Why is 6MT 10.0 compression, vs 10.5 for the 5A? - Honda Accord Forum : V6 Performance Accord Forums
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Old May 10th, 2008, 11:10 AM   #1
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Why is 6MT 10.0 compression, vs 10.5 for the 5A?

Did anybody notice that? I'd think the opposite would make sense.

The reason I also bring this up is it's practically impossible to have IDENTICAL power ratings (at the same rpms) when one engine has a lower compression ratio and different intake. Seems to me the 6MT engine wasn't rated (dynoed) separately.

What's your take gang? Half a point less is significant, and I'd like to know how it was achieved: Thicker head gaskets? Different heads? If the latter, was it just thicker bases or different heads altogether? Inquiring minds want to know.

Mods: if you feel this discussion belongs to one of the other forums, feel free to move. Good day.
JC
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Old May 10th, 2008, 12:06 PM   #2
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I'm not sure that they're even different compression wise in the first place because I see conflicting information. The 6MT is listed as 10.5:1 elsewhere. Even if it's only 10.0:1 though, it's still easily possible to still have the same exact ratings. The auto version is using VTEC for VCM, so I believe they're using the same active cam profile from idle to redline, which might mean they needed to crank up the compression ratio to still make the same power. The 6MT still has a performance oriented SOHC VTEC system with no VCM, which means they probably have the usual "hot" VTEC cam to make that power and don't need the extra compression. That's just one way that it could be working out, but there's other ways too.
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Old May 10th, 2008, 06:10 PM   #3
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Thanks for your analysis man. Makes sense. And besides, the brochure could be wrong, as you said. This info came from the dealer's brochure, by the way. I've found several errors on previous cars, so that wouldn't surprise me at all.

Car felt plenty powerful, so it was more curiosity than anything else. Thanks again.
JC
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Old May 11th, 2008, 03:24 AM   #4
 
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is there a way to trick the ECU on a AT to turn off the VCM just like you can take off the speed limiter with a tuner
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Old May 11th, 2008, 04:14 AM   #5
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Noticed this a while ago as well,

Hondanews.com lists identical CR's
while hondacars.com does not.

Im going to make an educated guess and say that both V6 motors use 10.5 CR's.

Honda admits that the 6spd has better low/mid range performance however over the VCM equipped V6 Accord, which is as always is due to the variable intake maifold that the 6spd has and the AT does not. Basically the 6spd has more power from its inatke manifold design, reduction in parrasitic losses as a result of its 6spd manual and probably overall tune since the car seems to be be quite underated.
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Old May 11th, 2008, 04:20 AM   #6
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NVA-AV6 mentioned something to me about getting the HG smashed for an specific thickness to achieve a certain low CR. So maybe HG can be a factor... in that case i don't need to get my pistons re-done by Arias
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Old May 11th, 2008, 07:43 AM   #7
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EX-L V-6 EX-L V-6 6-Speed V-6
Engine Block/Cylinder Head Aluminum-Alloy
Displacement (cc)3471
Horsepower 268 @ rpm 6200
Torque (lb.-ft. @ rpm) 248 @ 5000
Redline 7100 6800
Bore and Stroke (mm)89 x 93
Compression Ratio 10.5 : 1 ( 10.0 : 1 M/T )
Valve Train 24-Valve SOHC i-VTEC® ( 24-Valve SOHC VTEC®
High-Performance Intake Manifold Standard M/T ).
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Old May 11th, 2008, 07:46 AM   #8
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Ok ! Don't get it yes we're talking about compression and horsepower being equal on a V6 A/T V6 M/T but also the 6 speed has a High-Performance Intake Manifold why ?
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Old May 11th, 2008, 10:44 AM   #9
 
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if thats the case cant a A/T V6 swap out the intake manifold to put the same intake manifold as a M/T V6.. same engine diff. tranny..
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Old May 11th, 2008, 12:34 PM   #10
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Intakes look the same whats the diffrence ? Does it have better air flow ?
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Old May 11th, 2008, 02:07 PM   #11
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CR is probably same guys I rather take the technical articels from hondanews.com as fact and not hondacars.com, since i've noticed mistakes on that site before.

