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Big Bore Exhaust Manifold for 2V Engines

Discussion in '308/328' started by bill308, Oct 1, 2019.

  1. mk e

    mk e F1 World Champ

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    Again you're ahead of me.....I'm sure I'll need to do all of that too. My plan also includes testing a tuned airbox which might be something that could help with you 5k dip. For your engine, you'd need to separate the banks like the more modern stuff, then the airbox can be build as a Helmholtz resonator tuned to 5k rpm and fill in the dip.

    Careful on that path, normally what happens is you "fix the dip" by reducing everything above it.

    Horn height makes a big difference so don't discount that.

    I have 12 MAP sensors so I can calculate fuel needs of each cylinder individually, do the TB sync and compensate automatically as they drift out of sync and light the "slow down" light when they exceed whatever compensation limit I set but they do not respond fast enough to collect port wave data, you'd need pizo sensors for that....i think. I was just focused on will it run and styed below 3k so I saw the cylinders pull vacuum and drift back to baro pressure each cycle but no waves even logging at 1kHz...I think the ECU reads at 2kHz but 1kHz is the logging limit on my system.

    Google tells me the LM2 is a 32 channel logger but its got you AFR, so I guess you can add 31 additional sensors. looking quickly I didn't see the logging feq spec but I suspect its nowhere near high enough to log port waves even with the right sensors...10Hz is usually more than plenty for AFR which is what its built for so......

    Do you have AFR date for your dyno runs? Everything look ok at 5k or is it wonky?


    Most gain is within an inch or so of the seat. The stock exhaust flows way too much for the stock intake (Stock headers were apparently intentionally mis-aligned to the exhaust ports to help the flow balance) so improving the intake by 10-15% makes everything better. Your engine is making good power so whatever they did seems right.
     
  2. mk e

    mk e F1 World Champ

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    Do you know what cams are in the engine? That effects all this too.
     
  3. bill308

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    Hi Mark,
    My cam is a Cats Cam 1700402
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    The following is 5 minute data segment, the last set of readings I did on my 308 before engine tear down. The MAP signal is the average of 8 cylinders, so very very stable. I think the sampling period is about 1/12 sec, so more than fast enough to capture RMS flow data. I'd like to compare pressure drops along the path, starting at the duct entrance, then inlet side of an filter box, outlet side of filter box, air adjacent to carb inlet horn, and of course down stream MAP. MAP is a particularly good replacement for a tps and a lot simpler and more rugged. I hope my LM2 works as well as the LM1 with aux box. I'd like to get at least 6 pressure channels.
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    This is the muffler system I plan to use. The front bank inlet tube 2 inch OD and 26.8 inches long, from the flange end to the face of the muffler. There may be more inside the muffler. The rear bank tube is 12 inches long.

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    Looking at the exhaust system as a whole, one could do a flow model as shown below. If one assumes equal flows for front and rear banks, the flow network gets simple, it defaults to a series network. A reduction in flow resistance to any portion of the network will help everywhere. Big resistances, offer the biggest opportunities.
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    Pizo electric accelerometers, like an Endevco 2222b's were good to at least 5 kHz, if paired with a good, analog,charge amp system. Lots of maintenance and calibration to get accurate results. One could subject the data to FFT and pull out dominant frequencies and associated magnitudes. The usual rule is to sample 10 x rate of the highest frequency of interest. So if you want to capture 1 s events, you need to sample at a 10 samples/s rate.

    I will forward my exhaust system to Vince and see what he can recommend. Great discussion.

    Bill
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  4. mk e

    mk e F1 World Champ

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    The cams are quite similar to mine so the wave stuff I posted earlier will be similar for you.

    This is a log from my setup.

