#21  
Old 07-16-2021, 07:53 AM
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Can the chambers be opened up on the 48’s?

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Old 07-16-2021, 09:13 AM
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I am certainly not a fan of loosing the quench. It seems like once the quench is around .070” for most engines the quench looses it’s effectiveness and increasing the quench distance more yet wasn’t noticeable over the marginal quench. Would rather make efforts to deal with the bad quench up front than try to nurse an engine along with to high of compression and a marginal quench. Poor quench higher compression engine I would keep at least 10 degrees more on the exhaust side. Doesn’t cure end gas issues, but it seems to help manage it. Going to act more like a open chamber. FWIW…We are every bit as high on compression for pump gas with open chamber heads and other engines with no quench.


Unless it was a unbelievable smoking deal on some 92-96 cc head, before letting those ported 48 heads go I would sell the flat pistons and get some pistons with a good dish. I know DSS has a nice 27 or 28 cc D dish.. 455 pistons in the photo look like nice pistons, selling them, buying dished pistons and not having to get the expensive thick Cometics would be what I would try to do first. I would do the thick cometics if that fell thru. Rather let the pistons go before I ground on another set of iron heads. Lots of guys don’t realize how much work it is when you do extensive porting.

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Old 07-16-2021, 10:04 AM
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Seems like there are certain quench ranges that cause issues too. For some reason quench from .070” to .09” range is worse than .09 to .14”. Then after sometime after .14” issues start to show up again. See that on open chamber stuff to where we milled the heads and quench end up in that .070” -.090” range, has some extra issues, each engine acts different though. Not sure the RA heads will be much different, my guess is they are going to respond similarly, I would keep out of that .07-.090 quench range.


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Old 07-16-2021, 10:20 AM
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Keeping the #48 heads?

Can’t blame you for wanting to.

If so resign yourself to cracking open your wallet to purchase some dished pistons and for the ensuing balancing job. Some new custom pistons will give you the opportunity to set the compression height to zero or whatever number is right for what you’re doing.

Get ‘er done.

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Old 07-16-2021, 10:31 AM
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Trade them with someone for some # 64 heads

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Old 07-16-2021, 12:05 PM
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Mark,
In rough numbers every .001" of head gasket equals 0.22 cc's

Is it possible to do a combination of things ?

David Vizard talks about putting a radius on the valve relieves which he says helps improve flow.

Opening up / soften the combustion chamber

Finally increasing head gasket thickness.

Stan

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Old 07-16-2021, 01:19 PM
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Quote:
Originally Posted by Half-Inch Stud View Post
Working my Spare 455 +030, and have flattops and "48s".
BOP 1-piece Rear Seal in, Forger 4.21" Stroke, 3.25" Mains TQ'd with Factory Bolts. 1973 2-Bolt Block.

Wondering what Octane is needed to drive on the Street THESE DAYS.
Which #48's ? The extra smaller 66 cc chamber ones off a 350 HO or the 72-75 cc? 400 ones


If like my 465 cid flat top 74 455 (undecked) 80's TRW forged.. with 62's that are 75-77 cc ish I can run a can of Torco Accelerator to maybe 10 gallons of 93 Super and it works never pushed it less than that and or I mix 50/50 93 and 110 race fuel

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Old 07-16-2021, 06:33 PM
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Quote:
Originally Posted by Stan Weiss View Post
Mark,
In rough numbers every .001" of head gasket equals 0.22 cc's

Is it possible to do a combination of things ? Count on it. RA IV valves have the tulip.

David Vizard talks about putting a radius on the valve relieves which he says helps improve flow. Okay, alot of detail work for 1 or 2 a cc. Maybe i try it.

Opening up / soften the combustion chamber: DONE. Chambers are at 78 cc

Finally increasing head gasket thickness. Yea, is where i'm at. Thanks

Stan
Tally done. The CYLs lack the factory chamfer. Wonder if i go long on unshrouding CYL chamfers.

Dang Slugs are at zero deck.

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Old 07-16-2021, 07:49 PM
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I am slowly assembling a engine now that doesn't have cylinder chambers at all and my first gen second head bolt design Edelbrock RPM head chambers meet the edge of the cylinder,
No hang over either way, may want to settle on a head package before cylinder chamfer
+.030 400 block

You can occasionally get the thicker steel shim composite stock head gaskets on ebay I picked up 4 pretty cheap

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Old 07-16-2021, 10:09 PM
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Dad successfully ran a flattop 455 (bored .040 over if I remember correctly) with a set of ported #12 heads. It was zero decked and a typical .039" head gasket.

