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So, besides the obvious bump in compression, any foreseeable issues with running s5 NA rotors in an REW? I sold my set of REW rotors which turns out I actually need now lol, but I have a good set of s5 NA rotors laying around. I wouldn't mind saving the $500+ trying to source another set of rotors. The motor will be on stock twins/PFC.
you will loose power, as it will be very knock limited. there was a back to back dyno of 9.0 vs 9.7's on an REW on another forum, and the 9.7 car was down 50hp.
you will loose power, as it will be very knock limited. there was a back to back dyno of 9.0 vs 9.7's on an REW on another forum, and the 9.7 car was down 50hp.
At the same boost level? Hard to see that adding up if it's a stock twin car on 10-12psi. I know Kevin at rotary resurrection had an auto FD back in the day on 9.7:1 Rotors and downpipe only. Ran great.
I've driven a manual running 11ish psi and it certainly didn't lose any power. I'd say that it was significantly snappier during regular street driving. Overall power difference felt negligible.
At the same boost level? Hard to see that adding up if it's a stock twin car on 10-12psi. I know Kevin at rotary resurrection had an auto FD back in the day on 9.7:1 Rotors and downpipe only. Ran great.
i assume it was because the 9.7 can't run safely at the higher boost levels so it lost power because it was boost limited.
if the engine won't ever run over 14psi then i can't see any power loss, but on the track, even 14psi with the latent heat could become unsafe in a hurry.
high compression and turbo don't mix. the 9.0 rotors are the best all around compromise and should stay in the engine IMO. in a stock-ish car it probably would get by, but still isn't necessarily wise for the slight bit of throttle response and spool. i could also picture the car winding up down the road with a single turbo on it and a blown engine.
Also you will need to get creative with the front and rear counterweights. The rotors and front/rear counterweights make for a balanced rotating assembly. If you used FD counterweights you'd have a serious balance issue.
You'd have to do some more research on it, but in general when you go for rotors from another engine you are going to have a weight difference.
You may be able to run the front and rear 89-91 NA counterweight, or might have to have the assembly professionally balanced.
I have no vibration problems and couldn't be happier. I used MATCHING rotors or within 1 letter code and an 89-91NA rear counterweight paired to one of the rotors I used. Yes ignition timing is far lower. 1ATDC is not out the realms of what the engine might want under certain load and RPM points at full power, but that doesn't matter, if the peak chamber pressure is at the correct time ignition timing is just a variable, not a power effecting parameter.
Firstly the engine has better fuel economy by about 3% and every low load condition, 3% better power, better throttle response, better BMEP at lower rpm to spool the turbo.
I built my car to be a compromise of fast on road, track, autocross and on the drag strip. But I'm not about to trade out increased power whilst retaining linear power delivery for 1.3 to 2 times the power.
Would I do it again? Probably not. I'd buy a mazda reman engine if they are still available and replace the side seals with OCD spec side seal clearances and leave it it that.
you will loose power, as it will be very knock limited. there was a back to back dyno of 9.0 vs 9.7's on an REW on another forum, and the 9.7 car was down 50hp.
Um, doesn't entirely compute under "normal" circumstances... I ran S4 NA rotors in mine and the low/mid was phenomenal!!!
Originally Posted by DaleClark
Also you will need to get creative with the front and rear counterweights. The rotors and front/rear counterweights make for a balanced rotating assembly. If you used FD counterweights you'd have a serious balance issue.
You'd have to do some more research on it, but in general when you go for rotors from another engine you are going to have a weight difference.
You may be able to run the front and rear 89-91 NA counterweight, or might have to have the assembly professionally balanced.
Dale
Unless he has the S5 rotors lightened and balanced with S6 counterweights then he'll need to use the S5 front and rear counterweights. Additionally he'll also need to use an S5 front stack (unless the bearing sizes are the same between the two. I know the S4 ones are different diameter so I had to go with an S4 front stack in my engine due to S4 rotors).
Unless he has the S5 rotors lightened and balanced with S6 counterweights then he'll need to use the S5 front and rear counterweights. Additionally he'll also need to use an S5 front stack (unless the bearing sizes are the same between the two. I know the S4 ones are different diameter so I had to go with an S4 front stack in my engine due to S4 rotors).
