Discussion
insaneron said:
Here's a couple I did a couple of weeks ago. Does anyone have any ideas. they are both at the front the other 6 were perfect as were the bearings and rods and yes I was using a little nitrous. Any comments would be good as I'm just about to put it back together.
Need more info. Could be detonation, too lean,
is this blown
Ok some back ground
The motor
BBF 572 TFS A460 heads and inlet,1250 dominator, Carrillo custon nitrous piston
Ignition
MSD, programmable 7 didital,MSD crank trigger, MSD pro billet large cap dizzy, MSD HVC coil, Taylor 11.5 wires, Autolite AR3932 plugs
The motor has the timing locked at 30deg with 15deg timing pulled out.Fuel is Vpower with power pour. (SE rules)
Our problem happens when I step it up from 400bhp jets to 500bhp. I've run for 3 meetings on 400 and no problems change to 500 first run game over.
Fuel pressure on the carb is 6.5psi and the nitrous each engine damage a different setting last time was 6psi with a gauge on the dash.
I've also tried different piston manufacturers and compression ratio's still the same outcome
Ron
PS I am getting rather good at lapping valves now though
I'd also like to point out that there was no damage to any bearing, rod, crank, or cam on any of the piston failed runs just the front 2 cylinders each time
The motor
BBF 572 TFS A460 heads and inlet,1250 dominator, Carrillo custon nitrous piston
Ignition
MSD, programmable 7 didital,MSD crank trigger, MSD pro billet large cap dizzy, MSD HVC coil, Taylor 11.5 wires, Autolite AR3932 plugs
The motor has the timing locked at 30deg with 15deg timing pulled out.Fuel is Vpower with power pour. (SE rules)
Our problem happens when I step it up from 400bhp jets to 500bhp. I've run for 3 meetings on 400 and no problems change to 500 first run game over.
Fuel pressure on the carb is 6.5psi and the nitrous each engine damage a different setting last time was 6psi with a gauge on the dash.
I've also tried different piston manufacturers and compression ratio's still the same outcome
Ron
PS I am getting rather good at lapping valves now though
I'd also like to point out that there was no damage to any bearing, rod, crank, or cam on any of the piston failed runs just the front 2 cylinders each time
itake it the 400 to 500 jump was done with a jet change?
firstly in my experience we found jet sizes can be and are often out by a few thou that can hurt, its worth having a proper jet checker, single 4 barrel is naturly going to run leaner on the two front pots down to g force acting on the mix inside the manifold, pm me your jet spread if you dont want it known here, we used to make 600hp on a 481 ci motor without any damage fred hone probably makes more,
but the timing may be an issue, although my knowledge of pump gas is zero, i had the timing down to 13 degrees total with race fuel, we know we could have gone higher but it ran ok there no one was realy chasing so we diddnt do too much tuning, we found it needs less timing if its also getting leaner, in the blower cars if we get hot cylinders we give them bigger fuel jets. to fatten up the mix and keep those pots cooler, another posibility for you there,
good luck
firstly in my experience we found jet sizes can be and are often out by a few thou that can hurt, its worth having a proper jet checker, single 4 barrel is naturly going to run leaner on the two front pots down to g force acting on the mix inside the manifold, pm me your jet spread if you dont want it known here, we used to make 600hp on a 481 ci motor without any damage fred hone probably makes more,
but the timing may be an issue, although my knowledge of pump gas is zero, i had the timing down to 13 degrees total with race fuel, we know we could have gone higher but it ran ok there no one was realy chasing so we diddnt do too much tuning, we found it needs less timing if its also getting leaner, in the blower cars if we get hot cylinders we give them bigger fuel jets. to fatten up the mix and keep those pots cooler, another posibility for you there,
good luck
Yes it was with jets.
