Dynamic Compression Ratio issue
03-03-2009, 10:12 AM
#21
Drifting
03-03-2009, 11:55 AM
#22
Le Mans Master
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Also, does anybody else have anything bad to say about Comp Cams? I thought they were a reputable cam company.
Scott
03-03-2009, 12:24 PM
#23
Race Director
My calculations are based on using the 60759 70cc aluminum heads from edelbrock and stock dished piston that add 12cc to the combustion chamber. Is this an accurate amount for stock 1980 L48 pistons? The old corvette L98 aluminum heads have a 58cc chamber, and they are supposed to have decent flow, kinda small valves, tho, but I could probably pick up a pair used for pretty cheap money. I think they have the changed intake bolt angle, too, is this correct? If so, I'd have to get a new intake manifold, or have my old one (edelbrock pewrformer) drilled. Only thing is, with the thin head gasket to keep the quench tight, that would give me a 10.14:1 static CR, with a 8.82:1 Dynamic CR, with a CC 252H cam, that's a little high for the cheapo gas, I think
Also, does anybody else have anything bad to say about Comp Cams? I thought they were a reputable cam company.
Scott
Also, does anybody else have anything bad to say about Comp Cams? I thought they were a reputable cam company.
Scott
Last edited by 63mako; 03-03-2009 at 12:26 PM.
03-03-2009, 01:04 PM
#24
Le Mans Master
Scott, I agree you need a bigger cam than the CC 252H, and that a 268H should work out nicely as mentioned by 63mako. I can't speak for others, but based on my experiences with them, I don't have anything bad to say about CompCams products, and will be putting a custom CC solid roller in the 427 BB I'm building up (already have the heads assembled with CC's matching springs, titanium retainers...); tho I am electing to go with a steel core w/iron gear in lieu of trusting this engine to an austempered roller core. Guess that brings me up to $.04.
03-03-2009, 01:56 PM
#25
Le Mans Master
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Keep in mind, guys, that this is a bone-stock, two bolt main, all cast iron bottom end with 60,000 miles on it. I'm scared to push it too hard, ya know? I really don't wanna rev it past 5 grand or so. Maybe I could meet ya half-way and consider the 260H or it's equivalent from a different maker.
Scott
Scott
03-03-2009, 05:44 PM
#26
Race Director
Keep in mind, guys, that this is a bone-stock, two bolt main, all cast iron bottom end with 60,000 miles on it. I'm scared to push it too hard, ya know? I really don't wanna rev it past 5 grand or so. Maybe I could meet ya half-way and consider the 260H or it's equivalent from a different maker.
Scott
Scott
Last edited by 63mako; 03-03-2009 at 06:02 PM.
03-03-2009, 09:42 PM
#27
Le Mans Master
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OK, let's try this again!
I have spent a little time doing some research and here's what I have come up with:
Edelbrock E-tec aluminum heads (essentially, an aluminum Vortec head made by Edelbrock) these have a 64cc combustion chamber, 1.94 in intake valves, 1.55 in exhaust valves. Ya have to use a vortec style intake manifold, but no biggie, 175 bucks for an Edelbrock E-tec Performer w/ spreadbore flange.
All righty-then, here we go:
with these heads, and a Comp Cams 268H cam, .015 head gasket thickness, 4.125 in gasket bore, I get a static CR of 9.48:1, a dynamic CR of 7.86:1, and a quench distance of .040 in.
Now, the cam is rated for 1500 to 5500 rpm
the intake manifold is rated at 1500 to 5500 rpm
I have a reasonably tight quench
I have a Dynamic CR of less than 8:1
a fast-burn combustion chamber
aluminum head
I can still use my Quadrajet
I have a reasonably free flowing exhaust system (block hugger headers, 2 1/2
exhaust, true duals w/ cross-over pipe going into magnaflow mufflers)
What do you guys think of that? I think it's pretty good, all the parts are made for the same operating range, I have alot of factors pointing to resistance to detonation, I think this might be it!
Scott
I have spent a little time doing some research and here's what I have come up with:
Edelbrock E-tec aluminum heads (essentially, an aluminum Vortec head made by Edelbrock) these have a 64cc combustion chamber, 1.94 in intake valves, 1.55 in exhaust valves. Ya have to use a vortec style intake manifold, but no biggie, 175 bucks for an Edelbrock E-tec Performer w/ spreadbore flange.
