 7A-FE Compression Ratio, Looking at changing the CR of my 7afe when I rebuild. |
 Mar 30, 2012 - 12:00 AM
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 Enthusiast  Joined Mar 15, '12 From Wrightstown, NJ Currently Offline Reputation: 6 (100%)  |
Hey all, I'm trying to decide what to do with my 7AFE (have to take it apart due to a rod knock anyway). I've kicked around a few ideas (or maybe a lot
 ), and I'm currently researching what an increase in compression ratio might do. Does anyone have any info on this? I'm unsure of the potential difference in performance, and I can't seem to find any hard data on what pistons (4age, smallport 4age, 4agze) result in what CR. I've been trying to make sense of these tools and formulas - http://www.csgnetwork.com/compcalc.html http://s-86.com/s-cr.html and http://s-86.com/s-cr-chart.html - but I'm having a hard time digging out the relevant numbers. Doing the math myself or using the calculator I come up with significantly different numbers than their little handy chart, so I don't know what to think. Is this a futile exercise? Will I even be able to notice a performance difference over the stock 9.5:1 without having to use higher octane?-------------------- 1989 Celica ST Automatic "King Cobra" -- 2005-2006
1994 Celica ST 5-speed "King Cobra II" -- 2011-???? |
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Replies
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Apr 20, 2012 - 11:01 AM
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Enthusiast Joined Feb 8, '10 From North Carolina Currently Offline Reputation: 0 (0%) |
Let us know what you decide to do, the progress and the results. Im in the same situation. I know i need a rebuild. Wanna have a little fun when i open it up. Was thinking 4afe pistons or getting it bored to 82mm and running 2zz pistons. Wouldnt know my route until i open her up though. Does anyone by change know how to advance/retard the timing with the distributer on the 7a by chance? Might be useful to know.
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Apr 20, 2012 - 11:23 AM
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 Enthusiast Joined Oct 29, '11 From Haltom City, Texas Currently Offline Reputation: 1 (100%) |
QUOTE (celica74 @ Apr 20, 2012 - 11:01 AM)  Let us know what you decide to do, the progress and the results. Im in the same situation. I know i need a rebuild. Wanna have a little fun when i open it up. Was thinking 4afe pistons or getting it bored to 82mm and running 2zz pistons. Wouldnt know my route until i open her up though. Does anyone by change know how to advance/retard the timing with the distributer on the 7a by chance? Might be useful to know. Feed it lead paint chips there should be two bolts on your distributor that bolt it to the head, one on the top left and one on the bottom. This is how it is on the 5SFE but I imagine the 7afe is similar if not identical. Loosen them with a 12mm until you can just barely turn the distrubutor by hand. Turning the distributor clockwise will advance it and spinning it counterclockwise will retard it. Also, the idle will raise up when advanced and slow down when retarded. You could probably go 5 degrees advanced for some more power but make sure to listen for knocking and pinging at higher rpms. And make sure to mark where the distributor was before you moved it if you dont have a timing light, just scratch a mark around the dist hold down bolt. Another thing to note is that on the later models(maybe 97 and up?) the distributor does not spin and cannot be mechanically advanced or retarded |
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Apr 20, 2012 - 2:41 PM
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Enthusiast Joined Feb 8, '10 From North Carolina Currently Offline Reputation: 0 (0%) |
QUOTE (Special_Edy @ Apr 20, 2012 - 12:23 PM) QUOTE (celica74 @ Apr 20, 2012 - 11:01 AM) Let us know what you decide to do, the progress and the results. Im in the same situation. I know i need a rebuild. Wanna have a little fun when i open it up. Was thinking 4afe pistons or getting it bored to 82mm and running 2zz pistons. Wouldnt know my route until i open her up though. Does anyone by change know how to advance/retard the timing with the distributer on the 7a by chance? Might be useful to know. Feed it lead paint chips there should be two bolts on your distributor that bolt it to the head, one on the top left and one on the bottom. This is how it is on the 5SFE but I imagine the 7afe is similar if not identical. Loosen them with a 12mm until you can just barely turn the distrubutor by hand. Turning the distributor clockwise will advance it and spinning it counterclockwise will retard it. Also, the idle will raise up when advanced and slow down when retarded. You could probably go 5 degrees advanced for some more power but make sure to listen for knocking and pinging at higher rpms. And make sure to mark where the distributor was before you moved it if you dont have a timing light, just scratch a mark around the dist hold down bolt. Another thing to note is that on the later models(maybe 97 and up?) the distributor does not spin and cannot be mechanically advanced or retarded Thankyou for the info. Ill have to take some time to mess with it later. |
Posts in this topic
PaukST 7A-FE Compression Ratio Mar 30, 2012 - 12:00 AM
Bitter 9.5:1
Will need cams too
Tune
Higher octane Mar 30, 2012 - 7:31 AM PaukST My initial thoughts were to replace the 7AFE pisto... Apr 2, 2012 - 2:07 AM Smaay dont bother trying to drop in 4A parts. its not wo... Apr 2, 2012 - 11:51 AM PaukST Hm, I guess it may just be the wrong route to go f... Apr 2, 2012 - 1:58 PM stephen_lee import performance parts . net sell "HP KITS... Apr 3, 2012 - 2:27 PM Smaay the problem is you have a 7A-FE, that was the econ... Apr 4, 2012 - 8:58 AM PaukST QUOTE (Smaay @ Apr 4, 2012 - 9:58 AM... Apr 4, 2012 - 11:33 PM Smaay did you see the thread i made in the stickys? its ... Apr 5, 2012 - 9:24 AM Special_Edy My local import machine shop charges $35 to d... Apr 5, 2012 - 12:37 PM
mandrek QUOTE (Special_Edy @ Apr 5, 2012 - 1... Apr 5, 2012 - 10:17 PM Special_Edy QUOTE (mandrek @ Apr 5, 2012 - 10:17... Apr 6, 2012 - 11:47 AM PaukST As far as I can tell, it would only take 3cc less ... Apr 5, 2012 - 5:38 PM Special_Edy Just have it decked. Do the stock rebuild.
