Effective Dome Volume on a 360

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CirusP

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Hi all,

Im new to this forum as a registered user, thou I have read many articles in the past.

I have recently come accross a 360 that was overbored .060 over. I got the Whiplash from Hugues as I wanted to try a low compression engine for a street car. This might be going to my Dart or my Dakota, haven't figured it out.

I really suck at math, but the compression numbers im getting are terrible. I dont know If i should re-do the build with a different set of pistons, or that Im just not figuring out the math.

So, its a 1976 .060 over 360. dish pistons with CH 1.576, and the deck was milled a .010 to give what I measured with a bridge to .110 down the bore.

Am I just idiotic or this is a real low combo and will not do any power? PLease help!
 
Last edited by a moderator:
oldkimmer said:
Ur about 8-1. That’s pretty sad. Kim
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You crazy. He's less than that. .110 in the hole WITH a dish and at the least a 65cc head "IF" he's lucky. I say he's at about 7.3
 
oldkimmer said:
Ur about 8-1. That’s pretty sad. Kim
Click to expand...

meh...you might be about right. I used 6cc for the dish, .038 for the gasket and sittin .110 in the hole got 8.3.....but I BET that dish is a little more than 6. So 8:1 is probably dang close.....but that's what the Whiplash cams are made for.
 
oldkimmer said:
I did actually figure 7.5 ish but that just sounds bad. Lol
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That could be right because I'm sure I was kind with the head cc and the piston dish cc. The heads are probably closer to 72 and I bet that dish is about 10.
 
Apples to oranges comparison. Or, more appropriately, small blocks to big blocks. I have a 1970 Gran Coupe vert with a 1976 Chrysler 440. Re-gasketed with thicker head gaskets. That engine factory would've been a real 7.5 to 1. I've measured it. Has headers, an Edelbrock Performer RPM intake, 750DP, 2000 convertor, 4.11 gear, 28 tall rear ET Street Radial. Best E.T. to date is a 13.66. Best MPH is 100.6. Not achieved at the same time. Oh, yeah. Forgot. I run that"worthless" Whiplash cam.
 
oldkimmer said:
I did actually figure 7.5 ish but that just sounds bad. Lol
Click to expand...

Sounds PurrFect for this....
C6CD984F-10E2-43D1-A109-C1FD9450FE7C.jpeg
 
CirusP said:
Hi all,

Im new to this forum as a registered user, thou I have read many articles in the past.

I have recently come accross a 360 that was overbored .060 over. I got the Whiplash from Hugues as I wanted to try a low compression engine for a street car. This might be going to my Dart or my Dakota, haven't figured it out.

I really suck at math, but the compression numbers im getting are terrible. I dont know If i should re-do the build with a different set of pistons, or that Im just not figuring out the math.

So, its a 1976 .060 over 360. dish pistons with CH 1.576, and the deck was milled a .010 to give what I measured with a bridge to .110 down the bore.

Am I just idiotic or this is a real low combo and will not do any power? PLease help!
Click to expand...
I haven't studied stock POS Pistons but I tell you... I didn't know they had such a crummy compression height, in the hole .110??
1.56??

You really ..really... want to change the pistons in this thing.
 
CirusP said:
Hi all,

Im new to this forum as a registered user, thou I have read many articles in the past.

I have recently come accross a 360 that was overbored .060 over. I got the Whiplash from Hugues as I wanted to try a low compression engine for a street car. This might be going to my Dart or my Dakota, haven't figured it out.

I really suck at math, but the compression numbers im getting are terrible. I dont know If i should re-do the build with a different set of pistons, or that Im just not figuring out the math.

So, its a 1976 .060 over 360. dish pistons with CH 1.576, and the deck was milled a .010 to give what I measured with a bridge to .110 down the bore.

Am I just idiotic or this is a real low combo and will not do any power? PLease help!
Click to expand...


You can’t know the actual volume of the dish if you don’t measure it by doing a down fill on it. Just like a dome volume, the published numbers can be off a quite a bit. And some of that depends on where the volume is measure relative to the deck.
 
Thanks all. I know its terrible, its what I had. Because of the .060 I decided the whiplash was good for it. I might change pistons in the times to come. Its a bummer, but I appreciatte everyone's comment. Even the laughters :(
 
408 swinger said:
Apples to oranges comparison. Or, more appropriately, small blocks to big blocks. I have a 1970 Gran Coupe vert with a 1976 Chrysler 440. Re-gasketed with thicker head gaskets. That engine factory would've been a real 7.5 to 1. I've measured it. Has headers, an Edelbrock Performer RPM intake, 750DP, 2000 convertor, 4.11 gear, 28 tall rear ET Street Radial. Best E.T. to date is a 13.66. Best MPH is 100.6. Not achieved at the same time. Oh, yeah. Forgot. I run that"worthless" Whiplash cam.
Click to expand...