Intake manifold just has some valves in it to change the volume of the manifold so that your low/mid range is better as a result of the resonance tuning, at a higher rpm (3800rpm for me and I think 4000 for the 7th gens) the valve opens and allows for maximum air capacity, over faster air. The idea is pretty much the same as switching IM runners from long narrow ones for low end to short wide ones for high end.
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Old May 11th, 2008, 03:28 PM   #12
 
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hmm again i ask is you put a 8th gen v6 M/T intake manifold on a A/T will you get gains? it is a "High-Performance Intake Manifold" with more flow so i see why not..
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Old May 11th, 2008, 05:52 PM   #13
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Quote:
Originally Posted by _JuztAJ_ View Post
hmm again i ask is you put a 8th gen v6 M/T intake manifold on a A/T will you get gains? it is a "High-Performance Intake Manifold" with more flow so i see why not..
hmm again I say that the 6spd has more low/mid range power, you infer from that what you like.
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Old May 11th, 2008, 06:25 PM   #14
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All this new technology on engines is crazy but good . Look what i found on a V6 with A/T it give this on the specs (Dual-probe spark plugs) wich it doesn't inply to a M/T .

The Accord's 4-cylinder and V-6 PZEV-compliant engine uses special dual-probe spark plugs (a first for Honda in North America) for faster mixture ignition speed and improved combustion stability. With the spark arcing just beyond the relatively large surface of the ground area, the air/fuel mixture is exposed to a larger portion of the spark, which enhances stable combustion.
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Old May 11th, 2008, 08:51 PM   #15
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It's the cams kiddos.
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Old May 12th, 2008, 12:01 AM   #16
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It's the cams kiddos.


The 6MT's V6 has a normal SOHC VTEC system, which means seperate intake cam profiles for low/mid rpm, and high rpm.

The auto's V6 just has cylinder deactivation (no VTEC). They still call it VTEC (in fact, it's called i-VTEC), because it uses a mechanism similar to VTEC to close the valves for cylinder deactivation. The "i" means intelligent, which refers to the engine's ability to activate/deactivate cylinders at varying engine speeds according to driving conditions.

As a result, even without the variable intake manifold, the 6MT's V6 makes more low-end and mid-range torque than the auto's V6 (thanks to the intake cam profile dedicated to the low-end and mid-range). Add the variable intake manifold to the mix, and the 6MT V6's torque curve becomes extremely flat, increasing its advantage over the auto's V6 even more.

As for the compression ratio, who knows? All I know is, on the 7th gen, the VCM-equipped J30Z i-VTEC V6 in the Accord Hybrid had a 10.5:1 CR while the J30A4/5 in the standard Accord V6 had a 10.0:1 CR.

I'm thinking that a higher compression ratio is somehow beneficial to variable displacement engines, but have no evidence to support that theory.
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Old May 12th, 2008, 12:43 AM   #17
 
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so do you guys know of a way to disable the VCM and always run on 6cyl..
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Old May 12th, 2008, 02:53 PM   #18
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I doubt there's an easy way. You could obviously tap the VTEC solenoid lead and supply power to it to stay on the "non-ECO" cam, but that's not going to tell the ECU to deliver fuel and spark to it by osmosis.
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Old May 12th, 2008, 02:54 PM   #19
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Regardless, why do you want to disable it? When you get on the gas, VCM instantly shuts off...it's not like it takes a few seconds.
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Old May 12th, 2008, 04:13 PM   #20
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Thanks for the explanation TH23. However, I'm not more convinced Honda didn't rate the 6MT engine separately, as it seems almost impossible for both to have identical power/tq numbers at the same rpms.
The higher CR probably erases most of the advantages of VTEC and the intake, but it has to change the numbers some (HP/TQ peaks and/or their respective rpms). And he curves HAVE to be different; that's for sure.

