FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: fe66comet on August 16, 2014, 05:20:14 PM
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At one point I had all this figured out and lost my notes, I decided to go with a higher compression ratio but the numbers do not add up? So here it goes I have a basic 390 block with a 10.17 deck height. Stroke is 4.25,rod 6.7. Piston is a SRP 271155 compression height 1.325 inverted dome -26 dish. I thought originally with a Fel Pro 4.060/ .040 gasket I would be at 10:1 with the Edelbrock head, it looks more like 9.5 which is dismally low? I would like to be at about 11:1, the hard has a max mill of .060 and I could get a copper gasket I suppose. What do I need to do to acomplish my goal?
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PS the ring to top of piston is .25.
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I think your comp ratio with a piston dish that big would be somewhere around 9-9.5 to 1 depending on your other numbers and flat top pistons with 5-6 cc valve reliefs would have gotten you closer to your target ratio.
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It was all that was available at the time, and I had to wait several weeks for those. If I mill and use a .010 copper Cometic gasket where would I be then and how much would I need to mill?.
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It appears if I go 4.40 bore .16 compressed thickness on the head gasket I would be right at 11:1 could someone verify that? I hate to be wrong.
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At one point I had all this figured out and lost my notes, I decided to go with a higher compression ratio but the numbers do not add up? So here it goes I have a basic 390 block with a 10.17 deck height. Stroke is 4.25,rod 6.7. Piston is a SRP 271155 compression height 1.325 inverted dome -26 dish. I thought originally with a Fel Pro 4.060/ .040 gasket I would be at 10:1 with the Edelbrock head, it looks more like 9.5 which is dismally low? I would like to be at about 11:1, the hard has a max mill of .060 and I could get a copper gasket I suppose. What do I need to do to acomplish my goal?
What is your deck height with current setup?
What are the CC's of heads? I have seen them all over the map
72cc head
.010 deck height
26 cc dish in piston
4.080 bore
4.25 stroke
head gasket bore of 4.100 and .040" thick
You would be at 9.37 to 1
Same combo zero deck you would be at 9.54
4.400 x .040 gasket would give you 9.43
same setup with a 80cc head would be 8.85 comp
setup as above with stated 72 cc head you would need a dish of only 9.1 cc's to get you 11 to 1
if as above and .010 deck the comp would be 10.77
.020 deck comp 10.55
Just not going to get to 11 to 1 with a 26cc dish
64cc head
zero deck
4.080 bore
4.25 stroke
26 cc dish piston
.020 head gasket
then you are at 10.65
Realistic with a 4.080 bore
4.25 stroke
72 cc head
zero deck
.040 gasket x 4.100
10 cc dish
that would get you 11.04 to 1 comp
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You have the wrong pistons for your goal, too much dish and not enough compression height.
If your numbers are where you say, you have a stack (rod, CH, 1/2 stroke) of 10.150, if your deck height is 10.170, which makes them .020 below deck.
Also, most Edelbrock heads run a little large unless one of the FE guys preps them for you, what I have seen is 74+cc from the 72cc CJ head, sometimes even bigger.
Also, not sure which gasket you are using because the standard blue Felpro for a 390 I believe is closer to .050 and the 1020 is a 4.4 inch bore and .041.
Using the stuff we usually build with combined with what you gave us:
So static compression with 4.08 bore, 4.25 stroke, .020 below deck, 1020 gasket, 26 cc dish, 73 cc (remember it could be much bigger) = SCR = 9.02:1
If you used 72 cc = 9.09, and if you used 75ccs for the head (very well could be if out of the box) SCR = 8.88:1
So you probably need to do something, but boring to 4.40 won't get you there, the block likely wont even get you to 4.13, and even if it does, you are potentially building a grenade
If it were me, I would cc the heads, see where you are, then look at a new set of pistons, accounting for a deck height of your choosing (my guess would be 10.155-ish) and potentially cutting the heads if you needed to get the chambers to fine tune the compression.
