Who here really knows how to make BOOST?

[ijs12fly]

Here is my question. For a high horsepower drag racing application, using a manual transmission what are the best ways to make boost?

I have heard of several different techniques and do not know who to believe.

One school of thought says reduce timing down to a minimum - say 5-6 deg and pull fuel out of the map, this will cause lean popping in the exhaust thus allowing the turbo to create boost.

Then I heard the opposite, pull timing out and add a lot of fuel, the intent here is to force fuel into the exhaust so it burns there and spools the turbo.

Assuming we can make boost, how about controlling it?

I hear some guys use a waste gate on the exhaust and also the intake side to control the boost instead of just using an exhaust side gate. Does anyone have some ideas here of the best way to do it?

So what is the best way to make boost at the starting line with a stick?

 

[mgeo]

I have a friend with a GSX that uses DSMlink to retard his timing to 5 degrees atdc. He builds 21 psi off the line and pulls 1.7 60' times on street tires (awd).

Another way of building boost of the line is to completely cut fuel to one cylinder (or I suppose two on an 8 cylinder?). The system I am aware of that does this builds about 6 or 7 psi doing that. You could also cut the ignition to that cylinder, but then you are dumping lots of unburned fuel.

-Mike

 

[patprimmer]

A short shot of NOs works wonders

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[ijs12fly]

mgeo: at 5 deg, does he change his fuel to make it lean or rich?

21 PSI, what size turbo?

patprimer: NOs does work wonder but is illegal in the racing I do. So we have to make as much boost as possible and control it so we can tune the clutch for consistency.

 

[SBBlue]

Mike wrote:

"Another way of building boost of the line is to completely cut fuel to one cylinder (or I suppose two on an 8 cylinder?). The system I am aware of that does this builds about 6 or 7 psi doing that. You could also cut the ignition to that cylinder, but then you are dumping lots of unburned fuel."

????????????????????????????

Well, I'm not into racing, but I've never heard of anything like this -- and I'm mystified as to why it would work.

Otherwise I agree with Pat. . . .A Short Shot of NOs works wonders.

 

[TTmotors]

Well you have the introduction of oxygenated air into the turbo header without injection which will cause a burn in the header. On the flip side if you eliminate the spark you have air and fuel introduced into the header. He already said he cant use nitrous.

 

[mgeo]

When you cut fuel (or spark) to that one cylinder, its just along for the ride. It creates enough load on the engine to create boost, although it seems not as much as by retarding the timing. JWT offers this.

My friend does not change his a/f ratio. Some people like to make it run rich, but since he has been able to create 21 psi off the line there has been no need to. The turbo is a 16G. The motor is a 4g63. And yes, 21 psi is really pushing that turbo. He is upgrading right now.

-Mike

 

[chrisman2]

hi, im guesing the prob is building boost off the line- to launch harder.. i have a turbo front drive-- what ive done is installed a hydralic staging brake that i operate by hand pressure..this applies the brake(front in my case) loading up the engine.. my feet are free for gas pedal and clutch.. when i release the staging/hand brake, my hand is then free for shifting..
in my opinion, traction would be a bigger obstacle to overcome..once the tires break lose, boost or no boost, your waisting time..

automotive imagineer--making the stuff is the hard part- thinking of the stuff to make is the fun part..watching it work is the best part..chrisman2

 

[ijs12fly]

Thanks all, but no one has offered a technical explanation of which choice is better, rich vs lean.

Are we better off lean popping in the exhaust or pumping more fuel in there?

Traction has never been an obstacle, making enough power at the line is the problem. We are trying to get our 60' times down under 1.1 sec, 1.01 is our goal. Running a 94mm turbo.

 

[ijs12fly]

With that 94mm turbo and our 302 motor we can make about 1675 hp. We used to run a 100mm that made around 1850 hp.

This setup with our 2600lb pro mod should run around 6.7 sec in the 1/4. We have been 7.0 but our short times are off because of spooling issues, hence the reason I am asking the question.