All righty-then, here we go:
with these heads, and a Comp Cams 268H cam, .015 head gasket thickness, 4.125 in gasket bore, I get a static CR of 9.48:1, a dynamic CR of 7.86:1, and a quench distance of .040 in.
Now, the cam is rated for 1500 to 5500 rpm
the intake manifold is rated at 1500 to 5500 rpm
I have a reasonably tight quench
I have a Dynamic CR of less than 8:1
a fast-burn combustion chamber
aluminum head
I can still use my Quadrajet
I have a reasonably free flowing exhaust system (block hugger headers, 2 1/2
exhaust, true duals w/ cross-over pipe going into magnaflow mufflers)
What do you guys think of that? I think it's pretty good, all the parts are made for the same operating range, I have alot of factors pointing to resistance to detonation, I think this might be it!
Scott
03-03-2009, 10:03 PM
#28
Race Director
Bet it will run on 87 octane with a properly curved distributor. Sounds like a well matched combination that will do exactly what you want.
03-03-2009, 10:34 PM
#29
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Nice combo!
For maxpwer (timing) you would need 89-91 at least.
You can gain gas mileage with more timing that may offset the 10% increase in fuel cost to 93 octane. All you need is ~1.5 more mpg to offset the costs.
I had some knock on very hot days with 93 oct and 7.75:1 DNCR.
For maxpwer (timing) you would need 89-91 at least.
You can gain gas mileage with more timing that may offset the 10% increase in fuel cost to 93 octane. All you need is ~1.5 more mpg to offset the costs.
I had some knock on very hot days with 93 oct and 7.75:1 DNCR.
03-03-2009, 11:03 PM
#30
Le Mans Master
Now we're talking.
I, too, would suggest this is going to be a ~90 octane motor. howarsc also brings up a good point concerning better mpg w/higher octane gas, which I've seen proven time and again on my DD's fuel computer. Whenever there's not a big difference in cost between grades, it doesn't take a big improvement in mileage to make it a wash.
I, too, would suggest this is going to be a ~90 octane motor. howarsc also brings up a good point concerning better mpg w/higher octane gas, which I've seen proven time and again on my DD's fuel computer. Whenever there's not a big difference in cost between grades, it doesn't take a big improvement in mileage to make it a wash.
03-03-2009, 11:21 PM
#31
Race Director
He could quite possibly get by with 87. Those fastburn chambers will allow best power @ 32-34 degrees instead of the 36 we generally need. A couple degrees retard can make the difference. Max DCR on aluminum heads to run 93 is generally 8.5 minus a safety margin. Good combo though.
Last edited by 63mako; 03-03-2009 at 11:24 PM.
03-04-2009, 12:10 AM
#32
Le Mans Master
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I live in Massachusetts, so a "hot day" is a relative thing! (howarsc, I see from your avatar, you are in Florida) plus, while I'm doing the cam, the radiator has to come out, so I'm planning on installing an aluminum radiator while I'm at it, should help to keep things nice and cool. I figure, aluminum heads to dissipate heat to the coolant really well, and an aluminum radiator, to dissipate coolant heat to the atmosphere really well, they kinda go hand in hand. Plus, it weighs less than a copper radiator, and any weight you can remove from a car without sacrificing anything, is never a bad thing. Win-win! (unless you take my wallet's point of view into consideration!)
As far as better mileage offsetting the cost of better fuel, it really irks me to pay more for fuel, but if ya burn enough less of it, it does make sense. Probably a little better for the environment, too. (less fuel burned=less emissions?) Although, I guess one of the benifits of the fast-burn combustion chamber, is that you can get away with less spark advance to make peak power. Something to do with the air-fuel mixture burning faster, so you don't need to light it up quite as early. I'm sorry to be going on and on about it, but if you do some research on the fast burn combustion chamber it's quite interesting. I found out that it's origins date back to the 1920's, when some british dude invented it to cope with the crappy fuel they had to deal with back then, and was a pretty common feature in automotive engines up until the 50's, when better fuel quality lessened the need for it. It then became a "forgotten art" up until recently, when it was "re-discovered" for the same reason it was invented in the first place----crappy fuel!!