You won't get where you want with the parts you have though
or..............see if you can open those chambers up MORE and put a centrifugal blower on it :)
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I went through the numbers again, the deck height I took from the standard engine specs. @10.17. The total of the rod length 6.7 + .5 stroke 2.125 + compression height 1.325 + top ring land distance .25 gave me 10.15 so with that I came up with .02 deck to piston. The bore is 4.080 and piston dome is -26. I did not check the chambers but I can do that myself. Near as I can figure if I use a .010 compressed, 4.165 bore gasket with a 65cc chamber it would work out. According the the Edelbrock instructions it takes .005 for one cc, so if they are above spec. it looks like about .040 would need to be milled. I will match the chambers while I am at it and break the edges along with removing the burrs.
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I went through the numbers again, the deck height I took from the standard engine specs. @10.17. The total of the rod length 6.7 + .5 stroke 2.125 + compression height 1.325 + top ring land distance .25 gave me 10.15 so with that I came up with .02 deck to piston. The bore is 4.080 and piston dome is -26. I did not check the chambers but I can do that myself. Near as I can figure if I use a .010 compressed, 4.165 bore gasket with a 65cc chamber it would work out. According the the Edelbrock instructions it takes .005 for one cc, so if they are above spec. it looks like about .040 would need to be milled. I will match the chambers while I am at it and break the edges along with removing the burrs.
You will not get there with those pistons. It would take zero deck and no head gasket w/ 65cc chambers to get you to your target 11:1, which we know is not possible.
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Maybe I'm a moron but I'm having trouble with how you got 10.15 with the numbers you provided.
For rod length you gave 6.7 + .5.
For the ch you gave 1.325 + .25.
When added with everything else I get 10.9.
Should that be 6.7 minus .5, and 1.325 minus .25?
When I subtract those numbers from 10.9 I get your 10.15.
I guess my question is why the .5 added (or subtracted) to the rod length?
I kinda get subtracting .25 from the ch.
Thought I knew how to get cr but now I'm not so sure.
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Maybe I'm a moron but I'm having trouble with how you got 10.15 with the numbers you provided.
For rod length you gave 6.7 + .5.
For the ch you gave 1.325 + .25.
When added with everything else I get 10.9.
Should that be 6.7 minus .5, and 1.325 minus .25?
When I subtract those numbers from 10.9 I get your 10.15.
I guess my question is why the .5 added (or subtracted) to the rod length?
I kinda get subtracting .25 from the ch.
Thought I knew how to get cr but now I'm not so sure.
1/2 of stroke = 2.125
CH = 1.325
rod = 6.7
Total = 10.15
Subtract from 10.17 = .020 deck clearance
Here are the real problems to the original poster. Blunt for for clarity only, I actually feel bad for you and want to help
1 - Have not measured chambers and do not know what your deck height really is
2 - Have the decks been squared to the mains, if not, you could have 8 cylinders all with different compression
3 - The pistons are likely wrong for the application before you considered #1 and 2.
4 - You are assuming you can cut the block or heads to make them work. You are too far off to do that. FYI My truck 445 is 10:1 with a 17cc dish and 72cc chambers, 10.155 deck.
5 - You are focusing on chambers, it is smarter to get it closer to zero deck to gain some quench. That's why I said expect closer to 10.155 later
6 - The head gaskets you are referencing likely do not exist, recommend you just plan with 1020s. The data is there and they are affordable
7 - Your solution puts you with a .010 head gasket (tin foil?) and cutting the head to the point that you will have intake fitment problems, which I estimate as closer to .055 to get you there, and only .030 quench distance (.020 deck clearance +.010 gasket). If you could get there, it would be a mess
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1/2 of stroke = 2.125
CH = 1.325
rod = 6.7
Total = 10.15
Yup, get that. I guess my question was where are those other numbers coming from in the equation. The +.25 and + .5.
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Your may to have to chew on the lead projectile and get some small dish or flat tops.
To even get close to 65 with the Ed's your going to have to whack off close to .100" and then do some creative milling
on the intake to get it on.
It may be cheaper to buy new pistons then do all the machining required.
