Compression and Cam selection

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Are you worried about it being soft down low? If you're that worried about it, you could always install the cam a bit advanced to increase cylinder pressure a tad. Is it really worth losing sleep over if it's just a street cruiser though (my assumption)?
 
mopowers said:
Are you worried about it being soft down low? If you're that worried about it, you could always install the cam a bit advanced to increase cylinder pressure a tad. Is it really worth losing sleep over if it's just a street cruiser though (my assumption)?
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I wasn't worried about anything until I read Dave's email. I don't want it to be a dog, that's for sure. BUT I'm not looking for a race car.
 
plumkrazee70 said:
Yes
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Well I have it at 10.2 with the numbers you have posted and 10.3 if those pistons have 6cc valve pockets as listed.
Having said that, you won't be using a .039 gasket with those pistons
 
A .060 gasket will put you just under 9.7 and 9.9 if you go to a .050.
 
Bakerlite said:
Well I have it at 10.2 with the numbers you have posted and 10.3 if those pistons have 6cc valve pockets as listed.
Having said that, you won't be using a .039 gasket with those pistons
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The 6cc is wrong from what I understand from KB. They said to use 7.3.

I'm going to have my machinist measure actual compression,.so I can be sure and go from there.
 
Bakerlite said:
A .060 gasket will put you just under 9.7 and 9.9 if you go to a .050.
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Dang,.maybe I have something wrong in my numbers. I haven't bought anything yet, except the rotating assembly and the heads. So the HG and cam can be altered once actual compression is measured. But I do know the pistons are out the hole .018.
 
plumkrazee70 said:
Dang,.maybe I have something wrong in my numbers. I haven't bought anything yet, except the rotating assembly and the heads. So the HG and cam can be altered once actual compression is measured. But I do know the pistons are out the hole .018.
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Any of the static compression ratios talked about so far will be fine. Most anything over 10:1 though will still probably need super, regardless of aluminum heads. Contrary to the folklore and wives tales, they do not "change" the compression ratio.
 
plumkrazee70 said:
Dang,.maybe I have something wrong in my numbers. I haven't bought anything yet, except the rotating assembly and the heads. So the HG and cam can be altered once actual compression is measured. But I do know the pistons are out the hole .018.
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Well the piston to head clearance will pretty much dictate what head gasket you need to use, so with what you have at the moment, you will be around 9.8:1.
I'd think a 224@50 Flat tappet hydraulic would be OK for that sort of comp and induction.
 
With the overall goals with the car, I think a milder cam is the best course of action. I’m taking that it’s a hydraulic flat tappet with these specs?
226/234 @0.050, .494/.513 lift, 110 LSA.
 
1MeanA said:
I think the piston head volume reduces the combustion chamber volume but I could be wrong.
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Yeah, I think that may be wrong. Your total volume measurement is taken with the piston at bottom dead center.
 
My advice to you is wait till you get it to your machinist or engine builder. Have him cc your heads and figure out your compression ratio with the pistons you have and then recommend a cam profile for your intended use of the car. Make sure he knows your gear ratio of your rear axle. Remember, dave hughes, although well versed in all things mopar, is a salesman. Another option is send your engine and parts to hughes engines and have him build your engine. Expect it to cost way more than you want to spend( he’s a salesman).
Now if it was my car and engine, I would want at least 11 to 1 compression ratio to run unleaded premium and that would mean milling the heads and intake. But I’m not you so…….
 
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plumkrazee70 said:
I just want a strong street car (high torque) that has excellent street manners and great drivability. Couldn't care less about HP.
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DODGE Howards Cams 710031-12 Howards Cams Street Force 2 Hydraulic Flat Tappet Camshafts | Summit Racing
This will get you where you want to be. Sure, there are cams that that would make more power. It may not be the most popular choice, but it would probably make the FI Tech system easier to tune. The intake centerline (ICL) is on a 108, so I would consider installing it advanced. I’m not sold on the reliability of most retrofit hydraulic roller setups to recommend one for the goals laid out here.
 
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Garrett Ellison said:

DODGE Howards Cams 710031-12 Howards Cams Street Force 2 Hydraulic Flat Tappet Camshafts | Summit Racing
This will get you where you want to be. Sure, there are cams that that would make more power. It may not be the most popular choice, but it would probably make the FI Tech system easier to tune. The intake centerline (ICL) is on a 108, so I would consider installing it advanced. I’m not sold on most retrofit hydraulic roller setups to recommend one for the goals laid out here.
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I would endorse that!
 
you have and intake valve closing of 50 for the 703 cam?
iam 110 lsa 106 icl same as that cam the 703 has more duration
mine closes 60 seems yours should be 64 ish
 
still seems low 1 of those is 114 110 the other is 110 106
50 closing at your specs at 10.1 to 1 gets you dcr of 8.62 180psi cranking comp and161v/p index not bad with 4.10s good low end
60 closing 8.33 165psi 138v/p index
 
I wouldn't use DCR. About as useful as a sun roof in a submarine....
The DCR formula does not take into account how well the induction system flows, & therefore it does not know much air is packed into the cyl.
Also agree that a cam around 224 @ 050 would be good [it is always a compromise ].
Such as the Comp 270H Magnum or Isky 264 Mega. These should have good vacuum, they are on 110 & 108 LSAs. Use wider LSAs if you want to kill the power...
 
When I moved a year ago I did not even consider the effect of altitude on engine vacuum... fuel air for sure. I was pulling 17 inches at sea level... at 11 now sitting at about 5k feet. I have read a lot of the EFI setups are sensitive to low vacuum. let us know how your install goes.
 
74Scooter said:
I have read a lot of the EFI setups are sensitive to low vacuum. .
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I'm finding it a little hard to understand why this would be a problem?
Geez.. what's the EFI doing at full throttle and almost zero vacuum?
If the issue is vacuum pulsation at the lower vacuum readings, then you need to dampen it.
 
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