Oh, and VTEC is a joke now. Honda even threw it on their Interceptor 800 motorcycle, when all it does is change from 2 to 4 valves. What ever happened to 'Variable-valve Timing and Electronic Control'? And VTEC itself is arcaic technology now, where most manufacturers have the infinitely variable variety (rather than 2 steps), on both intake and exhaust. And don't forget the timing chain, rather than belt, and DOHC, rather than SOHC. Okay, I'm done. That's my only gripe with Honda; it's time to change, just like Mercedes did with their supposedly advantageous SOHC 3-valve motors.
And don't get me started on the ancient pushrod engines like the one on my GTO; it's even worse. I'm just an honest, non-brand loyal guy. Later.
JC
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Old May 12th, 2008, 06:00 PM   #21
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GM's pushrod motor may be ancient, but it works... and will continue to work. Name me a car that has a sohc or dohc with 500hp that gets 25mpg highway.
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Old May 12th, 2008, 06:17 PM   #22
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Originally Posted by ELP_JC View Post
And VTEC itself is arcaic technology now, where most manufacturers have the infinitely variable variety (rather than 2 steps
VTEC = Cam profiles
VVT-i, CVCT-S, etc... = Cam phasing

Don't knock the technology if you don't know what it does.
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Old May 12th, 2008, 06:18 PM   #23
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Regardless, why do you want to disable it? When you get on the gas, VCM instantly shuts off...it's not like it takes a few seconds.
Great point indeed.

I had an idea to use a 3.5 TL ecu, dont say no until you've tried it. I also had idea to use the type s 6 speed for the 150mph limiter instead of the accord 130mph limiter, but I am sure a Speed Limit Defencer would work to
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Old May 12th, 2008, 06:26 PM   #24
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Personally the case for disabling VCM is pointless, it's not going to transform your car and magically drop the 6MT cams into your head. I highly doubt it will increase performance at all.

I don't own an 8th gen, but I'm actually borrowing an 08 V6/5AT for the week while my car's in the shop getting some work done and the VCM doesn't bother me at all. If that light wasn't on the gauge cluster, you wouldn't even know it was working.
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Old May 12th, 2008, 06:49 PM   #25
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VTEC = Cam profiles
VVT-i, CVCT-S, etc... = Cam phasing

Don't knock the technology if you don't know what it does.
just to add to that, only BMW (Valvetronic) and Infiniti (VVEL) have continuously variable lift. so 2 = most?

oh, and the almighty GT-R which is newer than the G37 doesnt even have VVEL. neither do any of the ///M cars or the N54 (3.0tt engine used in the 335). hows that for archaic?

honda still might have a few tricks up their sleeve for the J-series though. the 09 RL's J37 has SOHC-VTEC that works on both intake AND exhaust...and thats never been done before by honda on a SOHC motor.
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Old May 12th, 2008, 07:22 PM   #26
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Personally, I can do without VTEC, give me straight DOHC and 8-9k rpms any day...
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Old May 12th, 2008, 08:51 PM   #27
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Thanks for the explanation TH23. However, I'm not more convinced Honda didn't rate the 6MT engine separately, as it seems almost impossible for both to have identical power/tq numbers at the same rpms.
The higher CR probably erases most of the advantages of VTEC and the intake, but it has to change the numbers some (HP/TQ peaks and/or their respective rpms). And he curves HAVE to be different; that's for sure.
I already explained in the first reply how it would be entirely possible just with different camming despite the CR. If you don't believe it or accept it I really don't know what to say. Yes, the curves will be very different, but there's no reason at all that they couldn't have the same exact peak horsepower and peak torque at the same RPMs. In fact they probably planned it that way to simplify marketing. All other factors being equal though, without a dedicated low-end cam (or variable intake) the 5A/VCM version of the motor will have much poorer low-end. That could be part of the reason why the Camry V6 which also has the SAME exact ratings is nearly a full second faster in the 1/4 mile.