My motor pulled 850bhp and 729lb tq on the motor on pump gas at Pete Knights. From memory the jets in the carb are 99 front 93 rear
Due to the nature of the nitrous system we were thinking that it may be possible for Gforce/forward motion to stop the 6 psi of fuel coming out of the system but I'm keen to find out wheather people think they went lean or detonation
My motor pulled 850bhp and 729lb tq on the motor on pump gas at Pete Knights. From memory the jets in the carb are 99 front 93 rear
Due to the nature of the nitrous system we were thinking that it may be possible for Gforce/forward motion to stop the 6 psi of fuel coming out of the system but I'm keen to find out wheather people think they went lean or detonation
youd have to have some g to stop 6 psi of fuel flowing, remember the n20 dont only rely on the fuel suply from the jets, if the front pots have a lean mixture from the carb it will affect the mixture altogether,
if this is the second time this has happend id look at the tune up in those cylinders
if this is the second time this has happend id look at the tune up in those cylinders
Edited by wicked fish on Tuesday 21st June 15:28
Just a thought , but we suffered from a nitrous fuel supply problem for a while which by nature would obviously hit the front cylinders hardest. We ran a Holley blue regulator and harmonics on a pass were affecting it pretty badly: we could set the fuel pressure at 5.75psi in the pits, do a lap, check it again and it'd be down at 1 or even 0! Swapping to a Magna Fuel regulator sorted it instantly, luckily we were running pretty soft at that point til we had things figured out so there was no damage. Oh and WE were chasing, it was just after two runner up finishes, by the time we got our s
t together, won a championship and set a speed record that stood for nearly 2 years the "other" car had disappeared ha ha 
I notice you run 6.5psi at the carb, is this a pump gas thing? Somewhere around 7.5psi is usually more common.
t together, won a championship and set a speed record that stood for nearly 2 years the "other" car had disappeared ha ha I notice you run 6.5psi at the carb, is this a pump gas thing? Somewhere around 7.5psi is usually more common.
As Wicked Fish said, blocked jets a good bet. When I raced we had problems like this with 2 out of 4 getting burnt. It turned out to be the fuel distribution blocks - the fittings were too close and stopped fuel getting through. Found it by removing the nitrous injectors and measuring fuel quantity coming through when activated. In our case not enough to two cylinders.
fuel jets are in the solinoids so I would have taken all 8 but the have been checked. we flow tested the system I can't find the results at the moment but all 8 legs flowed the same in the workshop
Here's a video clip that a friend did and see if you still have the same thoughts about the G forces
http://www.youtube.com/watch?v=S-VTy4h2Sa8
Here's a video clip that a friend did and see if you still have the same thoughts about the G forces
http://www.youtube.com/watch?v=S-VTy4h2Sa8
are you running a plate or a fogger type system
im not sure for me any of that proves anything you say the jets are in the solanoid? then you say you checked the flow in all 8 legs, so im guessing we are not talking about a usual NOS fogger type system??
i wouldnt run a 500 hp system with a pump like that i take it yours is a much better pump the fuel wasnt ever realy flowing just running downhill which isnt surprising as all that fuel was comming from 1 jet,
the long and short of it is you dont have the problem at 400 hp and a simple jet change and you get the problem if the g force wasnt enough to affect it at 400 why would it suddenly be the cause just with a jet change
also remembering that there is vacuum and prety big airspeed inside the runners so fuel would be sucked by the vacuum and also in the case of a fogger type nozzel by the low presure zone that exists on the front side of the nozzel (side nearest the valve)
we run a Fogger with big jets and never had any difference front to back and we had egt probes in all
cylinders to tell what was hot and what was not
if its a plate/spraybar type system then yes as with the carb the fuel can be thrown to the back of the intake as all the cylinders are sucking in a small area the fuel will be affected by g force and wont have individual intake runner air speed to keep things normal
if your pump isnt up to it then anything could happen volume is as if not more important as presure
im not sure for me any of that proves anything you say the jets are in the solanoid? then you say you checked the flow in all 8 legs, so im guessing we are not talking about a usual NOS fogger type system??
