V-12 Engine into 308 Build, over on Grassroots

I'll share this because I found it amusing in a scary way. I made a spread sheet that takes the estimated torque curve from the simulation and calculates wheel torque in each gear. The idea is to calculate that best shift point in each rpm because as rpm climbs above the torque peak the torque drops and shifting to a higher gear the get back closer to the peak puts more torque to the wheels. The very general rule is you shift at hp peak and land back at the torque peak. But I ran the simulation out to 11k and the lines still don't cross so the correct shift point is redline....and increasing recline makes the car faster, which only encourages bad behavior

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Maximum acceleration will be running it at highest average horsepower. So always shifted above hp peak. Most are fastest shifting 10% above peak hp rpm.

 

That sounds good, but I don't think its exactly correct. F-=ma so a=F/m, mass is a constant so max acceleration is when force is maximize, and F is a proportional to wheel torque, so max acceleration is when the average wheel torque is maximized. In a perfect world the transmission ratios would allow the highest average hp to be delivered to the wheels (there is a reason F1 cars have 8 gears) and it would work out as you say.

My point though was I built an engine that just doesn't match the 308 transmission very well. I swapped the clutch and trans drop gears which changed the overall drive ratio 24%, but I increased torque by about 280% and hp by about 350% so in both 1st and 2nd the tires can't hold anywhere near full throttle and I'm not sure 3rd gear can't either. I need to add traction to the spread sheet i guess, that should make it say there is little point in reving to 11k where I technically set the redline even though I know the life up there is measured in seconds not hours

 

Yes average wheel torque is maximized if average horsepower is maximized (which is achieved by shifting at a higher rpm than where it makes peak hp).

Less gears just means you need to extend shift point past peak hp rpm -more- in order to maintain max average hp. (as there will be more rpm drop on gear change)

Where do you think yours will make peak horsepower? Must be rather high if torque has yet to peak at 7000. 9600-9800?

Would love to hear that!

 

Its not though, that is what the graph shows. Wheel torque in each and every gear stays above the next gear at least until 11k, so I 'm pretty sure fastest is shift at the highest RPM I dare, but I'll tune up the spread sheet when I get a chance. I'm pretty sure that is about the headers I chose specifically to hold the hp peak below 9k when the engine really want to peak higher.

The simulator says
peak torque = 519@ 7200
peak hp = 828@8800

I'm sure the simulator is off some but for sure when I hit the throttle in 1st the engine hit 6500 faster than I could get my foot back off it. os I[m pretty sure the torque peak is up there somewhere.

The hp peak is so close to the torque peak because the headers are tuned to street driving and are really too small but do nice job making a wide smooth torque curve. A set of larger step headers should move the hp peak well over 900hp at closer to 10200-10400, but only shift the torquer peak up a couple hundred rpm, or so says the simulator.

Soon hopefully. This video has a throttle blip to 9k...it was burning a lot of evans coolant so a lot of smoke and it ran out of gas during the video but it did hit 9k.

 

Guess I'm not really getting what you're saying then. At first you mention shifting it at peak horsepower so it drops to peak torque and now it would be fastest shifting it at as high of rpm as you dare.

I don't know what your simulator is predicting up to 11,000 rpm or how you could end up with any result other than fastest is keeping it within max average horsepower.

Sounds great, she's a beast

 

Thrust scalar chart for tq... Yeah those are fun.

https://www.ferrarichat.com/forum/posts/145429893/

Really highlights the short legs of the gear box.

 

So here is a stockish 308 dyno graph and the corresponding wheel torque
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Here the trans ratios are well matched to the engine and shifting works out about as you're general rule suggests, at about 10% over the peak hp the wheel torque is dropping fast and is higher in the next gear. The redline is 7700 (again about 10% over the hp peak and 7500-7700 is right place to shift.

But on my setup that doesn't happen, the lower gear is always putting more torque to the wheel than the next higher gear because wheel the torque falls, it more trails off than drops and just doesn't get low enough to make shifting better than not shifting. To you're point though about highest average HP, you see that in the HP curve. It starts to drop (because I on purpose tuned the header to below 9k) but then it starts to rise again so the highest average over the about 2000ish rpm shift drop is between 8500-11 somewhere it looks like. This is all simulated HP/torque, I'll see what the dyno says but probably won't run it past 9000 or maybe 9500
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I'll add that on those graphs the traction limit is somewhere about 2000-2500 so 1st gear has value only for parking lot driving, actual race starts want to be in 2rd or maybe 3rd. With the last blower engine that made about 420ft-lbs torque I always used 2nd and the little driving I've done with this engine second is WAY easier to control the wheel spin on launch, I haven't tried 3rd though to see if controllable spin can be had from a standing start.

