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Compression ratios

  
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Compression ratios

 
Ravoll Ravoll
V-6 Camaros rule! | Posts: 85 | Joined: 02/12
Posted: 09/02/12
11:43 PM

Hi all,
Need some help from more knowledgeable people on this.
Want to change my 75cc heads out for a pair of 60cc's.
the 75cc's are factory and specs say I have a CR of 8.2:1.
What CR will the 60cc's give me?  
The older I get,the faster I was.

pepsi1 pepsi1
Big Block power for the win | Posts: 940 | Joined: 03/11
Posted: 09/03/12
04:18 AM

Heay Ravoll:

Some more info if you can.

1. Head gasket thickness?
2. Are you using 2 or 4 eyebrow pistons. Or flat tops?
3. Your deck: Are you using the stock 9.020 for your Small Block.
That was punched .030 correct?

58CC heads if you use a steel shim head gasket i.e. .015 yield 10:1:1. I don't recommend a steel shim head gasket unless your heads and block surface are flat. Use a $1.00 can of Aluminum or Gold Spray Paint,they work fine. Spray 2 light coats on each side of of gasket letting it dry to touch between each coat.

60CC heads if you use a gasket i.e. .039 may yield 9:7:1 MLS Gasket

64CC heads if you use a gasket i.e. .039 may yield 9:4:1 MLS Gasket

76CC heads if you use a gasket i.e. .039 may yield 8:6:1 MLS Gasket
all figures with flat top 2 eyebrow piston = with 9.020.

Bob  

pepsi1 pepsi1
Big Block power for the win | Posts: 940 | Joined: 03/11
Posted: 09/03/12
04:30 AM

Ravoll:

Clean those head bolts really good.If your using ARP head bolt follow their torque specs, and their procedure. Chase the threads in the block, and the heads for the intake manifold bolts.

If your using a none ARP head bolt fastener use the GM torque specs, and use a sealer where the bolts go into water.

Ravoll: I know the gas where you are is very expensive, but can you get racing gas, or  AV Gas fuel from the airport?

Bob  

Ravoll Ravoll
V-6 Camaros rule! | Posts: 85 | Joined: 02/12
Posted: 09/03/12
06:28 AM

Hi Pepsi,
The gaskets I'm using now are normal run of the mill felpros.
The pistons are stock L48 corvette with four valve reliefs,or eyebrows.Decks are fac.and it's still standard bore .(I only honed and re ringed using the original parts.This engine had very little miles on it.Cylinders had no ridges and could still see the factory crosshatch all the way around).
Factory specs for this engine with the original 462624 cast heads,put's the CR,static, at about 8.2:1. Thats what's on it now.Now here's the deal.With this comp XE262H cam,the dynamic CR is probably only about 7.5:1, due to the later closing intake valve.

I have a set of 305, 60cc, 1.85/1.5, (cast 376450) heads in real good shape.I'm also looking at a set with 58cc 1.85/1.5,cast (14022601).Won't know what shape the 601's are until I get them, and tear em down.
Not trying to build a monster out of this thing,just want to see if I can get better mileage from a bit more compression,with little or no sacrifice in the performance a have now.

Plan is to take a set of 305 heads,port match the runners,blend the bowls,skinny down the guide bosses, and a little unshrouding.Figure I can get em to at least flow as good if not better than the 462624's I have now,and get my compression back up.Plus it's something to do in the winter months.Still driving it now with these horror gas prices.
As far as race fuel or avgas goes.I can get JP race fuel all day here,but I'd rather just pay the $9.00 a gallon for plain 94 octane at the pump. It's cheaper. Tongue


P.S. I always chase the threads and use sealant on the bolts into the water jacket. Smile

Alan  
The older I get,the faster I was.

pepsi1 pepsi1
Big Block power for the win | Posts: 940 | Joined: 03/11
Posted: 09/03/12
11:10 AM

Alan:

I know that you will chase the threads, and do a good clean-up job. I always mention things like that. Reason that we may get a newby on the forum , and they may not think of such a thing. I could believe the torque multiplication or (K-Factor) from a dirty bolt. In fact what you, and I see as a normal way of doing things someone else may just pass by.

