NITROUS OXIDE ( nos / n2o ) advice forum

Has no one else got any ideas or theories on this subject?

I'd love to know if i'm anywhere near on the Nitrous thinking.

...the rabbit will save you

cam timing...very good question..

pontiac 400 ..early 80's..we put 150 hp plate on..it ran fast..10.40's consistent..then we upped kit..175..it ran 10.45's..200hp , ran 10.50..what was happening?..the pontiac has an extremely fast small port, built for torque at reasonable rpm..with the cam timing we had, it had reached the limit of what the port could pull in and use effectively..but it wasnt as most suspected the intake was to blame, it was the exhaust..with out sufficient exhaust volume, our incoming charge ran into a wall, and stalled..ever so slightly..no damages, but the motor shook like a 6.5 richter..it was fighting with itself..back to 150 hp jets, and all was fine..no shake, best times..

learned then that each combo has a limit..step over the limit and bad things happen..then of course the nitrous gets blamed, when its the fault of the idiot who built the engine combo in the first place..

too many times, folks get greedy, and go for max power..ya wouldnt turn twin 106 mm turbos lose on a stock block would ya?..it may run for a minute at boost, and i mean a literal minute..then boom!..


if your gonna put nitrous in, ya gots to get it out..and cam timing becomes a balancing act between the port size, header size, cubic inches, rod length, stroke, etc..there is no one nitrous grind cam that works for all engine designs..i believe in flow at tdc overlap..and it works well..we see more power at the same jetting..i attribute this to more actual nitrous flowing into the cylinder, since the flow isnt as "stalled"..i also believe that the more nitrous you run, the exhaust size most grow..almost exponentially..people told me my pipes were too big, i'd lose torque.. ..we had some much we broke torque converters every pass..people actually took photos to try to dissect the "american junk" kit..tee hee, i couldnt resist that one for trevor..

if you know your cylinder heads basic flow figures at tdc overlap, about 20 degrees to both sides, you can arrange your timing to do the same..it cant go in if it has nowhere to go..waiting for the piston to drop just means less time to get the intake column moving,hence less nitrous into the cylinder..remember, all this goo has mass, and it needs to be moved..that takes power..use the most efficient means to achieve this..

so, bottom line..its not lobe separation that matters, its actual valve events..IO..IC..EO..EC..your flow at initial intake valve opening and their balance with your systems..

and stepped headers or bell tubes are a almost must..we need the expansion area to take the reversion pressure off the exhaust..i wish they would allow short zoomies, cuz the total nitrous ride will need that..it will run like a funny car

rainbow love, from not so sunny california..i couldnt live in wet cold britain..

..a "well designed kit"?..hmmm..i will let your ego slide on this one..but if your gonna make waves in america, you need to be more laid back, and let the numbers do the talking..

its too bad about barb, as i would have built him a neat engine, just to try it in a good chassis..

zoomies are gonna be the last deal..for common nitrous engines, a good stepped header will do..2-2 1/8-2 1/4 on our 355 chevy..basically enough for a n/a 540 inch rat..

bell tubed exhaust is far nicer than stepped, as the pressure changes are more subtle, and it retains greater energy..like a reverse velocity stack..bloody hell, go look at a rolls-royce merlin..

the rabbit has spoken..pay no attention to the man behind the curtain..

Where does this leave us though?

I understand that the valve events are more important than centres.But how do we use them best for nitrous use,especially if we haven't got a flow bench.

I know from experience that advancing my exhaust cam,stopped me blowing my plenum apart on full power shifts.But I also appreciate that the cam timing wasn't the "real" problem.the real problem being a restrictive exhaust with 2 very short headers coupled to 2 longer ones in a 4-1 collector. (I was only adding 60hp,but only had 75rwhp to start with)

But what can we do with cam timing now?When we run on the street and have to run restrictive exhausts.

I've read theories about opening inlet valves late to "suck" charge in.Or open exhausts early to "blow" exhaust out - Also A GrahamBell suggest camming as for superchargeing ie: less overlap to avoid wasting charge straight out the exhaust.

BTW I've just ordered stainless bends to fabricate some much bigger bore open headers for the bike,but these will have to be fitted for track use only.

Ok been chasing lots of combustion info,one thing I've come across is a suggestion that all "useful" combustion energy/pressure has been used by 100degrees after TDC.

