2 sets of heads and once decision.

[BeepBeepRR]

I was looking into this Cam now Xe262H

That's not a bad thing. If you can find the published specs for the Comp 911-16 springs, you could compare them to your damper springs if you had a spring tester. They look like factory HP springs to me, but age and time may have rendered them useless.

The heads look to have been rebuilt.. I would hope the springs wouldnt be worn out.

 

[wyrmrider]

xe
expensive for a chevy downgrade cam
comp has no mopar cams under 275
do you know your compression yet
if not quit wasting time on cams
or
pick a rev range
pick a cam duration for that rev range with as much lift as reasonable
then get compression to match

 

[BeepBeepRR]

good info thanks...

 

[BeepBeepRR]

Ok I have sort of an update.. Pulled the head on one side today and I have .030 pistons. They appear to be flat top pistons. I dont have a bridge to check piston height but I used the pin side of my micrometer I know its not accurate but I believe they are between 5 and 10 thousands in the hole. That is a guess. The heads are the 516 heads an still have the smaller exhaust valves. And the engine had .039 head gaskets installed. According to what I have read the 516 heads are around 84cc I was using the compression calculator but had 2 items I was not sure of. The are listed below.

I found this info about the pistons on another site.
383 366NP E233K 59-71 Std.,20,
30,40,60 8.8-1 compression, Flat top no valve reliefs, ch=1.848" This says 8.8-1 Would CH=1.848 be my effective dome height? If so that is what I used in the calculator on the 9.26:1 calculation.

Here are the unknown things

Effective Dome Volume:
Use (-) for Dome and (+) for Dish.

And here is what I came up with when putting in the known information.

Compression Ratio : 9.26 : 1
Total Displacement (in.3) : 389.03
Total Displacement cc's : 6377.54

Bore: (diameter) 4.280
Stroke: 3.38
Cylinder Head Volume:84cc
Effective Dome Volume:?
Use (-) for Dome and (+) for Dish.?
Deck Clearance: Kind went in the middle with .006
Compressed Gasket Thickness:.039
Number of Cylinders:8
Compression Ratio : 9.26 : 1
Total Displacement (in.3) : 389.03
Total Displacement cc's : 6377.54

When changing the effective dome volume to 0 which I now know is correct for the flat top pistons.
I get
Compression Ratio : 9.42 : 1
Total Displacement (in.3) : 389.03
Total Displacement cc's : 6377.54

 

[BeepBeepRR]

Forgot to add the pictures.. Here is a piston down in the hole dont mind the gunk in there I knocked off a chunk of cork gasket and it fell into the cylinder.
The second picture is of how far they come up to the deck.

 

[qkcuda]

Put a straight edge across the cylinder and use feeler gauges to determine the depth of the piston.

 

[Curiousyellow71]

Just looking at the pictures you are down the deck a ways. A Blueprinted block with those pistons are .084(edit...had wrong rod length) down which puts in the low 8s at best w 516s. .006 seems unlikely, Unless it's been decked a bunch.
Even w lower compression I would put the 346s on. If you want more compression have some(more like a lot of)metal taken off the heads and use a .020 head gasket instead of a .039. .070 off 346s is about 74 cc. The extra compression of the 516 is not going to offset the port flow. Especially if you have headers, intake port flow unported are similiar between the two heads, but the small exhaust valve 516s are sad. If you bowl port the 346s their will be a even bigger difference in performance.
Also...It's not hard to figure out what springs you have measure how many coils and the diameter and do some comparing. You can measure your installed height and figure out the coil bind height. They look like decent springs on the 346s. You may be surprised what you have. Pick a cam once the springs are figured out. As far as the 6400 cam it does not take much for springs. It's got slow ramps and not much lift with 1.5s most oem springs will work with it. But there is no telling what you have until you research it. Most companies have their springs listed on a chart.

 

[1 Wild R/T]

Ok I have sort of an update.. Pulled the head on one side today and I have .030 pistons. They appear to be flat top pistons. I dont have a bridge to check piston height but I used the pin side of my micrometer I know its not accurate but I believe they are between 5 and 10 thousands in the hole. That is a guess. The heads are the 516 heads an still have the smaller exhaust valves. And the engine had .039 head gaskets installed. According to what I have read the 516 heads are around 84cc I was using the compression calculator but had 2 items I was not sure of. The are listed below.

