I remember reading ages ago an article where in the big show blown nitro classes they were saying that the more nitro percentage actually is easier on the motors and less expensive because they dont have to raise compression and destroy everything to copensate for the methanol content . IS there any truth to that ?
Nitromater
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Nitro %'s and engine part life
- Thread starter Mooseman
- Start date
Porkchop
Nitro Member
Yes there is,when at 85% it killed the crankshafts
MM
Nitro Member
William......the long in the short of it is this.....at 85% the crew chiefs are turning up the compression and timing so much (to compensate for the loss of power) that the rods are banging so hard that they are bending the cranks and thus causing destruction.....at 90% you dont have to run as much compression or as much timing and therefore you're not as hard on the cranks
Nitrohelper
Nitro Member
It's easy to burn exhaust valves with any "too lean" percentage. (even on gas)
I was part of a testing program for Angus Nitro in the '80s.
We ran several different admixtures, & tested other fuels than only methanol.
In the middle ' 60s, Dodge did some research for Garlits on Nitro & compression.
They found back then ,and we confirmed again with lab tests in the ' 80s that ;
{after 93% Nitro becomes more "unpredictable" when changing compression upward}.
[ and after 95% , the chance of a "compression firing" (hydraulic) goes up very quickly] .
This is why Angus recommended 90% when NHRA started going down from 100%.
whitelightning
Nitro Member
i will give you alittle insight on what we have run into with nitro and what has been passed on to me from those who have blown up enough parts to trust. when i got my nitro car i was told no lower then 80% all the way to almost pure 100% is safe then on the weak side 0 to 30% is safe for some reason the percents between are to risky. we run our nitro car around 85% and adjust to the track with that if we can hook we throw more at it if we arent hooking we take it down some. but thats just what we do theres always someone that knows more then me so maybe they will answer yall better
It's easy to burn exhaust valves with any "too lean" percentage. (even on gas)
I was part of a testing program for Angus Nitro in the '80s.
We ran several different admixtures, & tested other fuels than only methanol.
In the middle ' 60s, Dodge did some research for Garlits on Nitro & compression.
They found back then ,and we confirmed again with lab tests in the ' 80s that ;
{after 93% Nitro becomes more "unpredictable" when changing compression upward}.
[ and after 95% , the chance of a "compression firing" (hydraulic) goes up very quickly] .
This is why Angus recommended 90% when NHRA started going down from 100%.
Jerry, doesn't Fuel volume and mag lead play into that as well? But your right most Nitro tuners I've talked to said the tune-up from 94% on up the change is Huge!
Nitrohelper
Nitro Member
You are right to a degree,
Mag timing is still a controlled event, (maybe wrong), but planed at a certain degree.
With the larger volumes , tuners would would run lower compression to give the chamber more combustion area for the extra fuel & air.
Low compression makes the move to running 97-100% possible. (but expensive)
The change from 94% to 98% can be expensive if the cylinder pressure gets in front of the mag timing, from too much compression.
Gene Snow put a complete head, with the top half of the block bolted on , over the wing at Gainesville.
He was testing a Scott fuel pump, with 50% more nozzle area than normal for that pressure.
"Compression Firing" (heads up or rods down) happens before mag timing can control the burning event.
It can be caused by any of several things A) too high a compression, B) too much volume, C) Nitro above 97%, & Mag timing,
D) Manifold boost & temperature , E) all on one run.
When this happens, a cylinder pressure spike causes the activity in the chamber to go from a burn to true explosion, at anywhere on the track.
Before the Nitro limit ,this caused the folks sitting at 1000' to go "WOW" !
d'kid
Nitro Member
You are right to a degree,
Before the Nitro limit ,this caused the folks sitting at 1000' to go "WOW" !
And in the days before blower restraints, and all the sweet safety equipment, It caused alot of us in the top end bleachers to spend half the day ducking...
d'kid
Ask any of the old timers who have been involved in racing since the front engine days and they will all tell you that 85% on down is extremely dangerous because the motor literally leans itself out from the faster flame front caused by the methanol. Ive never heard of 94% burning up valves, but you can pretty much burn the valves up on any type of fuel when you lean the motor out.
Nitrohelper
Nitro Member
From my experience, I would say it's more like 78% on down , yes because of the methanol,
plus the loss of the combustion oxygen from the Nitro reduces the heat energy.
Since the early 60s, I've found the most stable area to tune in is 86 to 92%.
The real truth to parts life in a nitro motor doesn't necessarily lie in the percentage of nitro as much as it does the tuning of the engine to the vehicle you are racing.
One must consider the fact that reducing % actually richens the fuel mixture if all else is left the same. In round figures, the stoich of nitro is @1.7:1 whereas methanol is 7.0:1. That means the more you decrease nitro%, the more air you need to make it work properly. So then how does reducing % make the engine lean? You haven't changed anything else so therefore the fuel you are burning can't handle the load you've put on the engine (weight of vehicle, clutch load etc.)
So when the change from 90% to 85% came, they learned to increase fuel volume and compression, added more blower OD so the lower % could burn properly. Yes, it put a greater strain on the parts, not because of %, but because you have to run it so much harder to get the same result.
In the end all this means is it really doesn't matter what % you run that will affect parts life, it's how hard you want to run and how you make your tuning decisions that will have the greatest effect.
There are those whos say a 50% mixture won't work because the engine gets confused. I guess this is maybe somewhat true only in the fact that no one has probably spent enough time (and money) trying to figure it out. I would venture to say that any % can work, but there is really no good reason right now for trying anything other than what most are already doing.
One must consider the fact that reducing % actually richens the fuel mixture if all else is left the same. In round figures, the stoich of nitro is @1.7:1 whereas methanol is 7.0:1. That means the more you decrease nitro%, the more air you need to make it work properly. So then how does reducing % make the engine lean? You haven't changed anything else so therefore the fuel you are burning can't handle the load you've put on the engine (weight of vehicle, clutch load etc.)
So when the change from 90% to 85% came, they learned to increase fuel volume and compression, added more blower OD so the lower % could burn properly. Yes, it put a greater strain on the parts, not because of %, but because you have to run it so much harder to get the same result.
In the end all this means is it really doesn't matter what % you run that will affect parts life, it's how hard you want to run and how you make your tuning decisions that will have the greatest effect.
There are those whos say a 50% mixture won't work because the engine gets confused. I guess this is maybe somewhat true only in the fact that no one has probably spent enough time (and money) trying to figure it out. I would venture to say that any % can work, but there is really no good reason right now for trying anything other than what most are already doing.
The Boat Drags used to have a TF Jet class which was limited to 50%. Dave Kirkland used to be the man when it came to tuning those 50%er's. That has to be a fine line. I used to hear (but never saw in person) the Big Dirt track circle track guys like Kinser used to run 10-15% in their Fuel back in the 80's till it was Banned!
I did not know that Joe- Steve lives a few doors down from me, I will ask him about this.... Be kool if it were true....
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