    The gold saw tooth is crank angle 0-720, so each saw tooth is a complete engine cycle. TPS is also gold....smooth line at the bottom.
    The red is the signal from my "multiMAP" which is a piece of hardware I had made with 12 MAP sensors then a diode circuit that selects the lowest value and sents it to the ECU. I have no filtering on this signal and you can see its pretty easy to pick off individual cylinders. Each flat is about 60 degrees but just the capacitance & resistance of the hoses damp out any variability.....that's about all that is possible with a MAP sensor. Logging was 1000hz but there is also a limit with how fast the ECU updates the signal....I had MAP on a 3ms loop at the time
    Cyan line is the processed and filtered MAP signal that's used for global calculations
    Blue was some additional filtering I was playing with....clearly too slow to be helpful

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    Back pressure is a bit more complicated than your model as its pulsatile flow and moving as about mach 0.5 at times in the header tubes.

    Also the flow loss in the headers is a balancing game....smaller tubes mean stronger waves which mean better vacuum during valve cross-over and better extraction and better cylinder filling.... but more friction loss. So its a balancing act....smaller straighter tubes vs larger or more twisting tubes. Everything after the collector is bad but often required.
     
  5. Brian A

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    … I have no idea what you guys are talking about but it is still fun to read!
     
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  6. nerofer

    nerofer F1 World Champ

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    My own thoughts exactly...

    Rgds
     
  7. mk e

    mk e F1 World Champ

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    You got it exactly, I was just saying its never as simple :)
     
  8. mk e

    mk e F1 World Champ

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    A lot to unpack in this, I didn't have time last night.

    At say 7000rpm it's 117 rev/sec (hz) , is 0.00857 sec/rev...but 2 revs per cycle so 0.0171 sec/cycle which is 58 hz. Data logging at 12Hz means you see about every 5th cycle and you are not looking at the same time point in the cycle so you'll get a good amount of noise that will need to be averaged out ....so the you end up with a 10-20 cycle or so lag. Fine for basic steady state type stuff which is most stuff but transitions will be a bit sketchy.

    The header tubes and intake runners are normally tuned to the 3rd reflection so these pulses are happening at 58x3 = 174Hz, see these at all requires sampling at least 1kHz and my understanding is the systems designed to look at them operate in the 10kHz range. Simulation is the only way I get to "see" them on my very limited budget :(

    TPS and MAP really can't be used as a substitute for each other. TPS is a leading signal meaning it triggers change in the system, MAP is a lagging signal mean its the system reaction to the TPS input. The way I think of it is TPS is what the driver is asking for, MAP is what the engine is delivering. Taking that idea 1 step further, most modern OEM ECUs use the TPS as a "torque request" sensor then calculate the best combination of throttle, boost, gear ration to deliver the driver's request. Again for relatively steady state stuff I would rather have MAP but TPS is pretty critical to understanding transitions.


    Ahh the simplicity of carbs that have none of this :)

    ....or they seem until you have a big torque dip to deal with. I've never messed much with webers so I'm not going to be much help. On bike cabs that point would be the cross-over from the emulsion tubes to the mains and probably fixed with the needle height or profile.....but you don't have needles so I don't know without buying a weber book and reading....I'd guess a tube change is in order but its a guess without reading.
     
  9. derekw

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    Bill, I would just take the Burns suggestion and use the extra intellectual bandwidth that decision provides to get out a bit more or read a good book :)
     
  10. bill308

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    Hi Derek, I think that's good advice.

    Hi Mark, Below is Vince's last design. Note it does away with the stepped primaries and is beginning to look a lot like the OE design. This design retains the 1.5 inch OD primaries and specifies a 30 inch length.

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    The following is what I believe Vince used for the above design. I wish there was a way to get a copy of the inputs used, to match the outputs.

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    My OE rear manifold has tubes of 19-25 inch in length that I can reasonably see and measure. Measurements were done with a 1/4 inch tape held over the pipe centerline, in segments. When I peel back a portion of the OE heat shielding, I see fiberglass strand wrapping an unknown foam in between tubes, and of course the aluminum skin. I measured the front primaries to be 27-29 inches in length.

