since they are already seated to match.
 

Rockabillyrat

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I was planning a big port job on my build. With bigger valves and 1.6 rockers...But after TSP posted his flow chart the other week I've reconsidered. It looks like the GEP heads flow around 175cfm at max stock valve lift. So that times 8 is 1400cmf total flow. And with the 2hp per 1cfm rule the GEP heads should support 350ish hp without a turbo.

I then put the 6.5l through a turbo calculator to see what CFM the engine needs. At 4400 rpm @ 30psi with no intercooler it's close to 1000cfm. With an intercooler its just under 1400cmf. Obviously this is all ball parked because I couldn't change the VE in the calculator.

I remember reading a head porting article from engine builder magazine. One big name builder was quoted saying "pick the heads that flow the most with the smallest ports" and "The 3 keys to head work is port velocity, port velocity, and port velocity ". And that made me really rethink my build. The GEP heads will support the power levels I'm after. I might max them out in the upper RPM range. But with what I'm using the truck for I dont want to lower port velocity because that will take away low end torque and effect turbo spool up. With my truck being a daily driver 5 speed I really want that low end torque. So my plans are a simple gasket match and polish and call it done on head work.

I was always under the assumption on a turbo engine bigger is better, but that's not the case. The same rules that apply to a N/A engine apply to a turbo engine. It's kinda like muscle car guys back in the day. Everyone build engines with the biggest heads and carb they could buy. Then wonder why the car fell on its face off the line.... no port velocity.
 

Chewy1576

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I was thinking that I would gasket match the intake and exhaust sides and smooth maybe 3/4 to 1 inch in to each side and call it good. I may look at the turbo flange, turbo adapter, and exhaust housing too.
 

WarWagon

Well it hits on 7 of 8...
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What are you doing with this engine? DD, working it, towing?

How long did it take you to figure out I didn't use "The Right Stuff" to glue the heads to the pallet? :angelic: Asking for a friend ... who helped me load em up.
 

Chewy1576

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What are you doing with this engine? DD, working it, towing?

Any how long did it take you to figure out I didn't use "The Right Stuff" to glue the heads to the pallet? :angelic: Asking for a friend ... who helped me load em up.
It is a hauler and occasional driver. I have a 27' travel trailer and family it will haul around for camping trips and I like to take it to work here and there. It was this same trip a month and a half ago that took out the current heads. I had to take the father-in-laws 7.3L Powerstroke this weekend for a trip we had planned but I wish I had my truck here instead.

Haha about 5 seconds after looking at it and thinking they were bolted to the pallet. Exactly how I wouldn't have done it. I loosened the bolts and had to look them over, they look damn near new. Even tested the precups with a magnet, stainless diamond cups as expected. I can tell these were done right, and I thank you for that.
 

FellowTraveler

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I was planning a big port job on my build. With bigger valves and 1.6 rockers...But after TSP posted his flow chart the other week I've reconsidered. It looks like the GEP heads flow around 175cfm at max stock valve lift. So that times 8 is 1400cmf total flow. And with the 2hp per 1cfm rule the GEP heads should support 350ish hp without a turbo.

I then put the 6.5l through a turbo calculator to see what CFM the engine needs. At 4400 rpm @ 30psi with no intercooler it's close to 1000cfm. With an intercooler its just under 1400cmf. Obviously this is all ball parked because I couldn't change the VE in the calculator.

I remember reading a head porting article from engine builder magazine. One big name builder was quoted saying "pick the heads that flow the most with the smallest ports" and "The 3 keys to head work is port velocity, port velocity, and port velocity ". And that made me really rethink my build. The GEP heads will support the power levels I'm after. I might max them out in the upper RPM range. But with what I'm using the truck for I dont want to lower port velocity because that will take away low end torque and effect turbo spool up. With my truck being a daily driver 5 speed I really want that low end torque. So my plans are a simple gasket match and polish and call it done on head work.

I was always under the assumption on a turbo engine bigger is better, but that's not the case. The same rules that apply to a N/A engine apply to a turbo engine. It's kinda like muscle car guys back in the day. Everyone build engines with the biggest heads and carb they could buy. Then wonder why the car fell on its face off the line.... no port velocity.
Things do change turbocharged with low boost big dense air and rpm, but why risk it on a IDI when you can have it all with a Cummins?
 

Rockabillyrat

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An engine is just a big air pump. Air density will change but that's calculated into the turbo CFM calculator I used.

I have a VE pump 12v for my 46 I plan to build for towing. You cant go wrong with any Cummins. But the 6.5 is just fun because no one builds them. And EVERYONE Cummins swaps square body Chevys, so I went with a optimizer for my 78.
 