Quote:
Originally Posted by ELP_JC View Post
Oh, and VTEC is a joke now. Honda even threw it on their Interceptor 800 motorcycle, when all it does is change from 2 to 4 valves. What ever happened to 'Variable-valve Timing and Electronic Control'? And VTEC itself is arcaic technology now, where most manufacturers have the infinitely variable variety (rather than 2 steps), on both intake and exhaust. And don't forget the timing chain, rather than belt, and DOHC, rather than SOHC. Okay, I'm done. That's my only gripe with Honda; it's time to change, just like Mercedes did with their supposedly advantageous SOHC 3-valve motors.
And don't get me started on the ancient pushrod engines like the one on my GTO; it's even worse. I'm just an honest, non-brand loyal guy. Later.
JC
You should check out this thread: What's so bad about 2-valve SOHC and OHV engines?

Pushrod engines are actually newer than DOHC. They were developed for V-8 engines to help minimize the huge amount of physical space required by an overhead cam V8. Pushrod V8 engines are tiny in comparison, extremely space efficient, and can actually fit into Miata and other 4-cylinder engine bays that even some DOHC V6 engines cannot fit in.

I agree with you on VTEC though. It's outdated and old school. The patents on it have long expired and who made copycat systems? Almost nobody. Why? Because the other systems work better out there and do more for 99% of the market. I think Mitsubishi came out with a copycat VTEC, but that's it. Big whoop. VTEC's time has come and gone, but Honda is still building the same ol thing.
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Old May 12th, 2008, 09:57 PM   #28
 
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I had an idea to use a 3.5 TL ecu, dont say no until you've tried it. I also had idea to use the type s 6 speed for the 150mph limiter instead of the accord 130mph limiter, but I am sure a Speed Limit Defencer would work to

thats actually not a bad idea..
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Old May 12th, 2008, 10:06 PM   #29
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just to add to that, only BMW (Valvetronic) and Infiniti (VVEL) have continuously variable lift. so 2 = most?
Let's see: Nissan, Infiniti, BMW, Toyota, Lexus (you forgot about their VVTi ); that's most to me . Don't want to start a war here; was just stating facts. But they have bragging rights, yes; they started it. It's just time to improve it IMO.

VTEC-V6: I know exactly what variable timing is; I wasn't discussing methods to achieve it. All I said is Honda does it in 2 steps only, rather than infinitely variable, like Toyota, BMW, Nissan, etc.

Schu, I agree with you completely on a DOHC engine with no electronic crap. After owning many expensive cars that only gave me trouble, I want simplicity now. That's why I went with my goat. Unfortunately, some of its quality issues left me disappointed. The main one is the noisy valvetrain, which you might get it or not with GM's crappy quality control, but with my luck, I got one of the noisiest ones. It sounds like an old clunker with 150K miles, even with thicker oil (dealers blame the aluminum block). But didn't have Nav, auto climate control, stability control, TPMS, or any crap like that. That's why the VCM scares me, and the fact the 6MT doesn't have it is the only reason I'm considering the Accord. I'm going to do some research on the 335i because the turbo 6 doesn't have the complicated VANOS system, and it's a DOHC with chain-driven cams and hydraulic lifters. And RWD too. All cars will have some complication nowadays, but I want the minimum possible, to avoid countless trips to dealers. I just not particularly fond of any kind of force induction, but choices of RWD coupe (4 seats) vehicles are limited. The G37 didn't impress me at all, especially for the price. Much rather own the 6MT, which I'm seriously considering, even with its FWD.

As a final comment, our CR-V also left us disappointed at Honda, even though it was built in Japan. It now rattles like no other car we've had, with only 14K miles. It consumes oil since day 1, but less than the quart per 1K miles necessary to do something about it; a first for a Honda. All my V8 Lexus cars (4 of them) had issues, so it's not just a Honda thing; it's car quality in general. BMW same thing. Oh well. Now Wall Street is #1, rather than the customer. And with motorcycles is even worse, so I learned how to live with it. Sorry for the ramble. Later.
JC
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Old May 12th, 2008, 10:25 PM   #30
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VVT-i is continuously variable cam timing, not continuously variable valve LIFT. honda already has continuously variable cam timing in their K-series motors.

cam timing is rotating camshaft forwards or backwards.

valve lift is changing how big the valve can open (like what VTEC does with the low and high cam profiles).
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