Getting head temps down, I also need Megasquirt 1.7 STOCK fuelmaps Options

[bd1308]

So this gets much broader than a drip pan removal.

I need like 20 degrees. I only hit 400 if i am really hard on the car or if i'm on the expressway.

I adjusted the dwell a while back, but I dont remember what I ended up setting dwell AT. I think it wouldnt go past 40 degrees or something, which puzzled me.

See, this all started when I hooked up my new CHT guage. First thing it tells me is that i'm running real hot.....thanks (IMG:style_emoticons/default/headbang.gif)

I'm already building a zero-mile engine, along with a rebuilt 1.7 engine as a spare....

I also would like fuel maps for a stock 1.7 engine...I have a MS computer I am planning to install, and I know someone has the maps for a 1.7 engine somewhere. I will be gutting a laptop and installing it into a centre console for my guage set as well. (IMG:style_emoticons/default/wink.gif)

Engine is a 1.7 engine with *ALL* 1.7 components.

oh and BTW, the sender for the CHT is on cyl #3. I just did a valve adjustment using a tight .007 feeler guage gap.

b

[Bleyseng]

Is it a VDO CHT gauge? Is it set for the outside temp of 70 degrees so if you are driving around in 80 degree weather its gonna be off.

Are you running djet or the ljet now? Adjust the a/f ratio and toss the points and get electronic stuff and set the timing to 27 degrees BTDC at 3500 rpms for Djet and 7.5 degrees BTDC at 950 rpms for Ljet using a timing lite.
Bad too far advanced timing can raise the temps rather high. (IMG:style_emoticons/default/mad.gif)

[Brett W]

Too far advanced timing will not raise head temps. Timing that is too retarded will raise head temps and put lots of heat into the exhaust. Try adding a couple of degrees to your timing. Run the engine and see if it pings. If it doesn't add some more timing. Most stock engine will like 30+. Are you running premium or 87 octane? Premium can raise head temps a little if you have too low a compression ratio.

[bd1308]

I run premium fuel, due to the high compression of the 1.7

I'll do some testing (IMG:style_emoticons/default/wink.gif)

b

[lapuwali]

Which year is the 1.7, and is it still stock? The '73 1.7 had the compression ratio lowered to run on regular gas.

[Bleyseng]

I thought that spec was for Calif only 1.7L. The rest of the USA got the 80hp engine.

[bd1308]

its a EB engine I think.

It had the 1973 only paper round filter on it, so I would assume its a 73....stock.

which means i wasted $$ and heated up the heads from premium gas?

so....it was high 80s yesterday maybe it was just reading too high? I dont understand how outside temp even has a influence on the CHT guage....

I'll put regular in it next time and see what happens to the head temps....i can always go up in grades....

b

[r_towle]

Slow down.
Do the proper engineering diagnostics we all know you can do.

Set the valves, then set the dwell, then set the timing...all BY THE BOOK.

then run some tests, and look at your results based upon outside temp, along with driving conditions..RPM of motor etc...

Rich

[Mueller]

PM Fiid, he might still have the config setting from his original 1.7 install.....you should be able to use a 1.7,1.8 or even a stock 2.0 to get close enough start the car and be able to tune it with a WB02

[Brett W]

Compression ratio is not that high. Run it on 87 first.

[lapuwali]

Most CHT gauges (including the VDO) use a thermocouple as the sensor. Thermocouples generate a voltage based on the difference in temperature between the two ends of thermocouple wire (any pair of dissimilar metals will do, but certain metals are used for calibration purposes). The "reference" temp (the "cold" end) for the VDO is assumed to be 70dF. So, the gauge shows the difference between the "hot" end (at the plug) and whatever temp the "cold" end sees, adjusted so a 70dF "cold" end shows 0dF on the gauge.

So, if it's colder than 70dF, the sensor will see a larger difference for the same head temp, so the gauge will read high. If it's hotter, the gauge reads low.

Dakota Digital makes a (much more expensive) gauge that's compensated for ambient temp differences, using thermistor to measure ambient temps.

They don't use thermistors for most head temp sensors, as themistors tend to flake out beyond 250dF or thereabouts. The stock D-Jet CHT is a thermistor, but it's positioned in the head to top out at roughly 220dF, and it's only measuring temps colder than this, anyway (warm-up sensor). Thermocouples have higher and wider temp ranges, are generally more accurate, and typically react faster, than thermistors. However, they also generate very small voltages (0.1-0.5 mV), and very small differences make a big difference to the measured temp. I think the difference between 300dF and 500dF is under 0.2mV. So, you need an accurate, non-distorting amplifier, or a very sensitive gauge movement, to use them. This is why the CHT gauges are all over $100, where a water temp gauge is under $40.

If it's 90dF outside, add 20dF to what the gauge shows to get the actual head temp. If it's 50dF outside, subtract 20dF.

I have no idea how accurate the VDO gauge actually is, and I'd doubt if it's much better than 10dF. Unless it's blazing hot out, or freezing cold, I'd not worry much about the ambient temp variance.

From what data I've been able to glean from Jake, a stock D-Jet engine will NORMALLY see 375dF or thereabouts under load, with spikes to 405 or so if you're climbing a grade. This has to do with a head and cam design more optimized for emissions than cool running or power.

[bd1308]

the new engine I am planning to build will contain a better cam for cooler running...I was thinking the 9550.

b

[Mueller]

the new engine I am planning to build will contain a better cam for cooler running...I was thinking the 9550.

b

one thing nice about the MS is that you can run any cam you can readily purchase......

going to keep it simple with a single plenum design and a single throttle body??

[bd1308]

Yes. From what I read, independent throttles are very pricey and would definately set me back a while...I'd rather use the KISS method and just use the 1.7 plenum.

b

[swl]

James,
Thanks for the great explanation of how these guages work. Certainly you need to know the accuracy of your guage before you do any troubleshooting based on it.