360 compression and cam questions

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Joseph24251_200

The Mopar Kid
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I'm currently building a 360 and I have a few questions. First of all I need to calculate my compression which I have already done, but i just need to make sure i'm correct. I also wanna know if i'm using the correct cam for my application. First off I have the

Keith Black 107 flat top pistons -5cc,

Blocked deck for the piston to be 10 thousands in the hole

J head cleaned 3 angle valve job about 68 to 69cc's

and every thing else is stock includeing the head gaskets.

I calculated the compression to be 10.1 to 1 now for the cam i wanted to use the Compcam XE274 or the Compcam Nostalgia plus/ purple plus pp284H. Lately I've been hearing that the cam I wanna use and the compression will be to high for 93 oct. Just wanted to double check.

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I can't answer you compression question. Make sure you check your lifter preload when you install the cam. After decking the block the preload will increase and could wipe out your cam. As far as the cam goes, either of those should work good as long as your compression is as you calculated. You may want to gasket match the intake ports on the head. It is fairly simple to do,will increase the HP, and is almost free. Your 10.1 to 1 compression should be fine with 93 octane. I have 10.58 to 1 and I plan to run 91 in mine. That's the best we have here.
If you are interested, I have a new in the box MP 284/484 cam with lifters and break in lube you can have cheap. PM me if your interested.

Jack
 
I used the Desk Top Dyno compresion calculator to figure the comp. ratio. I however do not know a needed part in the figuring of the ratio, so I put in a guess.

The piston cc's was added to the head volume and the (Missing) gasket thickness was .039, and gasket bore of 4.1 was used, typical of a fel-pro.

Ratio came out to be, 9.83

Ethier cam will work well. When a certain comp. ratio is stated by a cam grinder, it is given as a guide line and best followed. However, at a point down, it's probably only about a 3 - 4 % power loss.
You should be good for pump gas. It's a stout ratio for pump gas, but you should be OK. Did you do any anti detionation mods?
Polish cambers? Coatings? (Thermo)
 
A couple of points. Did you actually cc the heads? Most J heads are over 70 cc's. Also, the bore on a typical Fel-Pro head gasket is 4.180" which lowers the compression. Unless you have accounted for all those dimensions you compression is more like 9.5 to one.

In any case you should be able to operate at 10:1. I amy running 10.6:1 in my 360 but with magnum heads which are much more detonation resistant and it runs on 89 octane.
 
@ 4.180, ratio drops to 9.79.
Thanks DGC. I could not remember the actual gasket bore.

If the heads are unmilled and cc @ 73cc's, the ratio drops to 9.3.
(Pump gas city!)
 
I'm pretty sure the gasket bore is 340 sized witha .060 overbore. That's the largest possible factory oversize. 4.04 + .060...meaning 4.1.
I agree most open chamber heads regardless of casting have much bigger than claimed size. Add to that re-using factory valve sizes and a valve job, and that grows. Most I see are in the 72-74cc range. Using 73ccs and the 4.10 gasket I get 9.:1. Still fine IMO.
 
The Fel-Pro head gasket was advertised a 4.180" bore and it measured that when I got them.
 
Ok say i use the 4.06 gasket with the .023 to .028 compressed height. I also cc the heads and came up with about 69 on most before it flowed over and out the chamber. Does this mean my heads have been milled some time ago. Also do i need to cut my intake down to match.
 
Joseph; You will run fine on 93 octane. I have a similiar built 360 only I went the next cam up to the XE284 grind. The gas around here tops out at 91 octane, no problem. You probably wont know for sure on the intake until you go to install it, mine matched up well with 69 cc chambered J's.
 
408duster what does that XE284 sound like idle wise I mean. I decided I was going to go with the PP284H. Is it possible to run AC just askin cause my car is a factor AC car, and do you have power brakes or manual. If power does the cam produce enought valcumm for the brakes.
 
It sounds very healthy. I run power brakes and I also replaced the factory AC compressor with a newer style Sanden type. The cam works well with this car because Iam using a 9.5" converter that flashes at 3500 rpm with 3.91 gears. I suspect it wouldnt be happy with a tighter converter that stalls in the 2500 range and or less gearing, but I dont know that for sure.
 
The motor that 408duster is relating to has .046 thou. piston to head clearance. It is real close to 9.72 to 1. Motor is lumpy, but it is not shaking the car. Idles well at 800 with the ac on. Kicks along at about 3600 on the highway, sings like a bird. 35 degrees of total timing, around 17 at idle. Don't be scared of the cam, you'll like it. This is at 4000 ft elevation, and still plenty of vacuum to run the power brakes. Trust me his wife would kill him if that brake pedal ever got hard from not enough vacuum.
 
dartdoc said:
The motor that 408duster is relating to has .046 thou. piston to head clearance. It is real close to 9.72 to 1. Motor is lumpy, but it is not shaking the car. Idles well at 800 with the ac on. Kicks along at about 3600 on the highway, sings like a bird. 35 degrees of total timing, around 17 at idle. Don't be scared of the cam, you'll like it. This is at 4000 ft elevation, and still plenty of vacuum to run the power brakes. Trust me his wife would kill him if that brake pedal ever got hard from not enough vacuum.
Click to expand...

not to rain on the parade - 408duster also has 40 more cubes which helps eat up more cam. IMO the XE284 will not be street friendly in a 360 like Joseph is building. Do not overcam.
 
The XE 284 is in our 360 Duster. We are at 4000 ft , power brakes and A/C works perfect with a very healthy sound at idle. 388dart, I shared your concerns on streetability of this cam also in the 360 as I did use it in the 408 for some time. When I changed to a mechanical in the 408, the XE284 and the 9 1/2' converter were hand me downs to the fresh 360 in our other Duster. If Joseph has enough converter and gears the 284 is awesome. If not, the 274 would be wise.
 
Well I have the PP484 and I absolutely love it, haven't gotten it fine tune yet but it's nice. Lookin in to carb's and gears now the 2800 to 3200 stall seems to be doin the job nicely. I know it's a cheap converter but untill i get the money for better I'll do.
 
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