Safe EGT'S?

[HotPursuit]

Originally Posted by Throttle Fever

EGT is EGT no matter what the hardware. Take some timing out and then richen up if that doesn't get you down temp wise. As ezstriper said. 1300 is getting warm, iron or aluminum. Probe at the port (is where you want it). What timing are you running?

I have run supercharged engines for 25 yrs now and every set up is different and all EGT gauges are not equal!!
Steel heads will not even come close to handling the same egt that a aluminum head motor can run. Head Heat absorption plays and important part on how much a piston will absorb.
Why do you think mercury started piston oilers??
If your to rich and take timing out the problem will get worst.
Air fuel ratios reading spark plugs and inspecting piston during inspections will give the true meaning to cylinder temps!!
Piston companys can use different slugs that can take anywhere from 1100 to 1500*f and more if you coat the domes. My JE piston cant handle the same cylinder temp as my Aries, If his running stock cast piston were all wasting finger time. I run 1400 to 1500 all day long,,The head water temp never gets above 150. Raise that temp to 200 and everything changes!!

[Young Performance]

I absolutely agree with Keith. Every engine is different and every piston can take varying amounts of heat and temp. In a larger sc engine(over 1000 hp) you would be doing damn good to get egt's under 1400 deg. at steady wide open throttle. Mine will run 1400-1450 all day long and I have never melted a piston. The piston is the biggest deciding factor. The rate at which the head removes the heat of combustion is a HUGE factor. Cast iron heads hold more heat for longer periods. Why do you think you can run more compression with aluminum heads??? They take away the heat and lessen the chance of detonation. Also, water temp plays a big role. You can get away with more on an engine that runs cold. Now, the engine has to be built to run cold. You can't just run any engine without a thermostat at 110-120 deg. You must have the correct piston clearance, etc. Hope this has shed a little light on egt's. You need to know exactly what parts are in it to determine what egt's will be acceptable.
Eddie

[LAKE EFFECT]

I have a couple questions for Young and/or HotPursuit, and I dont want to steal the thread, but I'm sure your responses will help the thread.

I'm running 509cid, aluminum heads, 9:1, JE 2618 pistons, 7/8psi of Procharged/intercooled boost, Blow thru carbs on Victor Jr. intakes, MSD 6M ignition, and Cometic head gaskets. This year I started running a 2 bank FAST wide band and Livorsi EGT gauges. I have bungs welded into my risers, right above the flanges of my GIL manifolds. I usually monitor 1 A/F and 1 EGT per motor. I made it 50/60 hrs this year and pulled the boat still running, but havent pulled the plugs or done a compression check yet. I'm running Autolite AR3911 racing plugs that are a pretty cold plug, and the last few runs of the year, when water and air were colder the engines were loading up and missing. But the boat had ran great up untill then.

Anyways, I few questions. I'm seeing EGT's in the 1450* range when cruising above 3500rpm and they back down to the 1400* range at WOT. A/F is on the rich side at about 10.4 to 10.8 range pretty much thru out my RPM range. Total timing comes in at 3000rpm and is set at 27*. Can running it that rich finally foul the plugs beyond recovery? What is a safe total timing to run with 8psi of boost? Can measuring EGT's in the riser raise the # because of the exhaust flame? (someone told me that might be possible). I'm looking for a good baseline for next season. I was going to lean the A/F to the mid 11's as a start. You guys definitely know your stuff and any advice would be appreciated.

LE

[HotPursuit]

Originally Posted by LAKE EFFECT

I have a couple questions for Young and/or HotPursuit, and I dont want to steal the thread, but I'm sure your responses will help the thread.

I'm running 509cid, aluminum heads, 9:1, JE 2618 pistons, 7/8psi of Procharged/intercooled boost, Blow thru carbs on Victor Jr. intakes, MSD 6M ignition, and Cometic head gaskets. This year I started running a 2 bank FAST wide band and Livorsi EGT gauges. I have bungs welded into my risers, right above the flanges of my GIL manifolds. I usually monitor 1 A/F and 1 EGT per motor. I made it 50/60 hrs this year and pulled the boat still running, but havent pulled the plugs or done a compression check yet. I'm running Autolite AR3911 racing plugs that are a pretty cold plug, and the last few runs of the year, when water and air were colder the engines were loading up and missing. But the boat had ran great up untill then.

Anyways, I few questions. I'm seeing EGT's in the 1450* range when cruising above 3500rpm and they back down to the 1400* range at WOT. A/F is on the rich side at about 10.4 to 10.8 range pretty much thru out my RPM range. Total timing comes in at 3000rpm and is set at 27*. Can running it that rich finally foul the plugs beyond recovery? What is a safe total timing to run with 8psi of boost? Can measuring EGT's in the riser raise the # because of the exhaust flame? (someone told me that might be possible). I'm looking for a good baseline for next season. I was going to lean the A/F to the mid 11's as a start. You guys definitely know your stuff and any advice would be appreciated.

