Maximum boost for autocross on stock 1.6
 

Quick question, just dyno tuned my 1.6L and it put down 243hp @ 11.5-12psi. Do you guys think I should turn the boost down to maybe 10psi for autocross/ daily driving? 8psi yielded ~ 200hp
The engine is stock, freshened up with Mazda parts around 15000 miles ago. I have a stock 5 speed transmission as well. I don't have money to be blowing on rebuilding the engine, I hope it lasts this season, maybe 10-15 autocrosses.

For the record, I am running a sr20 t25 turbo, water to air cooler.

Thanks!

Depending on torque, you are pushing the limits of the stock rods. I would turn it down based on that alone.

shut your mouth, there is only 1 correct answer to this question. He should run ALL OF IT!!!!!

I'd turn it down for DD purpose/stock rods, crank it back up for autox where it counts :bigtu:

Right, because rods bend in every other situation but not an autocross. Idiots

His torque number is nowhere near the danger zone.

I'd run where it sits.

Would you mind posting your dyno graph with the T25? I would love to see how well your 1.6 spools that turbo.

I posted it under the dyno section

I am subbed to your build thread, but didn't see you post it. Just assumed you were wanting to keep it private or something. :)

Your max torque wouldn't have gone above 225ftlbs on that graph, on a dyno that isn't likely to be a heartbreaker. ;)

ALL OF IT

180kpa should be fine as long as you're not knocking. If you want to ease your mind, set it to 170kpa and just enjoy it.

All of it for autocross. So little time spent at peak torque with RPM's rising so quickly in second gear it becomes hard to hurt anything other than transmissions if you have any kind of decent tune.

came in here to post this

Nope not trying to keep it private. I have to post it there as well. I like to show off my water to air cooler and how effective it is. Credit to Harold Hammerly for building it.

I think I'm going to turn it down to 10psi just so it lasts this summer. Maybe throw rods, oil cooler, be pump and a 6 speed next winter and crank it up to 14 psi

Easy to be cavalier with someone else's car and money.

Run ALL OF IT if you can get any of those giving said advise to sign a contract stating they will fund the rebuild if it fails.

Now where is that chirping cricket smilie......

I think my plan is to run ALL OF THE AUTOCROSSES instead of all the boost. I think 10psi will do. I was trying to get advice from someone with the same/ similar setup

Make less than 240ftlb at the crank calculated from the dyno sheet.

This is literally the only correct answer.

Dann

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. ;)

Ok, so how often are you not between 35mph and 72mph? Thats how wide my powerband is. If you have more thrust below 35mph in 2nd gear thats cool, my car handles well enough to never have to go that slow on a national sized course.

^this.

Basically between 34mph and ~65mph Im pretty much traction limited and I have the RPM range to go to 74mph without shifting. With that I can go a fraction quicker than a top level CSP car usually if I can manage to put a good run together.

All I can say to the both of you is show up at an event with Eric, nationals would be great, and prove it since you're in the same class. :)

That the plan this year.

How did I get drug into this? I haven't even had my car run for both days of an event yet this year. I'm not a threat to anyone.

I grabbed your paintless monster by the wing and drug it in. :bowrofl:

Really I was complimenting you buy saying your car (and mine) was a superior autocross car as far as usable power. But somehow it turned into an implication that it's not superior. Therefor, I threw down the gauntlet for you. :facepalm: Lost my head for a minute. Strip em down and come to XP boys. I can't pass for SSM. :)

With any luck, I'll bring my toy too!

Glad you said wing and not wang.

:inout:

Following year is going to be XP I think. Car is coming off the road and I'm tired of converting it for the track and would like a cage in it anyway.

There is time yet. I'm scrambling to make it to Crows. Just got the car running again tonight. I made some changes to the setup. hopefully I don't screw it up too much.

No fucken way.. Is your car road registered?

Yeah, chasing down Fred isn't out of the question down the road sometime. It'd let me put a cage in the car and use it on the track as well. :)

His car is and my car was registered and tagged for street duty. Makes it easier to get it to alignments and such.

My car is tagged and insured as well.

As was mine. I pulled it this year because I can get its actual replacement value on my insurance for $200 a year if the car doesnt get driven on roads and isnt registered, but its still passes inspection. VS the ins co giving me at best 4k for it and paying 450/year.

There is no way an insurance company is going to provide actual replacement value on a race car for $200 a year.

They might give you replacement value on the chassis for that....but there is zero chance of getting actual replacement value on a race car for that little money. Hell, you couldn't get it for that much per month.

The assumed risk drops dramatically when the car is only covered when locked in a garage, on the trailer, parked or driven in paddock, and being loaded and unloaded. Call Hagerty and quote yourself if you dont believe me.

So I can get 50,000+ coverage on a race car for $200 bucks a year. You can't even get that amount of personal property insurance for $200 a year.

There is something in the "fine print" of the policy you aren't reading OR it is simply a rider to your homeowners policy that will only pay if something happens at your house.

If insurance is available that will cover a $50,000+ race car against fire, theft, acts of god...etc etc etc for $200 a year I am quitting my job today and going to work for that company. I will be able to double my income selling only that policy to racers and race teams.

Pick up the phone and call. You want Limited trailer paddock + storage.