Blew up again short rant

[NZGTRA17]

Originally Posted by Rich F

Update:
Engine builder opened things up. #1 piston detonated & ruined. Appears to be detonation in every other hole as ring gap shrunk in all the other pistons. There was a little scuffing on the cylinder walls. Other than a little valve damage on #1 piston head area everything else looks ok. From a basic repair standpoint sounds like hone all bores, replace 1 piston, replace all rings, bearings etc. and replace valves on # 1.

Unfortunately my builder has no idea what's causing the failure. We were running timing 15 deg idle and 35 deg. full advance 3K rpm. The carb is jetted fat and plugs read rich.

He is looking at all the pieces and parts trying to find a cause. I'm going to send my 6AL-N box along with the distributor to MSD for testing and inspection.

Fuel quality is the last unknown which is now a month old.

Not sure where to go as he tries to sort this out.

Rich, have the heads been cc'ed to check compression ratio? I would also check the dynamic compression ratio. There are some handy online calculators for doing this. Assume all stuff like head gasket orientation etc was OK? No signs of any vacuum leaks?

I run 14/34 or 15/35 timing on my current 347 which is 10.5 compression. I run it on our 98 octane pump gas which is probably the same as your 93? No probs to run on this octane detonation free. We really pushed the envelope on this gas in our last 6 hour as we used quite a bit of oil due to valve guide issues and still had no detonation problems.

Regards carb jetting, has this been baselined to maunfacturers specs then jetted up from there? I have had plugs read rich when the engine was actually experiencing a lean condition before. This can happen due to incomplete combustion in the lean condition fouling/wetting the plugs. Was an exhust sensor used to provide airfuel ratio info during tuning Rich? If not then that combined aith a knock sensor should be a must for post rebuild runs. I would also do the runs on a chassis dyno as opposed to an engine dyno so that all installation dynamics are accounted for in the dyno runs. Or you could do initial runs on an engine dyno and then re-run the car on a chassis dyno post installation. Personally I do all my tuning in a chassis dyno as I find it more convenient, less expensive and it accounts for all installation variables.

Kel.

[Rich F]

12.0 to 1 compression 93 octane motor go boom!!

I thought my engine was factory GTS spec. Guess not. 60 cc Edelbrock heads and at or near "0" deck clearance equals lots of compression.

Still going to have the MSD box and distributor checked by the factory.

My builder is providing labor and any machine work at no charge. I'm buying 1 piston, rings, gaskets, 2 valves and some small parts plus the joy of putting the engine back in.

As Kel and others have suggested I'm going to break in and tune the motor on a chassis dyno while in the car. Cost locally for a half day is about $450.00 which should get me 6-8 pulls.
Hopefully on the road to recovery.

Still considering selling after it's back together.

Rich

[boothkc]

Well that explains alot. To detonate you either have to have too much timing, compression, not enough fuel, or limited detination margin (ie. octane). Usually, we can't change these easily...

Stock GTS is 10.5:1 (I think) and runs on 110 Leaded.... ie very high detonation margins. Sounds like your builder should have been more specific on the octane required and messed up. Nice you are going to help with the learning cost...sometimes it is the easiest way to keep the relationship and peace.

Since our cars (GTS) lack knock sensors and any real way of hearing detonation (pinging) under full throttle noise, I think burning the good stuff is cheap insurance. Also, I think it is critical to run these race engines on a dyno to get the tuning right. Full load on a dyno would have shown detonation and problem prior to boom! BTW supply the fuel or verify what the dyno tuner will burn.

Kevin

[Cobra4B]

So did you spec out a 12.0:1 compression motor? Or, did you just tell the builder to build you a motor to a certain power goal and he came up with that?

I mean the engine builder should know the compression and advise on fueling accordingly.

[Rich F]

Actually I didn't spec anything. When the motor broke the first time he rebuilt it as I purchased it. Used the same heads with mostly new valves,valve job, valve springs, upgraded the push rods, replaced pistons with new (SRP) as were in when it broke, gaskets, rings, bearing blah blah blah etc.

We did not discuss compression or required fuel at the time. I didn't have the history on the car but thought I'd had an older bone stock 9.5:1 early GTS.

I should have pushed him for more information. The pistons are 0 clearance and the Edelbrock heads are 60cc. He ran a calculation yesterday after I spoke with him about the fuel because thing's just weren't adding up for me.

I'm sure if I pushed the issue he'd eat the whole thing. He's not a jerk and I have a long standing relationship with him. I can call and reach him almost anytime and he'll come to my shop to help me out and it's been that way for about 12 years now.

We both made a pretty big and costly mistake. I made the first before he ever got inside the motor the first time and was pretty dumb on round 2.

