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Miniram - Thermally insulating fuel rails

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Old 04-30-2017, 04:40 PM   #1
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Miniram - Thermally insulating fuel rails

So I started thinking about the fuel getting hot in these fuel rails. Particularly with no front crossover and the fuel essentially dead-heading on the front end of the rails (especially on the side without with the regulator) until the injectors consume the fuel.

What I did was buy some .060" thick PTFE washers and some fiberglass bolts from McMaster Carr. I put the washers between the rail and manifold as well as bolt them in with the fiberglass bolts. The hardware has a max operating temperature of 500F, plus the bolts don't need a lot of torque on them since they're only there to keep the injectors seated. There is now no metal-to-metal contact between the rails and the manifold.

What I'm noticing is a better consistency in how the engine runs between when it's cold and when it's hot. After playing around with the MAT tables for a while and seemingly getting that optimized, I started thinking about the fuel.

Any rate, It's not a huge night and day difference since the car already runs well, but for someone picky like me, I can tell a difference.

When I get home after driving around for a while and the engine is at full operating temperature, I can literally put my hand on the rail indefinitely and and it's just a little above ambient underhood temperature (just a little warm). Where as the manifold itself, I can't keep my hand on it for more than a couple of seconds before it gets too hot to touch.

I'll probably go ahead and put in the front crossover on a little later to get the full effect of this thermal improvement. My guess is I won't see as much as an improvement since the rails are already pretty cool, but I"m still curious and it can't hurt.

What this helps prevent too is the fuel acting like a heatsink and carrying engine heat back to the fuel tank (thereby heating the fuel in the tank over time). Which may help explain the improvement being more noticeable the longer the drive is.

Last edited by ULTM8Z; 05-01-2017 at 10:37 AM.
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Old 05-03-2017, 10:02 AM   #2
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Re: Miniram - Thermally insulating fuel rails

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So I started thinking about the fuel getting hot in these fuel rails. Particularly with no front crossover and the fuel essentially dead-heading on the front end of the rails (especially on the side without with the regulator) until the injectors consume the fuel.

What I did was buy some .060" thick PTFE washers and some fiberglass bolts from McMaster Carr. I put the washers between the rail and manifold as well as bolt them in with the fiberglass bolts. The hardware has a max operating temperature of 500F, plus the bolts don't need a lot of torque on them since they're only there to keep the injectors seated. There is now no metal-to-metal contact between the rails and the manifold.

What I'm noticing is a better consistency in how the engine runs between when it's cold and when it's hot. After playing around with the MAT tables for a while and seemingly getting that optimized, I started thinking about the fuel.

Any rate, It's not a huge night and day difference since the car already runs well, but for someone picky like me, I can tell a difference.

When I get home after driving around for a while and the engine is at full operating temperature, I can literally put my hand on the rail indefinitely and and it's just a little above ambient underhood temperature (just a little warm). Where as the manifold itself, I can't keep my hand on it for more than a couple of seconds before it gets too hot to touch.

I'll probably go ahead and put in the front crossover on a little later to get the full effect of this thermal improvement. My guess is I won't see as much as an improvement since the rails are already pretty cool, but I"m still curious and it can't hurt.

What this helps prevent too is the fuel acting like a heatsink and carrying engine heat back to the fuel tank (thereby heating the fuel in the tank over time). Which may help explain the improvement being more noticeable the longer the drive is.
I've never been able to get a miniram to run consistently. I ran one on my C4 back in 2005-2008, using $8D on a 1227730 ECM.

Now I'm running one on my Formula using a Megasquirt. It still won't run the same day to day.

It's like a carb. I gotta start it, and let it warm up before I try to drive it. Doesn't seem to matter if I add or subtract fuel, play with ae, etc, when it's cold it's a turd. Once it's hot it's fine, but my wideband shows different AFR's from day to day and I can't correct it via IAT because my air temp is almost always consistent because of the blower.

The singleplane wasn't like that.

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Old 05-03-2017, 08:01 PM   #3
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Re: Miniram - Thermally insulating fuel rails

yeah, it's a fickle manifold... and YES, AE was an ENORMOUS challenge to get just right. But I've always loved how the torque curve felt in seat of the pants (not to mention how clean it looks under the hood), so I stuck with it (though I will admit there were times I thought about changing to some other manifold).

I've had to do some re-engineering on it to get it to run the way I want...

A few years ago I generated that separate idle air distribution manifold to avoid having the cylinders competing for air out of the main plenum at idle. That killed of the split BLM issue and smoothed out the idle tremendously (since I couldn't tailor the fuel per cylinder due to batch fire, figured I'd tailor the air instead).