Chewy1576

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I broke the dreaded "Not returnable if seal is broken" tape on the gasket set box and put the new gaskets on the heads to see what kind of material removal I'm looking at if I go ahead with the gasket matching. The intake side really isn't that bad, if anything I may need to trim back some gasket material to get it out of the air path. I could probably remove 1/8"ish of material around the entire perimeter of every exhaust port to get them to match the gasket. I don't have the intake and exhaust manifolds off the engine yet to see what that side looks like, but at least I have an idea for the heads.
 

WarWagon

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Don't run exhaust manifold gaskets! These dirty engines spit enough soot to seal up the exhaust on their own. Otherwise you blow the damn things, loose turbo boost, and high EGT's don't help engine life. BTW: If the manifold bolts won't go in: replace the warped manifolds. (I learned the hard way and soot coated everything under the hood by not replacing a warped manifold.) Knock-offs are now cheap on fleabay.

You don't want to know how many manifolds I went through on the Cummins.
 

Chewy1576

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Don't run exhaust manifold gaskets! These dirty engines spit enough soot to seal up the exhaust on their own. Otherwise you blow the damn things, loose turbo boost, and high EGT's don't help engine life. BTW: If the manifold bolts won't go in: replace the warped manifolds. (I learned the hard way and soot coated everything under the hood by not replacing a warped manifold.) Knock-offs are now cheap on fleabay.

You don't want to know how many manifolds I went through on the Cummins.
I was thinking these don't use exhaust manifolds, it was more for a point of reference as I cant see how the ports line up between the heads and manifolds directly.
 

FellowTraveler

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An engine is just a big air pump. Air density will change but that's calculated into the turbo CFM calculator I used.

I have a VE pump 12v for my 46 I plan to build for towing. You cant go wrong with any Cummins. But the 6.5 is just fun because no one builds them. And EVERYONE Cummins swaps square body Chevys, so I went with a optimizer for my 78.
I had posted boost to cfm to rpm numbers here somewhere to evidence the cfm flow numbers climb and keep climbing the higher the rpms are this is why motors that scream in the upper rpms can make so much crazy power.

I found it: https://www.thetruckstop.us/forum/threads/rpm-to-ve-cfm-flow-through-the-6-5td.45002/
 
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FellowTraveler

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A side bar here: On the topic of gasser motors 1k psi water injection will eliminate all detonation up top where it is common to pull timing with 1k psi water injection you can advancing timing more resulting in massive gains in tq & hp...

I have not seen anyone dyno diesel fitted with 1k psi water injection but suspect it will help...
 

Husker6.5

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Vic Edelbrock (yeah, that Edelbrock) did extensive flow testing on intake manifold port matching on SBC's back in the late 1950's and early 1960's and came up with some interesting results concerning the "common wisdom" of gasket matching the ports. Essentially, other than for aesthetics and bragging rights, for about 90% of engines it doesn't make much difference if there's up to 1/10 to 1/8" of mismatch between the manifold to head to the overall flow. More than that, the extra turbulence caused by the obstruction does restrict flow. For the other 10% of engines, those seeing operation above about 5,000rpm and up, it made a big difference the faster the motor spun.

This of course was dealing strictly with port matching, using both stock GM manifolds/heads and Edelbrock-designed manifolds and GM heads. His determinations were the same as @Will L. stated above, bowl work and unshrouding the valves make much more difference for increasing flow than just port matching alone ever would.
 

Chewy1576

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Hmmm... Maybe I'll shy away from port matching then. In the interest of getting the thing done, it would just take more time if I went down this road.
 

Will L.

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I wouldn’t say dont do it, but take 2 days and work them over. Number and pop the valves out. Unshroud a little and open the bowl. The gasket match while your there. The 6.5 has worse fitment than sbc did, I learned on 18436572, camel back heads, ram horn exhaust mannies, etc. Also why I am so mad about the 6.2/6.5 waterpump being so insane. Gm could have used EXACTLY same as mouse or rat motor for that design and just a deeper timing cover with taller body. Pretty sure only engine I rebuilt more than 6.5 is sbc, bbc.
 

Husker6.5

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I learned my engine building skills as a tyke hanging out watching (and once tripping and sitting down in a pan full of freshly drained crankcase oil one night when I was five years old) my dad and the team build a 600+HP N/A motor for the Sprint Car from a '63 Vette 375/327 fuelie motor. I know dad did correspond with Vic Edelbrock himself concerning the amount of nitro needed to get the methanol to fire off without blowing the motor apart running 12.5:1CR TRW forged pistons turning 9500 rpm, as well as what pill to use in the Hilborn fuel injection system.

He had Iskenderian custom grind to his specs a solid lifter cam for that motor, too.
 
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