That's not true. The S4 rotors and CW are heavier, but the S5 and S6 parts are the same weight. The front CW on FD has a larger thrust area. S5 rotors can be used in S6 with no balancing, provided the rotors are withing one letter weight of each other.
The difference in S5 and S6 rotors is the machining of the combustion pocket in the S6 and the coating. The compression ratio for S5 and S6 turbos are 9.0:1 and NA S5 is 9.7:1
That's not true. The S4 rotors and CW are heavier, but the S5 and S6 parts are the same weight. The front CW on FD has a larger thrust area. S5 rotors can be used in S6 with no balancing, provided the rotors are withing one letter weight of each other.
Well ****, thank you for the correction.
Yeah, I went with the S4 N/A rotors on mine for the thicker casting on the rotor faces, the minor increase in compression ratio was a perk but not a deciding factor.
That's not true. The S4 rotors and CW are heavier, but the S5 and S6 parts are the same weight. The front CW on FD has a larger thrust area. S5 rotors can be used in S6 with no balancing, provided the rotors are withing one letter weight of each other.
The difference in S5 and S6 rotors is the machining of the combustion pocket in the S6 and the coating. The compression ratio for S5 and S6 turbos are 9.0:1 and NA S5 is 9.7:1
That's what I thought! I've been reading these comments and going WTH???? I personally was able to swap out matching all "C" weight 9.0 rotors out of my 20b for a matching set of 9.7 "C" rotors out of S5 because of that Mazda Trix info from years back.
Interesting! Didn't realize that was the case. Whenever you mix and match rotating assembly it's worth taking a beat and making sure everything will work like it should.
Would be interesting having a high compression FD motor, but it would most likely be power limited but you'd gain a lot more low end grunt. Running a lot of boost would probably be out of the question, though.
Would be interesting having a high compression FD motor, but it would most likely be power limited but you'd gain a lot more low end grunt. Running a lot of boost would probably be out of the question, though.
Dale
One thing I wonder is how is a 30psi 9:1 engine any different than a 15-20 psi 9.7:1 as far as knock threshold. I'm no tuner, but I feel like saying an engine will be severely boost limited, but at the same time applaud a 30+psi engine is interesting. I obviously need more research. I do know that a higher compression engine needs less timing than a lower compression at the same boost pressure. I just wonder if there is a ratio:timing relationship that is consistent:
Example 9:1, 15 psi, 15A timing 30psi 0? timing? I'm not entirely sure
9.7:1, 15psi, 10~timing 30psi -5 timing????
S5 and S6 turbo rotors are identical, the S5 non turbo are not enough of a weight difference to need a special counterweight of its own.
higher compression generates knock at lower boost levels, so the higher the compression the less boost you can safely run. you could offset that by running race fuel, E85, water injection or other methods but then you have more potential failure points and more care and cost needed to simply drive the car 'safely'.
Thanks for the link. I'll give it a better look later.
I have a T2 S4 engine I'm messing with. I also have 9.4 and 9.7 rotating assemblies in the garage. My thought was to drop the 9.4 rotors in to help with throttle response, but a quick glance makes it look like 8.5 rotors can make substantially more torque with boost and the relationship of CR, boost, and timing doesn't seem to be a simple formula.
fendamonkey said he had 9.4 rotors, so I may still consider it. Worst case, I'll build two engines because I feel like I'd like to have a spare ready to go in case the worst case kaboom happens. With how rare some parts are getting, I have kicked around getting another engine to add to the 5 I already have (3 of 5 are S4 NA blocks, 1 is a trashed S5 NA, and one is the S4 T2 with unknown history)
Sorry to derail the thread here, but I am curious about the results of a mostly stock FD with 9.7 rotors.
Has anyone run stock boost with stock twins but with 9.7? I would be highly interested in running higher compression with low-ish boost to gain low-mid range power. I would assume low end torque would increase as well, probably reduce turbo lag as well.
Has anyone run stock boost with stock twins but with 9.7? I would be highly interested in running higher compression with low-ish boost to gain low-mid range power. I would assume low end torque would increase as well, probably reduce turbo lag as well.