It's an expensive lesson both financially and physically with the work required to pull thing apart and put it together.

Even with a lot of experience I messed up.

[PanozDuke]

Originally Posted by boothkc

Well that explains alot. To detonate you either have to have too much timing, compression, not enough fuel, or limited detination margin (ie. octane). Usually, we can't change these easily...

Stock GTS is 10.5:1 (I think) and runs on 110 Leaded.... ie very high detonation margins. Sounds like your builder should have been more specific on the octane required and messed up. Nice you are going to help with the learning cost...sometimes it is the easiest way to keep the relationship and peace.

Since our cars (GTS) lack knock sensors and any real way of hearing detonation (pinging) under full throttle noise, I think burning the good stuff is cheap insurance. Also, I think it is critical to run these race engines on a dyno to get the tuning right. Full load on a dyno would have shown detonation and problem prior to boom! BTW supply the fuel or verify what the dyno tuner will burn.

Kevin

Kevin,
I saw that 110 recommendation in the GTS manual and I think you are correct that the compression ratio is 10.5 to 1. I run a 10.5 302 with 36 degrees of total advance all in at 2200 RPM and have no problem with 93 unleaded pump gas on the track. No pinging until I set total advance north of 38 degrees. I am in favor of having a safety margin, but 110 is what 14 to 1 drag motors usually run.

Can someone explain to me why a 351 10.5 motor @ 34 degrees total advance and aluminum heads needs 110?

What I have believed is that using excessive octane for the compression ratio can cause incomplete burn, lower power and carbon build up in the cylinders (raising effective compression possibly enough to actually bring on detonation at some point and or require reduced total advance and retardation of the advance curve to avoid pinging). I'd really like to understand the relationships.

Mike

[boothkc]

I suspect it has to do with reliability from Panoz on the new cars. 110 leaded seems to be available at every race track in the US. It is "overkill" with very good detonation margins in our mid performance engines. They might be fine with 100 or lower on cool days or less timing etc....but 110 will always be safe. Painful that it runs about $8/gal at our tracks in California, though. Our tracks seem to stock 110, 97, 93 so 110 is the only practical choice.

Aviation fuel (100 low lead) would also be fine as this is about 115 octane if you convert it to the R+M/2 scale we are used to at US pumps and runs about $4.5/gal.

To build a 450hp engine that runs reliably on 110 is pretty easy, but to build one that runs on 93 or 91 takes some serious engineering, electronics, and maybe boosting.

my .02

Kevin

[NZGTRA17]

Originally Posted by Rich F

12.0 to 1 compression 93 octane motor go boom!!

I thought my engine was factory GTS spec. Guess not. 60 cc Edelbrock heads and at or near "0" deck clearance equals lots of compression.

Still going to have the MSD box and distributor checked by the factory.

My builder is providing labor and any machine work at no charge. I'm buying 1 piston, rings, gaskets, 2 valves and some small parts plus the joy of putting the engine back in.

As Kel and others have suggested I'm going to break in and tune the motor on a chassis dyno while in the car. Cost locally for a half day is about $450.00 which should get me 6-8 pulls.
Hopefully on the road to recovery.

Still considering selling after it's back together.

Rich

Rich, you may want to check the calcs on compression. I also run 60cc chamber heads and flat top pistons on my current 347 for approx 10.7 compression. The 12:1 calculation seems to high if your 351 is say .030" overbore and has flat top pistons.

May be worth checking again just to make sure it is nailed.

Kel.

[Rich F]

I have gone through it again with my builder Phil. According to the SRP catalog the flat top pistons I have with a 64cc head on a 351 with SVO block come up to 12.1:1 compression. The heads have been worked (shaved with valve jobs) over the years most recently when I had the engine rebuilt so the chambers are probably a bit tighter.

I have actually had him order new AFR heads to replace the stock GTS Edelbrock heads. Should result in 10.5:1 compression and ability to run pump gas / lower octane fuel but gain HP.

We are also changing the timing cover from the aftermarket part that came with it to a stock for cover due to the size of the water ports.

I think I'm on the right track.

FYI stock Edelbrock heads are now for sale for $350 including rockers as is. The valves in # 1 need to be replaced and valve job done in that hole, along with milling heads to clean them up. Sale price finished would be $600.

[PanozDuke]

Rich,
Sent you a PM concerning your old heads.

Mike

[Rich F]

Originally Posted by PanozDuke

Rich,
Sent you a PM concerning your old heads.

Mike

Mike,
Sent 3 responses and they are not showing up in my sent box. Please let me know if you did not receive any of them. you can e-mail directly rfracer25 at comcast.net.

Rich