The Dynamic CR is a little higher than I would like, it's cutting it pretty close, but I'm hoping that the combination of aluminum heads, fast-burn combustion chamber, and reasonably tight quench will get me by. The one thing that concerns me is that, if I understand how the fast-burn type combustion chambers work, my dished pistons will not be using the combustion chamber design as efficiently as a flat-top piston would. The only quench area will be around the outer perimeter of the piston. I hope it's enough. I could get a little less Dynamic CR by using a little bit thicker head gasket, but then I lose the quench........OH NO! DON'T OPEN UP THAT CAN OF WORMS, PLEASE!!!! I guess the only way to find out is to buy the parts, bolt it all together, do a little tuning, and see what happens! If I do end up with an engine that demands good gas, well, so be it, "ya live and ya learn", as my Dad used to say.
What sort of engine combo are you running? Do you have the fast-burn type heads, tight quench, and all that anti-detonation jazz? Just curious.
OK, that all for now, I feel good about this plan, it's much better than my original plan, (which I actually thought was pretty good, I spent a pretty good amount of time coming up with it, too! Oh well.....) and now comes the tough part----financing the whole project! I figure I'll aquire the parts one at a time as money allows, then when I'm ready, I'll do the whole thing over a long weekend at my brother's shop, or maybe one of my corvette club buddy's shops. I'll let you guys know how she runs when it's done, sure enough!
Scott
As far as better mileage offsetting the cost of better fuel, it really irks me to pay more for fuel, but if ya burn enough less of it, it does make sense. Probably a little better for the environment, too. (less fuel burned=less emissions?) Although, I guess one of the benifits of the fast-burn combustion chamber, is that you can get away with less spark advance to make peak power. Something to do with the air-fuel mixture burning faster, so you don't need to light it up quite as early. I'm sorry to be going on and on about it, but if you do some research on the fast burn combustion chamber it's quite interesting. I found out that it's origins date back to the 1920's, when some british dude invented it to cope with the crappy fuel they had to deal with back then, and was a pretty common feature in automotive engines up until the 50's, when better fuel quality lessened the need for it. It then became a "forgotten art" up until recently, when it was "re-discovered" for the same reason it was invented in the first place----crappy fuel!!
The Dynamic CR is a little higher than I would like, it's cutting it pretty close, but I'm hoping that the combination of aluminum heads, fast-burn combustion chamber, and reasonably tight quench will get me by. The one thing that concerns me is that, if I understand how the fast-burn type combustion chambers work, my dished pistons will not be using the combustion chamber design as efficiently as a flat-top piston would. The only quench area will be around the outer perimeter of the piston. I hope it's enough. I could get a little less Dynamic CR by using a little bit thicker head gasket, but then I lose the quench........OH NO! DON'T OPEN UP THAT CAN OF WORMS, PLEASE!!!! I guess the only way to find out is to buy the parts, bolt it all together, do a little tuning, and see what happens! If I do end up with an engine that demands good gas, well, so be it, "ya live and ya learn", as my Dad used to say.
What sort of engine combo are you running? Do you have the fast-burn type heads, tight quench, and all that anti-detonation jazz? Just curious.
OK, that all for now, I feel good about this plan, it's much better than my original plan, (which I actually thought was pretty good, I spent a pretty good amount of time coming up with it, too! Oh well.....) and now comes the tough part----financing the whole project! I figure I'll aquire the parts one at a time as money allows, then when I'm ready, I'll do the whole thing over a long weekend at my brother's shop, or maybe one of my corvette club buddy's shops. I'll let you guys know how she runs when it's done, sure enough!
Scott
03-05-2009, 08:00 PM
#33
Le Mans Master
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Hi, just bumping my post back up to the top, hoping someone will see and tell me what they think of my idea that the dished pistons won't be using the fast-burn combustion chambers as well as a flat-top piston would. This is aimed at 63mako specifically, as he seems to be very knowledgeable about the subject. Thank you,
Scott
Scott
03-05-2009, 11:09 PM
#34
Race Director
Flat tops are more resistant to detonation than dish pistons if the quench and compression are the same. I really don't think you will have an issue. Your using the stock bottom end so your somewhat limited in what you can do. Bottom end, cam and intake are all about 5500 RPM parts. With a 3.08 and stock convertor I think you have a nice well matched build planned that will give you a substantial power increase in your operating RPM, good MPG and not bust the budget.