So as we've got loads of combustion products to get rid of,how soon can we open the exhaust valve?

I haven't got the actual figures here, but the "nitrous" roller cam we are using gets the exhaust valve off the seat when the piston is about 1/2 way down the bore- so somewhere around 90-100 deg ATDC...

This cam also has BIG overlap.........there is barely 0.020" between the valve heads on overlap!
The intake valve doesn't close until the piston is a long (again,somewhere around 1/2!) way up the compression stroke.

Our old 545ci engine (with the above cam) had a pretty lacklustre performance N/A....10.08 in the 1/4, but, with the nitrous on(approx 500 shot)........8.17 in the 1/4

An interesting comparison to the borrowed engine we ran last year- it had a much smaller cam (street roller) and was 503ci- that went 10.004 N/A!!! It picked up 7/10ths with a VERY conservatively tuned 150 shot, but when we stepped it up to 220 it only went 1/10th quicker and no matter what we did with it (within reason- not our engine ) It didn't want to go any faster......I think we may have been getting some form of reversion issue as there was always a lot of fuel staining on the bulkhead behind the carb......

Brain.

Hi guys,

I'm currently distracted on some personal matters, so my head is not in gear for the tech stuff at present (it's also why I haven't called you yet Brain) but even at a glance and while I'm out of gear, that post from Brain says a lot.

My brief estimation on the post would be as follows and it falls in line with my statements that factors need to change as the amount of nitrous used changes and quite often to the reverse of what works well at low levels;

The low flow motor is more efficient NA and on modest amounts of nitrous but choked up (on the exhaust side I say), once you reached the limit of what it could flow and that resulted in the intake charge being pushed out of the inlet by the exhaust gases still in the engine when they shouldn't have been.

The higher flow engine was less efficient NA and on small doses of nitrous but allowed you to use much more nitrous and eventually you would have (or maybe did) reach the sweet spot and anything beyond that would have ended up doing what the street engine did, choking up.

I remember one dumb ass fool saying to me some 30 years ago "nitrous is too easy, it doesn't need any skill to achieve optimum results, you just throw it on and you get all the power you want" but even then I pointed out to him that was a load of bollox and its now even more apparent that even more skill and knowledge is needed to achieve the ultimate optimum results and as pioneers on this path, we don't have the text books to refer to that NA tuners have.

That also reminds me of the FOOL who ran Twisted Sanity who claimed I over complicated things and all that anyone needed to know about nitrous could be printed on the back of a postage stamp - WANKER!!!!

Hope to be back to normal service soon.

Hope it's nothing serious and you're back on the ball soon Trev.

Really interesting stuff Brains,backs up what the rabbit has said,lots of overlap to keep things flowing/moving for as long as possible.Would be very interesting to see the valve event timings,but I understand,you can't give too much away.

There is good reason to open the exhaust as early as possible,even NA,as once the piston is past bdc the power to push the rest of the exhaust gases out must be supplied by the other pistons.

It's looking more and more like we're going to need special cams to run large doses,as Brains and the boys already have.
I think I'm going to have to play with one of my spare engines on the bench,do some measuring to check valve clearances and see how far I can push the cam timings.
I know for sure that I can't just swap the cams over,as the valves are offset,they're pretty similar profiles anyway.Going to be an interesting experiment to see how far I can push my little motor.

Anyone know a friendly cam grinder? There's no nitrous cams for my engine,Oh the joys of being different

It's looking like the conscensus is for overlap, the opposite of what I guessed.

My thoughts were based on making the best of the engines std restricted exhaust though.
Would anyone agree I may have been on the right track there?

Tony at Kent cams can be pretty accomadating for bike regrinds.

Joy engineering? they must have been going for longer than you Trev?

I'm going to have to have a serious look at the cam wheels,so that I can adjust them,easily.They're pegged and retained by a single centre bolt,but strangely the peg is attached to the cam wheel with a "hole" in the end of the cam.Have to do some tooth counting and some maths too
I'm trying to formulate a plan of action reference nitrous use,looks like cam timing is now added to the list. Luckily I'm putting the bike on the road this time-at least for a while- so i can do some setup work without wasting track time.

Yeah I understand that with a roller cam there would also be the rocker ratio to take into account.