Back 2 years ago or so I was doing some load tests on different bolts. (Makes and materials). I have a strain gauge set-up I made way back as  project for myself as I had nothing to do that day HAH...HAH.I could not  believe the torque values or (K-Factor) that results from a dirty clamping bolt.I won't bore anyone with with the results as they are very interesting. If you want the info I will post it.

Do any of those heads have 3/8ths valve stems on the exhaust valve. The list I have for the 462624 head says they are heavy duty truck heads. Used on engines 350 to 400. Sometime GM has even put sodium filled valves in some of the heads.But they list a small valve for those heads. the 1.72/1.5 or 1.94/1.5 or 2.02/1.6. Very interesting. If you are going to try and unshroud the back side of the head. I would put as much back cut on the intake and exhaust valves as possible. A 5 angle valve cut will help getting things moving. Grin  Cool

I hope all your labor reworking the smaller valve heads, doesn't cause a loss of performance. If I were to install a small valve head on a 4.00" bored block I would stuff as much lift and duration on the cam as possible. To make up for the lack of valve diameter, and flow on those heads. Good Luck Alan. Grin  Cool

Bob

Keep the valve open long and higher...  

Ravoll Ravoll
V-6 Camaros rule! | Posts: 85 | Joined: 02/12
Posted: 09/04/12
12:59 AM

Hi Bob,
I forgot to add,I'm going with a 30 degree back cut on the valves.My machine is old and not set up for any multi angle cutting.Doing this all my self so I'm only in it for the price of gaskets.
The 462624's I have on now are 1.94/1.50 and the others are 1.84/1.50.I'm hoping that the .462in , .469ex lift and 218in/224ex duration will offset the effects of smaller valves.We'll see.
Alan  
The older I get,the faster I was.

pepsi1 pepsi1
Big Block power for the win | Posts: 940 | Joined: 03/11
Posted: 09/04/12
05:23 AM

Alan:

When I started out back in the day. I actually made a cutter. I had the old stone type valve seat grinder. I then just lapped the seats to make sure they had a seal. I didn't have a stock pile of old used up valves. Any that were questionable I pulled a vacuum on...

So I went to the grumpy old guy at the machine shop. I think grumpy isn't harsh enough, he was nasty. I asked him if I could have the old valves he didn't want. He said (KID) see the parts over there they need to be washed. Get the idea. So I would get what he had and if I destroyed them so beit. Grin  Cool

You can do just fine with a 30* degree angle back cut that will work also. Those heads really need to have angles. But any angle you put on the valve should go in the head also.I know you will get it to work. Let me know how you make out. Okay.

Heay have fun doing it, and take your time. I know Alan I'm giving you a little hard time.But talking to you over the past you work outside the box. You will make it work.... I know parts are not as easy to get in Germany as in the States. That's something that is beyond our control, and prices.... Laugh

Bob  

pepsi1 pepsi1
Big Block power for the win | Posts: 940 | Joined: 03/11
Posted: 09/04/12
06:03 AM

Alan:

I went looking for my old data on cylinder heads (I like to call budget heads).

Let me pass this on to you and anyone who would like the values.
30 degree angle versus the 45 degree angle....

Starting at the top cut of the exhaust valve seat angle. Now if you can cut  the following...
30*X 0.050" wide
45*X 0.020" wide
60*X 0.035" wide
75*X 0.050-0.10" wide then blend into the port.
I know you said you can only cut a 30* angle, but if you ever find an old valve cutter and seat cutter these numbers work well on a budget.Those angles on the buget head will flow to over .600 cam lift. With all the correct valve train components....

Now the Intake Valve seat angles. 30 degrees versus 45 degrees. Starting at the top cut of the Intake vale. Now I know these are very thin seats, but they work!!
Top Cut-30" X 0.01" that translates to .010 of an inch...
Now the Seat 45" X 0.060"
Or sneek this in.. 60" X 0.020"
75* X 0.04-0.08" The rest blend to the port.  It's fun cutting angles like that..
I'm only having fun with you Alan, so don't get pizzed at. All those cut angle numbers are good. They flow very well .600 cam lift is a good round number.

