EGT probe location

[Underdog88]

I have EMI thunder exhaust on my mild 454s and a set of 4 SS Competition egt gauges and probes(Thanks Bob!). My original plan was to mount one in each collector where I have a 1/2" aluminum wedge spacer to align my tails. This would give me a read on each side of each engine.

I've read where they should be placed @2" from the exhaust ports for best reading and can see where my original plan would give lower reading due to the distance and the water cooled manifolds.

It's going to be tuff to find a place in the manifolds while staying out of the water jackets. I may be able to put them in the rear of #7 and 8 cyls in the rear but space is very limited on the manifolds. I've attached some pics...

I'm asking for any suggestions and wondering where you guys who have them have installed them. Would the collector/wedge be so bad? I know the reading would be cooler but while reading plugs and using an Innovat wide band O2 sensor for tuning, I have access to, couldn't I get a baseline number, even though less than optimum to watch for?

What have you done and what would you do? Drill manifolds,(looks tricky) or used collector/spacer with lower temps compaired to O2 readings and plugs.

Thanks for your input!
Mark

[Underdog88]

Anyone got any advice on this one?
Thanks

[Rookie]

I think EGT's are good for reference. Tune it in with the plug readings and AFR. Note what the EGT's read at this point. If you see any changes then shutdown and investigate. Take my snowmobile for example, there is a difference weather I am 6" or 8" from the center of the piston. Hotter at 8". And for reference on my sled 1280*F is good and 1360*F silver coats the the inside of the exhaust pipe. *Note* add jet at 1360*F

[Ratickle]

What about drilling and tapping the head itself above #1???

[Underdog88]

What about drilling and tapping the head itself above #1???

I don't think I have room but I'll check it out. Thanks

Rookie, Kind of what I'm thinking by putting them in the spacer/collector. Find the right setup and use those numbers. Whatever they may be. shrug

Thanks for the replys.
Mark

[Ratickle]

Did you add them? If so, where and how are they working?

[Underdog88]

I did. I put them in the wedges. Install went fine but I havn't hooked them up yet. LOL Going to this spring to get a reference point. It runs great as is with the 750 Ebrocks but I have a set of 850 Holleys to try. This will help in the set-up of those.

[Underdog88]

BTW I hate when someone starts a thread like this and never posts the end results! ha ha
I forgot about it... Soon as the weather straightens out I'll wire up the power supplys and post some numbers.

[Spencer]

Just out of curiosity, why are you installing temp senders? I could see it if you were running turbos (which you may be) but for anything else, O2 would probably be more useful.

[Underdog88]

Agreed. Short answer is I got a great deal from SS Competition when I bought my all my new gages on Bob's lightly used set he had for his blower boat.

I have an Inovate A/F meter we use on the Dyno for motorcycles. The Bosh sensor won't fit in the spacer and can't get wet. I can use a temporary mount w/an extension on the tails to check one bank at a time. It belongs in the bike shop and can't be left on the boat all the time. I'm going to try and use both when dialing in the new carbs.

[Ratickle]

Weather's almost good enough to start thinking about that dial in.....

[Hellbent]

Ahhhh.....good 'ol EGT's....lol. I've seen them do more damage than good in my years I think. Not by fault of the sensor mind you, by fault of the operator's tuning based on EGT readings. You should NEVER tune based solely on EGT readings. Quite honestly, having only 1 per side way back in the wedge isn't going to tell you much of anything anyways. To get the information you want they need to be 2-3 inches away from the head. This distance is important because a lot of things are going on as your exhaust is exiting the cylinder head. If you put them too close you may be surprised to find that your readings can be much lower than if they were an inch further out in the pipe. I mean a few hundred degrees lower. This is because when you have a rich condition you're actually dumping unburnt fuel out into the exhaust where it will typically detonate but not before it washes down your sensor and gives you a low reading. Additionally, that fuel igniting in the pipe can also give you a false high reading. Basically, rich conditions are a bitch to measure with an egt and lean conditions aren't much easier....lol. I couldn't tell you how many guys I've seen make tuning adjustments based on egt's and melt down their mill on the next pass. They're a reference only. In a case where you have a data logger and are measuring all 8 egt's along with a lot of other things, that information can be very valuable to a person who knows what to do with it. For example, that's what first tipped me off that I needed to taper the jetting on my tunnel ram. Upon launch, inertia was forcing more fuel to the back of my tunnel ram which richened up the rearward holes. It was barely enough to see on the plugs, but it was real obvious when looking at egt readings. They can be a great monitoring tool. If you're watching an egt reading (snowmobiles are a great example) you can often times save yourself from a meltdown. But very few guys are walking the rich/lean line that a snowmobile lives in every day. The plugs should ALWAYS be your most important tuning reference regarding fuel/air mixture!!

Okay...that's my novel for the day

[old377guy]

good stuff - hellbent

[Hellbent]

Behind that post is a lot of piston ashtrays and several bags of oil-dry used at drag strips across the Midwest....lol.

[Underdog88]

I hear ya HBent. Kinda why I havn't rushed to hook them up yet. But they're on there and won't hurt anything unless do something stupid w/the data.
I'm running a pretty safe mixture now and just going to use whatever numbers I get with these carbs as a baseline when I put on and jet the 850s. Not a substitute for plug readings. Just one more bit of info.
I too have a bunch of melted pistons from my nitrous drag bike daize.
Rat. We had sleet here today... 80s and boaty in March but not April.

[keith2500hd]

i have seen the aluminum exhaust cylinder spacers drilled and tapped, wired to log all cylinders. spacers suck on tight engine spacing. cpperformance has riser spacer with O2 sensor port and plug.

[Ratickle]

We did that on the dyno, but not in the boat.....

[Tinkerer]

I know it is too close but I drilled my heads right next to the flange. Works great.

[Ratickle]

Have some pics? And what do they read? Do you think they are pretty accurate where they are?

[Tinkerer]

I don't have any pics handy. But I did this on the stock heads also. I looked at a cross section of the heads at that point and felt there was enough meat there to go for it.
All I can say is when they read 1425* I tend to back out of the throttle. I have my engines dialed in preatty close. Dry cool day I have to watch the EGT's. They usually run about 1350 to 1375* WFO. I did watch plug color when dialing them in. OH and If they go over 1450* I tend to remould the eyebrow on the pistons. BTDT. I don't have a lot of room between the pistons and the valves. My pistons come up level with the block. Head gasket is the only clearance. Been a while since I built these engines so I don't remember exact VTPC but .080 comes to mind.