Compression and Cam selection

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plumkrazee70

plumkrazee70

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So I have the new block and rotating assembly at the machine shop now. He is going to look at everything next week, and unless something isn't usable, we will be moving forward with my rotating assembly. I am heavily considering changing cams because the Lunati 703 didn't produce very much vacuum (10-11") and for the EFI, I'd really like it to be higher.

So I reached out to Hughes and I was surprised at his response. (see below) Keep in mind I used a calculator for the compression calculation. (attached). I didn't realize that altitude decreased vacuum.

You have some things working against you. Aluminum heads only 9.3:1 compression. Aluminum heads should be about 1. Above what you would run with iron head and your 1300’ altitude works against you too. Both of them will lower the vacuum even more. I suggest our SER1822ALN Ca, 5006 lifters, and 1199 spring kit or you could go with the next size larger cam SER2226AL and use the 5007 lifters which “bleed down” at idle and lower RPM, giving you more vacuum and more mid-range power.

I am going to have the machinist measure my actual compression, to be sure but, my question is how do I increase the compression so that factor isn't working against me?

Here is what the calculator looks like with the first cam he recommended.

69 340 block
KB 243 (assuming .018 out the hole, just like the old 68 block)
Eddy aluminum 65cc heads (pn 60179 for the piston clearance)
Air Gap
EFI

Calculation.png
 
As altitude increases, air gets thinner, less oxygen by weight so hp decreases.
Mill the heads if you want more compression.
I would NOT use any recently made FT lifter. Find some 25+ yr lifters & have them re-faced. Then you have maximised your chances of NOT wiping lobes/lifters.
 
Bewy said:
As altitude increases, air gets thinner, less oxygen by weight so hp decreases.
Mill the heads if you want more compression.
I would NOT use any recently made FT lifter. Find some 25+ yr lifters & have them re-faced. Then you have maximised your chances of NOT wiping lobes/lifters.
Click to expand...

Ok, makes sense. I don't really want to increase compression, unless it will benefit the build. The dynamic on the calculator seems to be in the ball park for pump gas, no?
 
with alum heads you can go much higher on pump it will help your dcr
 
8.9 dcr would be good
why is hughes saying 9.3 if you are9.8?
what trans and gear ratio tire diameter ? are you racing/crusing?
you could run rhoads lifters with the 703 and pick up vacum and low speed torque under 3k
alum heads id want 11 to 1 with 230@50 duration
 
What heads and head gaskets? And what’s the overall intent of the vehicles usage, and what transmission, gear, and converter? I seen that Hughes recommended a hydraulic roller. Are you planning on the hydraulic roller switch? When you get into milling the heads enough to raise compression and running high lift, it’s a good idea to co talk to Mike at B3 about rocker geometry correction. Those heads have a .060 deep relief cut around the combustion chambers. You can get a pretty decent bump in compression by milling the thickness of the head gasket off and still maintain a .042 piston to head clearance for quench. If it’s primarily a cruiser and you’re changing to a hydraulic roller cam, there are several computer controlled cams available that would make more vacuum and DCR if you don’t want to get into raising the compression.
 
Don't use those 340 chamber Ede heads. Get 60779's, closed chamber, and set up the head clearance with your gasket thickness.
 
Garrett Ellison said:
What heads and head gaskets? And what’s the overall intent of the vehicles usage, and what transmission, gear, and converter? I seen that Hughes recommended a hydraulic roller. Are you planning on the hydraulic roller switch? When you get into milling the heads enough to raise compression and running high lift, it’s a good idea to co talk to Mike at B3 about rocker geometry correction. Those heads have a .060 deep relief cut around the combustion chambers. You can get a pretty decent bump in compression by milling the thickness of the head gasket off and still maintain a .042 piston to head clearance for quench. If it’s primarily a cruiser and you’re changing to a hydraulic roller cam, there are several computer controlled cams available that would make more vacuum and DCR if you don’t want to get into raising the compression.
Click to expand...

So they are the Edelbrock aluminum heads 65cc open chamber because of .018.out.the hole. felpro .039 head gasket. I just want a nice fun sreet car. It's a 4 speed with Passion Hemi OD gear set. .78 (4th) and 4.10 gears with 25.7" tires (245/45/17).