03-05-2009, 11:41 PM
#35
Le Mans Master
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OK, thanks again for all your help, guys, I really appreciate it, and I also feel like I learned quite a bit from our discussion. And with that I will finally stop bugging you guys......at least for awhile......
Scott
Scott
03-06-2009, 01:06 PM
#36
Burning Brakes
I share your pain and went through many of the same decisions (with the help of many of the same people!).
As a result, I have almost your exact combo, but using different parts.
Edelbrock Performer (Gen II, older) Intake
041 casting double hump heads (cast iron)-62cc chambers
Comp 268H cam
Probe forged dish pistons (13cc dish)
.015 thick steel shim head gasket
Pistons are .025-.026 down in the hole for a .041 quench
I'm running 2.5" dump RAMs Horns into true 2.5" duals all the way back
SCR is almost perfect at 9.5
DCR is 7.8 something
I've had no detonation problems, but do run on premium just to be sure since I live in NC and we do get 'hot' days in the summer. You should be fine with Aluminum heads.
I've been real happy with the combo, but must admit I do secretly wish I had gone with a set of Brodix aluminum heads instead of my combo. Oh, well, that's what the next rebuild is for right?
Good luck.
As a result, I have almost your exact combo, but using different parts.
Edelbrock Performer (Gen II, older) Intake
041 casting double hump heads (cast iron)-62cc chambers
Comp 268H cam
Probe forged dish pistons (13cc dish)
.015 thick steel shim head gasket
Pistons are .025-.026 down in the hole for a .041 quench
I'm running 2.5" dump RAMs Horns into true 2.5" duals all the way back
SCR is almost perfect at 9.5
DCR is 7.8 something
I've had no detonation problems, but do run on premium just to be sure since I live in NC and we do get 'hot' days in the summer. You should be fine with Aluminum heads.
I've been real happy with the combo, but must admit I do secretly wish I had gone with a set of Brodix aluminum heads instead of my combo. Oh, well, that's what the next rebuild is for right?
Good luck.
03-06-2009, 02:13 PM
#37
Le Mans Master
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I share your pain and went through many of the same decisions (with the help of many of the same people!).
As a result, I have almost your exact combo, but using different parts.
Edelbrock Performer (Gen II, older) Intake
041 casting double hump heads (cast iron)-62cc chambers
Comp 268H cam
Probe forged dish pistons (13cc dish)
.015 thick steel shim head gasket
Pistons are .025-.026 down in the hole for a .041 quench
I'm running 2.5" dump RAMs Horns into true 2.5" duals all the way back
SCR is almost perfect at 9.5
DCR is 7.8 something
I've had no detonation problems, but do run on premium just to be sure since I live in NC and we do get 'hot' days in the summer. You should be fine with Aluminum heads.
I've been real happy with the combo, but must admit I do secretly wish I had gone with a set of Brodix aluminum heads instead of my combo. Oh, well, that's what the next rebuild is for right?
Good luck.
As a result, I have almost your exact combo, but using different parts.
Edelbrock Performer (Gen II, older) Intake
041 casting double hump heads (cast iron)-62cc chambers
Comp 268H cam
Probe forged dish pistons (13cc dish)
.015 thick steel shim head gasket
Pistons are .025-.026 down in the hole for a .041 quench
I'm running 2.5" dump RAMs Horns into true 2.5" duals all the way back
SCR is almost perfect at 9.5
DCR is 7.8 something
I've had no detonation problems, but do run on premium just to be sure since I live in NC and we do get 'hot' days in the summer. You should be fine with Aluminum heads.
I've been real happy with the combo, but must admit I do secretly wish I had gone with a set of Brodix aluminum heads instead of my combo. Oh, well, that's what the next rebuild is for right?
Good luck.
Hey thanx, that's very encouraging. How does she go? I mean are you happy with the power? what tranny and rearend ratio are you running?
Scott
03-06-2009, 02:23 PM
#38
Instructor
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I've read through this thread with great interest. I have very similar car, '80 L48, but with flat top pistons. Have done much of the same research on replacing heads and cams but came up with slightly different result. Why didn't you select a larger head, 2.02/1.60 ports since you have the exhaust capacity? The cost over the smaller 1.94/1.50 heads is minimal. Or, does the Vortec head give "good enough" flow for the total set up?