Unless you have a shop on standby, than of course never mind. :D
Also the quench is very important when trying to make power. .040" is where you want to be so when doing your
calculations you want to take that into consideration.
Flat Tops it is. ::)
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Last time I looked, Ross could supply pistons on very short notice. They've dons so for me on several occasions.
KS
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Well let me explain a little, when I went into this project my health was much better and I could solve equations. Now it is more difficult and I make mistakes, making it even hard at times to do mathematic equations. I used to be able to do this type of thing off the top of my head , now at times it is hard to grasp.
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Let me run over what I do know, I have a 445 stroker engine. The piston specs are 1.325 compression height, 4.080 bore, .25 top ring land and -26 dish. The rod is 6.7 my stoke is 4.25 and my deck is stock 390 deck height, whatever that is specified to be on a 1968 car engine? I can mill up to .060 off my head and go as small as .010 compressed height and I would suspect 4.100 bore on a copper gasket. So if we assume a 74 cc chamber as suggested, that would give me a minimum of 62cc chamber. Give or take a cc +or minus. So given the numbers that I have so far what are the possibilities? I hate to trash the rotating assembly from Barry and start over again that would be expensive to say the least being that the pistons have been fitted along with the rings and everything is balanced and assembled. I thought Barry stated it all worked out to 10:1 but I guess I was wrong.
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Devil's advocate here!
Go with what you have and don't be so concerned with hitting a target c/r for what essentially is a street motor. Agree that that a .040 quench is more important than hitting your alleged ideal c/r. Jesh, if its a full race engine then you have WAY TOO LOW a c/r......so it's not.
Heck, have a lower than "idealized" c/r may pay more benefits than you'd suspect with a much greater tolerance to poor fuels......unless you believe that magically in the very near future much higher pump gas octane levels will be available....NOT!
JMO!
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No miracle fuels predicted here but I would like to get a little more than stock smog engine compression. At 9:1 to 9.5:1 everything I have done so far would be a waist and I may as well throw a two barrel on it and call it a day. I guess I will have to weigh the options. Maybe a piston change and rebalanced assembly? Hopefully it would not set me back too far to straiten out my dilemma? I had plans for further head work in the future but that would be pointless also.
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I just looked on the Probe site rather than the SRP site and they gave a listing of compression per cylinder head cc. The ratio ranged from 9.73:1 for a 76cc head to 10.46:1 for 68cc, but no gasket specs. Stock gaskets spec out as .041 compressed and 4.440 Bore so if I plug in a copper.010 gaket with a 4.165 bore. What chamber size leaves me a 11:1 ratio? Sorry to be a pain in the but
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http://www.jepistons.com/Catalogs/SRP/Ford/390-428_invert.aspx
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A .010" copper gasket will leak like a sieve.
I agree that you should run what you have.
Although I would use the FEL PRO 8554PT head gasket.
This is the gasket that comes in the full FEL PRO kit and has 4.232 bore and works great.
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It is not a JE it is a probe piston, specs are different, if yo go to the probe site and punch in the part number 271155 it comes up. Specs are completely different for compression ratio. If it were that low I would do a piston change for sure, my roller cam, valves, heads, intake and injection would never work. So the pistons would be at the sacrifice of every part i currently have.
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I would guess at this point regardless I am asking the wrong question. The right one is what piston would best yield the correct ratio? I guess I will have to eat the rings, pistons and balance. Its only money right LOL another FE lesson learned the hard way.
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A question first, are you sure you have a 26cc dish?
My Probes are 17.5, Barry's website seems to hover around the 10:1 which would lead me to believe 17-ish for his custom Mahle, and Diamond makes a 6cc and a 17cc off the shelf for a 4.08 bore. Were yours custom or are you remembering wrong?
That being said, the Diamond is a 6cc 1.33 CH for a 10.155 stack.
Assuming a 4.08 bore, if you cut your heads to get a measured 72cc, run a Felpro1020 gasket, cut the block to 10.160 you'll be at 11.19 static, if you zero deck it, you'll be at 11.32, and if you go 10.165 (.010 below), you'll be at 11.07 static. Although sometimes there isn't enough material to cut an old block square to 10.165, so I wouldn't bank on that.
