 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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May 1, 2012 - 12:18 AM
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Enthusiast Joined Mar 15, '12 From Wrightstown, NJ Currently Offline Reputation: 6 (100%) |
Got my engine fully apart, I'll put up pics or start a build thread or something later, but my cylinder 3 and 4 rod bearings were obviously damaged, and the two main bearings at that end of the engine as well. The crank shows it, so it looks like I'll be having the crank cut. I was considering boring the cylinders over, but the cylinder walls look like they're in excellent shape... Haven't measured them, though. We'll see what the machine shop has to say about it, I'd enjoy not having to shell out for a new set of pistons if I don't have to. I had thought of porting and polishing the head myself (being that port/polish kits are decently cheap), but after reading into the subject I think I'll pass. It'd cost less up front, but I'm fairly confident I'd get (a lot) more for my money having it professionally done.
I did have a few open questions for anyone who cares to chime in with an opinion: 1) Assuming I do end up getting it milled, would the cam timing be adversely affected by the change in distance between the crank pulley and cam pulley? 2) Assuming that I need to have the cylinders honed, would that necessarily mean I'd need oversize pistons/rings? 3) Does anyone have a machine shop to recommend in the general Charlotte, NC / Rock Hill, SC area? 
-------------------- 1989 Celica ST Automatic "King Cobra" -- 2005-2006
1994 Celica ST 5-speed "King Cobra II" -- 2011-???? |
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 celica74 Let us know what you decide to do, the progress an... Apr 20, 2012 - 11:01 AM Special_Edy QUOTE (celica74 @ Apr 20, 2012 - 11... Apr 20, 2012 - 11:23 AM celica74 QUOTE (Special_Edy @ Apr 20, 2012 - 12... Apr 20, 2012 - 2:41 PM 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 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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