Cranking Compression

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skep419

skep419

5.9 Magnum 4 speed afficionado
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360 405p SP pistons, stock rods, cast crank. 9.5 comp
Comp XE284 cam. I was told the cam I am running is a mismatch with the compression ratio. I did a cranking compression test last night and it was 160 on all cylinders (engine warmed up, throttle zip tied open, MAC Tools gauge) 9" of vacuum 6" in gear (shaky reading)

Let me know if you need more info. What are your thoughts?
 
Manufacturer's Part Number 20-225-4
COMP Cams Xtreme Energy Camshafts
Hydraulic flat tappet
Basic Operating RPM Range 2,300-6,500
Intake Duration at 050 inch Lift 240
Exhaust Duration at 050 inch Lift 246
Duration at 050 inch Lift 240 int./246 exh.
Advertised Intake Duration 284
Advertised Exhaust Duration 296
Advertised Duration 284 int./296 exh.
Lobe Separation (degrees) 110
Grind Number CRS XE284H-10
 
skep419 said:
360 405p SP pistons, stock rods, cast crank. 9.5 comp
Comp XE284 cam. I was told the cam I am running is a mismatch with the compression ratio. I did a cranking compression test last night and it was 160 on all cylinders (engine warmed up, throttle zip tied open, MAC Tools gauge) 9" of vacuum 6" in gear (shaky reading)

Let me know if you need more info. What are your thoughts?
Click to expand...

I think the 275HL would have been a better choice given 9.5:1. How does it drive and accelerate?
 
Thunder valley last year
[ame="http://www.youtube.com/watch?v=V7eAEae0kFg"]http://www.youtube.com/watch?v=V7eAEae0kFg[/ame]

[ame="http://www.youtube.com/watch?v=ZIt2L6Js0Cs"]http://www.youtube.com/watch?v=ZIt2L6Js0Cs[/ame]
Birthday present last year
[ame="http://www.youtube.com/watch?v=znd0kyderPY"]http://www.youtube.com/watch?v=znd0kyderPY[/ame]

It drives and accelerates fine. I was just wondering if these numbers are normal. If there is something to gain by swapping cams. The car is street driven most of the time but I don't mind sacrificing street manners for better ET.
 
Not trying to steal your thread, but our car's are almost the same setup but your's is running 1 second faster than mine. What do you suppose the difference is? I've always felt it should be running mid to high 12's.
68 dart/340 motor/10.75 to 1/same cam/air gap/700dp or 750dp/3400 dynamic 9.5"/4.10 741 suregrip/open headers/235-60-15 drag radials/ss springs/j heads but I had eddy's on also and it didn't pick up any
 
jefflock said:
Not trying to steal your thread, but our car's are almost the same setup but your's is running 1 second faster than mine. What do you suppose the difference is? I've always felt it should be running mid to high 12's.
68 dart/340 motor/10.75 to 1/same cam/air gap/700dp or 750dp/3400 dynamic 9.5"/4.10 741 suregrip/open headers/235-60-15 drag radials/ss springs/j heads but I had eddy's on also and it didn't pick up any
Click to expand...

what distributor are you running (what is the timing set at)? 10.75 With the J heads or eddy's (which are you running right now)
 
Non ported J heads cut to 65cc's and 18 initial and 34 total. Running MP dist and FBO ignition
 
160 to me is the lowest I'd use for performance. I try to hit 175 or as close to it as I can without going over 190 psi with pump gas.
 
If you've got those pistons in there and there was no excessive milling on the block or heads, it's closer to 8.0:1 static compression. They are short (end up .110" down in the hole if your block is "only" 9.60 deck height) and they have a 14cc dish in them. In order to get 9.5:1 static, you'd have to have milled the block over .100", or cut the heads down a ton AND milled the block a bit. The problem is the pistons IMO. If it were me I'd be looking to go down a couple steps to the XE274H. 160 psi is ok for an iron open chamber head, but not great. And truthfully, it's low for an aluminum head combo.
 
moper said:
If you've got those pistons in there and there was no excessive milling on the block or heads, it's closer to 8.0:1 static compression. They are short (end up .110" down in the hole if your block is "only" 9.60 deck height) and they have a 14cc dish in them. In order to get 9.5:1 static, you'd have to have milled the block over .100", or cut the heads down a ton AND milled the block a bit. The problem is the pistons IMO. If it were me I'd be looking to go down a couple steps to the XE274H. 160 psi is ok for an iron open chamber head, but not great. And truthfully, it's low for an aluminum head combo.
Click to expand...

Federal Mogul/Speed Pro Piston Part
Number
Application Power Range Special requirements Compression information
Ring groove size
Pin diamater
Rod length
Stroke
Deck clearance
Skirt clearance
H405CP plus Perfect Circle/Hastings moly rings (2M139)


At time of listing, STD, +.030, and +.040 are available. Please contact us to inquire about other sizes.

Chrysler 360 (4.000" STD bore) 1971-95 flat top with 4 valve reliefs

idle to 6000+rpm Good for street/strip or light race 1.637 compression distance
Compressions:
w/63cc heads 9.11:1
w/65cc heads 8.94:1
w/68.4cc heads 8.66:1


5/64" 5/64" 3/16" ring grooves
.9842" pin diam.
6.123" (stock length) rods

3.578" stroke
PRESS ONLY


.050" deck clr
.0015" skirt clr




w/63cc heads 9.11:1. I'm using the thin head gasket. I may have exaggerated the compression gain of the head gasket a little :-D.