    OE primaries are a bit shorter, so tuned to a higher rpm for a 2.9 liter engine, rather than the 4500-5500 rpm range my this design targets (the gap). I would expect this difference primary length difference as I'm trying to emphasize low-mid rpm torque, again for drive-ability with more inherent torque.

    I still need to interrogate my engine builder for details of the test header, specifically, primary length and diameter and collector diameter with down stream pipe length and diameter.

    The interesting design detail of the Burns pieces are the merge details. Four tubes dumping pulses, or slugs of compressed gas into what appears to be a converging/diverging nozzle, before the 2 inch down stream system. The converging entry to the nozzle speeds up the flow until the throat where the diverging portion slows it down for entry into the down stream system. What I think is happening is kinetic energy from high velocity is being transformed into a slower flowing, but now higher pressure exhaust stream, will flow through the muffler assembly. I think a bigger bore here hurts nothing but packaging.

    My hats off to you Mark. Evaluating exhaust pressure data, to facilitate breathing is pretty interesting stuff. There's a lot in this thread to wrap my head around.

    Bill
     
  11. mk e

    mk e F1 World Champ

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    I took a couple minutes and guessed at a bunch of things but here's what I got in DM6....a little high on hp at 370 but not bad for guesses. This is the cam you posted and the burns header design.

    The second pic is the waves and flow velocities at 8k rpm. Everything looks pretty good at this rpm.

    The 3rd is the same at 5k rpm....looking at the waves it is pretty badly out of tune down there and the sim is showing a dip, just a but lower rpm than you results, but i don't have the info for the dyno headers so that might be the difference....that had a much longer collector that could easily help fill in near 4k. The intake is also badly out of tune at that 5k so ideally you'd have the header in tune to compensate a bit.

    Edit: this is the burns step header...let me check the new design

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  12. mk e

    mk e F1 World Champ

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  13. mk e

    mk e F1 World Champ

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  14. mk e

    mk e F1 World Champ

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    Here's another tri-y design compared to the non-step burns. Here the mid range dip is pretty much completely gone with an 8hp gain 3800- 4600rpm, but the price is an 8hp drop at 8000. This will drive much nicer on the street especially with carbs, the burns will be faster on the track. This one has a 6" section of 1.375 Dia coming off the head, a little shorter primary length, a little long 2nd collector. Compromises
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  15. mk e

    mk e F1 World Champ

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    #40 mk e, Oct 9, 2019
    Last edited: Oct 9, 2019
    Should have given you this...the specs for that header. I the numbers in cyan are what I used. Up top in grey are what the software things would be a good starting point for a 4-1, very close to the burns design.

    Edit: and these are pipe ID (or where it says 1.375, that is 1.5OD with 16g pipe...I was kind of forgetting that detail) and the primary length includes port length, so length is measured from the vales, you'd build it about 3" shorter.
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  16. bill308

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    Hi Mark,

    Great stuff. Would you kindly run a case moving the exhaust tuning down to 4000 rpm? How long would these primaries be? Please assume 1.5 OD primaries transitioning into the existing, 2 inch muffler system.

    I really like the Burns collector pieces. It almost looks like someone did some CFD work on them. I wonder how effectively they could be characterized on a flow bench and how much they actually alter the flow over a similar piece without the necking? Ever see any test data?

    In an earlier post you referenced 0.5 mach number. Was this at the exhaust port exit? All down stream bulk flow should be slower. Outlet/inlet muffler flow area (based upon OD's) is 6.70/6.28=1.07, so the 4 x 1.46 muffler outlet pipes are about 7% larger than the 2 x 2 inch OD inlet pipes. As the flow area gets bigger, pressure and density increase and velocity decreases, all good qualities to push the gases through the muffler system and minimize resistance to down stream flow.

