Pinging 390
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Pinging 390
I have an issue with the new motor pinging.
I am running TRW 2291 forged pistons, a Crane 901 cam, performer intake, headers with dual 2.5 inch exhaust.
The pistons are advertised at being close to 10 to 1 compression but after reading some past posts, it sounds more like they may be closer to 9.5 to 1 pistons.
I run mid grade gas with octain booster and at 6 degree advance on the timing still get slight pinging when it is warm outside.
The truck has a new radiator and seems to run decently cool without a fan shroud
Not sure what heads I am running, I know they aren't GTs.
I was wondering if going to a 941 cam would help enough to make the investment?
I will be towing a trailer with a Jeep on it at times and don't want to destroy pistons when I am going over the grades
I was wondering what other options I might have to help with the issue.
Any help would be great.
Thanks, Ken
I am running TRW 2291 forged pistons, a Crane 901 cam, performer intake, headers with dual 2.5 inch exhaust.
The pistons are advertised at being close to 10 to 1 compression but after reading some past posts, it sounds more like they may be closer to 9.5 to 1 pistons.
I run mid grade gas with octain booster and at 6 degree advance on the timing still get slight pinging when it is warm outside.
The truck has a new radiator and seems to run decently cool without a fan shroud
Not sure what heads I am running, I know they aren't GTs.
I was wondering if going to a 941 cam would help enough to make the investment?
I will be towing a trailer with a Jeep on it at times and don't want to destroy pistons when I am going over the grades
I was wondering what other options I might have to help with the issue.
Any help would be great.
Thanks, Ken
Last edited by woods; Mar 28, 2005 at 02:56 PM.
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Going to a bigger cam will lower the "dynamic" compression, so you might get some benefit from going to a bigger cam. You might not have a big enough one for those pistons.
I used the L2291F's, flat-top w/valve-reliefs, decked block, milled heads and got 11:1 compression with C8AE heads. What casting #'s do the heads have? That will change a lot too, earlier heads were generally smaller chambers, so if I had used a smaller-chamber head on my motor, the compression would be way over the top (and useless).
You might be able to fix this with a cam, or different heads, or both. Get back to us with the head casting #'s. Should be D2TE-AA, C8AE-H, C7AE-x, C6AE-x, etc. etc. D=1970, C=1960, D2=1972, C8=1968, etc.
I used the L2291F's, flat-top w/valve-reliefs, decked block, milled heads and got 11:1 compression with C8AE heads. What casting #'s do the heads have? That will change a lot too, earlier heads were generally smaller chambers, so if I had used a smaller-chamber head on my motor, the compression would be way over the top (and useless).
You might be able to fix this with a cam, or different heads, or both. Get back to us with the head casting #'s. Should be D2TE-AA, C8AE-H, C7AE-x, C6AE-x, etc. etc. D=1970, C=1960, D2=1972, C8=1968, etc.
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Originally Posted by Annihilator
I don't really think that there is anything special about the 390 GT heads.
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Well thanks for all of the responses.
The casting numbers on the heads are C8AEH.
I did have the block decked so that might be where the issue started.
I haven't ran premium in the truck yet.
I figured that mid grade with booster would bring up to being equal or higher than the premium fuel sold around here.
The casting numbers on the heads are C8AEH.
I did have the block decked so that might be where the issue started.
I haven't ran premium in the truck yet.
I figured that mid grade with booster would bring up to being equal or higher than the premium fuel sold around here.
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don't count on the booster stuff to help, it only raises the octane by about .2, not enough to matter.
Keith
Keith
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Originally Posted by woods
Well thanks for all of the responses.
The casting numbers on the heads are C8AEH.
I did have the block decked so that might be where the issue started.
I haven't ran premium in the truck yet.
I figured that mid grade with booster would bring up to being equal or higher than the premium fuel sold around here.
The casting numbers on the heads are C8AEH.
I did have the block decked so that might be where the issue started.
I haven't ran premium in the truck yet.
I figured that mid grade with booster would bring up to being equal or higher than the premium fuel sold around here.
I have (had) the same setup - flat tops (with eyebrows) and C8AE heads and a decked block. Pinged like a SOB - It definitely needed 93 octane and then it needed some creative timing modifications, but it DID run great after tuning it right. But, I had a cam that was meant for that compression.
Keep us informed, your cam might be too small. The higher compression lets you run a bigger cam, and a bigger cam lets you use higher compression
I don't know anything about Crane cams, but just looked on their website, and the 901 is only recommended for 8.0-9.5:1 compression ratios. You are already nearing 11:1, I'd say based on my own build, and the Crane 941 is good for 8.75-10.5:1 ... so, the 941 is almost a good match. You could retard/advance it a little (not sure which way reduces dynamic compression) to make up for that. At this point, I'd certainly say the cam is too small...
art k.
