2007 MS6 2.3 L4 Compression ratio?
- Thread starter Rishiko
- Start date
mysleeper6
Member
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- 2006 Mazdaspeed6
Yes it is 9.5:1
(at least this is what Mazda posted in their "Mazdaspeed6 Driving Event" brochure, a document intended for their sales force, and maybe the media).
And somewhere on here is a thread explaining why low back pressure is not a restriction for our engines...can't remember why.
(at least this is what Mazda posted in their "Mazdaspeed6 Driving Event" brochure, a document intended for their sales force, and maybe the media).
And somewhere on here is a thread explaining why low back pressure is not a restriction for our engines...can't remember why.
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- 2011 Mustang GT
Wait, the CR is that low on this motor? I thought with the DI, they ran a slightly higher CR as a result (allowing for more power and low end torque)?
Edit: NVM, it's 9.5:1 per the manual. Wow.
Edit: NVM, it's 9.5:1 per the manual. Wow.
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- 2007 Mazdaspeed 6 Sport
Just an FYI, on turbocharged engines such as this, the turbo itself provides the backpressure on the engine, not the exhaust from the turbo back.
Also, not sure what context Batou079 was referring to, but these cars run really rich throughout the speed range of the engine in stock trim and tune.
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- 2011 Mustang GT
Blender, correct me if I'm wrong, but removing the back pressure post-turbo will help with spool up to some extent, right? Downpipe and test pipe freeing up flow will allow the exhaust side fof the turbo to spool up quicker, as more flow can exit through?
On the exhaust manifold itself, the housing is the neckdown point of the exhaust system, followed by the two cats?
On the exhaust manifold itself, the housing is the neckdown point of the exhaust system, followed by the two cats?
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- 2007 Mazdaspeed 6 Sport
You're on the right track, to a certain extent. You can notice improved spool up at lower revs (and many do on the MS6) by removing post-turbine resistance. You will only notice this improvement if the post-turbine exhaust is more restrictive than the pre-turbine exhaust (the header/manifold). Basically, the setup will only flow as much as its most restrictive point. On the MS6, the catted downpipe is the main culprit, with the second catalyst being only partly to blame.
By removing the second catalyst, I noticed spool-up around 100 to 150 revs earlier than before. This was done over the course of ten runs with the cat in and ten runs with the cat out (all in the same day) doing 3rd gear WOT pulls. The only tool I had to record results was my AP. I simply recorded revs, boost pressure, and wastegate actuation.
It wasn't perfect, and it's been half a year since I did it, but I remember the results showing a slight pickup in the time (in revs) it took to spool up. You must keep in mind that you're only going to spool up to the boost pressure of the corresponding boost table for that rev range. This might be confusing if you're trying to test it yourself as you may be overboosting per the appropriate boost table for that specific engine speed.
You may get to a point where the ECU is opening up the wastegate to prevent you from spooling at full potential for that rev level. It's important to understand that it is for engine safety reasons that you should not bypass the ECU to attain a better spool rate without the help of a professional tuner. I could go into twinscroll manifold/turbo combinations, but your question didn't really ask about that. However, you should know that if you're wanting the best spool up that's what you should be looking toward.
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- 2011 Mustang GT
Thank you for the reply. Gold star of the day!
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- 2007 Mazdaspeed 6 Sport
Yes!!!
That means I'm 1/1 so far on the week!
That means I'm 1/1 so far on the week!
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- 2007 Mazdaspeed 6 Sport
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- 2011 Mustang GT
TexasSpeed6
Member
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- 2006 Speed6
The static compression ratio of the factory engine is 9.5:1, the dynamic or net compression ratio after cam overlap and duration are factored in is around 8.19:1 which is slightly on the agressive side for a pump gas engine.
You can add a full exhaust of any flavor you like and the engine will run without issues with the factory tune and boost controller. If you have tuned the engine, you will have to retune the engine if you change the enhaust, and if you have a aftermarket boost controller you will have to get it tuned if you put a exhaust on or it could run lean. I dont recommend running a exhaust cutout on a untuned car with the factory boost control because the factory boost controller is too slow to react to the extremely fast spool times which leads to worse boost spikes and engine damage.
You do actually lose torque from a free flowing exhaust in a turbo application, but the additional torque added by the turbo in responce to the increased pressure differential between the inlet and outlet sides of the turbine will give you a net increase in torque output.