Thats how I cut angles for guys that have to run stock 305 heads. For stock and super stock classes....

Anyway if you are replacing the valves they are usually cut @ 45*. Then just back cut them to you 30* and they should work fine....Watch that the seats are good and you have NO LEAKERS. Run the exhaust valve a little on the loose side. The clearance gets taken up really quick. Even if it puffs when the engine has sit over-night. When you start the engine it puffs, and thats it.

You know about watching the retainer to valve seal height. Then coil bind. At Maximum valve lift that you want 0.060 between the coils. Let us know how you make out with the smaller valve heads...

Bob  

pepsi1 pepsi1
Big Block power for the win | Posts: 940 | Joined: 03/11
Posted: 09/04/12
06:17 AM

Alan:

If you have a 1.6 rocker arm even a cast iron set. Try putting the 1.6 rockers on the exhaust valves. If the engine pulls harder, put them on the intake side also. I know I dumped a lot of information on you. But that is why we have storage disks today...LOL...

Do you have swap meets in Germany like back in the States? If you do and you go to any. I'll give you head numbers to look for.If you want them PM me and we can do something that way. How about if we do it that way. Winter is coming,and the refreshen's we be coming in. Let me know and I'll do anything I can to help you.

I just hope your engine pulls atleast to 5500RPM out of the hole. I would hate to see it pull hard and then at 3300RPM fall on it's face. Or the opposite. We can talk about what you have. Have a super good one.

Bob  

Ravoll Ravoll
V-6 Camaros rule! | Posts: 85 | Joined: 02/12
Posted: 09/05/12
04:03 PM

Hi Pepsi,
Yeah, a lot of info you gave me there Bob.Gonna stick to the 45's with a 30° back cut.Not sure about the width of the 30° cut though.I know now that if the seat's riding high on the valve, it don't leave you much to back cut.Did a few cuts on some junky old valves for practice.I still have the original, cracked 462624's,so I use them as "practice blocks". I face cut the 45°on an exhaust valve,and lapped it in so I could see where the seat is riding.Right in the middle.So I back cut the 30° just enough so the 2 angles meet just above where the lap track starts ,but not into it.The 30° surface is about just as wide as the lap track.I think that's gonna be what I want.If not to much.
If I could find my camera I could post a pic.I really am quite proud of itGrin

Thinking out of the box ? You bet. It's a box of old valves this time. Grin  
The older I get,the faster I was.

pepsi1 pepsi1
Big Block power for the win | Posts: 940 | Joined: 03/11
Posted: 09/05/12
06:16 PM

Alan

Like I said with the conversations we've had in the past you've cut the sides of the box way down. Those 2 angles are probably the mosi inportant for a small valve head. I told you may story, and how I taught myself. I'm here if you need any help, what the HECK am I saying. Confused

To bad you can't do a before, and after flow curve. Then you can see the difference it really does make. Not for anything, but just a reference for yourself. If you ever do another set. Grin  Cool
                                       Bob

Just a little FYI if anyone is looking for a nice inexpensive package together. Cool  

My oldest son did a set of plain jane #998 heads for his 1986 Monte Carlo SS. Back in 1995. I guided him what to do, and he saw the difference between a 1" port down the hole and the 2" port down the hole. Pocket, and exhaust bowl work.GM lacks flow on the exhaust side. Then he did a 3 angle valve job.We kept the 194./150 valves. He installed a Fel-Pro Steel Shim head gasket, and we were at 9:3:1 with the junk gas. He started using av/gas and 93 Mobil. really everything was a nice combination.