I haven't heard nor read one single dissapointment comment on the whip cams. I have all of the same performance upgrades that you have except for it being a 360. I also run a A833, and its a daily, so Im good with this.
 
RustyRatRod said:
That could be right because I'm sure I was kind with the head cc and the piston dish cc. The heads are probably closer to 72 and I bet that dish is about 10.
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They are 66cc and I dont wanna mess with them because of my geometry. 66 its still sad CR...pretty pretty sad.
 
CirusP said:
Thanks all. I know its terrible, its what I had. Because of the .060 I decided the whiplash was good for it. I might change pistons in the times to come. Its a bummer, but I appreciatte everyone's comment. Even the laughters :(
Click to expand...
It will work, run 87octane, it wont need more. After re reading, here's what's going on.... you're using a bridge and you're getting the center where the dish is... so of course it's .110.. but the perimeter of the dish or ledge is probably at least half of that, so the raised portion of the piston is about .055

8.1 comp
You can mill the heads to compensate and then youll be just fine.
Its .0048 per cc
 
"...In the 'Magnum Manifesto' article from 1998 Hot Rod Magazine they list what appears to be an official number of 11.20 cc's from Mopar Performance..." Internet
 
CirusP said:
Thanks all. I know its terrible, its what I had. Because of the .060 I decided the whiplash was good for it. I might change pistons in the times to come. Its a bummer, but I appreciatte everyone's comment. Even the laughters :(
Click to expand...

Dude, just build the thing. Don't get all hung up on compression. I have my 7.7:1 400 sittin on the stand. It's goin in a A body for God's sake! It'll be quick! Just build it and go.
 
MOPAROFFICIAL said:
It will work, run 87octane, it wont need more. After re reading, here's what's going on.... you're using a bridge and you're getting the center where the dish is... so of course it's .110.. but the perimeter of the dish or ledge is probably at least half of that, so the raised portion of the piston is about .055

8.1 comp
You can mill the heads to compensate and then youll be just fine.
Its .0048 per cc
Click to expand...

Mine are flat tops. No valve reliefs and they are in the hole .115. I don't care. I'm sendin it. LOL That's how it was when it left the factory and that's how it's leavin my factory. **** man, it's a big block with a DP4B intake, mild cam and HP manifolds goin in a 64 Valiant with a manual transmission and 3.89 gears. It ain't got a chance of bein a dog. lol
 
CirusP said:
Thanks all. I know its terrible, its what I had. Because of the .060 I decided the whiplash was good for it. I might change pistons in the times to come. Its a bummer, but I appreciatte everyone's comment. Even the laughters :(
Click to expand...
If you do indeed change your pistons, then you need to be careful with that Whiplash. If you use that cam with higher static compression, you'll send your cylinder pressure through the roof. Time for race gas. I'm with Rusty, put it together and run it. There's way more satisfaction working miracles with "junk" than new parts anyway.
 
RustyRatRod said:
Mine are flat tops. No valve reliefs and they are in the hole .115. I don't care. I'm sendin it. LOL That's how it was when it left the factory and that's how it's leavin my factory. **** man, it's a big block with a DP4B intake, mild cam and HP manifolds goin in a 64 Valiant with a manual transmission and 3.89 gears. It ain't got a chance of bein a dog. lol
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True, n at the same time...light car..more ability to run a higher dynamic and no pingy ping...
 
RustyRatRod said:
Dude, just build the thing. Don't get all hung up on compression. I have my 7.7:1 400 sittin on the stand. It's goin in a A body for God's sake! It'll be quick! Just build it and go.
Click to expand...


How you'll fit that into an Abody is what I'll want to know! I wanted for some time put a stroked 400 on my 63Dart. BUt yes, I'll leave this 360 for low compression and easy gas. I have some other bloks I can highcompress, i guess. It just sounds so cringy...7 to 1....
 
408 swinger said:
If you do indeed change your pistons, then you need to be careful with that Whiplash. If you use that cam with higher static compression, you'll send your cylinder pressure through the roof. Time for race gas. I'm with Rusty, put it together and run it. There's way more satisfaction working miracles with "junk" than new parts anyway.
Click to expand...

I know, I just thought i might've been off with the numbers. But Imma just take a little off the heads to make sure they are flat and then Im off to the road. Thanks thou
 
CirusP said:
How you'll fit that into an Abody is what I'll want to know! I wanted for some time put a stroked 400 on my 63Dart. BUt yes, I'll leave this 360 for low compression and easy gas. I have some other bloks I can highcompress, i guess. It just sounds so cringy...7 to 1....
Click to expand...

Oh it'll fit right in and bolt in. My only concern is how the drivers side exhaust manifold is going to interact with the column shift three speed. I'm using C body HP manifolds and that puts the outlet several inches forward of the B body HP manifold, which is what I need. I've done some preliminary measurements and from what I see, it'll fit. Course you don't know till you really try it.
 
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