Thread:

Machine shop mix up - need advice

i had a machine shop assemble my engine 2 months ago. i supplied all parts except bearings and pistons. i purchased those through them because he was giving me a labor discount since they were so slow. this weekend i found the receipt and ran the part numbers for the pistons. i had asked them to build it around 10:1, instead they used a deep dish blower piston that left it at 8.6:1
The block was decked to zero. I talked to them and he said he would tear it back down and install the right pistons and re balance everything. i already have it completely ready to go to the river, so its a real pita the pull it and start over again.

i plan to run at least 150 nitrous, considered going to 250. is it worth it to pull it and have them redo everything? how much power am i going to lose? will i be able to run 92 octane @ 10.1:1? with nitrous?

specs-

sbc, speed pro forged pistons, powdered rods, cast crank, comp cams xm 276 roller, weiand tunnelram w holley 450's, msd ignition, edelbrock performer rpm heads 64cc

Left a whole lot on the table, I would have him make good on the deal or give me a nice fat check! Whats a weekend of labor? It's not river season yet, still have about a month and a half... Then again, we are going this weekend...

On a typical 350 ci the difference in 8.6 and 10.1 is about 65 hp at 6500 rpm..roughly.

They boned you, I agree.

Did you do the math to see exactly (or close to exact) what compression you really have ?

Originally Posted by cfm

They boned you, I agree.

Did you do the math to see exactly (or close to exact) what compression you really have ?

4" bore, 3.48" stroke, 64cc head, .041 deck height w/gasket

that was the exact math, used an online compression calculator. a blower isnt in the budget.

how much more nitrous could i safely run with the lower compression? if it allowed me to run way more nitrous, i might be able to deal with it.

Originally Posted by TryMe

4" bore, 3.48" stroke, 64cc head, .041 deck height w/gasket

that was the exact math, used an online compression calculator. a blower isnt in the budget.

how much more nitrous could i safely run with the lower compression? if it allowed me to run way more nitrous, i might be able to deal with it.

Not much. - it's the cast crank thats your limit here, not the compression. with another 250 ponies your flirting heavy with a broken crank. Keep it to 100-150. stock rods are good to about 700hp

Nitrous tends to quell detonation anyway which is why you can squeeze a built 10-1 engine pretty hard.

The "juice" load you can pump is determined more by the rest of the package and running gear that the compression of the engine.

Get your rig redone. A "re-balance" on a cast or any crank can often swiss cheese it- youd be better off trying to get a custom piston weight that matches the weight of the 8.6 slug. You want the bob weight as low as possible so you rev freely and get a long engine life- rebalance deals often end up adding bob weight.

Upside with that low of a compression is that you can easily take a tank of crap gas youre likely to get on the river.

Id stay away from the smaller blowers especially if you boat at the river as they generate too much heat for the boost you get- (dont ask how I know this) if you are going to get a blower- go whipple or 6-71.


Good luck on this one- can I ask who did this rebuild for you?

Uncle Dave

Originally Posted by Uncle Dave

Not much. - it's the cast crank thats your limit here, not the compression. with another 250 ponies your flirting heavy with a broken crank. Keep it to 100-150. stock rods are good to about 700hp

Nitrous tends to quell detonation anyway which is why you can squeeze a built 10-1 engine pretty hard.

The "juice" load you can pump is determined more by the rest of the package and running gear that the compression of the engine.

Get your rig redone. A "re-balance" on a cast or any crank can often swiss cheese it- youd be better off trying to get a custom piston weight that matches the weight of the 8.6 slug. You want the bob weight as low as possible so you rev freely and get a long engine life- rebalance deals often end up adding bob weight.

Upside with that low of a compression is that you can easily take a tank of crap gas youre likely to get on the river.

Id stay away from the smaller blowers especially if you boat at the river as they generate too much heat for the boost you get- (dont ask how I know this) if you are going to get a blower- go whipple or 6-71.


Good luck on this one- can I ask who did this rebuild for you?

Uncle Dave

thanks for the advice, i guess i will pull it and send it back. i just wish i would have caught this before, would have saved a lot of headache. id rather not say who did it, im sure it was an innocent mistake. the pistons are the same price, so this job is probably costing him money at this point.

the rods are stock, lt1 powdered rods

Is it possible the part number on the receipt is wrong and the pistons in the motor are correct?

I would pull a spak plug and bring a piston up to TDC and take a look in the bore to confirm for sure which piston is actually in the engine. paper work errors are pretty common.

Good luck with it.
Scott

i verified the piston was wrong by using a borescope to look in there, its at the machinists now getting redone

the error in your words are (im sure it was an innocent mistake) so here you have an honest business man who has said whooops and he has enough balls to take care of it !!!!!!!! he eats new pistons balance job and labor !!!!!! sounds like a stand up bro to me so i would be happy to tell every one look i found an honest business here !! how many tears have we all seen spilled on these boards and threats of violance and on and on all to no avail just trying to get some satisfaction after takin a bad screwin !!!! so why not tell the busines name unless im think wrong !!!!!!!