The bottom end was put together by a local shop roughly 8 years ago. 4 years ago I moved to the same town as Victory Engines. After watching a couple small block strokers pull 500+ HP on the dyno. I wanted to build one of my own (but there was nothing wrong with my bottom end) Talking with Matt I decided to go with some ede heads and lose the DEH275 comp cam for a XE284. The parts would work great with the later stroker build that I had planned and still pick up some HP.

I am basically trying to add power to a crap bottom end.

"The problem is the pistons IMO" The pistons are the problem. What would the cost ($/labor) be to just put better pistons in. I have asked this question numerous times. Not sure what the word is for it but whenever I start talking about it. The mine as wells, and if I buy this I should get this, etc. I always end up with a fire breathing stroker.

At work today the idea came up to buy a boneyard 360. Do a little work to the heads and bolt them on with the DEH275 cam. Drop the bone yard block off at Victory. Become a hooker to buy the stroker kit. Sell the old long block to pay for gas and tires. :burnout:
 
I thought it was the sealed power pistons (also called 405p)you had in the motor and the other guy is right, those sealed power pistons are about .100 down in the hole. (1.576 comp. ht)
I guess the speed pro pistons at 1.637 and .050 off the deck would make a ton of difference. 160 aint too bad then. great for pump gas and aluminum heads. You dont need racing fuel. The video is bad-***! 2 thumbs up
 
There are two possibilities on the pistons so maybe I'm incorrect here... But this is taken from Summit's site:




Brand
Sealed PowerManufacturer's Part NumberZ405PPart TypePistonsProduct LineFederal Mogul Cast PistonsSummit Racing Part NumberSTL-405P Bore (in)4.000 in.Bore (mm)101.600mmPiston StyleDish, with four valve reliefsPiston MaterialCast aluminumCompression Distance (in)1.576 in.Wrist Pin StylePress-fitPin Diameter (in)0.984 in.Piston Ring Thickness5/64 in. x 5/64 in. x 3/16 in.QuantitySold individually.NotesRecessed piston head is 0.0705 inch deep x 3.140 inch diameter.

That being said... You dont have enough compression for that cam, even if it's 9.5:1. It should be 10.5:1 for those heads, even using the old "ad a point" rule for aluminum. Truthfully I would have liked to see 10.75:1 with those heads and a good quench for a cam like that.
 
Your camshaft is the problem with your combination. You can easily raise compression pressure significantly if you choose a dual pattern camshaft with very widely spaced intake and exhaust durations. something on the order of 10-12 degrees. What you have now is a four degree spread. what that will accomplish is opening the intake valve early and closing the exhaust valve late. This will result in filling the cylinder completely. The rest is up to you. A tight lobe center will result in a rougher idle and the power peak will be slightly higher in the power band, while a wider lobe center will result in the opposite. with the bottom end you have, "I" would recommend limiting your .050" duration to 240 degrees at the absolute max. Better would be 236. So, probably something like 222 intake and 236 exhaust would get you there. With a spread like that, you will fill the cylinder much more completely than you are now and the cylinder pressure will increase resulting in more power with the same bottom end. Go shop through the cams on the Hughes Engines site and look at all their specs. They have wide duration spreads just for that same purpose. Because they work.
 
StrokerScamp said:
Your camshaft is the problem with your combination. You can easily raise compression pressure significantly if you choose a dual pattern camshaft with very widely spaced intake and exhaust durations. something on the order of 10-12 degrees. What you have now is a four degree spread. what that will accomplish is opening the intake valve early and closing the exhaust valve late. This will result in filling the cylinder completely. The rest is up to you. A tight lobe center will result in a rougher idle and the power peak will be slightly higher in the power band, while a wider lobe center will result in the opposite. with the bottom end you have, "I" would recommend limiting your .050" duration to 240 degrees at the absolute max. Better would be 236. So, probably something like 222 intake and 236 exhaust would get you there. With a spread like that, you will fill the cylinder much more completely than you are now and the cylinder pressure will increase resulting in more power with the same bottom end. Go shop through the cams on the Hughes Engines site and look at all their specs. They have wide duration spreads just for that same purpose. Because they work.
Click to expand...

The cam that was in it sounds like a better choice.
275DEH comp cam
RPM range 2000-6000
.462/.482 valve lift
219/235 Duration at .050
275/284 Adv. duration
110 degree
 
lil low for aluminum heads.jmo

if you are at a 1500 minnesota elevation , it's more like 9.2 comp.

I would mill the heads, and or use a thinner gasket to get to 170.

then again going to even 175psi [like going 9.5 to 9.9 comp] on a 400 hp motor is only worth around 5hp...
You would maybe feel more response, maybe.
going to 180 would do something.

I kinda thinking don't worry about it.


in all reality, wide cl's give up 'some' peak power to a similar narrow cl, but wider cl's make power every where while the narrow cl's are light swithes....you don't wanna be caught with the lights off.lol
 
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