PRE IGNITION FORD 250 crossflow

Hi i have an XD falcon 250 Crossflow, its been worked, 30 thou over pistons its stroken out to close to a 270, 3.3 rods compression is 10.5:1. I started off with a 600 holley. that was way too big i was getting flat spots getting bogged down low.. and lots of pre ignition, it would turn off sometimes. The block was deck to 0.

I then put on a 450 holley, i have had better economy and performance out of it but still down low it boggs, but i think thats cause of my gear ratios 2.92, im going to go to 3.5s.

Anysways i still have pre ignition, the motor has been on a gas analyser its been tuned properly what can i do to stop this??? Can anyone help me?

okies.. first of its no where near 270 cubes..... long rods dont increase the ci of a motor.... . And using 3.3 rods doesnt allow for an ofset ground crank. So u mean its pining???.
tighen the advance curve up in the dissy. run around 12-14 base with a total of only 28-30. If it still detonates keep tightening the advance curve up in the dissy.
Im running 32 deg with a locked shaft dissy. AS in at idle its running 32 deg and at 6000 rpm its 32 deg. I get no detonation becasue of the converter the motor isnt loaded up under 4000-4200 .
With a manual a locked dissy isnt realy a great idea.

By running a tigher advance curve in the dissy it will allow more igniton down low which will increse low end torque a shit load without making to much top end igntion timing

What about fuel?

good point... he might be running it on 91 or somthing.. but i kinda assumed he was using at least 98 :>.. but hey who knows

I didn't rush to discredit the stroker bit because of remembering stroker kits "back in the day"; they were advertised in "Street Rodding" and similar mags. Never looked into the how-to of one, though.

D'you think he might benefit from water or water/alcohol/methanol injection?

ive never actaully seen a stroker kit... and i figured since 200 rods were all ready WAY long with just a 250 crank ( the pin is nearly as high as the oil ring) i figured there is no way using 200 rods u would have enuf height left at the top of the bore to squeese a pistion in there

I am running premium unleaded 98 octane. most of the time shell optimax. The seats have been hardened so unleaded fuel can be used. So you think its all in the timing?

What do you suggest i do to get my throttle smoother... with the 465 holley the lower i am on revs if i put my foot down, it gets a little caught and then kicks off.. All my spark plugs are not black so its not running rich at all... but i get a bad smell at the back of the exhaust and black smoke sometimes. On the gas analyser my mechanic set it right. It maybe a bit less for fuel economy from what i remember. the higher i am on revs the less it kicks... and when i get closer to where the cam kicks in which is around 2700-2800, (i got a stage 5 cam) it doesnt kick????

I could be completely on the wrong track here...but I'll say it anyway
You might want to consider Addo's suggestion about water injection, but in a tempory way. If there is any build-up of carbon within the cyclinders, that could be contributing to the pre-ignition....hot carbon from previous ignition starts the burn in the next cycle....so on and so forth, you probably know the drill. (and you probably don't need a rich mixture to get carbon forming, there'll always be some present, just greatly reduced in stoich or lean running) One thing I have heard of is pouring water down the carby while the engine's running, and the water can then help remove the carbon build-up. On occation I have done this with my old XY, just set the hose going at a constant dribble and then pour the water down the carby while running. You may need to manually rev the motor to keep the rev's up, but it shouldn't stall the motor (not unless the water is gushing out!!) You'll be surprised just how much water you can put down the throat of a car and not stop the motor. But of course, I must stress moderation. Try it for about 5-10 minutes and then see if has helped. If not, try it one or two more times. If anything, at least you'll know that the cyclinders should be fairly clean.

Regards.

Teddy

PS: If you want the detailed reason as to why water can get rid of carbon out of cylinders, let me know, and I'll tell you the chemistry behind it. I thought I'd better not put that in for the moment, as I'd bore people to tears

Does dropping water down the carby do any harm to the motor or carby? First ive heard of this illl give it a go.. But say it cleans wont it just come back again? Will the carbon build up again or do you think that is the old carbon build up from the 600 holley that was on there?

Any suggestions on the throttle?

Water down the carby shouldn't do any harm to the motor or the carby, but again I stress that you do things in moderation. When I've done this on my old XY, I get the hose going at a very small continuous dribble, with the stream no thicker than, say, a drinking straw. But the motor has to be running, and like I said previously, you may need to manually rev the motor to keep the rev's up.

Now if this method clears up your problem, then you have a couple of possible scenarios to consider. Either the carbon had built up previously and now that its gone, the correct tune should maintain things and prevent it coming back. If the problem re-appears after some time, then you can probably assume carbon has built up again and just repeat the treatment OR as Addo mentioned, install a permanent water injection system to keep the carbon at bay permanently.

If the treatment doesn't get rid of the problem, it may not be a pre-ignition problem from carbon. As I think someone else mentioned on another related post, have you considered the possibility of this being detonation, rather than pre-ignition?? If it is detonation, then installing a permanent water injection should help in that department. Seeing as you're running 10.5:1 compression, detonation might be a possibility.

Another thought that just popped into my head...you said earlier that it still bogged down a bit even after changing from the 600 Holley to the 450... are you sure that the 450 isn't still too much carb? I know that a lot of other people are running 350 Holley's which gives them good drivability for their application. Think about what your normal rev range is for general driving conditions. Changing diff ratio will merely bring up the revs, thereby bringing the larger carb into its prefered operation range for air flow. You be the judge as to whether its cheaper to change a carb or change a gear ratio.

That'll give you a few things to think about, so I'll leave it there.