Now, the fuel temperature seems to be making a difference (though again, more slight). I just got my AN fuel line and fittings the other day, so I'll probably generate my front fuel cross over in another week or so when I get the time.

It's funny how GM started the LT1 off in 1992-1993 without a front cross over and then promptly put one back in 1994. Not sure what the reason was for that, but it's curious that the TPI's always had them and then they tried to delete it, but then had to put it back... (unless it had to do with moving to sequential EFI in '94).
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Old 05-03-2017, 10:20 PM   #4
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Re: Miniram - Thermally insulating fuel rails

Ls1's dead head to rails with no return. They run 58 psi fuel pressure to help combat vapor lock in the fuel rails. You could do that as well
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Old 05-03-2017, 10:26 PM   #5
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Re: Miniram - Thermally insulating fuel rails

They're also mounted on a composite manifold which doesn't conduct heat into the fuel rails.
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Old 05-03-2017, 10:37 PM   #6
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Re: Miniram - Thermally insulating fuel rails

True but pressure still combats boiling
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Old 05-03-2017, 11:27 PM   #7
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Re: Miniram - Thermally insulating fuel rails

I don't think I'm boiling the fuel even at 40 psi. But thermodynamically it seems like it's better to have cooler fuel based on my results so far...
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Old 05-03-2017, 11:47 PM   #8
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Re: Miniram - Thermally insulating fuel rails

I don't think I'm boiling the fuel even at 40 psi. But thermodynamically it seems like it's better to have cooler fuel based on my results so far...
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Old 05-04-2017, 08:05 AM   #9
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Re: Miniram - Thermally insulating fuel rails

From what I've seen, generally speaking, a higher psi (to a point) also gives a finer, easier to burn fuel spray. Of course it does depend on inj type some as well.

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Old 05-04-2017, 10:44 AM   #10
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Re: Miniram - Thermally insulating fuel rails

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Form what I've seen, generally speaking, a higher psi (to a point) also gives a finer, easier to burn fuel spray. Of course it does depend on inj type some as well.
Yeah but this isn't direct injection, and it's not sequential. We're firing the injector at a closed intake valve 90% of the time. It puddles up, and then the valve opens and it atomizes again.

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Old 05-04-2017, 11:13 AM   #11
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Re: Miniram - Thermally insulating fuel rails

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Yeah but this isn't direct injection, and it's not sequential. We're firing the injector at a closed intake valve 90% of the time. It puddles up, and then the valve opens and it atomizes again.

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Oh yeah, a lot of truth to that to. A lot of shortcomings with the MR intake/stock ecm on these cars.
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Old 05-04-2017, 02:42 PM   #12
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Re: Miniram - Thermally insulating fuel rails

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Oh yeah, a lot of truth to that to. A lot of shortcomings with the MR intake/stock ecm on these cars.
I looked at the tune for my '94 Corvette and it's got crazy cylinder trims for the injector offsets. These intakes just don't fair well with batch fire.

The Corvette also has a hybrid MAF/MAP fuel blend.

I'm not willing to upgrade to an MS3 for sequential though.

I'll get it 'close enough' but it won't be perfect.

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Old 05-04-2017, 08:01 PM   #13
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Re: Miniram - Thermally insulating fuel rails

I've had my miniram for 14 years and it has always ran well. It's got distribution problems at low rpms but the tune will solve most of it. I can start it up n drive it immediately with no issues. The only issue I have is the fuel getting hot. I've got my rails fed from the front with a y off the feed line with the stock regulator return setup. On a hot day it will lose 4 psi when it gets heat soaked every time. I still can't figure out if it's the excess flow or the exhaust heating up the fuel pump. I know my pressure loss is coming from the pump because I can hear it change pitch when it does this. Might just be the nature of the beast with a 255 pump in a return system
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Old 05-05-2017, 09:54 AM   #14
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Re: Miniram - Thermally insulating fuel rails

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I've had my miniram for 14 years and it has always ran well. It's got distribution problems at low rpms but the tune will solve most of it.
How does a batch fire tune solve cylinders having different air distribution?

