Static Compression vs Dynamic Compression

[Screaming Metal]

Hey Lee, My DCR came out to 6.5 , I'm running a Comp Cams 12-404-4 blower cam. My Static CR is 8.1:1. I'm running KB Forge blower pistons with the -18cc dish. The heads are the Edelbrock Performer RPM aluminum heads with 70cc chambers.

I tried to email the guy that wrote the article and ask about the effects of a blower on his calculations, but the email address he has listed is bad. I did read another article that mentioned the VE while running a blower is about 115% if it's overdriven. I'm running mine 1:1 right now. ever since switched to EFI , I haven't been able to get a good idle and the engine seems to run rough, at least to me. I'm running 93 Octane with Octane boost and it still seems to me that it struggles to run smooth. Almost like the CR is too low even with the blower on it. At some point while we were tuning on it, we must have got it too hot or got too much pressure in the crank case because both front and rear seals are leaking pretty good. I figured if I was going to have to pull it out and replace the seals I'd look at maybe a cam swap and switching to a crank trigger for the ECU.

This close to Christmas, things tend to slow down at work, so I was trying to do some research to find a solution. I've gone through every HP book I have, which is quite a few and re-read the 3 books on Supercharging I have trying to find some answers.

Even the tech that was helping me tune it back in October, said it didn't sound like it had enough CR in it. He could hear the exhaust over the phone and said it didn't sound right. LOL I pulled the plugs and they were all over the place. I'm running those new E3 plugs and it just about every other one was sooty black while the others were nice and brown. I've had a few other folks look at it too, and we're all shaking our heads. I know I'll figure it out, eventually. I just have to find the right combination for the EFI and blower.

Hey, on your tuning problem....What type of ignition are you running and did you degree in your cam? Just trying to help you solve your dilemma....sounds like a simple problem. Blower motors are funny like that....they love low compression....but too high, they will definitely let you know about it. Also, what size is your blower and when you romp on it, at what RPM do you see boost pressure on your guage?

 

[Screaming Metal]

Also, did it run fine with carbs and you switched to EFI, and its a little off? If thats the case....you can change some parameters in the EFI and probably tune it out. Does she want to hunt, rpm wise? Or is she just idling slightly erratic?

 

[Screaming Metal]

DYNAMIC COMPRESSION IS A FUNCTION OF PLACING FIXED VALUES ON SOME OF THE VARIABLES INVOLVED IN BUILDING AN ENGINE.

The power produced for a given engine is is determined by the volumetric efficiency throughout the operating range desired. Set all of the variables to get the highest possible VE and you will make the most power and then if you are curious and have some time to kill calculate your DCR. The DCR formula does not consider RPM's and the dynamics of air and fuel motion. This is why the author gives such a wide range for the ideal DCR. Forced induction really throws the DCR formula for a loop. It isn't even reliable for calculating octane requirements as timing and A/F ratios at any RPM's are not included in its calculations.

It makes for interesting winter bench racing, but don't buy next year's cam based on it.

Al

Wanna know how to figure things out on paper and go out into the shop and build it? EVERYONE, GRAB ONTO SOMETHING!

ENGINE building, is fluid. (Please excuse me Mike, I'm grabbing the batton on this one and getting up on the soapbox. After my rant, you can slap me!)
You wanna get into splitting hairs on ENGINE building and tuning....here goes....

With any ENGINE, there are Variables. A carb is variable, because its got a butterfly in it. Rings are Variable, because as the ENGINE runs, your rings flutter and rotate....if they didn't, the rings wouldn't seat, they'd wear out,YES, Thats right....as the piston moves down the bore and rocks that .003-.005 thousandths of a inch....when that puppy changes directions....the rings WOULD try to unseat!. On....compression ratio this, compression ratio that....Dawm folks....we're talking about street ENGINES here!
You know what happens as the ENGINE runs and the rings are moving and fluttering and ALL THE END GAPS LINE UP?????? You beloved compression ratio drops! Guess what....you got 8 cylinders to think about now, with 3 sets on rings on each one. Odds are highly unlikely that any 2 cylinders will line up the gaps within any given decade.....BUT IT DOES HAPPEN!
Now, take in also that said ENGINE, being in a cold climate, staring it at a HIGH Altitude....like on top of a mountain in Arkansas....changes everything.
OH, Now you wanna throw a Blower on top of that....know what a blower does at high rpms to your compression ratio? It goes up!. You can get a racing cam.... throw a blower on top of that engine, and your pressurizing that thing internally.....and if your overlap and duration figures line up.....YOU can actually blow boost pressure out your gash darned exhaust valve. I've tested motors with these Experimental cams and have actually held the exhaust valve off its seat slightly with the boost pressure....

