Piston weight change to rebalance

I burnt #4 and #5 at the thin section where the valve relief is on Diamond 40525's. This happened from being 2 heat ranges up on the plug and the lame fuel distribution on the victor manifold. I'm looking at going .060 over instead of .040 over and the weight is going from 561 to 569 grams. Rebalance needs malory also may go to Probes instead. This engine stays below 7,000 rpm.

How much weight difference can I get away with without rebalancing?


Other details for what its worth....
547, E85, 13.5comp, roller, SCJ-B heads, 1050 dom, D9 block. The car ran 9.80's last outing and the plugs for both holes looked black from oil.
Noticed oil blowing thru the breather at shutdown. Leak down showed 60 and 70% all other cylinders are at 85% or higher tested cold. I spent 3 hours on the manifold with an angle die grinder to open up 1, 4, 5, and 8. To bad the slugs are already toast and the cylinders still have honing cross hatch, #5 hole has some shallow scoring. I almost thought about buying 2 pistons and sliding them in.
One of these days I'll get the motor, drive line and suspension to work right at the same time.

Dave

get the diamonds lightned, I did it on this last build.......and it may not be enough to matter.....


That thing musta been lean as hell and or in detonation to get two pistons n/a.......even w a victor intake. You might be at the limit of e85 and that compression.

So if you go with the bigger pistons and the weight goes up 8 grams,,,,,that's what's called reciprocating weight. There is a 50% factor of the reciprocating weight, so the "net" to the bob-weight is 4 grams. Personally I wouldn't worry about it too much because some engine builders overbalance and/or underbalance anyway.

However if your worried about it,,,, then the best thing IMO is to lighten the piston by 6 or 8 grams. The area to lighten is around the pin bosses and also underhead. Most knowledgeable machine shops can do some weight removal for you. No need to mess with the crankshaft or mallory metal.

Charlie

c.evans wrote:So if you go with the bigger pistons and the weight goes up 8 grams,,,,,that's what's called reciprocating weight. There is a 50% factor of the reciprocating weight, so the "net" to the bob-weight is 4 grams. Personally I wouldn't worry about it too much because some engine builders overbalance and/or underbalance anyway.

However if your worried about it,,,, then the best thing IMO is to lighten the piston by 6 or 8 grams. The area to lighten is around the pin bosses and also underhead. Most knowledgeable machine shops can do some weight removal for you. No need to mess with the crankshaft or mallory metal.

Charlie

I'll have to find out the weight of the Probes and if they are more I will probably have them lightened. Also looking at ceramic coating the tops for heat resistance so if they are to be lightened then may as well coat them?

Dave

Who did your E85 carb?



Ace

powerstrokeace wrote:Who did your E85 carb?



Ace

Horsepower Innovations
The carb is right, no I'm not using a wide band.

Coatings won't help if its detonating.

Have your piston weight when you order, no matter who you get them form. Most companies will get as close as possible if they can.

Mark O'Neal wrote:Have your piston weight when you order, no matter who you get them form. Most companies will get as close as possible if they can.

Mark,
I was looking at your 14792's but they have a CH for a 6.7 rod and I need a piston for a 6.8 rod with a CH at 1.25. Do you have anything for that rod?

Thanks,
Dave

dfree383 wrote:Coatings won't help if its detonating.

As previously described the burn was caused by the plugs being too hot and the manifold flow lean at the corners. I had burnt the straps off the plugs on 3 of the 4 corners. The other 4 holes looked great. The plugs did not have aluminum on them and I thought all was well and threw cold plugs at it but the damage was done.

When you look at the 1.25 compression height piston top section volume where the relief is, it is way thin and no doubt is the hot spot that will be the first to go. Having the top coated will help lower the temperature and protect the thin area.

Dave cant you hone all cyl. have dart coat your piston plus 2 new piston they can coat up to .008 then your all fresh and ready to go. we are going to ubly the 29 hope to see you there.

Dave with alittle more thinking leave it that way and break something else that way i got a chance of kicking your a$$ at ubly

quick 52 wrote:Dave cant you hone all cyl. have dart coat your piston plus 2 new piston they can coat up to .008 then your all fresh and ready to go. we are going to ubly the 29 hope to see you there.

quick 52 wrote:Dave with alittle more thinking leave it that way and break something else that way i got a chance of kicking your a$$ at ubly

I thought about that but there are two other holes that are not stellar for leak down as well.
Even with 2 holes at half power you'll be looking at my bumper the entire trip down the track thru the oil fog. The 29th may be possible if I lock up buying pistons Wednesday and get the block in to Jack's place.

Also got the John Callies Morels from Herbert going in to replace the Endur-X, it was time. The Endur-X are still tight after 80 plus runs and 1500 street miles. I'm hoping to keep more oil down at the bottom end with the Morels.

will have the malibu out there to its running 9.50s hope to get in the 40s . and hope to put the truck in in the 10.80s

The Malibu should be a good match if I got 8 good cylinders. I'll do my best to be there. How much are you spraying that to go 9.50's?

Dave De wrote:

powerstrokeace wrote:Who did your E85 carb?



Ace

Horsepower Innovations
The carb is right, no I'm not using a wide band.

ERIC knows his sh*t...


Ace

what spark plugs where in it?

BAD Reply. My apologizes for not reading the topic before responding.

Dave.

its my sons car and we have been hitting it with 180hp bc if we spray more it blows the tires off and run slower. we installed and controller last week and hope to hit it with 250hp then 300hp if every thing work out. the controller is sweet lot of options plan to start at 40% and ramp it in to 100% in 2.5 seconds see whats happens of there. the truck im hitting it with the 50hp first stage 150hp second stage hope those cast piston hold out been ok so far.

Dave OP, are you spraying at 13.5:1 on E85?

Dave De wrote:

Mark O'Neal wrote:Have your piston weight when you order, no matter who you get them form. Most companies will get as close as possible if they can.

Mark,
I was looking at your 14792's but they have a CH for a 6.7 rod and I need a piston for a 6.8 rod with a CH at 1.25. Do you have anything for that rod?

Thanks,
Dave

Sort of. I can put a Kaase intake pocket in the 10671 if you need me to.

Mark O'Neal wrote:

Dave De wrote:

Mark O'Neal wrote:Have your piston weight when you order, no matter who you get them form. Most companies will get as close as possible if they can.

Mark,
I was looking at your 14792's but they have a CH for a 6.7 rod and I need a piston for a 6.8 rod with a CH at 1.25. Do you have anything for that rod?

Thanks,
Dave

Sort of. I can put a Kaase intake pocket in the 10671 if you need me to.

Looks like a good possibility and the base weight is 21 grams less than what I need so at .060 over the weight will be very close. I will call on Tuesday.
Thanks

dfree383 wrote:Dave OP, are you spraying at 13.5:1 on E85?

No spray and have only gone 9.65 at 140mph with a bunch of chassis issues. I'd like to go just under 150mph and if I need spray I feel defeated.

richter69 wrote:what spark plugs where in it?

Autolite 3924 before the change to NGK "8"'s but the damage was done.

https://www.429-460.com/t14389-spark-plug-ground-straps-burned-off#170218

Dave De wrote:

richter69 wrote:what spark plugs where in it?

Autolite 3924 before the change to NGK "8"'s but the damage was done.

https://www.429-460.com/t14389-spark-plug-ground-straps-burned-off#170218

Dave you should be even colder like a ngk 5671a-9 or 10 autolite ar3933 or ar3932. you will have to show me how to fix that intake im running one so all the corner run lean. do you need a flo bench to get it right