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It seems to me that you're 99% there. All you need to know is the chamber volume and that is the most elusive. But for the margin of error you will be close anyway.

What are the piston specs? Start there. They could be compared to stock specs and the differences noted. The operating or dynamic compression ratio is a function of cam timing, too. Depending on IVC the actual engine displacement changes. This is referred to as engine VE. Due to crank and rod geometries and cam timing the entire charge may or may not enter the cylinder. In the stock configuration the valve closes at 47 ABDC capturing 89% of the cylinder volume. Compared to the discrepancy you are experiencing for the change in chamber volume due to unknown changes, you haven't changed much.

Had you considered the smashed-modeling-clay method? That considers changes in the piston's surface.
 

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re:

Thanks for the reply sarinas_dragons,

I'm not sure on the pistons specs. It's a long crappy story, hence the reason why I have to measure my CR myself. Question, why do I need to know the combustion chamber volume? Doing it my way, includes the combustion chamber volume in calculating the CR, without actually knowing what the chamber volume is. Anyway, I'm still not sure which way I'll do it as the head is a b#%ch to get in and out, so maybe doing it rwhites way is best? Maybe I'll get proactive and do it both ways :)

Sonny
 

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Measured Engine Results for Hybrid 5M/7M

Finally got around to conducting my engine measurements (with the help of my father). I initally tried to do it as I described a few posts back. However I ran into a few problems: A) trying to accurately fill the interior volume of the combustion chamber through the spark plug port while getting enough light into the hole to see when to stop is a lot tougher than I expected. And B) my exhaust valve ended up leaking coolant once it reached a certain level (even sealed with grease). Therefore I scrapped this method (albeit after a few lost hours) in favor of the more traditional method of cc'ing combustion chamber and cylinders separately using clear plexiglass and math to come to the answer. Note that my 5M engine has a 7M crank in it, high compression Arias pistons and some mild/medium headwork, so my results are not directly comparable to a stock 5M/6M.

Combustion Chamber Volume (with spark plug) = 55.8cc
Approx. Piston Crown Volume = 13.4cc
Bore x Stroke = 83.26mm x 91mm
Head Gasket Thickness = 2.5mm approx. (not compressed)
Compression Ratio = 9.8 approx.

I assume once the head is torque in place the head gasket compresses to around 2mm therefore raising my C.R. to 10.2. At this point I'm very tempted to switch to a 1.5mm gasket to reach an approx. C.R. of 10.8. This should still be acceptable using street gas, and should match nicely with my Shadbolt TRD replica cams. I'm still mulling over whether I have the time and energy to switch to a stand alone next year? We will see I guess.


Sonny

P.S. I initially thought my compression ratio was 12.0:1 (hence my other post looking for a thicker head gasket). But this turned out to be wrong as I forgot to subtract the piston crown's volume from the engines pre-compressed volume size.

P.S.S. I hope the original poster does not mind me sharing my results in his thread. I figured since it applied and was related to what he was talking about, it would be better than starting another thread on the topic.
 

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I wondered if you saw my stock vs. TRD rev study? I show that the TRDs are at .6 mach at 7510 rpm and that's not redline. If the redline is increased I don't know the compatibility with a stock ECU. I don't want you to get that far and find out later.

I give you permission for a standalone. I wish I could give you the money.
 

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I wondered if you saw my stock vs. TRD rev study? I show that the TRDs are at .6 mach at 7510 rpm and that's not redline. If the redline is increased I don't know the compatibility with a stock ECU. I don't want you to get that far and find out later.

I give you permission for a standalone. I wish I could give you the money.

Ha ha, thanks Kenny. I'll make sure to tell the fiancee that lol.

I don't seem to remember reading your TRD cam analysis, where is it located?

Actually, I'm a little conflicted at the moment. I'm not sure how much time and energy I should spend on fixing this engine (which was rebuilt by a shady mechanic)? Or wait until I get the car back to my place (it's currently 4 hours away at my parents house) and rebuild the nice 6M I have stored over the next year or two? Ahhh, decisions decisions...........

Sonny
 

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Discussion Starter #70
Sonny, thanks for posting your results!

I ran your numbers through the same speadsheet I have been using and was within a tenth of you numbers. Looks like some good work.

Does your 5mge head have dished valves in it? Also, did you repeat your measurements a few times? I seem to get slightly different volumes each time I cc the combustion chamber...it's very frustrating.