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Old 05-05-2017, 10:14 AM   #15
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Re: Miniram - Thermally insulating fuel rails

It doesn't but I've worked around it to make my car every day driveable. I run open loop only because my particular engine hates stoic at anything other than very light throttle cruise. Normal cruise it likes 13.5-14. Mild to heavy acceleration it wants 12.5-13.5 n it's silky smooth. At 14.5 it will buck n jerk like crazy. That's because of my cam n intake I'm sure. Back 4 plugs are always darker than the front but I did a compression test at 10,000 miles n I'm within 3% on every hole so no washdown worries. Even gets 22 mpg on the open loop tune. I like the fibreglass bolt n spacer idea though. I'm gonna give that a shot every little bit does help
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Old 05-05-2017, 10:20 AM   #16
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Re: Miniram - Thermally insulating fuel rails

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It doesn't but I've worked around it to make my car every day driveable. I run open loop only because my particular engine hates stoic at anything other than very light throttle cruise. Normal cruise it likes 13.5-14. Mild to heavy acceleration it wants 12.5-13.5 n it's silky smooth. At 14.5 it will buck n jerk like crazy. That's because of my cam n intake I'm sure. Back 4 plugs are always darker than the front but I did a compression test at 10,000 miles n I'm within 3% on every hole so no washdown worries. Even gets 22 mpg on the open loop tune. I like the fibreglass bolt n spacer idea though. I'm gonna give that a shot every little bit does help
That's funny. I've found the same thing. Open loop, slightly rich and it's fine. But it's hard to start sometimes, and the warmup is inconsistent.

I don't really care about closed loop correction on a hot rod. I just like being able to modify my fuel and spark curve with the laptop.

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Old 05-05-2017, 10:31 AM   #17
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Re: Miniram - Thermally insulating fuel rails

That is weird because cold start and warm up driving have never been an issue. Left those tables mostly stock. Always fires within 2 seconds. Fuel heating is really the only thing I have left to figure out. It will start to buck a little n I look at the fuel pressure gauge to see the pressure drop n then the wideband confirms it
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Old 05-05-2017, 10:33 AM   #18
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Re: Miniram - Thermally insulating fuel rails

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That is weird because cold start and warm up driving have never been an issue. Left those tables mostly stock. Always fires within 2 seconds. Fuel heating is really the only thing I have left to figure out. It will start to buck a little n I look at the fuel pressure gauge to see the pressure drop n then the wideband confirms it
The fuel heating is probably why mine run inconsistently. My engine bay gets stupid hot with the supercharger. I've measured 250 degrees on some surfaces, yet water temperature stays around 185-195

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Old 05-05-2017, 10:48 AM   #19
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Re: Miniram - Thermally insulating fuel rails

Your blower gets hot?? Try twin snails
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Old 05-05-2017, 10:55 AM   #20
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Re: Miniram - Thermally insulating fuel rails

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Your blower gets hot?? Try twin snails
I tried a single, and it was melting my wire looms.

I'll keep the turbos on my diesel trucks, and blowers on my cars

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Old 05-05-2017, 11:13 AM   #21
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Re: Miniram - Thermally insulating fuel rails

I guess my fiberglass hood is working well for me. I've measured the blower at 125* at idle. Nothing near 250 besides the headers. That's crazy hot n definitely could be ur problem!
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Old 05-05-2017, 12:05 PM   #22
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Re: Miniram - Thermally insulating fuel rails

My fuel rails get hot but never had an issue with pumps or performance. Single plane efi ftw
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Old 05-05-2017, 05:28 PM   #23
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Re: Miniram - Thermally insulating fuel rails

I've started driving my Trans Am again with the Minirammed 385. I run a FAST XFI fuel injection system (serial number 026) with really old firmware - and it's still currently batch fire. I'm considering buying the FAST distributor and converting it to sequential fuel injection so that I can fiddle with fuel trim on the cylinders. I've created an eight-channel EGT module, and I have eight EGT thermocouples, but no holes in my headers as-of-yet....

My problem isn't in starting, it's in the fact that when things get hot, part-throttle cruising around town, it will sometimes backfire into the manifold and snuff out the engine for a second. It seems to lean out under some conditions and cause the pop.

I haven't ever figured out a way around it. Maybe double the Accelerator enrichment curve? I just don't quite know where to go on the tune.

Oh, and... hello to all you long-term third-genners on this thread ! It's been quite a long time since I played with cars. I took almost seven years off. How did that happen?
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Old 05-05-2017, 08:39 PM   #24
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Re: Miniram - Thermally insulating fuel rails

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I've started driving my Trans Am again with the Minirammed 385. I run a FAST XFI fuel injection system (serial number 026) with really old firmware - and it's still currently batch fire. I'm considering buying the FAST distributor and converting it to sequential fuel injection so that I can fiddle with fuel trim on the cylinders. I've created an eight-channel EGT module, and I have eight EGT thermocouples, but no holes in my headers as-of-yet....

My problem isn't in starting, it's in the fact that when things get hot, part-throttle cruising around town, it will sometimes backfire into the manifold and snuff out the engine for a second. It seems to lean out under some conditions and cause the pop.

I haven't ever figured out a way around it. Maybe double the Accelerator enrichment curve? I just don't quite know where to go on the tune.