Regards,

Teddy

Thank you for your time ted and evryone else for their suggestions i really appreciate it. The motor revs out to about 5500-6000. I have noticed a huge difference in fuel economy for the 465. Being a 4 barrel it helps the 2 barrel 350 is a little questionable. IM happy with the 465. So the bogging down low could be the carby again? Well if i can improve it to the point where its not bogging as hard then im happy. coz sometimes its a ball breaker.. ur slowing down and u wanna put ur foot down a bit and it just wont go, it gets caught... stutters there for a bit and then slowly slowly it clears up and goes. 2.92s are a very low ratio for an xd... u cant even take off in second gear. no chance. Any other suggestions?

Thanks

Foti

Is the accelerator pump cam on the carby adjusted correctly?
Do the squirers operate when you crack the throttle? If they do then you may need to open up the size of your squirters.
On another note, the carby is a vac secondary right? You or your mechanic havent put a screw in the secondary linkage to make the secondarys crack like a double pumper? I've got a 650 double pumper on my corty and it loves it. You can really feel when you crack the secondarys, as it just breaks traction in 1st and 2nd. I've got a 600 vac sec. in my XE on a 302, on which I tried a screw in the linkages to make it a mechanical secondary. Made the car more lively on gas, but I got 60-80km less out of my tank. Really chewed the gas. And on petrol was just a real dog untill about 3000rpm. One big crazy flat spot.
Good Luck

Thanks for the input there Kiwi. I'm glad someone else threw in some more advice 'cos I'm not real savy with the finer points of the various carbs. I only have the original single barrel Stromberg on my old XY, and it does what its supposed to do.........most of the time. Maybe one day I'll look at upgrading things a bit.

In the end, I suppose it comes down to what you're happy with,or, prepared to put up with. If you're happy with the 465 that's great. As I see it, our cars are an extension of our own personality, and the little differences we each have on our rides can reflect this. What ever you do, don't stop tinkering with a problem if you think there has to be a better answer. Usually what we discover along the way to solving a problem teachs us more than we realise. Above all, enjoy your car, keep improving it, and have fun!

Regards,

Teddy

Well put buddy!

I did the water injection with the hose. I only did it for a couple of minutes and i was reving it a bit the same way id do it if i was using carby cleaner? is this process correct? i only did it for a couple of minutes before i was rudely interupted by my next door neighbur complaing about the noise and the smell!! and how she couldnt breathe.. there has always been a real bad smell behind the exhaust pipe it really stinks.. anyways... it kind of reduced it a bit... its only done it twice now.. and it hasnt pre ignited for a long period just a quick kick and thats it... should i continue the process and for roughly how long u said 5-10minutes... was that an exaggeration or seriously like 10 minutes...?? and should i be reving it real hard.. or just a little?

Is there any additive i could put in the petrol to help clean it out?


Thanks... sorry for the 100 questions....

ive heard of people running a tiny bit of diesel in there fuel just before they use the water method... Be care full u dont use to much water, its very easy to hyrdulic an engine and bend a rod

Glad to hear the water may be helping you out. The time you run it for with water going into it will be dependant on how much carbon has built-up. I wouldn't be trying to rev it too hard, just try and get away with the minimal amount of revs you can sustain. Its the unfortunate thing in life that situations beyond our control ie. complaining neighbours :roll: , can limit what you can do. To placate the neighbour, try running the car at the minimum revs you can get away with. The water will still be doing the cleaning effect in the cylinders. Try to at least sustain a 3-5 minute run. If you drop the water rate you might be able to add the water while the car idles. (Surely the neighbour wont complain about the car at or slightly above idle.... ) If after the next treatment the problem improves further, try it again. If you keep getting improvement, keep going. If you get no further improvement, stop. Simple as that. There are no hard and fast rules here.

Don't know much in the way of additives. Most modern petrol formulations include various agents that have a detergent effect to keep fuel systems clean. (unless they bugger it up and accidentally form some chemical species that gum things up, like one petrol company did a few years ago with their aviation fuel, which potentially caused a couple of plane crashes.......but that's another story.....) What you might be observing with the water is the cleaning out of old deposits, and hence forth, the system will hopefully remain clean from the various fuel additives. Apart from running premium in my old XY, I include a lead replacement additive (Nulon, I think). The only other thing I use very occationally (more so during the cooler weather) is a dose of methalated spirits into the tank. That helps take out any water that gets into the fuel tank from condensation and the like.

Kind Regards,

Teddy

Would urea hurt the chambers?

Urea That's a new one on me. The first thought that pops into my mind is that you might get a higher level of NOx forming in combustion.....can't see it harming the cylinders/chambers. Just rying to remember the chemical formula off the top of my head, I think its

CON2H4: ie, 1 carbon, 1 oxygen, 2 nitrogen and 4 hydrogen atoms per molecule.

I'm thinking on the run here so bare with me....I know its a relatively weak moecule so it might "crack-up" in the intense conditions in the chamber and form a few chemical species called "radicals" (no, not the type you find in a university art's department) which can help catalyse better combustion reactions, and hence cleaner combustion. Is that the general idea : Please let me know, I'd love to know if my off-the-cuff analysis was anywhere near the reality..

Regards,

Teddy

No, the general idea was could one theoretically achieve the cleaning effect of water injection, by taking a leak down the carby?

Ahh, I see. Sorry, that was completely lost on me last night, too tired to see what you were getting at......you can tell I'm the engineer.....always trying to solve the problem, even if one doesn't exist!

Regards,

Teddy