Something else to think about, if your heads come in at 75ccs, zero deck gets you to 11:1 without having to touch the heads, just cut the block to 10.155
All those combos have a nice quench distance too
As far as balancing, that's a 510 gram piston, if you are close, you may not even have to rebalance.
As far as reusing the rings, depends on dimensions, but if they are the same size and you can take them off gently, you can reuse them. I sure wouldn't throw them away unless someone wanted to buy the pistons and rings from me as a package.
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It is not a JE it is a probe piston, specs are different, if yo go to the probe site and punch in the part number 271155 it comes up. Specs are completely different for compression ratio. If it were that low I would do a piston change for sure, my roller cam, valves, heads, intake and injection would never work. So the pistons would be at the sacrifice of every part i currently have.
OK, here is something odd. 271155 is a SRP number and in Google it showed me a 26 cc dish, but I typed it into the Probe site search bar and brought me directly to the normal 17.5 cc piston everyone is using.
http://www.probeindustries.com/Ford_445FE_17_5cc_Reverse_Dome_SRS_Pistons_p/14785.htm
We need to figure out what you have. 17.5 wont get you to 11:1 either, but it's better than 8.8:1 ;)
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Unfortunately the engine is nearly completely assembled except the intake. I guess I will have to remove the heads, pan, a rod and piston to tell for sure? I doubt Barry would have sold me a set up for 8:1 though? It is a SRP box but I do not actually know what was in there or if they were custom cut due to a shortage at the time. It took quite a while to get the pistons as I recall. If they are 9:1 even those will have to go bye bye as it would turn my engine into a gas guzzling smog hog. I guess I will have to knock it down and give it a look see, at least pull the heads and see if there is a job number on them.
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It is not a JE it is a probe piston, specs are different, if yo go to the probe site and punch in the part number 271155 it comes up. Specs are completely different for compression ratio. If it were that low I would do a piston change for sure, my roller cam, valves, heads, intake and injection would never work. So the pistons would be at the sacrifice of every part i currently have.
Really? Then why did you say it was a SRP? This is the quote from your first post on this thread:
At one point I had all this figured out and lost my notes, I decided to go with a higher compression ratio but the numbers do not add up? So here it goes I have a basic 390 block with a 10.17 deck height. Stroke is 4.25,rod 6.7. Piston is a SRP 271155 compression height 1.325 inverted dome -26 dish. I thought originally with a Fel Pro 4.060/ .040 gasket I would be at 10:1 with the Edelbrock head, it looks more like 9.5 which is dismally low? I would like to be at about 11:1, the hard has a max mill of .060 and I could get a copper gasket I suppose. What do I need to do to acomplish my goal?
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At the time Barry had to put a piston set together for me, none were available and the label on the box is marketed over with a black permanent marker. Also being four years ago my memory is not exactly sharp on the brand. It. Could have been a used box with new pistons?
Well I pulled the head on one side and apparently it is a custom piston, started off as a flat top and went from there, no markings, job # or anything else. It is equal to or slightly above the deck, as a strait edge catches it at TDC. I guess I will have to CC the dish and see what I got?
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If its sticking up slightly @ TDC do you have a dial indicator to measure that? Do you have a way to measure CC's?
If sticking above deck the best way is to pick a number for piston below deck, I like to use .100 in the hole then measure the cc's
Easy to figure out from there.
Only way to get the proper numbers is to physically measure everything.
I did not catch it but where do you live?
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I used a feeler gauge and a stainless strait edge, it has a .005 pop up on one side, the other is slightly lower on the smaller area by the reliefs total volume when I filled the entire piston was 28 cc with a 17 cc dish. I measured the piston with a syringe, slow but extremely accurate. So I am guessing it is made up like a Probe as I thought. So where does that put me now?
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I think I'd call Barry and see what he knows
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He does not recall? I think I am going to have to swap them out in the end. Originally my target was 10:1 but it seems like I didn't reach that for some reason. I could always save them for a supercharger project.