Life started as a 1979 Z28 seasoned block. It had a balanced steel crank forged pistons, and the old pink roks with the latest GM HiPO rod bolts. Grin
Stock 600CFM Q-Jet Reworked
The #998 76CC Ported heads, and 3 angle vakve job.
Stock HEI Reworked curve.
Timing 12* base, 32* all in at 2,500RPM.
We can push the timing to a toal of 38* if he needs to.
Crane Blue Printed cam for the 350/327 hydraulic.
.444/.444 with .222/.222@.050 put in straight up.
Trw  flat top pistons
Cloyes roller timing chain.P/N 9-3100
We used Stock AC spark plugs we went 2 steps colder. The stock AC's called for to use were R45TS. We down to AC R43TS gapped at .032
The stock Heavy-Duty Radiator was used with a 180* thermostat, and my son wanted a lot of cooling. So he used the biggest electric cooling fans he could fit on the radiator. Blush  Blush  

Headman Hedders 15/8 primary tube with real dual exhaust
TCI Street Fighter TH350 standard forward shift pattern with 2,500 TCI hole shot convertor, deep pan and a 22,000 LBs. van trans cooler.
Stock 75/8 posi rear with 3:73:1 and stock axles, I don't know how long the little rear will old up. It does need a complete Ford 9" with 33 Spline axles, and a posi rear, with 3:73:1 will get the call.
He put wider tires on. I don't remember the size, but he stayed with the stock 15" wheel. I never drove the car, but as a passenger. It pulled really hard. He ran it for 3 summers. Then got married and the car has been  in his garage for about 14 years. He takes it out once in awhile, to blow the dust off...LOL... Grin  Cool
                                      Bob  

Ravoll Ravoll
V-6 Camaros rule! | Posts: 85 | Joined: 02/12
Posted: 10/29/12
10:43 AM

Hi All ,
Still trudging along on my head project.Have new questions regarding valve guides.
Mine aren't that bad,persay,but both sets of heads I'm rebuilding were using oil.So why not?
I've ordered some 11/32 + 0.030 guide "liners",an 11/32 ball hone,rocker studs,guide plates and hardened push rods.Have a Buddy with an industrial machine shop.Not automotive,but he understands what I'm doing ,and has machines we can adapt for reaming the guides,and milling/threading the stud bosses.Plus I have a cracked set of heads we can try first,before we wreck the good ones Tongue

Here's the question.Do these liners "need" to be broached?

I'm using the original 1.50/1.84 valves.They started life as 11/32 stem dia.,but since they're slightly used we will need to hone the straight. After we hone them they will be some what smaller.If I broach the liners to 11/32
I will possibly have the guides to big.

My thoughts now are;
Ream the guides + 0.030,install the liners and broach each liner to match the valve stem that's going in it,(I can get broach balls here for next to nothing.)

or...

Ream the guides only + 0.025 or so,making a tighter fit,skip the broaching, and just hone them to size. Grin

Any way I do it I will still basically have to match the guides to the stems.

Any feed back on this would be appreciated,before I have to call the automobile club to get me off the autobahn next summer. Tongue  
The older I get,the faster I was.

68scott385 68scott385
I have an SS396 tatoo | Posts: 325 | Joined: 07/09
Posted: 10/29/12
01:53 PM

http://www.kb-silvolite.com/calc.php?action=comp

this link will help you figure compression ratios  
68scott385 68scott385 68scott385

Ravoll Ravoll
V-6 Camaros rule! | Posts: 85 | Joined: 02/12
Posted: 11/01/12
02:11 AM

Thanks Scott,
Already have this.Just have to wait till I get the heads off to do any calculating.
My main concerns right now are the guides.
ALAN  
The older I get,the faster I was.

68scott385 68scott385
I have an SS396 tatoo | Posts: 325 | Joined: 07/09
Posted: 11/01/12
06:53 AM

I know there are several measurements required that most of us don't think about until it comes time to REALLY calculate the compression ratio of our baby. The shape of the piston top can really play games with the compression ratio.

I played with the numbers from several motors I've had over the years. Generally a chnage of 16cc in the combustion chamber changes the compression ratio 1.2:1 to 1.6:1. So your 8.2 becomes 9.4:1 to 9.8:1.

You quoted factory spec of 8.2, many tiimes factory specs are more generous than we realize. I have measured my own factory motors on teardown and found them to be closer to 7.75:1 than the advertised 8.5:1. Those were mid-70s smoggers too, if that makes a difference.  
68scott385 68scott385 68scott385