I'm going to chip in on this, but realise that I too am still learning all about LCA's and cam timing figures and all this was before I really thought about nitrous

My dilema is that I have a motorcycle cylinder head bolted to a car engine The stroke is longer than the bike engine but the bore is near as dam it the same. There are two common profiles for these heads a 254 7.9mm lift and a 284 8.8mm lift cam. I chose a combination of the short duration inlet and the longer duration exhaust in an attempt to give a nice smoth idle with good emissions levels. With the choice of cam out the way, the next problem was what to time the cams in at. I asked questions, did some research (kent Cams Catalogue ) and decided on 106/ 106 to get the engine running. Had the engine dyno'd with these figures and the results were surprising, if not initialy a little disapointing to what I had estimated. What was clear was the shorter duration inlet allowed the engine to idle at 600rpm 107bhp and 81lbft You can see from the chart that there is a small dip at 4.5k rpm, this is the same on every one of these engine conversions irespective of tune, which has strongly been suspected as being an induction length issue. It' s less noticable with the short duration cams than it is with the long duration.



After the initial disapointment at the peak figures, I changed out the inlet cam for the longer duration and extracted the factory timing data from the bike engine. Cams timed in at 102/105, and the results were even more disapointing, 104bhp and 79lbft. It wouldnt idle at 600 rpm either, no surprise there.

My initial disapointment was soon put to bed when I organised a dyno shoot out of 8 cars with the same head conversion, 4 NA and 4 Turbo. the 107bhp from 1275cc was not far off the mark with a 1380cc giving 114, and another 1380cc when optimised after the shoot out, at 120bhp.

Needless to say, I am swapping the short duration inlet cam back in and setting the timing back to 106/ 106 for this year at least. Next years task on the dyno is to optimise the cam timing, but i dont think its that far off the mark.

I was always under the impression that the lower the lift at TDC figure (or the higher the lift on overlap figure), the more you gain at the top end, but suspect this has an aweful lot to do with stroke and piston speeds. You bikers have short stroke motors that rev to stupid rpm which means the piston speeds are relatively low compared to us car tuners with long strokes, where piston speeds are higher. The good ol' A series at 8500rpm has already been said to give piston speeds that would be of concern to most engine designers what is it like at 9000rpm+ (Fast Carl)

Like I said, I am competely new to all this cam timing with two seperate cams, and im even newer to nitrous. I am keen to learn what is good and what is not but ultimately, that will happen on the dyno, of which I have no more spare cash to spend on this year

Can you just give us a recap of your thinking, as there's been so much said I've forgotten who said what.

Basically my thinking was with a restrictive exhaust port/system you would need as little overlap as posssible to reduce the ill effect of exhaust pressure overcoming inlet pressure at overlap.

That's the way I was thinking Ian.
I "know" that advancing my exhaust cam - reducing overlap-stopped me having backfires when shifting on nitrous.I understand what the rabbit and Brains have explained but if my engine holds together long enough to put really big shots in then I'll have to see what can be done about cam grinds.

As I have no cam options I will be exploring the limits of the cam timing.And it will start with advancing the exhaust and retarding the inlet.Gotta get that belt conversion K,you've got vernier cam pulleys I've got 2 covers in the way too

K1275 is using the 4 valve version of my cylinder head,which although it is a motorbike,it's not like many normal jap bikes.Standard bore/stroke is 67x70.It's more like a car than a bike engine,dry single plate clutch,separate gear box.

Nice looking torque plot K the bike feels that flat it doesn't matter what the revs are it just pulls regardless.To be honest the numbers you're getting on the dyno are much better than what the bikes are supposed to make.My 987cc 2valve is quoted at 90hp at 8000 and 63 ft/lb at 6000. RB racing reckoned they were closer to 75 hp so your figures for a 300cc increase are pretty good.The 2valve is 101/101.

This is getting very interesting now. I assume if you have the exhaust set up to give minimal or no back pressure, and the cam has the big overlap so you get more of a steady flow of inlet charge that you would waste a small amount of the charge into the exhaust. But would this also help cooling of the cylinder in some way??

Everything is big................(bear in mind this engine is nearly 10 litres)

Exhaust primary pipes 2 3/8"
Exhaust secondary (before H pipe) 4 1/2"
H pipe 4"

The rest of the exhaust is 4" . It has a pair of Flowmaster 30 series (I think!) race mufflers under the floor and a pair of very large (8" dia x 18" long) glass-pack silencers under the back.