I just posted inboard and also outboard of what a stock configuration twin turbo 9.7:1 13B-REW drives like on a tight autocross style circuit. There is no throttle lag at all, even at low throttle openings and low rpm. I can pull out of a corner at 25% throttle and 2000-2500rpm. I'd get more big track lap time by upgrading my AD08R's to Medium compound A050s or slicks and adding down force than any power upgrade. And to get more lap time from my setup on tight autocross style circuits would be bolting on soft compound A050 or hill climb slick tyres. You can't add power without adding grip, and you can't add power without upgrading braking. And you can't upgrade grip without revisiting suspension rates again.
I just posted inboard and also outboard of what a stock configuration twin turbo 9.7:1 13B-REW drives like on a tight autocross style circuit. There is no throttle lag at all, even at low throttle openings and low rpm. I can pull out of a corner at 25% throttle and 2000-2500rpm. I'd get more big track lap time by upgrading my AD08R's to Medium compound A050s or slicks and adding down force than any power upgrade. And to get more lap time from my setup on tight autocross style circuits would be bolting on soft compound A050 or hill climb slick tyres. You can't add power without adding grip, and you can't add power without upgrading braking. And you can't upgrade grip without revisiting suspension rates again.
That is really neat, do you have a build thread on this? I would love to know more about your setup, this is the type of setup I would love to go with. Stock twin with higher compression
Going to a higher compression rotor will increase the speed at which the engine revs up under no load/light load.
This is a positive trait for the street or for racing. It will decrease shifting/downshifting times and increase acceleration at low loads (lower gears partial throttle).
Higher compression rotors have very little power gain in the rotary and what gain it does have is in the high rpms!
Mazda found going from a 9.2:1CR to 10:1 gained only 2.3% increase in power on a Naturally Aspirated engine.
On a forced induction engine you can see that the higher boost you could run on 9.2:1CR would be higher than the 2.3% increase from higher compression ratio.
Here is my post #27 from that linked thread because I know many people will be too lazy to read that thread.
Originally Posted by BLUE TII
Okay, got some numbers and Mazda charts for you so you aren't just taking my word on the whole rotary Compression Ratio thing.
First, here are some great resources that this info is from- the Kenichi Yamamoto Rotary Engine books in PDF.
Sadly, because of the PDFs I didn't get good pictures of the charts- I will see how screen shots show up.
First this figure 9.11 from page 98 of the 1971 edition shows the curve of Brake Maximum Effective Pressure of the different Compression Ratios of the rotary between 6.5 to 12.6 CR.
BMEP is a theoretical tool to compare the torque a given engine can provide from a given displacement.
Fig 9.11 1971 ed pg 98
For a rotary engine BMEP is very flat from 8.5 to 11 CR with just a slight increase.
Fig 4.37 1981 ed pg 49
This again shows BMEP for 9.2:1 CR compared to 10:1 CR. I found that looked like a peak of 8.6kg/cm2 and 8.8kg/cm2 or 122.3psi and 125.165psi.
Only a 2.3% increase BMEP from 9.2:1 CR to 10:1 CR. 2.3% increase is definitely something, but when you compare that to the torque available from running more boost instead it is not significant.
Also note where the increase is. It is NOT in the low rpm!
Here for fun I have fig 4.34 from 1981 ed pg 48
This shows the BMEP difference between old 12A Leading Deep Recess rotor and Medium Deep Recess rotor (LDR vs MDR).
You can see the increase flame speed of LDR DOES increase low rpm BMEP.
Here is my video of 8.5:1CR ratio engine in kart track auto-x like Jobro's.
The boost gauge is the lower of the two Greddy gauges. Straight up 12 O'clock position is 14psi, pointing Right at 2:30 O'clock position is 26psi boost.
You can see there are plenty of ways to increase turbo response without raising the compression ratio.
granted, for racing it is all in the powerband, and while the higher compression doesn't make enough additional power to warrant it, it does improve the length of the powerband and torque curves so more of the gear lengths can be used.
such as a car that makes power from 5000-8500 but makes 350whp isn't as fast as a car that has a powerband from 3000-8500 that also makes 350whp. that is an exaggeration and turbos have come a long ways in recent years to bring that ratio to almost unnoticable, back when all turbos were journal, tight tolerances and very heavily constructed.
06-02-17, 06:03 PM