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will a -.005" deck with a .041" head gasket clear the head with a 4.25" stroke ? .036" deck, Quench is going to be very lively.
Can you cam it up a bit to build more dynamic compression ?
Is the 50hp loss really going to kill the driveability ?
You have pistons above the deck correct? = -.005 ? with a .041 head gasket you are at .036" quench clearence IIRC the rule of thumb is .010" X 4.25 (stroke) = .0425 min clearence.
What I'm saying is I don't think you can get away with less than a .041-.045 compressed head gasket. Without the piston hitting the head at RPM.
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Well everything I have, throttle body, custom machined 90mm EGR plate, camshaft, heads, T&D race rockers and the proposed intake to make it all work would be a lost cause at 9:1 compression. I would be back to the 300- 400 hp range at that compression, along with being sluggish and a complete dog. At this point I have way more invested than a 600 dollar set of pistons and three hundred dollar set of rings in everything else so it comes down to the pistons or everything else. If they were 10:1 pistons I would mill the heads and use a copper gasket. But I have a -26 volume, good for boost but that is about it. I also would have to ditch my 1000 dollar 2" primary headers as those would not work either.
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Here is the classic picture = 1000 words.
Show us a picture of the top and underside if you can.
I can post any picture you send me.
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Well I took the pan off and looked at the bottom of the piston, it is exactly what the box says on it . I have a nice set of 9:1 ashtrays too bad I do not smoke.
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http://www.jegs.com/i/Paxton/769/1001864SL/10002/-1?CAWELAID=1710769436&CAGPSPN=pla&catargetid=230006180000848976&cadevice=c&gclid=CKnw_eSbn8ACFcZQ7Aod5CwAEQ
lemonade?
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I pulled the rotating assembly apart last night, I am going to get some pistons and rebalance. It would seem the best way to handle the problem at hand and maybe I can use the pistons in another project later.
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Geez - step away from the internet for a little while and....
John
I cannot remember how we ended up with that set of pistons - it's been a long time since you got the stroker kit. I know that a year or so ago we could not get anything out of Probe & we may have gone another route expecting to mill the heads.
I have another customer who wants less compression.
Send me those pistons and I'll send you some with a smaller dish
It will not hurt the balance at all.
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Yeah! Barry to the rescue! Nice move Barry!
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Well that solves that issue. Good work Barry!
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Ok I could do that , I need to just have them pressed off.
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FEs aren't pressed on. Although removing the spirolocks will drive you crazy, once you get them off, the pins just slide out. All you need is a small screwdriver and some paitience
I will say this though, I think it's time to slow down to go faster. Seriously
- Measure your chambers
- Measure your deck height on all 4 corners if not off all mains to see if you are straight
- Then work with Barry to end up with as tight of a quench as you can and the compression you want
- Be sure to know the cam and the cam timing you will run. Barry doesn't like DCR calculations, but knows cams, some of us other guys also know cams and like DCR, so if you want to calculate it and get our opinion put the info up here. However, no-one can calculate anything until you have exact numbers
- You should not pick one without the other.
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2X to M427Stang's advice. Getting the pin locks out, once you've done a lot, is easy with two small screwdrivers and /or a driver and a steel dental pick. Have seen guys though mess up the soft piston material doing so. There is a tool that makes it a snap. Not cheap at IIRC $75-$95 per pop. Still, it makes it a snap.
http://www.lockintool.com/
Just be sure to get the right head diameter, if you buy the tool, for the pin o.d. (FE's will be all the same) and note if they are flat SpiroLocs. as round wire retainers (almost all aftermarket piston uses Spirolocs btw) would require a different head. 'Course, you only need to remove one lock per piston to pull the pin and send all back to Barry.
Try YouTube as well for vids on how to remove same without the tool. Practice, practice, practice and your fingers will hurt for a week!
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Or he can just send the (carefully packaged!) pistons and rods here and let me remove them.
He's gonna pay for some shipping either way - an extra few pounds won't matter much.