At the end of the day, when its all said and done....nothings perfect! OVER at Speedtalk, we got onto a subject of cylinder indexing. If your gonna index this, you gotta index that, that leads to this, and to that. YOUR COMPRESSION RATIO is never truely static. Therefore, it is what? Your speculating on your true CR unless you can actually screw a gauge into a running cylinder, We more or less do that when we run things in on a dyno.
Folks, I can can tell ya people....when you got a 8000 horse ENGINE romping and stomping in a dyno cell, 1 cylinder is 1000 horses....your running nitro....nitro burns slow compared to gas, you can burn more of it.....it more or less has oxygen in it and when you inject 2 times the regular amount, you can get.....welll, let me say a bunch of horsepower.

True, we're talking street ENGINES here. There are variables....the bores don't have to be within .002, the CR's don't have to be with 2 PSI, the indexing , the plug indexing.... so on and so forth.

Like Mike said once, if fishes were wishes. Pucker up, suck it up, and make the ENGINES run!
MAN! I've got a cigar, I'm going now to stand in the corner. :spank: :spank: :spank:
Then I'm gonna light said cigar, relax and try to tune my MOTOR.....and maybe get her broke in so I can think about putting back into my chassis....I had to get a gear reduction starter to start this thing. Anyway....

Merry Christmas and a Happy New YEAR to everyone! Everybody stay safe! And be careful!

 

[Screaming Metal]

Here's a good example of a nice built car, not a ton of power, good healthy motor in a T essentially. Goes up against some swift street cars. Anymore than that, you really can't use it....street tires, street suspension.
Unless Your a Ted Brown building a racing setup for a racer....for a race track.

 

[Gerry]

There you go
No fuss, no bother, just a quick car. I love it. If that was on the street it would kill most everything off the lights.
G

 

[coops]

Well I believe some of you have it all wrong.Coming from someone who now decided to have all the bling,big blower,ect.,I can not speak for Blown t,Lee,GT,Russ,and all the others but I could care less about several items mentioned.I built my car the way I did because that is the way I wanted it.100 or 2000 at the flywheel or rear tires,painted or primed,trailered or driven, that is ones own decisions and abilities.There is alot of talented persons in the automotive world,but I will always favor the person who does his or her own work,no matter how bad the tune,paint,welds,stance,ect.,because that may be their ability and the relative notion of how they would like the project.The notion of paying someone to do a build ;Foose,Boyd,Ted hehe,and then claiming done by ones self,is the one always rejected by me.I hope GT's problem is resolved and with all the changes he has made;efi,blower,cam,ect.,encourage the direction he wished to pursue on his project.I would think.. each of us would like to add,within our abilities, any support to help resolve the issue.

 

[Lee_in_KC]

Hey coops, I hear ya, bro! Yeah, I have a blower, but it's not for power. It's for the "cool" factor. My motor is way over-built for the way I drive, but that was for reliability. I had a vision for what I wanted in a T, with the primary factor being that I was going to drive the wheels off of it. Yeah, it sucks a lot of gas with the blower, but that's the cost of "cool." I'm enjoying this discussion about compression ratios and volumetric efficiency and whatever, but I'm sure as he|| not looking to wring every 1/4 horsepower out of my motor! I'm very happy with the way mine runs, although I know I could probably tune a few more miles-per-gallon into it.

The great thing about T-buckets is they are individual works of art, expressing their owner/builder's vision of what a hot rod should be. They are purely a matter of individual taste... one man's treasure is another man's... well, you know the drill.