Since I'm "waiting on funds"
I look forward to your results.
Good luck.
Since I'm "waiting on funds"
I look forward to your results.Good luck.
03-06-2009, 02:57 PM
#39
Burning Brakes
In general I'm pretty happy with the setup, but I honestly haven't had enough time to really work out all the kinks.
In addition to the above, my setup includes a Hayes 15lb Aluminum flywheel. Tranny is the optional close ratio Super T-10 4-speed and the rear is a 3.70. Carb is the original quadrajet.
Car sounds awesome at idle. The quick ramp on the comp cams 268h gives it a very nice sound in my opinion. Off the line it pulls strong all the way through 5500 (which is what you would expect), but I think there are a few things leaving HP on the table that I need to go back and fix....
The heads: My heads are very well worked 041 castings. They are fully ported and polished, have 2.05 and 1.6 valves with the chambers opened up around the intake to eliminate intake valve shrouding, have Ferrea 5000 neck-down valves and com roller-tip rockers. My local racing shop did a great job with them and the work is very high quality. Problem is they just can't match even the cheapest vortecs you can buy today, and that's just reality. I know I'm leaving a good deal of power on the table here.
The Exhaust: I wanted to go with something stock looking (kind of a theme), so I decided to get some repro 65 fuelie rams horns with the 2.5" dump (std Rams horns are 2" dump). I then used the front pipes from the 65 fuelie and the mid pipes from the 73 big block to create a true 2.5" all the way back to the muffler. A couple of problems here; the repro castings are terrible. Even after grinding them out to port match them to a fel-pro 1404 gasket (and the exhaust ports), I could just tell they weren't going to flow very well. If I had to do it over again, I would probably go with shorty headers, probably McJacks and the Pypes system from the headers/crossmember back. The difference in what I spent and this system would really only be about $600, but I was doing so much that I just couldn't do it. I love the sound, but like another poster said, an engine is an air pump, and mine could be more efficient.
If your open to some lessons learned, here's some free advice....
Cooling: Don't just concentrate on your power side, take a good hard look at your cooling system as well. Your new motor will make more heat than your old one, and the cooling system needs to be up to the task to help avoid detonation. The L-48 radiator has one less core than the L-82 radiator (atleast it did in 78), so you might want to think about replacing that as well. At the very least, pull the radiator and shroud and make sure it is all clean and undamaged. Replace the seals around the radiator to ensure you get good flow THROUGH the radiator, not around it. Get yourself a RobertShaw thermostat that has the bypass in it. I used a 180 degree model to lower the temp a bit from the 195 stock. The bypass hole will help eliminate air bubbles when filling the motor for startup. Most importantly, make sure your water pump is in good condition! I re-used my original water pump on my build as it felt just fine. The car had a vibration at around 70 that I thought was a driveline vibration that turned out to be the water pump. A Walker Stage II aluminum pump fixed the problem quite nicely. Check your fan clutch to make sure it is in proper working condition, it is a critical piece of the puzzle. If you need to replace it, look around on the web and by a real ACDELCO replacement.
Cam installation and Break-in: So much has been written on this subject and the fact that modern oils have less zinc and other additives that I won't go into it here. Needless to say I was petrified of wiping a lobe during break-in. A small bit of insurance that I had done was to send the cam and springs to High Performance Coatings in Whitsett, NC to have their anti-friction coating applied. Had the cam done to help with break-in and the springs to help them stay cool and extend their lifespan. Don't know if I overdid it, but everything is still working well 1100 miles later.
I hope I answered your question. Sorry about rambling on about the other aspects, feel free to discard the information you don't need, but having done the exact same thing you are now doing, I hope I've helped you avoid some potential missteps.
You will enjoy the build.
-Fred
In addition to the above, my setup includes a Hayes 15lb Aluminum flywheel. Tranny is the optional close ratio Super T-10 4-speed and the rear is a 3.70. Carb is the original quadrajet.
Car sounds awesome at idle. The quick ramp on the comp cams 268h gives it a very nice sound in my opinion. Off the line it pulls strong all the way through 5500 (which is what you would expect), but I think there are a few things leaving HP on the table that I need to go back and fix....