I wanted the higher vacuum so it will make the tune easier with the Efi. The roller was just a thought, they have Hydraulic FT with very similar specs.
 
a-bodyguy said:
8.9 dcr would be good
why is hughes saying 9.3 if you are9.8?
what trans and gear ratio tire diameter ? are you racing/crusing?
you could run rhoads lifters with the 703 and pick up vacum and low speed torque under 3k
alum heads id want 11 to 1 with 230@50 duration
Click to expand...

Great question. Not sure why he said that.maybe a typo. I emailed back with a screenshot of the calculator.
 
plumkrazee70 said:
I am heavily considering changing cams because the Lunati 703 didn't produce very much vacuum (10-11") and for the EFI, I'd really like it to be higher.
Click to expand...

OK, so you have EFI, and I guess that really means it's TBI, right? So why are you concerned about VAC when your using TBI?
 
plumkrazee70 said:
If the piston is .018 out the hole it's open for that reason? They are only 2 cc different between the two part numbers.
Click to expand...

Because it's a bad design. It's not about the cc's.

You set quench with a gasket, simple and easy. Those chambers, are not consistent. .018 out of the hole, put a .055-.060 gasket on it.

Your car, your stuff. As I say, pick your parts, pay your money.
 
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I don't want the thread to get too off track here. Back to the main question. How do my numbers look in the calculator? To me they looked pretty good so maybe I'm missing something.
 
plumkrazee70 said:
Yes, Fitech EFI. They are easier to tune with a higher vacuum reading for the MAP sensor.
Click to expand...
Well, I'm sort of skeptical of that, but if it's truly the case, then I'd be sending that Fitech system back for a refund.
 
Bakerlite said:
Well, I'm sort of skeptical of that, but if it's truly the case, then I'd be sending that Fitech system back for a refund.
Click to expand...

Not saying it's impossible to tune or that it's impossible to run at 10" of vacuum. I've seen guys run as little as 6".

I just want to make my life a little easier. I've been under the hood of this car longer than it's been on the road. To be honest, I'm losing interest due to burn out. I have the opportunity to get the right combination of parts once and for all. (I hope).

I just want a strong street car (high torque) that has excellent street manners and great drivability. Couldn't care less about HP.
 
Don't get real hung up on compression. Remember, it's only about a 3% increase from one ratio to the next going up, so that's not where the most power is made. All these guys around here will have you running on the ragged edge of detonation if they have their way. I would concentrate on getting a GOOD port job done on those heads. That in and of itself will add more than going up one compression point. A 9.3:1 small block with good flowing aluminum heads and EFI can make a lot of power. If it's a street car, the very last thing you want is to be fighting detonation sitting in traffic with heat soak.
 
RustyRatRod said:
Don't get real hung up on compression. Remember, it's only about a 3% increase from one ratio to the next going up, so that's not where the most power is made. All these guys around here will have you running on the ragged edge of detonation if they have their way. I would concentrate on getting a GOOD port job done on those heads. That in and of itself will add more than going up one compression point. A 9.3:1 small block with good flowing aluminum heads and EFI can make a lot of power. If it's a street car, the very last thing you want is to be fighting detonation sitting in traffic with heat soak.
Click to expand...

Thank you. So what do you think of the calculated numbers above?
 
plumkrazee70 said:
Thank you. So what do you think of the calculated numbers above?
Click to expand...
I think they are fine. At that compression with aluminum heads, it will very likely run and run GOOD on 87 octane. Why put yourself in the poorhouse driving something?
 
RustyRatRod said:
I think they are fine. At that compression with aluminum heads, it will very likely run and run GOOD on 87 octane. Why put yourself in the poorhouse driving something?
Click to expand...

Ok. I guess I was thrown by what Dave at Hughes said about the compression was working against me. I emailed him back to clarify. I though the dcr was right where folks like it for pump gas.
 
Are your pistons sitting .018 out of the hole? If so your numbers are out.
 
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plumkrazee70 said:
Ok. I guess I was thrown by what Dave at Hughes said about the compression was working against me. I emailed him back to clarify. I though the dcr was right where folks like it for pump gas.
Click to expand...
I wouldn't lose any sleep over it man. Are you lookin for the last 15HP? Or is this something you want to actually have some FUN with? It's totally up to you. I'd build it and let er rip.
 
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