I found this info about the pistons on another site.
383 366NP E233K 59-71 Std.,20,
30,40,60 8.8-1 compression, Flat top no valve reliefs, ch=1.848" This says 8.8-1 Would CH=1.848 be my effective dome height? If so that is what I used in the calculator on the 9.26:1 calculation.

Here are the unknown things

Effective Dome Volume:
Use (-) for Dome and (+) for Dish.

And here is what I came up with when putting in the known information.

Compression Ratio : 9.26 : 1
Total Displacement (in.3) : 389.03
Total Displacement cc's : 6377.54

Bore: (diameter) 4.280
Stroke: 3.38
Cylinder Head Volume:84cc
Effective Dome Volume:?
Use (-) for Dome and (+) for Dish.?
Deck Clearance: Kind went in the middle with .006
Compressed Gasket Thickness:.039
Number of Cylinders:8
Compression Ratio : 9.26 : 1
Total Displacement (in.3) : 389.03
Total Displacement cc's : 6377.54

When changing the effective dome volume to 0 which I now know is correct for the flat top pistons.
I get
Compression Ratio : 9.42 : 1
Total Displacement (in.3) : 389.03
Total Displacement cc's : 6377.54

As ready suggested grab a feeler gauge & a straight edge...

According to the math those pistons are about .090 in the hole....

Half of the 3.38 stroke is 1.69 plus the rod length 6.358 plus the C/H of the piston 1.848 gives you 9.896 Now you subtract that from the deck height 9.98 (blue print spec, true height would need to be measured but is almost always taller) gives you .084

With the 516 heads and a steel shim head gasket your at 8.26-1

With the 516 heads and a typical composition head gasket your at 7.98

with the 346 heads and a steel shim head gasket your at 7.77

With the 346 heads and a typical composition head gasket your at 7.52

I'd be keeping the 516 heads & a steel shim head gasket...

Curious 71 does have a point about the flow but I'd hate to give up the compression...

 

[Curiousyellow71]

I hate the idea of lowering the compression as well. But...I would still run the 346 heads.
...and I would talk to a machine shop about shaving the heads. Just have them shave off the intake port side as well. It will get the compression up about one full point.
But...if the engine is still in the car I would not do shaved heads. Not much fun fitting shaved parts in a engine bay.

 

[BeepBeepRR]

Ill get out a straight edge tomorrow and the feeler gauges. Why do you suspect the summit calculator puts me in the 9 range on compression? Im curious. Not an engine builder so all of this information is very helpful.

 

[1 Wild R/T]

Ill get out a straight edge tomorrow and the feeler gauges. Why do you suspect the summit calculator puts me in the 9 range on compression? Im curious. Not an engine builder so all of this information is very helpful.

You need to input an accurate piston to deck dimension...

 

[BeepBeepRR]

You need to input an accurate piston to deck dimension...

Ok that makes sense. I was wondering how I could have messed up that. And now I know. I guess since guessing lead me to getting it wrong.

 

[Curiousyellow71]

Ill get out a straight edge tomorrow and the feeler gauges. Why do you suspect the summit calculator puts me in the 9 range on compression? Im curious. Not an engine builder so all of this information is very helpful.

What you did was right if you are .006 down the deck. But its likely more then 10 times that w those pistons. Getting a good measurement is key. It really does not matter what we figure...only what you measure. It's not hard to cc heads either. With work nothing says they are less ccs then factory.

 

[BeepBeepRR]

What you did was right if you are .006 down the deck. But its likely more then 10 times that w those pistons. Getting a good measurement is key. It really does not matter what we figure...only what you measure. It's not hard to cc heads either. With work nothing says they are less ccs then factory.

Thanks. I assume alot and probably shouldn't due to the age of these old engines. I assume the heads have never been shaved I assume the block was never decked so a lot of assumptions can lead me in the wrong direction. But the more likely case is the engine which was in a machine shop at some point might have had some stuff done to it.