You are... Apr 5, 2012 - 7:43 PM richee3 QUOTE (Special_Edy @ Apr 5, 2012 - 7... Apr 5, 2012 - 8:00 PM Bitter timing advance is similar to a compression increas... Apr 5, 2012 - 9:41 PM PaukST Given what Smaay mentioned about the one he tore d... Apr 5, 2012 - 10:36 PM PaukST It looks like reducing the chamber height by ~ .5m... Apr 6, 2012 - 11:35 PM Special_Edy QUOTE (PaukST @ Apr 6, 2012 - 11:35 ... Apr 7, 2012 - 12:50 AM Bitter with 15 degrees total base advance (+5 from stock)... Apr 21, 2012 - 1:45 PM celica74 QUOTE (Bitter @ Apr 21, 2012 - 1:45 ... Apr 22, 2012 - 9:10 PM Special_Edy Well and besides the price of higher octane, lower... Apr 21, 2012 - 2:13 PM Bitter I think it'll turn all the way to 25 but the g... Apr 22, 2012 - 9:29 PM Special_Edy QUOTE (Bitter @ Apr 22, 2012 - 9:29 ... Apr 23, 2012 - 1:35 AM celica74 QUOTE (Special_Edy @ Apr 23, 2012 - 2... Apr 23, 2012 - 7:16 AM celica74 QUOTE (Special_Edy @ Apr 23, 2012 - 2... Apr 23, 2012 - 7:16 AM Bitter I found 15 deg gave me more low end actually, ther... Apr 23, 2012 - 7:34 AM celica74 QUOTE (Bitter @ Apr 23, 2012 - 7:34 ... Apr 23, 2012 - 8:45 PM Bitter What year is yours? I never heard knock, I monitor... Apr 23, 2012 - 8:58 PM celica74 QUOTE (Bitter @ Apr 23, 2012 - 8:58 ... Apr 23, 2012 - 9:48 PM celica74 QUOTE (Bitter @ Apr 23, 2012 - 9:58 ... Apr 25, 2012 - 7:31 AM Bitter http://www.contactmagazine.com/Issue54/EngineBasic... Apr 23, 2012 - 9:09 PM Bitter Did you set the base timing correctly and check wi... Apr 23, 2012 - 10:44 PM mandrek umm IIRC correctly its TE1 and E1, in the dieg por... Apr 24, 2012 - 12:19 PM Special_Edy Another thing to add- make sure your idle is 650-7... Apr 24, 2012 - 1:21 PM mandrek indeed, and assuming that the tension on the throt... Apr 24, 2012 - 1:38 PM celica74 Ha more things to do then i thought. Ive been driv... Apr 24, 2012 - 1:54 PM Bitter But did you have the pins jumped on a hot engine w... Apr 24, 2012 - 9:39 PM celica74 QUOTE (Bitter @ Apr 24, 2012 - 10:39... Apr 24, 2012 - 9:46 PM Bitter Fine, but were the pins jumped? Apr 24, 2012 - 10:59 PM celica74 QUOTE (Bitter @ Apr 24, 2012 - 10:59... Apr 25, 2012 - 12:01 AM Bitter QUOTE (celica74 @ Apr 25, 2012 - 12... Apr 25, 2012 - 7:17 AM PaukST Got my engine fully apart, I'll put up pics or... May 1, 2012 - 12:18 AM celica74 QUOTE (PaukST @ May 1, 2012 - 1:18 A... May 1, 2012 - 2:13 PM Special_Edy I think he meant having the block or heads milled.... May 1, 2012 - 2:28 PM PaukST QUOTE (Special_Edy @ May 1, 2012 - 3... May 1, 2012 - 10:10 PM mandrek there are no ARP bolts/studs that fit the 7afe sto... May 1, 2012 - 10:42 PM celica74 QUOTE (mandrek @ May 1, 2012 - 10:42... May 1, 2012 - 11:58 PM PaukST QUOTE (mandrek @ May 1, 2012 - 11:42... May 3, 2012 - 5:37 PM Special_Edy QUOTE (PaukST @ May 3, 2012 - 5:37 P... May 4, 2012 - 12:47 PM mandrek CAN you? yes. its is worth it? NO... sure you c... May 4, 2012 - 12:35 PM richee3 ^^ I love inline engines May 4, 2012 - 1:16 PM Special_Edy QUOTE (richee3 @ May 4, 2012 - 1:16 ... May 4, 2012 - 2:02 PM PaukST QUOTE (mandrek @ May 4, 2012 - 1:35 ... May 4, 2012 - 4:59 PM Special_Edy Id replace the oil pump while you have it apart. S... May 4, 2012 - 6:53 PM |
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