    In an earlier post you referenced the need for a silicone based pressure sensor, or transducer, for a fast enough response to reliably capture important pressure harmonics with a good amount of detail. I know folks like ComputerBoards used to offer a variety of multichannel USB, Ethernet, or other connectivity with a laptop. You could also capture the signal with a digital storage scope. Are there any off the shelf sensors available, at a reasonable cost? I once worked on a suitable OE sensor for a turbine mounted fuel controls. They were individually calibrated, but but fast, accurate robust and very expensive.

    Bill
     
  17. mk e

    mk e F1 World Champ

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    Man, I just mailed the software key off to a buddy trying to pick cams for a dino build...a 246 I think, so it will be a little bit before I can running anything more. Once he gets the key I can email the file I created and ask him to check a couple things for you....he should have it by the weekend.

    The headers I did and burns did are designed to match your engine and give you better performance in one place vs another. I was going for the smoothest torque curve I could get without killing the top end and they are in tune at 4k which is why they make so much more power there than the other options I ran simulations on....I didn't screen shot the waves but the simple fact that torque is good tells you its in tune. Its a tri-y so 2 collectors on each path that can act separately or together giving you a 5", 8" and 13" collector tuned on the 5th (at about8k), 5th(5th at about 6k), 6th (at 8k) reflection so each is coming in and out of tune 5 or 6 times idle to redline, all at different rpms....and you get a pretty flat torque curve. The primaries on the system are shortish at 21" (18+3 in port) which puts them on the 4th pulse so in and out of tune 4 times idle to reline and there is an effective length of 29 (18+8+3) which is on the 3rd a bit under redline or 2nd a bit over I think. There is a LOT going on.

    To actually tune for the very best result at 4K the software would spit out about a 1.25" primary and then choke by 6k you don't want that if that makes sense.

    None of the headers I've run are bad, they all give you something a little different from best average midrange to best hp. This kind of stuff always makes my head want to explode trying to choose, only you can pick whats best for you but I can tell you that being honest will get you the best result. What do you want? Having a high hp number you can talk up is not a bad thing, nor is pulling like a freight train when you roll in the throttle on the highway (around 3k-3500 usually). All good. When I had Burn recommend a setup for me (before I owned dynomation and could do my own) I told then I drive 2500-8500 and they came back with a system similar to what I did for you but matched to my cams and head flow numbers and now that I have software I really wouldn't change it, in DM it works as well as anything I could come up with for how I plan to drive. If I re-time the cams a like and go to a big step header I can get another 70+hp out of the engigne and a hp peak near 11k.....where it will blowup and has a huge hole down around 4500 where I will actually use it so not a good choice for me.

    If you look at the pics of the headers I build the collectors are like the burns type...merge collectors and there is dyno testing out in the world that shows they help a little...usually. If everything is already oversize and mistuned then you will likely not see and difference but on well done setups they add some....but the cheaper options work pretty well for most setups too:
    https://www.coneeng.com/
    https://www.coneeng.com/results.html


    I can't find it now but I saw a video on youtube where they smacked a header tube with a hammer than redyno tested. The question was how much does it hurt if you bent a tube to clear the frame....they ended up with more hp. They bet the snot out of it before it did any harm.....that header was too frikin big to begin with. I've also seen dyno testing where they down sized the header, mismatched tube length a bit to allow larger radius bends and gained hp everywhere.

    For your HP, 2" pipes and mufflers are probably too small. They are very short so maybe......but Burns is suggesting 2.5" (or maybe 2.25") and I think they are right about that. You need about 2.2cfm (@28") exhaust system flow per hp...

    here's a chart...not a great one but a chart
    https://www.exhaustvideos.com/faq/how-to-calculate-muffler-size-pipe-diameter/

    A little better:
    https://m.roadkillcustoms.com/determine-proper-exhaust-tubing-size/

    then you want mufflers that also have the correct flow. If the muffler doesn't publish flow then you probably don't want it unless you've seen dyno numbers on a similar engine.