 

[one finger john]

All theory aside, there are some "do it now" things to do that might help. First, as Mike has said, get a good medium range street spark plug (Champion, Autolite, N.D., etc.) in the car, open up the gap to .050 and see what happens. What type of ignition system do you run ? How much initial lead is there ? I would start @ 20* initial with 28* total. If you have a MSD Boost Master try 32* total until under boost then cut back. Since the injectors are in a "hat" that is on top of the blower, the injector set up is essentially an ecm controlled carburetor. If it had individual injectors for each port and was set up for individual vs batch fire then you could blame the injection system and adjust or repair accordingly. As it is now, the blower emulsifies the a/f mixture sufficiently that injection vs carb in not really on the table. If none of that helps or you have already tried my suggestions, run a compression test AND a leak down test BEFORE you tear it down and record all information for reference. A cylinder could be oiling (bad seal) or the valves need to be given a clean up lapping (maybe even a fresh valve job). After that, as Mike has suggested, put the cam in straight up and advance and retard the cam two degrees at a time (for a total of 6* each way) while taking a compression test at each stop to the check for the highest psi reading. My guess is that if the cam was originally installed straight up (or "kinda" straight up, timing marks were lined up) and that 4-6* advance will be real good. Most psi = best torque (old circle track trick). Also, try to get fresh, race gas no more than 100 RON that is detonation resistant but still active as far as burn. Are you running unleaded race gas ? That stuff in the can is most likely useless. try blending in some toluene (available at any paint supply, BE CAREFUL in handling [YOUR HANDS] and car paint, use in WELL ventilated area), check internet for blend ratios. Usually the SLOWER the fuel burns (higher the octane) the lazier the engine will act . Unless the fuel is blended to suit. Do not run avgas. Remember that essentially you have a relatively small cam with low compression (a smog motor) that is assisted by a supercharger for the upper rpm range (upper range being 5500 rpms w/hydraulic flat tappet lifters). Its a street engine. Treat it as such. My bet, ignition and timing followed by possible valve seal or valve job problems.

Just my $.02 , John

All comments welcome.

 

[Mike]

After my rant, you can slap me!

OK, but just remember you asked for it - <**SLAP**>

:rofl:

I built my car the way I did because that is the way I wanted it.

Hear, hear.

And this is how it always needs to be.

The great thing about T-buckets is they are individual works of art, expressing their owner/builder's vision of what a hot rod should be. They are purely a matter of individual taste... one man's treasure is another man's... well, you know the drill.

Another wise statement. You understood, from the very beginning, a blower wasn't going to be necessary to power your ride. But that is what you wanted and you then built the rest of the engine around the blower and have ended up with a car that has tons of wow-factor. But most importantly, you have built a car that puts a smile on your own face and nothing else really matters.

What I hate to see is someone spend a pile of cash on a bunch of parts that will not compliment one another. My ex-employer also owned a 3/8 mile dirt oval track and he had one class of cars that was originally intended to be an entry level class. To 'keep costs down' the class was originally required to use cast iron intake and exhaust manifolds, tiny cams, un-ported heads and a 500 CFM, unmodified Holley carb. Well, as anyone knows, there are cast intakes that are better than others. And people like Brzezinski can easily modify the intake with his undercover methods, so no one will ever be the wiser. Same with a set of cylinder heads. Make some slight runner modifications and then shotpeen everything to get it looking untouched again. And, as anyone knows, you can get a 500 Holley that will appear completely stock, will pass every gauge test under the sun and ends up costing $400 - $500 more than a box-stock 0-4412. The modifications don't cost nearly as much on those parts as the expense of hiding the modifications.

So, they decided they would just open up the engine rules. A stock, 500 Holley carb and an OEM distributor. The racers were all out trying to buy the biggest set of cylinder heads they could find, huge roller cams and boatloads of static compression ratio. :no: They just didn't get it. The fellow that had managed our engine shop for over a decade and ended up purchasing the shop from us decided it was time to build a car for the class. And he started at the top and built down. Every piece he purchased was selected with that 500 CFM carb in mind. A Victor intake and a set of Dart heads with some minor port-matching and a bit of bowl cleanup on the heads. A ridiculously-small flat tappet cam, a set of lightweight Diamond flat-top pistons and a set of small-tube headers. He was very familiar with the track and knew how to set up his car. He finished the car a bit late in the season, but in 15 races, he won 10, finished 2nd in 4 and cut a tire down for a DNF in 1.