LE

Are you talking about ilde missing , or when your running.
Does it miss after running hard, compared to loading the plugs at ilde speeds. Im thinking you should be able to increase your timing to 30-32 if your running a 116-118 cc head.
Sounds like you have alot of unburnt fuel going out the exhaust. Eddie may comment about the 9:1 which may change the total timing some. If you were running 8.5:1 32 would work, your compression is a little high for a supercharged pump fuel package. Im taking your going by a true cc test
cylinder with piston tdc and head camber + gasket ratios.

[Young Performance]

Actually, 9:1 is perfect on your set up with the centrifugal. They are like screw compressors in that they like some timing. I agree that you should be able to run 31 deg. This alone will help lower the egt's. The more timing you can run, the better for egt's. Your tune is def. on the rich side and very well may lead to high egt's (fuel burning out the head and into the pipes). You need to get the tune closer first, before messing with the timing. Then, the best thing is to monitor knock (I use MSD's knock monitor on carb engines) and raise the timing as much as you can. 3-4 deg of additional timing could possibly lower your egt's by 150-200 deg. Once the engine is tuned and you are running all the timing you can safely run, the egt's are what they are. They will be determined by the combo, parts, cam, quench, etc.
What is your stack height? (total height of piston to deck and head gasket) A larger quench can make an engine more susceptable to knocking. You want under .050 ideally.(.040 compressed head gasket and piston .010 in the hole)

As for the tune, at 3000-4000, in vacuum at steady throttle, you want high 12's to low 13's for economy(***only when you are not in boost***). Under boost at wot, shoot for high 11's. You will start to take a toll on plugs in the 10's. You want idle in the low 13's. Hope this helps you out. Give me a shout if I can help any further.
Eddie

[LAKE EFFECT]

The missing is under load, it idled ok. I drove thru it once, after it got on plane and got some heat in the motors it was running better, the next morning it was missing badly again(under load), that was the day I pulled it.

The compression is an educated guess, the heads are GM Performance oval ports made by Edelbrock, 225/188 valves with a 110cc chamber. They have been milled .008 for clean up purposes. Head gaskets are .060 Cometics, and the estimate on the CR is using JE's specs and playing with desktop dyno.

I'm sure my quench is less then ideal, I did melt #6 piston before monitoring A/F, and EGT's, but I did have a carb issue, and I was playing with timing. I started that season with new carbs after hurting #6 cylinder the prior year(lost psi in a compression test). I ran 30/31* timing all season and bumped timing up to 32* at the end of the year, shortly after I cooked #6. So I'm thinking 31* is the thresshold on this combo.

The combo was put together using parts from my old boat and what I bought with this boat(98' 353). I've been told my cam is less then desireable(its a HP525 EFI cam) for a blower combo, but it does run good, I just want to keep it as reliable as possible.

Boost at cruising is another issue, the motors are showing vacuum under the carbs, but there is 3/4 psi on top of the carbs(using fuel pressure gauges as reference), thats why I kept it rich at cruising. I can definitely play with power valves and jets though.

I will start next season with a little more timing(29/30*) and a leaner A/F and go from there. Any other advice would be great though. Thanks again. I'm sure I will be calling in the future as well.

LE

[LAKE EFFECT]

I didnt mean to steal the thread, and I hope my info and any advise given helps everyone.

LE

[HotPursuit]

Originally Posted by Young Performance

Actually, 9:1 is perfect on your set up with the centrifugal. They are like screw compressors in that they like some timing. I agree that you should be able to run 31 deg. This alone will help lower the egt's. The more timing you can run, the better for egt's. Your tune is def. on the rich side and very well may lead to high egt's (fuel burning out the head and into the pipes). You need to get the tune closer first, before messing with the timing. Then, the best thing is to monitor knock (I use MSD's knock monitor on carb engines) and raise the timing as much as you can. 3-4 deg of additional timing could possibly lower your egt's by 150-200 deg. Once the engine is tuned and you are running all the timing you can safely run, the egt's are what they are. They will be determined by the combo, parts, cam, quench, etc.
What is your stack height? (total height of piston to deck and head gasket) A larger quench can make an engine more susceptable to knocking. You want under .050 ideally.(.040 compressed head gasket and piston .010 in the hole)

As for the tune, at 3000-4000, in vacuum at steady throttle, you want high 12's to low 13's for economy(***only when you are not in boost***). Under boost at wot, shoot for high 11's. You will start to take a toll on plugs in the 10's. You want idle in the low 13's. Hope this helps you out. Give me a shout if I can help any further.
Eddie

Send um to Young Performance.. Sorry bro missed the screw pump not my cup of tea blowing through a carb!!
Sounds like the miss could also be electricial box,coil,wires,low voltage,or plugs shot. Give Eddie a call and buy something he will be ya best friend..

[Rookie]

Great 2nd page of info. Thanks guys.
I use EGT's in my snowmobile as a reference point, keep jetting it down until I burn down a piston, note the EGT temps and keep it jetted under that. I call it the trial and error method.

[Young Performance]

Originally Posted by HotPursuit

Send um to Young Performance.. Sorry bro missed the screw pump not my cup of tea blowing through a carb!!

Yeah man, they are definitely different than the roots. The Whipple is even that much more different than the roots blowers. You have to throw out everything you know about roots blowers and start over. The screw compressors and centrifigals are different animals than the roots blowers. Talk to ya soon.
Eddie