The heads: My heads are very well worked 041 castings. They are fully ported and polished, have 2.05 and 1.6 valves with the chambers opened up around the intake to eliminate intake valve shrouding, have Ferrea 5000 neck-down valves and com roller-tip rockers. My local racing shop did a great job with them and the work is very high quality. Problem is they just can't match even the cheapest vortecs you can buy today, and that's just reality. I know I'm leaving a good deal of power on the table here.
The Exhaust: I wanted to go with something stock looking (kind of a theme), so I decided to get some repro 65 fuelie rams horns with the 2.5" dump (std Rams horns are 2" dump). I then used the front pipes from the 65 fuelie and the mid pipes from the 73 big block to create a true 2.5" all the way back to the muffler. A couple of problems here; the repro castings are terrible. Even after grinding them out to port match them to a fel-pro 1404 gasket (and the exhaust ports), I could just tell they weren't going to flow very well. If I had to do it over again, I would probably go with shorty headers, probably McJacks and the Pypes system from the headers/crossmember back. The difference in what I spent and this system would really only be about $600, but I was doing so much that I just couldn't do it. I love the sound, but like another poster said, an engine is an air pump, and mine could be more efficient.
If your open to some lessons learned, here's some free advice....
Cooling: Don't just concentrate on your power side, take a good hard look at your cooling system as well. Your new motor will make more heat than your old one, and the cooling system needs to be up to the task to help avoid detonation. The L-48 radiator has one less core than the L-82 radiator (atleast it did in 78), so you might want to think about replacing that as well. At the very least, pull the radiator and shroud and make sure it is all clean and undamaged. Replace the seals around the radiator to ensure you get good flow THROUGH the radiator, not around it. Get yourself a RobertShaw thermostat that has the bypass in it. I used a 180 degree model to lower the temp a bit from the 195 stock. The bypass hole will help eliminate air bubbles when filling the motor for startup. Most importantly, make sure your water pump is in good condition! I re-used my original water pump on my build as it felt just fine. The car had a vibration at around 70 that I thought was a driveline vibration that turned out to be the water pump. A Walker Stage II aluminum pump fixed the problem quite nicely. Check your fan clutch to make sure it is in proper working condition, it is a critical piece of the puzzle. If you need to replace it, look around on the web and by a real ACDELCO replacement.
Cam installation and Break-in: So much has been written on this subject and the fact that modern oils have less zinc and other additives that I won't go into it here. Needless to say I was petrified of wiping a lobe during break-in. A small bit of insurance that I had done was to send the cam and springs to High Performance Coatings in Whitsett, NC to have their anti-friction coating applied. Had the cam done to help with break-in and the springs to help them stay cool and extend their lifespan. Don't know if I overdid it, but everything is still working well 1100 miles later.
I hope I answered your question. Sorry about rambling on about the other aspects, feel free to discard the information you don't need, but having done the exact same thing you are now doing, I hope I've helped you avoid some potential missteps.
You will enjoy the build.
-Fred
03-06-2009, 05:24 PM
#40
Race Director
The heads: My heads are very well worked 041 castings. They are fully ported and polished, have 2.05 and 1.6 valves with the chambers opened up around the intake to eliminate intake valve shrouding, have Ferrea 5000 neck-down valves and com roller-tip rockers. My local racing shop did a great job with them and the work is very high quality. Problem is they just can't match even the cheapest vortecs you can buy today, and that's just reality. I know I'm leaving a good deal of power on the table here.
If the porting work is as nice as you say your not giving up anything. Everybody always says the Old 1960's early 70's heads are just not on a par with the modern heads. I worked in a high performance machine shop in the 70's. These were all we had. Used to have 10 second cars running these. It's true the chamber design is different getting them to flow well is an art and a lot of hard work.
Scroll down and look here at the Chevy '461X C/ED Ported Meaux Racing Heads.
http://users.erols.com/srweiss/tablehdc.htm#Chevy
The 461 X was a early 60"s fuelly head. Stock GM. You can port these big time. They are a very similar design to your 041 heads with a few minor differences. The accessory bolt holes are added and the temperature sending unit hole is different. The Ported 461X flows 282 on the intake side and 253 on the exhaust side with a 89.7% I/E ratio. Those numbers blow the vortec's out of the water. They even beat out the New AFR 227's on exhaust flow. Too bad you didn't check your flow numbers on a flow bench before you installed them. Probably would have suprised you.