Brian is casting 90° V-6 blocks and splayed valve heads for the race car. How about this for wow-factor? Use those pieces to build a motor for a T. 4.125" bore and 3.75" stroke would make 300 cubic inches, so it would be able to hold its head up against the smaller small-block cars. The heads are raw castings, so build them up with small runners and small valves, to keep low RPM throttle response where it needs to be. Have Comp grind a tame camshaft for it an then build a sheet-metal single 4BBL intake. Sleeve a 750 CFM Dominator down to a more reasonable size. Run a Jesel belt drive, a cam trigger ignition system and a belt drive distributor. I SOOO badly want to do it. You could have something that looked like it just crawled out of an NHRA C/SR, but that would drive like a tame puppy. Of course, it would likely cost something in the $25K - $30K range to build it. :suicide: Maybe one of these days, but I'm smart enough to see that would amount to building a car I could never get my money back on. One of those cars where you throw all kinds of money at it, just to achieve 'the look'. it wouldn't make much sense, but I still want to do it.

So, you see, I can walk on the wild side with the best of 'em. :winkn:

 

[coops]

I hear you Mike and Lee,the justification of monies for a build for one person may not be a consideration for another.I can say for myself that when I started my project I had compiled a build list and after totaling the cost and comparing to the market noticed that I could not get out of it what was put into it,but non of that mattered because I had a vision for the project and if it took longer for the build,because of funds towards the project..time..ect..,then it would just have to take longer.

 

[GT63]

OK, I see I opened a can worms, LOL I for one love to see a good discussion covering all the points. I think that adds value to the forum all the way around.

As for my engine, It's a 1970 4 bolt main truck block that has the 010, 020 high nickle content markings under the timing cover. It's been bored .030 and the crank is a forged unit from Scat. The rods are GMPP "pinked" rods with KB forged blower pistons with -18cc dish. As stated above the cam is a Comp Cams blower cam 12-404-4. The heads are Edelbrock performer RPM aluminum heads with 70cc chambers. The ignition is all MSD with a 6a box, Billet distributors and MSD 8.8MM spark plug wires. When I ran two Edelbrock 1405 carbs Initial timing was 18, advance to 36 all in by 2500. It ran great, but everynow and then acted like it was running out of gas, especially during sharp turns. I decided to switch to EFI to see If I could get a little better than 5MPG out of it. So I switched to a custom Injector plate underneath an Enderle bugcatcher that acts as the throttle body. The ECU is an Accell DFI Gen 7 unit and I added the Accel Wide Band O2 unit to go with it. AS it sits right now, we have the initial timing at around 22, and once it starts it won't idle below 1500 RPM, without going into severe blower lope and eventually dies. I spent a long time with the Accel Tech emailing profiles back and forth and on the phone making adjustments trying to get it to idle down. At one point we got it too lean and it overheated just a bit. Ever since that time, both front and rear seals have started leaking pretty good. I figured since I was going to have to take the water pump off to ge the timing cover to fix that seal I'd look at finding a more suitable cam. While I'm at it I may look at some other changes. I also need to track down and serious RFI issue too. I'll continue with my research and try to come up with a solution.

 

[Mike]

I don't see it as a can of worms at all. I think there has been some healthy discussion taking place.

 

[one finger john]

Hi Grant, One Finger here (I really have a eight). Ya know, every once in a while ya gotta let those worms out and let them run free. Some more thoughts on what is happening with your car.

1. How many miles do you have on this engine? Is it fresh or does does it have some miles on it?
2. When you say RFI is that Radio Frequency Interference? Do you know where that interference is coming from (is it that 100 foot transmission tower across the street ?). What
is the RFI effecting, when is it effecting what it is effecting, how is it effecting whatever and when does it effect it. Are all connections and joints solid and no frayed or
partial connections hidden under connecter protecters? (I'm sorry, I'll stop).
3. To get an engine so hot that it either melts or deforms the end oil seals kind of boggles my mind. Hope that replacement alone fixes the problem.
4. Are all the ignition components compatible? And grounded ?
5. Have you checked all the lobes to see you have a flat lobe (or more) ?
6. How much overdrive is in the blower right now? When does it start to build even a minimal amount of boost?
7. Do you have a way to increase timing during steady state, non boost conditions? Maybe a vacuum advance? Would help mileage.

