Compression Ratio and RAU Advice

T

timray87

Active member
I should be receiving an assembled aluminum head and 4bbl intake in a few weeks, I'm planning on installing it on my stock bottom end (1970 Maverick) that was rebuilt .030 over about 80k ago. The aluminum heads online are supposed to be 50cc +-1, with my calculations online compared to my log 62cc head should change my CR from 8.7:1 to 10:1? Does that sound right? I'm looking for some advice on the head gasket that I should use with this because I don't want to go much over the 10:1 if possible.
Secondly, I've been seeing some of the 1.65:1 RAU setups on here, and I'm thinking about doing that as well, but once I rebuild the motor I'll be using a pretty tall camshaft and I don't know if the new higher ratio rocker arms would be too much with a big camshaft and I'd have to replace them back with stock?
Thanks! I'll be posting more as I receive the goodies!
 
Howdy Tim:

My advice is to wait til you have the new head in hand. Measure the chamber volume and go from there. No good can come from guessing.

Once you have the head, your only readily available choices of head gaskets will be a Fel Pro at aprox .050" or a Victor at .046".

On the rockers, I'd go for the lift in the cam. Good Luck and Keep us posted.

adios, David
 
Tim, you may have checked out the dyno room on the classic inlines site, but if not, it shows you several different packages that may help you to visualize your build. You are right, the 1.65 rockers will alter the personality of your cam, which you will have to identify so you can do the dynamic compression calculations. Good available head gaskets have similar thickness', but will help you dial it in perfect when you know what the other pieces of your awesome Ford puzzle are!
 
Do you know what cam you are going to use? Check out the flow numbers and dyno room links on the CI web page. The flow page shows that things kind of peak around 0.500 lift. There are marginal gains after that but they will start to get expensive (think HP/ $). There are a couple decent online calculators you can use for DCR. Keep it below 8.5 or so and you should be good to go. The aluminum head is supposed to be a little more forgiving than the cast iron.

Disclaimer: I'm parroting what I've read in the past. Always do your own research because I've been known to make mistakes. This one time, I even bought a pencil with an eraser on it. That was just a waste of money....
 
David, I am building a 250 for drag race only turbocharged on E-85, I will need a copper head gasket, who manufacturers those? Thanks Randy
 
hotrodguy":16zfetfw said:
…need a copper head gasket, who manufacturers those?
Click to expand...

URself, some here suggest the copper spray on one side.
 
With some good snips and an assortment of punches you can cut your own copper gaskets using the stock gasket as a template. Dead soft copper, annealed before installing, use copper spray to help seal it.

But for a turbo application you should consider also o-ringing the block.
 
RichCreations":pfi7c8s2 said:
Not sure there is one…
Click to expand...
Pretty darn expensive, but moot point - didn't he say "turbo'? Try the "turbo/nitro/etc forum on here hotrod.
AND
back to timray's Qs.
 
Thanks for the replies. Sorry I've been busy and couldn't hop on the last few days.
I was thinking something like the 274-274-110, but I'll be installing that when I do the rebuild and forged bottom end to prep it for about 20lbs on a turbo. At that point I'll be getting new forged pistons and asking advice for a good CR for the turbo (probably 8.5ish?). In the mean time I'd like to get some fun out of this build, hence the questions I'm asking. With the RAU set up, from what I'm reading they may not work well with the 274-274-110 cam? If I'll be able to use the RAU long term on my big kid build, then I'll probably go through with it, otherwise I'll be throwing $600 away for a short term build.
I'll take your advice and check the CC on the new head once it arrives and get the appropriate head gasket at that time. I live in Colorado with high altitude, so I've heard you can go as high as 10.5:1 on pump gas if you dial everything in well... I'd like to stay closer to 10:1 to play it safe.
 
"…with high altitude…"
not till U pass those big rocks to Estes!
:eek:
 
What in particular are you concerned about with the RAU setup? I'm running the 1.65 ratio on a stock head right now. My new head will be done soon. Only thing he has to really check yet is for the valve spring clearance with the new damped springs. The lift on that 274 cam should be 0.300" which will be just shy of 0.500". So as long as you're not advancing the cam beyond 4* I don't know why it should be an issue. I think you're good to go.
 
chad":346ohw0x said:
"…with high altitude…"
not till U pass those big rocks to Estes!
:eek:
Click to expand...
Not sure if you know Estes well, but I have a story about a '79 Camaro driving on a sidewalk that I thought was a road :D
 
cr_bobcat":2l9rupfa said:
What in particular are you concerned about with the RAU setup? I'm running the 1.65 ratio on a stock head right now. My new head will be done soon. Only thing he has to really check yet is for the valve spring clearance with the new damped springs. The lift on that 274 cam should be 0.300" which will be just shy of 0.500". So as long as you're not advancing the cam beyond 4* I don't know why it should be an issue. I think you're good to go.
Click to expand...

I was just worried that the lift of .500" on that cam with those rockers would be too much and the car would then just be a race motor, but very poor drivability and I'd have to go back to stock. The new head is supposed to have the dual-coil springs, so maybe this would be a good investment for my existing NA build and then the turbo build after this?
 
timray87":1sgffmg9 said:
Not sure if you know Estes well, but I have a story about a '79 Camaro driving on a sidewalk that I thought was a road :D
Click to expand...
I usta live @ Sunrise Ranch & went up the hill a few times (1980s - in my 30s then, 60s now).
So, no EP was in the clouds. :cool:
Love 2 hear bout anything "out there". Might help me feel like a kid 'gain.
:unsure:
('n my joy/life is about sharin stories)
 
timray87":32gjm086 said:
cr_bobcat":32gjm086 said:
What in particular are you concerned about with the RAU setup? I'm running the 1.65 ratio on a stock head right now. My new head will be done soon. Only thing he has to really check yet is for the valve spring clearance with the new damped springs. The lift on that 274 cam should be 0.300" which will be just shy of 0.500". So as long as you're not advancing the cam beyond 4* I don't know why it should be an issue. I think you're good to go.
Click to expand...

I was just worried that the lift of .500" on that cam with those rockers would be too much and the car would then just be a race motor, but very poor drivability and I'd have to go back to stock. The new head is supposed to have the dual-coil springs, so maybe this would be a good investment for my existing NA build and then the turbo build after this?
Click to expand...

You will be better off with the bronze bushing and hard chrome shaft rau than the steel on steel stock stuff.
Have your custom turbo cam designed for the 1.65 , that is what they do.
 
Howdy Back Tim:

What is the lift on the 274 cam you are considering? FYI- there comes a point of no returns on cam lift. While the Aluminum head flows well at the higher rpm ranges, there is still a point where no gain is had. Yes, the turbo will raise that, but still? Also be aware of coil bind on the valve springs as well as the bottom thickness of the valve spring retainers. Just some thoughts.

Ps- both your elevation and the alloy head will allow somewhat higher CR, as well as the lower cylinder pressures because of your proposed cam durations. You have a very interesting build going. Keep us updated on your planning and your progress.

Adios, David
 
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