So now the magic number is 240 at the crank? I thought it was 240 at the wheels?

If so, I probably have some more head room than I expected.

This thread has way to much real advice and logic in it. I was expecting more "allofits"

The only way to calculate torque reliably in the real world is to do a dyno run on a rolling road, and then calculate the engine torque from the HP and the rpm.

If you dont use torque at the wheels then youwill make 1000ft lb+ in 1st gear on a stock na6 because it has like 150 ft lb, and then thats multiplied by 5 in 1st gear and another time multiplied by 4.3 at the differential.

So you do a pull, find the point where it makes peak torque, and then you use a basic online calulator for hp/torque/rpm, input the rpm it makes the power at and the power and you find the torque.

This is torque at the engine, after driveline losses.

http://www.boostnetwork.com/database...5406940608.jpg

This sheet has both HP and AFR and RPM, but no engine torque shown.

You can see that peak torque is going to be at around 5000rpm because its the top leftest part of the curve, however for safety on your own car pick a few points.

For this example ill use 5000rpm, which looks to be around 300hp.

Using this calculator : HORSEPOWER TO TORQUE CALCULATOR

This is 315ft lb.

If we go to redline and calculate (im using 317hp, 6600rpm) we get 252ft lb, meaning he is leaving 65 ft lb on the table, which would equate to 395rwhp.

So by controlling his boost while carefully monitoring peak torque, he could pick up 50whp peak (about 100 at redline) and a LOT of area under the curve, all the while never exceeding the torque (and therefore piston, rod, crank, clutch and driveline stress) he is already producing.


https://www.miataturbo.net/attachmen...ine=1426911408

The above is an NA with a 5 speed I recently tuned, with careful VVT control, timing and boost we have kept torque almost dead flat from onset of boost to redline, but have kept the torque at a safe level of just 240 ft lb odd, and holding this to redline gives us much more HP than most stock engine/5speed safe setups. Go ahead use the calulator and check for yourself what the torque is, and yes the car has been raced at this level a few times now. Also see how the Dyno shows a bit over 1000 ftlb of torque, thats 240x4.3 (the diff ratio).

Dann

If you're taking Dann's word, you have less headroom than you expected. 240 at the wheels is more than 240 at the crank.

I'm comfortable at 220 using the method I outlined if the car needs to be guaranteed reliable.

Dann

Are we to assume that the 250 comes from guys who tuned on engine dynos, or was it confirmed like me by calculating off of reliable cars rolling road dyno sheets?

Considering a stock 1.6 can put out somewhere around 1200 ft-lb of wheel torque in first gear, i'd say measuring the crank torque is probably your best bet, regardless of where you take that measurement from.

Whoops - math backwards.

I autocrossed for several years on my SR20 setup with some stupid tune mistakes and never had an issue. Braineack also ran around 240hp at 15psi or so on his 1.6 and autocrossed with me with no blown motors. A 1.6 and a 2554 will not blow things up if he has a decent tune.

2554 probably hits 250 wtq once during an autocross run, in 1st gear at 3000 rpms. The rest of the run, you're 5-7k rpms where it's breathing like an old fat woman who just ran up 3 flights of stairs.

Okay, so by this thread, a 1.6 at around 240 hp is close to the limit of the rods......im running a t28 at 14-16 psi and am around 250-260 WHP and obviously judging by the comments am closer to the limit than i knew.

So moving forward, If my new engine build has suitable rods (949 rings and pistons already) ...what is the next performance step failure point...(motor only)... ???

Are you running it will an oil cooler or higher flowing oil pump? I think those would be likely contributors to problems

Forget the peak HP. What's the peak torque and the peak rpm.

Below 7500rpm and 250tq? Good to go.

Dann

The 250wtq number is what's been tossed around here for i don't know... years.

I don't understand why your question is relevant.

He's well below both those numbers on his current max boost setting.

You shouldn't even bother turning it up when you get it built, you won't make any more power anyway. Buy a bigger turbo at that point.

About 250tq is all that traction will allow for an autocross even with a big double element wing and 275 Hoosiers. When I data log autocross runs or anything like that I can't get any more load on the engine than that I never really even see full boost on an autocross it is ether spinning the tires or climbing RPM too fast to produce full engine load anywher near peak torque rpm. needs higher gears than 2nd to actually load the engine fully which you don’t see much autocrossing.

What I have found however is I am faster with more torque available than I can use over a wider rev range. Throttle response and being able to use rear tires for attitude control with some skill makes the car faster.

When I put in my stock internaled junk yard backup 1.8 motor I believe it makes around 250 ft-lbs with the turbo setup maybe a bit more. haven't bent a rod with it even on large tracks with top speeds ~140mph and a full throttle RPM sweep in top gear however. Ring and cylinder wall wear seem to be the worst thing that happens pushing a stock motor that hard with good tuning. I broke a valve once however on the backup motor.

Which makes me and TNTUBA geniuses. :skid:

I think I have made it pretty good by having excessive amounts of torque and tailoring gearing to my torque curve aimed at autocross. At 4000 rpm and above there is no response lag and there is enough torque that the right pedal is an instant attitude control device rather than just a go pedal.

Yep, and we have that starting about 2000 rpms sooner. ;)