I would say that for a "street" exhaust you're not going to get much better flow than that.It's also surprisingly quiet!! Trevor actually complained that he couldn't hear what the engine was doing at the finish line because the tyre and gearbox noise drowned out the engine........

You chaps might want to think about silencers now................in the next couple of years noise restrictions WILL appear....................


Assuming you have little to no backpressure, overlap helps with cylinder filling......It's all to do with inertia.( that clever Newton bloke again...) As the exhaust pulse leaves the cylinder it creates a vacuum behind it (momentum of the exhaust gas). You can take advantage of this by using it to start the intake charge moving into the cylinder before the piston has created it's own vacuum by moving down the bore.
Although some of this mixture may be lost into the exhaust, the important thing is you have started the intake gasses moving (overcome it's inertia) earlier than would otherwise be the case.
This allows more TIME to fill the cylinder...........
Momentum also comes into play at the end of the inlet cycle. the column of gas flowing down the inlet port wants to keep moving........again,you can take advantage of this by keeping the inlet valve open, even though the piston has started the compression stroke......These effects only work at higher engine speeds, that's why long duration and/or high lift cams have poor low speed performance.

Brain.

That car is FAR TOO QUIET and as a consequence MUST be losing power.

In my opinion it is the ONLY car in that class which is genuinely street legal on that basis and if all the others were made to be so quiet, they'd add at least a couple of tenths to their times.

On the cam timing front, can't argue with any of that.

So, working on Brains set up and applying it to a bike, seems to me we now have a serious compromise. I would imagine a 10ltr V8 produces an immense amount of low down torque to get it off the line before adding enough nitrous to really make it sing? The problem then on a bike application would be a serious lack of power to get it moving in the 1st place. I suppose this is not such a problem in wheelie bar classes as large doses of gas can be used off the line, but for street classes such as Superstreet this would be more of an issue.
Superstreet being predominantly ruled by the "busa" in turbo/supercharged form + nitrous. There are several dyno queen busa's out there producing 6-700BHP which just cant lay this amount of power down on the track, but 450BHP should get you in the low 7's. Now for a nitrous only motor thats around 260BHP over stock, so if you went this way with the cam overlap, that would reduce the N/A output by how much roughly? And how much gas could a motor take to compensate for this?
The reason why i ask is that i have a 1216 GSXR which i want to run gas only in Superstreet, and following on from previous discussions where Trev also mentions lowering CR for gas motors, I'm gonna be struggling off the line as i know the chassis needs to launch on around 110BHP for a clean launch, and this wouldnt be far from max N/A power with these mods, and then would need to be able to take another 330BHP ish to make the numbers.
One thing that is blatantly obvious is that this motor will HAVE to be a REVO motor, just a shame finances wont take giving the bike to Trev and saying ring me when she makes 450BHP!! Lol

Cheers
Steve

Is there anyone making that sort of power on a GSXR?

The big dogs in usa promod are still GSX "based" ..all be it 1800 cc monsters
although Bill Vose is running a busa.

Have you seen his thread on 200mph? getting interesting.

You'll probably need a good 7 to qualify in ssb this season.FFS they're quicker than most of the comp bikes and some of the funnies.

Hi Nige
Yeah theres a few old oil burners out there pumping 450 albeit with turbo's, but thats not a route i particularly want to go down, although potentially its the easiest.
I know of one or two people who have gone down the busa + BigCC path, and all is not as it seems. The bikes undoubtedly make the ponies, but its the chassis side letting them down, so its feasible it can be done with a gas gsxr. Just the usual time effort and money equation.
I dont understand why the fields are so low in comp and funny and even pro stock for that matter, but i did see a 1600cc gsxr last season, but unsure why they arent much quicker than sst if at all, EXCEPT that the tuning shops campaign in sst. Bit bizarre when you think how much harder a wheelie barred bike can launch.
Must admit I'm looking forward to seeing what Tim Blakemores new ZZR14 can do, purely coz theres the possibility of piloting one next season, albeit more aimed at ssb.
As for the gsxr again, it looks like its gonna need to go 1371 and possibly stroked to over 1400cc just to keep base BHP up to build on with the gas..... We will see, i think to start with i need to find the limit that a 1216 can take before the engine has to be re-configured for even more gas

Steve