 

I like the mph chart...it makes it easier to see time to shift I think.

 

What do you have for tires? I switched from regular radials to road race tires on one of my cars and it made a huge difference. (but then you have to worry more about breaking the trans)

 

New tires are on the list, but for after its running good. It currenty has sumitoma HTRZ , 285/35-18. New they were decent with a 320 Tear wear,...but that was 22 years ago. They were new with the last blower engine and 2nd gear was by far the better launch option than 1st.

 

Here's the MPH graph with the rpm limited to a sort of reasonable 9400. This makes it not look as bad other than 1st gear which as I said is not all that useful. The way to read it is go to the end of the line then drop straight down to the next gear. The other thing to notice is the mph, between the increased rev limit and the changed drop gear ratio redline in 5th is about 240mph

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But reving to 11k they are nearly touching , again other than 1st. it needs about an 11500 redline....or an 8speed trans maybe,.
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That is zinging for sure. Have you thought about altering the cam timing to bring the power in earlier or would not play well with header and induction length?

 

Here is the stockish 308 and you can see what I was on about line crossing. This is reving to 8k, which is slower than shifting at about 7500 it looks like where the lines cross.
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I played with it in the old version of simulator way back and its not as much difference as you might expect. The intake has the most impact, this is 100/110 center vs 110/110, I'm running 103/110 iirc (I lent out the sim key so I can't open the file to confirm)
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As a reference here is what I was on about it being tuned to drop the rpm as much as I could vs tuning to best hp. That is the tri-Y header and the 102/110 cam time.

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The newer version of the software doesn't make the difference as large and it probably closer to right. As tuned is more power up to about 7500rpm, with a lot more 200-4500 where most street driving happens and 11k rpm scares me
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The only thing I could think of, though there's no room. Increase the trumpet length by another wavelength to focus on low rpm. Probably end up with 6"-9" tall trumpets feeding the heads. Or is it 13"ish for the next step? Imagine the visual!

The 4L with 348 heads I built for Nick is designed to 13k.. we've run it to 11k. It sings like nothing else and also sounds like it's going to explode at any second. Then there's keeping any and all fasteners in their place gets tedious. The harmonics above 9.5k is a bit much, safety wire highly recommended. That build has at least one full stick of blue loctite in it. Every single nut, bolt and stud got either red or blue. Green was threatened.. But thankfully not used.

 

Actually work. The old gear adpter was a bit damaged and all my ring nut wrench did was bend





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So, since I'm only saving a small bit of the existing adapter I cut the nut and gear off.

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Then I thought I ordered SS foil that was a lot more like shim stock, but I wrapped the top and bottom and heated it up to pull out the hardness so I can machine it.

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The heads should easily handle 12k and likely 14k,,,,its all race bits for a GSXR1300 motorcycle....I just really want the rods to stay inside the block

My intake track length is 10.25", which is little like 1.5" stacks. The next tuned length is around 13.25", then 15, then 17 or 18. What happens though is its nearly impossible to keep the pulses from messy with all the pulses the tri-y header creates...it does make more but a very wavy torque curve with some ugly dips so i decided to not to go that as way it would also mean a hole in the deck lid. the longer the stacks, the more pronounced the waves/dips

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Yup, motor cycle race bits for best in the tiny Ferrari cyl heads. Same thing for Nick's build. Bottom end... Yeah that gets expensive too, had custom rods designed to spin that fast. Alternator as well.

Interesting effect with the wavey tq line. Push pull effect with the exhaust.

 

yeah, looks that way....plus the short stacks make it fit under the hood so it all works out.

The pulses in the exhaust are pretty complicated, it took me quite a while to figureout what Burns Stailess did when they designed it. Dynomation 5 couldn't really handle it, version 6 gets it, it rings as lime 15 rmp points.

 

I think burns uses pipemax, could be wrong. Pipe max is good, better then dynomation 5. 6 is better as you've noted.

 

Nah, pipemax had no idea what Burns designed. Steve told me he was double checking stuff the Burns software spit out. Once I understood what was going on and imput it right, DM5 did get the right answer, Steve was using DM4 iirc. DM6 gets it right without me needing to understand anything, I like that

I had pipemax but since DM6, I never bothered to get a new key 2 computers ago. Have you found the feature where DM gives you the baseline header and intake dimensions? No need for pipemax imo

 

Out of curiosity what is the header spec? Primary/secondary length and ID.

 

I mean, I would still do that. Brings up everything sub 9500 and brings ideal shift point below stratospheric