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Thanks again for the reply's.
I guess it will be a 941 cam since I don't want to deal with installing adjustable rockers right now.
The heads are fresh with new heavy springs so they should be fine with the 941 cam
I was hoping that I would be able to dial it in so that I could stay away from premium fuel but it looks like I will have to run the higher octane
Thanks for all the effort.
Ken
I guess it will be a 941 cam since I don't want to deal with installing adjustable rockers right now.
The heads are fresh with new heavy springs so they should be fine with the 941 cam
I was hoping that I would be able to dial it in so that I could stay away from premium fuel but it looks like I will have to run the higher octane
Thanks for all the effort.
Ken
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Your probably going to need adjustables with the 941 because from what I have read, you don't want to try and use the non-adjustables on a cam with more lift than .550, I read that on Erson's website. It can be cheap, somewhere in between about 2 other options, or get really expensive. I would look at some other cam companies and see if they have something that suites your engine better. What about the Crane 801? I would have someone compare that and the 941 at least, to see what it could look like. I would get a cam that had more duration than the 941 if you are near 11.1:1 compression ratio.
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My 390 I recently took apart had non-adjustables and .554/.554" lift. They took the strain at least for the 10K miles or so it was used... The tops of all the exhaust valves were a little chewed, but that was most likely a bad heat-treatment process - it's pretty evenly chewed, right in the center, and no marks on the rocker arms. And the (stock) intakes were fine.
But I understood it was a risk, and would have gone to rollers if I was going to seriously keep running it...
But I understood it was a risk, and would have gone to rollers if I was going to seriously keep running it...
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Thanks for the help.
I went to Cranes website and looked at both the 801 and 941 cams.
They both work for the same compression ratio (8.75 to 10.75).
I still think that since I will be using this truck to haul some weight, the 941 cam still sounds more like what would work best for this setup.
The 801 might help better for the pinging but I think the 941 would pull better with a trailer and get a little better milage.
Sell me on the 801 cam if you think it is better.
It will be a few weeks before I could buy one anyway.
I went to Cranes website and looked at both the 801 and 941 cams.
They both work for the same compression ratio (8.75 to 10.75).
I still think that since I will be using this truck to haul some weight, the 941 cam still sounds more like what would work best for this setup.
The 801 might help better for the pinging but I think the 941 would pull better with a trailer and get a little better milage.
Sell me on the 801 cam if you think it is better.
It will be a few weeks before I could buy one anyway.
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What tranny do you have?
My '74 highboy with a lopey idle, 292/292 adv dur cam, pulled about 4000lbs of scrap iron in the bed (local church needed help getting rid of a 1910 or so boiler)... and did it with some exceptional ability. It was quite scary doing about 4000RPM in 3rd pulling onto the highway. Scary as in it flew... Using 2nd gear in my 4spd (granny first), it pulled that load from a dead stop pretty well. I would think it would start to have problems at around 6000lbs, but I could always get it moving with 1st if I had to. My rear gear is 4.10 and I had 33" BFGs on it at the time. Your Mileage May Vary (literally)... With an auto it's easier to get a lopey idle cam to pull from the hole. But you need a big tranny cooler.
My '74 highboy with a lopey idle, 292/292 adv dur cam, pulled about 4000lbs of scrap iron in the bed (local church needed help getting rid of a 1910 or so boiler)... and did it with some exceptional ability. It was quite scary doing about 4000RPM in 3rd pulling onto the highway. Scary as in it flew... Using 2nd gear in my 4spd (granny first), it pulled that load from a dead stop pretty well. I would think it would start to have problems at around 6000lbs, but I could always get it moving with 1st if I had to. My rear gear is 4.10 and I had 33" BFGs on it at the time. Your Mileage May Vary (literally)... With an auto it's easier to get a lopey idle cam to pull from the hole. But you need a big tranny cooler.
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ping ping ping
Woods, the C8AE-H chambers are smaller than most. The D2TE-AAs also have the smaller chambers. Have the heads been setup for unleaded gasoline ? If not, they ought to come off anyway. You need hard exhaust seats, in whatever head you choose. The D2s ( usually) have them, but they have the same chamber you have now, and that wouldn't help. C7AE-A has a bigger chamber ( soft D ) and C6AE-J has a bigger still chamber ( sharp D ). But before you pull the heads off, get a shroud. It might help. How fast are you spinning the water pump ? How does it do on premium ? DF