I don't recall the exact compression ratio (I'm sure it was pushing close to 12:1 or so) but I do remember it pumped 210-215psi. He ran a Harold Ultradyne solid flat tappet in it that was pretty healthy, duration in the 250/260 range. That engine ran on the street for a few years on Sunoco 94 octane and I was able to make it work. But the tune had to be spot on and routinely checked. It would not have worked with todays 91.

Anytime he went to the dragstrip with it he did mix a little 110 in the tank for good measure.

These days with more knowledgeable people and better parts I've pushed the pump gas deal with a few engines on the crappy 91 we have now. One is 11:1 with iron heads and a pretty healthy camshaft running on 91 octane for 5 years now (daily driven to 50k miles so far) and it acts like it would run on less. I keep the tune pretty spot on but I don't have to monitor it like it's life or death.
My bird I also drive regularly and it's 10.13:1 with it's #12 heads and does fine on 91 with a very small 068 cam (albeit a 400) put about 25k miles on it in the last 3 years.
Neither car acts finicky even in the AZ summer heat but I don't know if I'd push the issue any more than that. Aluminum heads I would, but iron heads that's about as far as I want to go. I don't think pump gas is going to get any better in the coming years.

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  #31  
Old 07-17-2021, 07:06 AM
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Quote:
Originally Posted by Formulajones View Post
Dad successfully ran a flattop 455 (bored .040 over if I remember correctly) with a set of ported #12 heads. It was zero decked and a typical .039" head gasket.

I don't recall the exact compression ratio (I'm sure it was pushing close to 12:1 or so) but I do remember it pumped 210-215psi. He ran a Harold Ultradyne solid flat tappet in it that was pretty healthy, duration in the 250/260 range. That engine ran on the street for a few years on Sunoco 94 octane and I was able to make it work. But the tune had to be spot on and routinely checked. It would not have worked with todays 91.

Anytime he went to the dragstrip with it he did mix a little 110 in the tank for good measure.

These days with more knowledgeable people and better parts I've pushed the pump gas deal with a few engines on the crappy 91 we have now. One is 11:1 with iron heads and a pretty healthy camshaft running on 91 octane for 5 years now (daily driven to 50k miles so far) and it acts like it would run on less. I keep the tune pretty spot on but I don't have to monitor it like it's life or death.
My bird I also drive regularly and it's 10.13:1 with it's #12 heads and does fine on 91 with a very small 068 cam (albeit a 400) put about 25k miles on it in the last 3 years.
Neither car acts finicky even in the AZ summer heat but I don't know if I'd push the issue any more than that. Aluminum heads I would, but iron heads that's about as far as I want to go. I don't think pump gas is going to get any better in the coming years.
Yes, all this matches my experience with Hi-Compr. Add humid summer days cause my HC to ping. Shows what "we-all" used to do 30 years ago. Aluminum Heads have the 0.5 to 3/4 point advantage. I'd rather stay with Iron and shoot for 9.3:1 thru 10.0:1

Since 2003 i have had 9.00:1 and have relied on munerous little things and a big cam to realize good results, in either compression.
Fear going back to Hi-Comp though. Is 10:1 to 10.5:1 of any use? I suppose a chart is helpful: Correction welcomed!

Octane. Compr on a 455 (Race/Tow-Street)
87. 9.0:9.5:1
89. 9.5-9.7:1
91. 9.7-10.1:1
93-94. 10.2-10.7:1

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  #32  
Old 07-17-2021, 10:24 AM
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I would not at all go to the point that 10.0-10.5 is of not any use in a 455. There are just to many factors to narrow the compression ranges in a chart like that, to me the higher octanes on the list are getting to high with respect to the lower octanes, ranges look to wide for the 87 and the 92,93.

I did a SR cam 9:0 462 with ported D ports that wants 91, I think it is borderline in some conditions to want 93, he is gunning for 10s 1/4 mile. Even though it is 9:0, you would swear it has 11:1. IRC, I think I have less cylinder pressure on my 461 at 11:1 than he would have. He is going after all the mid range he can find to launch his car, wants to drive it to the track. My car is a semi daily driver and I wanted efficiency @ low rpms, not a huge mid range, or crazy low end tq, but strong power up high. All things I did so my 4 speed would have a longer life. Complete different combos, same CID, 2 points different on SCR, basically the same octane.