Second hand diagnosis is like cooking spaghetti, when you think it's done you throw a piece against the wall and if it sticks it's done. If it slides down the wall then you cook it some more. I just throw these suggestion out to see if they stick, if not, then you let them cook some more ....

John

 

[one finger john]

Hi Grant, One Finger here (I really have a eight). Ya know, every once in a while ya gotta let those worms out and let them run free. Some more thoughts on what is happening with your car.

1. How many miles do you have on this engine? Is it fresh or does does it have some miles on it?
2. When you say RFI is that Radio Frequency Interference? Do you know where that interference is coming from (is it that 100 foot transmission tower across the street ?). What
is the RFI effecting, when is it effecting what it is effecting, how is it effecting whatever and when does it effect it. Are all connections and joints solid and no frayed or
partial connections hidden under connecter protecters? (I'm sorry, I'll stop).
3. To get an engine so hot that it either melts or deforms the end oil seals kind of boggles my mind. Hope that replacement alone fixes the problem.
4. Are all the ignition components compatible? And grounded ?
5. Have you checked all the lobes to see you have a flat lobe (or more) ?
6. How much overdrive is in the blower right now? When does it start to build even a minimal amount of boost?
7. Do you have a way to increase timing during steady state, non boost conditions? Maybe a vacuum advance? Would help mileage.

Second hand diagnosis is like cooking spaghetti, when you think it's done you throw a piece against the wall and if it sticks it's done. If it slides down the wall then you cook it some more. I just throw these suggestion out to see if they stick, if not, then you let them cook some more ....

John

Even my computer couldn't handle question No. 2 :jester: LOL or as Ted would say HeHe

 

[GT63]

Hi Grant, One Finger here (I really have a eight). Ya know, every once in a while ya gotta let those worms out and let them run free. Some more thoughts on what is happening with your car.

1. How many miles do you have on this engine? Is it fresh or does does it have some miles on it?
2. When you say RFI is that Radio Frequency Interference? Do you know where that interference is coming from (is it that 100 foot transmission tower across the street ?). What
is the RFI effecting, when is it effecting what it is effecting, how is it effecting whatever and when does it effect it. Are all connections and joints solid and no frayed or
partial connections hidden under connecter protecters? (I'm sorry, I'll stop).
3. To get an engine so hot that it either melts or deforms the end oil seals kind of boggles my mind. Hope that replacement alone fixes the problem.
4. Are all the ignition components compatible? And grounded ?
5. Have you checked all the lobes to see you have a flat lobe (or more) ?
6. How much overdrive is in the blower right now? When does it start to build even a minimal amount of boost?
7. Do you have a way to increase timing during steady state, non boost conditions? Maybe a vacuum advance? Would help mileage.

Second hand diagnosis is like cooking spaghetti, when you think it's done you throw a piece against the wall and if it sticks it's done. If it slides down the wall then you cook it some more. I just throw these suggestion out to see if they stick, if not, then you let them cook some more ....

John

1. This engine has about 1000 miles on it. Ran OK with carbs.
2 yes, It's coming from the ignition somewhere. It causes the Laptop to disconnect from the ECU when we try to tune it. It's RPM related. the laptop connects to the ECU via a USB cable which is very sensitive to RFI. I have added RFI filters to the cable on both ends and that didn't help. also tried wrapping it in foil. LOL
3. I'm guessing it was excessive heat. It didn't leak like it is now before the EFI conversion. I can see it leaking out the timing cover.
4. All ignition is MSD components. I had to modify the distributor per Accel instructions. I had to remove the vacuum advance and lock down the mechanical advance. The ECU now handles all timing. All grounds run to the battery as per Accel DFI instructions.
5. That's something I'm thinking about checking this spring. The Accel DFI tech said he thought it sounded funny over the phone when it was running.
6. The blower is running 1:1, suppose to be 8-10lbs at 6500. When the carbs were on it I'd start seeing boost around 4500 RPM when I got on it hard.
7. The initial timing is set at 22, it wouldn't start with anything below that. We tried at 24, 26, and 28. Still wouldn't idle down. The Accel tech had me record and send him the data logs from the ECU several times and then sent me new profiles to try. We did this probably 20 or so times.