 

[33 IMP]

Mother Mopar tended to lie about their compression ratios in the sixties and seventies, as do rebuilder piston manufacturers now. Note the information you found for those pistons. They confess they are lying by giving out the compression height. Do you think they would sell a lot of pistons if they said their pistons give a 7.5-1 compression ratio, so they claim 8.8-1. I am much more likely to believe wild R/Ts numbers in post#28.
As others have said, and you admit, without accurate measurement, this is all guesswork. Head cc's can be all over the place, ive seen pistons .160 in the hole that were supposed to be nine to one, that were really less than seven and a half, a small bore steel shim head gasket compared to a large bore composite gasket can be a half point difference, etc. And almost all of these numbers can be adjusted . You just have to know your goal, and how best to get there.

 

[1 Wild R/T]

Mother Mopar tended to lie about their compression ratios in the sixties and seventies, as do rebuilder piston manufacturers now. Note the information you found for those pistons. They confess they are lying by giving out the compression height. Do you think they would sell a lot of pistons if they said their pistons give a 7.5-1 compression ratio, so they claim 8.8-1. I am much more likely to believe wild R/Ts numbers in post#28.
As others have said, and you admit, without accurate measurement, this is all guesswork. Head cc's can be all over the place, ive seen pistons .160 in the hole that were supposed to be nine to one, that were really less than seven and a half, a small bore steel shim head gasket compared to a large bore composite gasket can be a half point difference, etc. And almost all of these numbers can be adjusted . You just have to know your goal, and how best to get there.

Like many I use to believe advertised specs, Mopar sez 10.2 it must be 10.2... TRW sez 12.5 it must be 12.5...
I also trusted my machine shop to build me a performance engine.... When it was a lazy pig I started to wonder why...
I tuned & tweaked, then I pulled the heads & thought wow, I expected the piston to come to the top.... Well, it was .090 down the hole...
I started reading & measuring & measuring & measuring & eventually a light bulb came on... You've got to do it yourself or at least truly know what you want, if you don't get specific & get it in writing then your probably not gonna get what you thought you were...

 

[PRHeads]

For a real world example of how the 516’s aren’t all that bad on mild street stuff......
Done around 1987.

Mid-70’s 400 with 140,000 miles on it, pretty noticeable ridge at tops of bore.
Hot tank, hone, cam bearings, gallery plugs, freeze plugs, dist bushing.
Polished crank.
PAW re-ring kit.
MP 484 cam, Holley SD, 650dp Holley carb, cheap 1-3/4 headers, stock rocker gear.

516 heads, new ex guides, cut ex seats for 1.74 valves, valve job.
Milled .030(not cc’d), 933 springs, umbrella seals.

B&M weighted flex plate, dynamic 10” converter, TF-2 kit in trans, 4.10 gears.

1971 Charger R/T with PS & PB.
3950lb race weight

Mid-13’s at like 101-102.

Trouble free until it was replaced with an Ede headed 446 in 2005.

The 400 was still running great when removed, and got sold.

 

[qkcuda]

When you cut the 516's for 1.74 valves, would you have done a plunge cut under the seats?

 

[PRHeads]

That motor was done before I worked at a machine shop, and the guy at the shop who did them wasn’t really big on messing with HP type work.
It was done with the old three cutter style tooling that Tobin-Arp used.
The 60* cutter would have just been positioned to provide a pretty long cut below the 45, so there would be a minimal lip where that cut met the casting.

That was when I was very new to doing any porting....... and all I would have done is mildly blend away any ridge that might have been at the bottom of that cut, into the bowl.
I was using small grinding “stones”(mounted points) in a die grinder back then. https://www.unitedabrasives.com/category/mounted-points/)

I could do the equivalent work with a carbide burr nowadays in about 1-2 minutes per hole.

You have to be careful with the bulge on the intake side of the exhaust bowl.
There is water on the other side of it.

For the type of build being discussed here, anything more than the mildest of blending is a waste of time, IMO.
I doubt the 1.74 valve would have any impact on the seat of the pants driving experience either.

 

[qkcuda]

Thanks for the info.