FWIW. Power is in the heads. Compression more for efficiency. As long as the compression is adequate for the chosen cam, there is much more power with better head flow than compression. Nothing wrong with 9:0, depends on the rest of the combo. Not enough info in this thread to begin to determine where the perfect SCR should be. If in doubt, stay on the low side and sleep better at night.


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Old 07-17-2021, 11:16 AM
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This graph roughly shows cranking compression for 9:1, 10:1, and 11:1 CR verses IVC for a 455 + 030.

Stan
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Old 07-17-2021, 02:13 PM
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@ Jay; my 9.0:1 is all joy on 87, 1/4 mile on 89 due to the cam (combo below), butt hay the little things going on like cutting the Sparkplug GND lugs back, HEL finness, Phat Carb Primaries. And then aluminum water pump, alum water crossover, such things of no consequence really. I really dont tink the loud stereo is part of the deal though.

So, Flat HYD cam is likely a keynote thing.
Solid Roller is gonna give those static compression woes huh. Rollercams not in my recipe book.

Got grandkids here so chart comprehension will have to wait.

Stan, I has an Isky 245/245 104 LC 4* adv for 100/108 provide 285-300PSI cranking pressure on a RamIII 455 combo awhile back. The idle pulsations were spectacular.

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Old 07-19-2021, 01:40 AM
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Just open up the chambers.
Thats what I did to my 670's to 87cc and they work fine
with premium pump gas. I think it was around 10:2:1 comp.
I ran a 575-lift solid roller with 262 dur@50 on a 110 lobe seperation.

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Old 07-19-2021, 07:00 AM
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48s at 78 cc with Ram IV Valves. Not brave enough to eggshell up to 87cc.

My latest thought is to finish the shortblock, Top-end it, & break-in the cam on a super hobo stabilized engine Stand. Let it lay until Towncar engine is out and begging ready for the 455.

Meanwhile money gets committed to Dished slugs, or thick headgaskets. Possibly sell the Spare as a run-in flattop forged-crank shortblock. And look for a dished shortblock.

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Old 07-19-2021, 07:26 AM
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this conversation sounds very similar to my latest delima.....455 CAST piston ZERO deck motor and a selection of heads all with there own problem. The 7M5's...not enough exhaust bolt holes and 114 cc, the small valve 4X @98 cc then my lovely #62 @ 74 cc.....either get no compression (or header bolt holes) no flow with great compression, or TOO much compression with great flow.;.....lol
decided to work the 4X into a decent head. budget budget budget...

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Old 07-19-2021, 04:31 PM
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Quote:
Originally Posted by Half-Inch Stud View Post
48s at 78 cc with Ram IV Valves. Not brave enough to eggshell up to 87cc.

My latest thought is to finish the shortblock, Top-end it, & break-in the cam on a super hobo stabilized engine Stand. Let it lay until Towncar engine is out and begging ready for the 455.

Meanwhile money gets committed to Dished slugs, or thick headgaskets. Possibly sell the Spare as a run-in flattop forged-crank shortblock. And look for a dished shortblock.
78 cc? I think that is the most I have ever seen for a 48. Tullip valves and the chamber grinding must have added up.

The valve reliefs in the piston photo look big and deep. How many cc they? Kinda sounding like the compression is more like 11.0, not 12. Might not have that far to 10 scr with the parts you have. Connect the valve relief and make it more like a tear shaped trough, and unshroud the intake a little more. Little things like what Stan mentioned a few post earlier add up.

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Old 07-19-2021, 06:39 PM
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Quote:
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78 cc? I think that is the most I have ever seen for a 48. Tullip valves and the chamber grinding must have added up.

The valve reliefs in the piston photo look big and deep. How many cc they? Kinda sounding like the compression is more like 11.0, not 12. Might not have that far to 10 scr with the parts you have. Connect the valve relief and make it more like a tear shaped trough, and unshroud the intake a little more....
Both valve reliefs cut into the Top-Ring land. But a Unibrow ? hmmmm
48s have been unshrouded;
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Last edited by Half-Inch Stud; 07-19-2021 at 06:57 PM.
  #40  
Old 07-20-2021, 04:36 PM
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Red face

Getting ready to Slug the Rods. Super-lightweight assy. Sharpie is a key scribe for coordinating these things. Spiralocks!!!
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