I may do a head and cam swap this spring and while I'm at it make a few other changes I've had on my list for awhile.

 

[Screaming Metal]

==When the carbs were on it I'd start seeing boost around 4500 RPM when I got on it hard.==

You should start 'seeing' boost at a lower rpm. With a 'tight' blower, when you really romp on her, your boost gauge should jump to 1 to 2 psi at about 2000-2500 rpm. Now, this is really hanging your foot into it!Your motor is a airpump, so if your lightly rap-ing on it, its using the little pressure the blowers putting out.
Ideally, when you rev it really hard, flipping the throttle really fastand torning loose, your boost needle should for a second hit 2 possibly 3psi....and not going over 4000-4800 rpm. Its really hard to see 2 gauges at one time.
That being said....to me it sounds like your ignition, but you might want to check and make sure your injectors are functioning correctly. Spray pattern possibly.
If you've given the EFI-Blower Guru-guy from Accel all your info and he hasn't given you the correct parameters after 20 times....time to write all your settings down and start trying to fine-tune your injector timing yourself. He should've had you close by now....
Also, what is your fuel pressure @ each 1000 rpm interval?
Fuel injection and blowers have a tendency to blow out the spark in really hi-perf applications. Thats one of the main reasons for magneto's.

Thanks Mike....I needed that! :zingy: :beat: :wacky:

 

[one finger john]

Is your USB cable shielded ? I can't imagine you not being being able to get a shielded cable (or having gotten one) in your part of the country but if you need one I have one. I'll loan it to you for the cost of the ride. Also suggest a quick compression check & leak down test. That will show the offending cylinder(s).
Flat tappets unfortunately will/do go away quickly no matter what you do. Rollers are the way to go. If the heat hasn't warped your cylinder heads (not really feeling they are) then a cam w roller lifters should be under a grand and everyone is happy. BTW what heads are you looking at ?

Merry Christmas or what ever is appropriate and a Happy New Year, John

 

[Screaming Metal]

Dawm....that motor looks purty!!!! :spy:

 

[Mike]

Grant, when you made the change to the EFI, did you by any chance change the valve covers/breathers you were using? It's hard to imagine how much heat it would take to cause seals to leak like that. If it got that hot, you would definitely be able to smell it in the oil. To get oil that hot would almost require multiple spinning bearings. I suspect you're dealing with some crankcase pressure issues.

Hit your local speed shop and tell them you need an MSD 8830 filter capacitor. It should clean up your 12v line enough to prevent any more RFI problems from that end. The wiring from your magnetic pickup in your distributor needs to be run as close to metal as you can get it. If you could gather those wires in a small Adel clamp and grab the distributor hold down bolt or an intake bolt, that would be a plus. That may be difficult with your wiring, I don't know. You also want to twist those pickup wires around one another, to help with RFI issues on that line. I hope some of this will help.

 

[GT63]

Grant, when you made the change to the EFI, did you by any chance change the valve covers/breathers you were using? It's hard to imagine how much heat it would take to cause seals to leak like that. If it got that hot, you would definitely be able to smell it in the oil. To get oil that hot would almost require multiple spinning bearings. I suspect you're dealing with some crankcase pressure issues.

Hit your local speed shop and tell them you need an MSD 8830 filter capacitor. It should clean up your 12v line enough to prevent any more RFI problems from that end. The wiring from your magnetic pickup in your distributor needs to be run as close to metal as you can get it. If you could gather those wires in a small Adel clamp and grab the distributor hold down bolt or an intake bolt, that would be a plus. That may be difficult with your wiring, I don't know. You also want to twist those pickup wires around one another, to help with RFI issues on that line. I hope some of this will help.

I didn't change the valve covers, but I lost the PCV valve because there's no provision for it in the injector plate. Now I have breathers in both valve covers.

All the wiring is bundled together at the firewall, then runs under the body and up under the seat to where the ECU, Wide Band Controller, and MSD box is.

The Magnetic pick leads are twisted together and I also twisted the coil leads together to try and make it look a little cleaner. I also have wires for the Idle Air Control valve, the Idle Air Temperature sensor, The Water Temperature Sensor, The throttle Position Sensor and the MAP sensor. And there's another harness for the 8 injectors. It wasn't easy making all of this look neat on an open engine car. LOL