I am currently doing these measurements on another engine and so far I have come up with.

Stock 85 5mge
combustion chamber - 53cc with bosch +4 spark plugs
Bore X Stroke - 83.3mm X 85mm
Gasket thickness - 0.052" Gasket ring diameter 3.32
Piston Dome/Dish volume - 0cc

Comp Ratio - 8.76

And that was with the 0.090" domed pistons....I am not sure why these numbers are not coming out to be 9.2. Maybe the fluid was leaking around the piston rings or the valves, but everything seemed to be very stable when I completed the measurements. I wonder if Toyota measures comp ratio a different way? Uncorrected vs. Corrected
 

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Discussion Starter #72
I am trying to verify measurements. I was also interested to see how much different the comp ratio would be if determined by the two methods.
 

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Sonny, thanks for posting your results!

I ran your numbers through the same speadsheet I have been using and was within a tenth of you numbers. Looks like some good work.

Does your 5mge head have dished valves in it? Also, did you repeat your measurements a few times? I seem to get slightly different volumes each time I cc the combustion chamber...it's very frustrating.

I am currently doing these measurements on another engine and so far I have come up with.

Stock 85 5mge
combustion chamber - 53cc with bosch +4 spark plugs
Bore X Stroke - 83.3mm X 85mm
Gasket thickness - 0.052" Gasket ring diameter 3.32
Piston Dome/Dish volume - 0cc

Comp Ratio - 8.76

And that was with the 0.090" domed pistons....I am not sure why these numbers are not coming out to be 9.2. Maybe the fluid was leaking around the piston rings or the valves, but everything seemed to be very stable when I completed the measurements. I wonder if Toyota measures comp ratio a different way? Uncorrected vs. Corrected

Thanks rwhite,

glad to see our measurements are being validated by yours. Considering it was our first time doing this, it was a little of a learning experience initially, but we got the hang of it towards the end. We unfortunately were not able to verify our measurements of the #2 cyclinder compression ratio with the other cylinders as this one took us to the wee hours of Sunday morning and I had to head back home soon after (4.5 hour drive. Nothing a couple of redbulls couldn't fix). Anyway, after all that we've learned, I am very suspecious of the work the mechanic did on my engine and would not be surprised to see all the cylinders different. I am now thinking the best thing for me to do is conduct a complete rebuild/restoration of the engine (instead of just a quicky on the head). That way I know exactly what is in the engine, what the specs are, and what is the best way to tune it etc.... . I'm still debating whether I should try to fix this engine, or just rebuild my 6M?

Regarding your question about the valves, the exhaust valves are perfectly flat underneath, and the intake valves are slightly dished, about an inch diameter in the centre of the valve (overall valve diameter is about 1.75").

Regarding your measurements, I have a question. You state your piston dish/dome volume is 0cc, but then below you say it's domed .090" high? If you have an 85 Supra engine, that would indicate you have the slightly domed pistons, which would indicate you would have to subtract a small volume from both the before and after volumes to determine your static compression ratio. Did you do this? Also, your head gasket thickness is stated as .052". Is this compressed or none compressed? Also, how did you seal your valves and piston rings to do these measurements? I forced grease in the cracks, then cleaned up the excess. At any rate, our mearements are within spitting distance of each other, which is reassuring. Once I take possession of my new house in November, I will redo all these measurements with both engines and post everything here for us to compare. Thanks for the advice and motivation, hopefully this info helps others too.

Sonny
 

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Am I crazy?, or is this normal. Over the years my MKII's 5mge is much more responsive and powerful in the cooler weather than in the summer. This does not happen with any other car I drive (2003 Camry, 1999 Grand Prix GTP) only with the Supra. I notice this every fall and I'd like to know if this happens with anyone else? or am I really nuts like my wife says.
 

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help

i have a 82 supra i am wanting to swap the motor due to almost 400k miles. i am wanting to put the third gen motor in my 82. will that motor be a direct fit?
 

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corection 7m-gte and i believe the earlier 7mge used the W58 transmission then changed but youd need the different clutch and is this true i thought the 7mge was a direct fit but you have to do everything else could off been wrong
 

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i am not sure if im right or wrong but i believe the earlier 7mge had the w58 like i stated earlier ask someone whos done the swap already the 7mge is a good swap you can fit a 318 in there though yes ive seen it with my own eyes
 
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