    The mach numbers are shown on any of the screenshots I posted that have 3 graphs, its the bottom graph and is measures at the exhaust min area point which I assumed is 1.5insq at the valve guide....about 1.375in ID effectively and seems about right. The exhaust will cool some, the pipes get bigger, and its at that velocity for only about 30 crank degrees it looks like. 2" is really on the small side though and will probably be costing you hp IMO.

    I think earlier I said a pizo sensor direct mounted....and I don't think there is any affordable options, I live vicariously through a $500 software package:
    http://www.motionsoftware.com/purchasejac.htm

    This place specializes in port pressure trace equipment for racers, I don't know what the stuff costs but I'm pretty sure it isn't cheap:
    https://www.tfxengine.com/

    I googled and found a thread where they are showing it off a bit and there are also traces from another wave simulation type software similar in price to DM but I told by a couple guys with both a pain in the butt to use...good but hard to use.
    https://www.speed-talk.com/forum/viewtopic.php?t=37398

    Hope this stuff helps and does just confuse things :)
     
  18. mk e

    mk e F1 World Champ

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    1 more thing i didn't answer well. My simulations do NOT look at the mufflers and I don't thing the Burns software does either. I think I mentioned that the choke at the back of the collector effectively terminated the tuning and nothing that comes after is anything but flow restriction....the flow diagram/model you posted would apply from the choke to the tail tips, the goal is just make it big enough to be low pressure drop and basically invisible to the engine hence the 2.5" recommendation.

    On the stock system which is obviously an 80s design does not have a choke as they weren't invented yet. That mean that everything COULD be acting as both flow restriction and wave tuning. It probably terminated or mostly terminates at the muffler but that is not a given and builder used to add termination boxes to the system to know where the waves terminate. i didn't model this system and I'm sure Burns didn't either.....but many after market 308 systems are old 80s designs and would need to be looked at to figure out how much of the system needs to be in the model. This also means that their chosen pipe diameter is about more than just flow restriction...its tuned, there are waves in there that are needed so they might NEED a smaller dia pipe to get good results just like header primaries want to be pretty small and very high velocity to maintain wave amplitude. i wouldn't build a system like this today.
     
  19. bill308

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    The test pipes were made in house to dyno my engine. They did not come out of an IMSA car as I thought I remembered.
    The primaries are 1.87 OD with average 28 inch length. The collector is 10 inches with 2.5 OD exit, followed by a 33 inch long pipe.

    My engine builder recommends 1.75 inch primaries, 1.63 min dia, and a 2.5 inch collector/exhaust system. This may actually be something we all agree on, big bore down stream is good. That puts onus on the muffler system.

    I got an email from Vince asking if we need to do more. I'll send him the test pipe dimensions and hopefully agree on a 4 k tuned system design, with all the inputs agreed to up front. To date I have not been able to get a copy of the actual input parameters.

    My engine builder agreed to take a look at the 4500-5500 torque dip. He did float the idea that it was part of how he was operating the dyno. The question is where is the good data and where is the questionable data? I like plots to challenge the data. My engine builder does not. He likes numbers. Old school.

    Thanks for all the help on this problem.
     
  20. mk e

    mk e F1 World Champ

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    What you want to tell Vince is not 1 rpm, its the rpm range where you want the engine to perform best and then any other ranges you are also interested in....there isn't a tuned "point" if that makes sense.

    When I first got my stock and a bit tired QV I noticed that more of the time, even in normal driving above 4500. At the autocross I would rev to 5500 and dump the clutch which was just enough to get the tires spinning and then shift at redline.

    When I rebuilt it and added a blower it made 300rwhp, so maybe 360-370 crank? Much nicer! But I noticed that without even thinking about it or paying any attention my normal shift points changed. I now rarely ran it about 4500, normal everyday shifts were around 3500. Then I switched to a bigger blower and it was right around 600hp....and I found I routinely shifted around 2500 and going high was usually at part throttle just to hear the engine.