 

[Majik]

What they are trying to do is simple... is retard the combustion event to where some takes place in the engine and some takes place in the exhaust... hence the poping.. Look up ALS (Anti Lag Systems) for world rally cars. Their 80's systems would dump fuel and retard timming.. I wouldn't lean my car out for any reason espically if I was trying to create boost.. sounds like he's gonna be a 4g63 rebuild canidate soon if he keeps it up...

 

[PFM]

ijs12fly,

If you can add an injector ( in the rules) before the turbo, on the exhaust side, you can add fuel and spool up the turbo. This is the method used in the WRC cars someone already mentioned to prevent turbo lag. You may want to look at Greddy for a controller for the injector. I am quite sure if you get this thing to make boost traction will become a new problem on your way to a 1.01 60 foot.

I know of a turbo leaving the lights at 25 lbs boost and builds to 32 in .1 seconds on the data aq box using an aux injector. This keeps your mix and timing good and may keep all your pistons in tact.

Good luck.

PFM

 

[chrisman2]

what about using a nitrous type of injector--maybe a foger, in the exhaust before the turbo..how long could the aluminum hold up? i guess you could make your own from steel..
could you just use compressed air and fuel instead of nitrous and fuel?how much pressure can be developed in the exhaust before the turbo.?---all in the name of boost..

automotive imagineer--making the stuff is the hard part- thinking of the stuff to make is the fun part..watching it work is the best part..chrisman2

 

[royceso]

you don't need nitrous or extra injectors. anti-lag pretty straightforward, add fuel and retard timing. as the a/f exits the exhaust ports it's still burning and your turbo spools like crazy. this is what all the turbo drag guys do these days, it's standard stuff. in fact you don't even have to program it into most engine management systems. most usually have an anti-lag feature which cuts timing and adds fuel. it's normally tied into the 2 step, so it automatically engages with the 2 step when your at the line.

 

[ijs12fly]

royceso,

I am in the same school of thought with you. I believe that Rich is the way to go. Although I have been told by some other racers that "lean" is the way to go.

I am just trying to get an engineering explanation as too which way is the correct way to operate.

 

[GregLocock]

"an engineering explanation"

It is not an either/or situation. There are tradeoffs to be made. Real engineering is not rules of thumb, it is understanding the reasoning behind complex phenomena.

In this case you are trading off the temperature limits of the materials, against the ideal burn characteristics of the mixture, against the operating characteristics of your particular setup.

As such there is no one size fits all solution.

Cheers

Greg Locock

 

[royceso]

the key to anti-lag is retarding the ignition as much as possible you have a lot of unburned a/f exiting the head and combusting in the exhaust manifold. you run it rich for a couple of reasons. first it protects you from blowing your motor. since most of the fuel you inject is going straight out the exhaust, you might not have enough left in the combustion chamber when you light off. you just dump extra fuel to compensate. secondly, you want to get an inefficient and slower, later burn in the manifold. the more inefficient your combustion, the more you'll spool your turbo, you literally want a fireball exploding in your manifold and turbine housing to spin the turbine. the leaner it is, you get a cleaner and more efficient burn, which is the antithesis of anti-lag. just attend an import event and watch the rwd cars, these guys are all rocketing out of the hole w/ 40+lbs. of boost using anti-lag.

 

[timordog]

I know this will probably be against the rules, but I'm not really sure, but if you already use c02 somewhere else in the car for shifting or fire prevention it would probably be easy to disguise. A correctly sized nozzle positioned correctly in the compressor housing shooting even a tiny amount of highly compressed co2 will extremely quickly spool any size turbo to any boost you like. And all without ignition or fuel alterations or fireballs in your exhaust. Slight dilution of air mixture with the co2 (I know someone will bring it up) but with the nozzle correctly angled at the compressor blades the shot will be very small and be entirely gone very quickly.

Btw what sort of specs on the 302, heads, port work, manifolding, intercooler design if you don’t mind sharing? Also what boost pressure at what manifold temp was the 100mm build at for 1850hp and what was the max torque at this output?

 

[NickE]

http://www.rallycars.com/Cars/bangbang.html