i wouldnt run a 500 hp system with a pump like that i take it yours is a much better pump the fuel wasnt ever realy flowing just running downhill which isnt surprising as all that fuel was comming from 1 jet,
the long and short of it is you dont have the problem at 400 hp and a simple jet change and you get the problem if the g force wasnt enough to affect it at 400 why would it suddenly be the cause just with a jet change
also remembering that there is vacuum and prety big airspeed inside the runners so fuel would be sucked by the vacuum and also in the case of a fogger type nozzel by the low presure zone that exists on the front side of the nozzel (side nearest the valve)
we run a Fogger with big jets and never had any difference front to back and we had egt probes in all
cylinders to tell what was hot and what was not
if its a plate/spraybar type system then yes as with the carb the fuel can be thrown to the back of the intake as all the cylinders are sucking in a small area the fuel will be affected by g force and wont have individual intake runner air speed to keep things normal
if your pump isnt up to it then anything could happen volume is as if not more important as presure
Edited by wicked fish on Tuesday 21st June 21:51
Hi Ron, given that the best SE cars pull 2G, you would have to turn the spider through 90 degrees to do your flow test (and that would only simulate 1G). Regards the comment about a vacuum in the manifold pulling fuel out, at WOT there shouldn't be much of a vacuum anyway, assuming you have a big enough carb.
IMHO, you need to fit foggers or a plate system. While a spider might work in a low G street car, I can't see that a centralised jet in a spider would work in a (relatively) high G car. (however, if the jets were in the end of the spider pipes it may work).
Just my 2 cents worth.
Ade
IMHO, you need to fit foggers or a plate system. While a spider might work in a low G street car, I can't see that a centralised jet in a spider would work in a (relatively) high G car. (however, if the jets were in the end of the spider pipes it may work).
Just my 2 cents worth.
Ade
When running with low fuelpressure on the nitroussystem the flow can differ very much from jet to jet. My buddy did a lot of research many years ago and found out that the only way to get it right was to drill many jets with the same size of drill and then flow them and pick 8 good ones that flow exactly the same. And it also worked much better when using smaller fuel jets and then crank up the fuelpressure to get the right fuelflow. That helped a lot in more equal flow on the jets. But this was over 10 years ago and maybe things have changed? I switched to alcohol and blower in 2001 and never looked backed after that.
Edited by KP1 on Sunday 26th June 21:11
Sorry, perhaps I should have clarified - the vacuum is in the cylinder, not the manifold.
There is a small pressure drop across the Carb, but the manifold pressure wants to be as near atmospheric as possible at WOT (or even above atmospheric in the case of a blown car as you know ;-)).
From memory, I think Holley flow their 4 barrels at 1.5 inches of mercury pressure drop to rate the CFM of their carbs. (3 inches for 2 barrels just to confuse everybody).
if you take ballpark figures of 30 inches mercury = 15psi = atmospheric pressure, then the pressure drop across the carb is about 0.75 PSI, leaving the pressure in the manifold at 14.25 PSI at wide open throttle, (so there IS a very small vacuum in the manifold at WOT).
In reality, a racing engine would want less pressure drop (ie higher manifold pressure) than
1.5"HG and a bigger carb would be used, sacrificing low RPM driveability for all out top end
horspower.
i agree about the high speed flow of nitrous creating a vacuum as it passes over the fuel outlets, which I guess would help to pull out the fuel more evenly, but I would still say that the jets would be better placed at the end of the spider fuel pipes.
By the way, well done in winning yesterday.
Lets hope you can beat all comers in the Euro finals, it would be nice to see a Brit win...
Ade
There is a small pressure drop across the Carb, but the manifold pressure wants to be as near atmospheric as possible at WOT (or even above atmospheric in the case of a blown car as you know ;-)).
From memory, I think Holley flow their 4 barrels at 1.5 inches of mercury pressure drop to rate the CFM of their carbs. (3 inches for 2 barrels just to confuse everybody).
if you take ballpark figures of 30 inches mercury = 15psi = atmospheric pressure, then the pressure drop across the carb is about 0.75 PSI, leaving the pressure in the manifold at 14.25 PSI at wide open throttle, (so there IS a very small vacuum in the manifold at WOT).
In reality, a racing engine would want less pressure drop (ie higher manifold pressure) than
1.5"HG and a bigger carb would be used, sacrificing low RPM driveability for all out top end
horspower.
i agree about the high speed flow of nitrous creating a vacuum as it passes over the fuel outlets, which I guess would help to pull out the fuel more evenly, but I would still say that the jets would be better placed at the end of the spider fuel pipes.
By the way, well done in winning yesterday.
Lets hope you can beat all comers in the Euro finals, it would be nice to see a Brit win...
Ade
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