    My point is that with the increased displacement you have and the the additional power from the other changes the engine will feel very different form what you started with so memories of what rpms you use most may no apply well going forward. You have an engine build to run very well 5-8k but I suspect you will be operating it 2000-5000 95+% of the time....that is probably what you want to tell Vince but note you don't want to do anymore harm to the top end than needed.

    Back to basic tuning...the dyno header as described has a 43" long collector (waves reflect at dia changes not before so not where 2 same/similar pipes meet so it all counts as 1 collector) which will be I think a 3rd pulse tuning and your primaries are 3rd pulse and your intake is 3rd pulse...so the 3 are going in and out of tune together through the entire rpm range and also, off the top of my head setup to peak around 9000 with the goal of helping it pull a bit harder on top which is also where the large primaries start to shine. That's all fine for a race car but certainly not what I'd call a street setup and almost certainly you 4500-5000 dip but I'll need to plug in all the numbers (or ask Wade who I lent the program to to try it)

    Give Vince honest rpm ranges and honestly how you plan to drive and see what he comes back with....I'll be surprised if it doesn't look a whole lot like the one I did for you.

    Are you still running the 40mm oem carbs? On your setup going a say dcnf 44 should add 10-30hp (depending on head flow) and maybe give you back what a lower rpm header takes away up top. The basic sizing math says you need at least a 36mm choke and then want a 45-50mm body size.....44 is the best you'll do bolt-on. Something to think about.
     
  21. bill308

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    Hi Mark,

    I started out giving ranges to Vince and later digressed to giving a center target. So the new range to enhance is 3500-4500 rpm. As you can see I'm slowly moving the exhaust tuning range down in the rpm range. Your point about new gearing is a good one. The new top ratio will be 80 mph at 3000 rpm, much taller than the original 328 ratio that gives about 80 mph at 4000 rpm. There is really no need to go above 4000 rpm except to have some fun. It's the low end grunt, consistent with not loosing too much at the top.

    I'll define a potential final case to run, then start making some decisions.

    Bill
     
  22. mk e

    mk e F1 World Champ

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    I didn't even realize your gear ratios changed....how did you do that?

    I flipped the top and bottom gears in the drop gear case on mine but haven't driven it that way yet....its a 23% change. That was the only thing I could come up with. Hopefully nothing breaks once I put the power to it.

    What I was on about with dropping rpm is that as the engine power went up I just found no need to spin the engine as fast as I used to and would shift sooner and downshift much less often because there was plenty of acceleration without the noise or bother of higher revs. It was just something I noticed happened, I like brisk acceleration and that just needed a lot low rpm and effort once the hp went up.

    The high reving V12 will not have all the very low end torque the otherwise stock high boost supercharged V8 had but shold be about double stock down low and more than the V8 by 4500 or so. With that last V8 engine 1st gear was completely worthless so my hope is that between the slightly lower bottom end torque and gearing change it will be a nice driver even in 1st gear but then more explosive up top.
     
  23. bill308

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    I'm fitting a quick change, drop gear system. It, like the 328 and later cars, adds an outboard bearing for a lot more support, on both the input and output shafts. It's a stacked gear train. The middle gear stack (2 gears) and the input gear are replaced as a set, to change effective, overall ratios. It's Modena Engineering's kit, but with my design change of opposing, helical gear angles, to cancel out axial loads, on the center transfer gear.

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    The USA spec gears are very low, then the taller euro gears, then the Swiss market (CH) gear set which is the tallest factory option, then my custom ratio to take advantage of all the new torque. Most of my driving is in the 2-3 krpm range. I seldom need the extra torque, but nice to know it's there. I'm kind of a stealth driver, or at least as much as one can be, in a resale red, hot rod 308.

    Bill
     
  24. Jonny Law

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    So is anyone selling an oversized complete system or is this all hypothetical?
     
  25. mk e

    mk e F1 World Champ

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    Nice! I knew they had a straight cut setup and that there was talk about a helical setup for street use but I didn't realize it ever came to be. Hurry up and get the car driving so we can hear how you like them :)
     

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