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Fabulous customer service, Barry, which of course you are known for. 8)
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Fabulous customer service, Barry, which of course you are known for. 8)
X2 Barry. Bravo Zulu!
Question though. If he already has the SRP's .005" above the deck and he changes to another off the shelf piston which I was looking around
and most are showing a 1.330" comp height. Will this not put him .010" above the deck and thus causing even more grief. just thinking out loud.
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Or he can just send the (carefully packaged!) pistons and rods here and let me remove them.
He's gonna pay for some shipping either way - an extra few pounds won't matter much.
There you go! Best for all involved IMHO
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I do not blame anyone, it is what it is. I appreciate Barry helping me out, most people it is 30 days and that is it, it has been nearly three years. Now I am into finishing the engine up and when I took a look at the piston specifications they did not add up. I thought I was missing something so that is why I asked. My memory is so bad I forgot what rings and rods I used, the rods are full floaters and rings are standard gapped. I have done some other engines since starting on my FE and they kind of melt together. The rods are a plus I forgot about but I will upgrade the rings while I have it apart. Some Zero Gap street rings come to mind as a possibility. Eventually I am going to send my heads to Barry for the chamber and port work but for now I would like to just get the thing together. Barry has always been good to me so I would send others to him, I have already and would continue to do so regardless. I am certainly not done with building FE engines and actually am looking at getting the N-600 truck I discussed earlier, I will continue to deal with all the folks on the forum. If they can deal with my cranky butt LOL.
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Fabulous customer service, Barry, which of course you are known for. 8)
X2 Barry. Bravo Zulu!
Question though. If he already has the SRP's .005" above the deck and he changes to another off the shelf piston which I was looking around
and most are showing a 1.330" comp height. Will this not put him .010" above the deck and thus causing even more grief. just thinking out loud.
I thought he was .020 deep...
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WOW ... Awesome Barry , that is above and beyond on customer service .. Bud
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Fabulous customer service, Barry, which of course you are known for. 8)
X2 Barry. Bravo Zulu!
Question though. If he already has the SRP's .005" above the deck and he changes to another off the shelf piston which I was looking around
and most are showing a 1.330" comp height. Will this not put him .010" above the deck and thus causing even more grief. just thinking out loud.
I thought he was .020 deep...
I used a feeler gauge and a stainless strait edge, it has a .005 pop up on one side, the other is slightly lower on the smaller area by the reliefs total volume when I filled the entire piston was 28 cc with a 17 cc dish. I measured the piston with a syringe, slow but extremely accurate. So I am guessing it is made up like a Probe as I thought. So where does that put me now?
I may be thinking old school pop up. Above the deck.
I'm not sure where the .005 pop up is, but if it is above the deck a 1.330 comp distance won't help.
Like I said a pic would help a lot.
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I agree and see why you thought that, I am just as confused LOL
but to be .005 above he'd have to have a 10.145 deck height, that is pretty short...I think we are losing something in translation and/or measurement
In addition, I think he is claiming its a 17cc dish but he also measured the volume of the ring land above the piston, the calculators account for that, so my hunch is really he is just under 10:1.
On top of that he said he thinks maybe it was originally spec'd for 10:1, all that makes sense with Probe dimensions, not sure where the SRP part number came in though. Too confusing ::) time to get some real measurements
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At the top it was a tiny over if not level at the top, at the bottom it was far below. Total volume to the top of the first ring measured -28. The small area that was up was about 1/4 or less of the total piston top just above the reliefs. I suspect that the pistons are for supercharged applications? The pins and walls are definitely thick with double locks and such. When Barry get's. Them I am sure he knows what the intended application is? The .02 1 calculated by subtracting the block deck height from the crank, rod and piston specifications. That is when my brain had a miss fire and I could not figure out why nothing added up. I thought it was just me being goofy.
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Spiro locks are not a big deal, I get em with a sharp pen knife, it gets right behind them and walks them right out. Kenny Santfort taught me that trick when I worked for him. I have been around the block a few times, even had to push my ride home LOL.