Oh, and... hello to all you long-term third-genners on this thread ! It's been quite a long time since I played with cars. I took almost seven years off. How did that happen?
Without seeing actual data, it's hard to pinpoint a cause.... but I will say that based on my experience, you're going to want to play around with stuff that varies your fueling with temperature...

Things like... (and these may 7730 specific, so I'm not sure what you're running)

Accelerator enrichment....

AE delta TPS vs coolant
AE delta map vs coolant


Air temp.... not sure what kind of intake ducting you're running, but if you're still running the old TPI Inv MAT Term Lookup table you're going to have problems (especially on a Miniram).

I've also had a lot of success with the AE TPS scale factor in the fuel constants table (note this is NOT the PW scale factor). THere are two requirements that read very similarly. Both are set to .125 from the factory, but I have my AE delta TPS scale f factor set at .300. It seems to make the AE delta TPS react much faster (solving my neutral throttle blip hesitation issue).

Any rate, if you're running a 7730 ECM, PM me your e-mail address... You can try my Miniram Start Bin 2.0 and see if you get better tuning results using that as a baseline.
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Old 05-20-2017, 09:44 AM   #25
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Re: Miniram - Thermally insulating fuel rails

I made an interesting discovery yesterday. I pulled the passenger side fuel rail to start drilling for the front crossover. Fortunately I started examining it more closely before I started drilling.

Started examining the interior found that it consists of two passages that run the length of the rail. An upper and a lower passage. The main fuel line coming in at the rear feeds the lower passage which the injectors draw from. At the front, the lower passage connects to the upper passage which then runs all the way back to the rear and feeds the rear crossover. I didn't pull off the driver side rail, but my suspicion is that the fuel enters the upper passage from the crossover, runs to the front where it connects to the lower passage. From there, it runs back to the rear, feeding the injectors with the excess exiting out the regulator.

So in effect, the front crossover is integral into how the fuel rails are designed, such that the fuel doesn't dead head into the front of the rails after all.

Thermally insulating the rails themselves seems to be all the optimization it needed.

Last edited by ULTM8Z; 05-24-2017 at 06:56 PM.
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Old 06-18-2017, 07:14 PM   #26
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Re: Miniram - Thermally insulating fuel rails

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I've started driving my Trans Am again with the Minirammed 385. I run a FAST XFI fuel injection system (serial number 026) with really old firmware - and it's still currently batch fire. I'm considering buying the FAST distributor and converting it to sequential fuel injection so that I can fiddle with fuel trim on the cylinders. I've created an eight-channel EGT module, and I have eight EGT thermocouples, but no holes in my headers as-of-yet....

My problem isn't in starting, it's in the fact that when things get hot, part-throttle cruising around town, it will sometimes backfire into the manifold and snuff out the engine for a second. It seems to lean out under some conditions and cause the pop.

I haven't ever figured out a way around it. Maybe double the Accelerator enrichment curve? I just don't quite know where to go on the tune.

Oh, and... hello to all you long-term third-genners on this thread ! It's been quite a long time since I played with cars. I took almost seven years off. How did that happen?
If you ever decide to do the sequential jump send me a pm. Im switching over to a Holley DIS and I have a in new condition dual sync Fast distributor. Time flies I guess. You get caught up in life and other things.
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Old 06-18-2017, 07:21 PM   #27
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Re: Miniram - Thermally insulating fuel rails

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I made an interesting discovery yesterday. I pulled the passenger side fuel rail to start drilling for the front crossover. Fortunately I started examining it more closely before I started drilling.

Started examining the interior found that it consists of two passages that run the length of the rail. An upper and a lower passage. The main fuel line coming in at the rear feeds the lower passage which the injectors draw from. At the front, the lower passage connects to the upper passage which then runs all the way back to the rear and feeds the rear crossover. I didn't pull off the driver side rail, but my suspicion is that the fuel enters the upper passage from the crossover, runs to the front where it connects to the lower passage. From there, it runs back to the rear, feeding the injectors with the excess exiting out the regulator.

So in effect, the front crossover is integral into how the fuel rails are designed, such that the fuel doesn't dead head into the front of the rails after all.

Thermally insulating the rails themselves seems to be all the optimization it needed.
Why do you think the heat is doing anything to the fuel? It may be those passages as long as they are are keeping the fuel in there longer because some parts of the rail is just a passage way. I would say if your tank is full and you have the heat shield on it even if the fuel gets warm ,the dump to the tank and new pickup negates any heat. I have the earls braided nylon line for a feed. It doesnt pick up heat thay can be transfered from underneath the car. I just say this because the factory design actually puts the rails down on the hotter lower manifold vs the top like the MR. And there was never an issue. Coated headers, maybe wrapping reflective heat tape on feed lines. Alot of ground to cover.
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