High IATs? Supercharged EFI no intercooler

[Dr J]

After doing an EFI conversion and street tuning most of the VE table, I decided it was time to reinstall my rebuilt supercharger and take it to a dyno to tune boost and high RPM sections. When I talked to the dyno guy I told him I would have the supercharger belt off until I got there to ensure I don’t get into boost. He said to use the engine protect function of the ECU and limit MAP to not allow boost. So I did that and it worked. But, as I drove the car, I found something that concerned me.

Having IAT readings for the first time, I saw that it went very high when accelerating, even at a very conservative rate. They would go 150F or even 180. I’m sure I could get it to 200, and this without boost!

So I completed installation of a water meth kit to discharge at the inlet to the supercharger and used water alone to see if it helps. I did not see significant improvement in temps. So I calculated heat transfer from water at 90F to IAT at about 150F and found that it doesn’t have a big impact, particularly since the water doesn’t change states until 212F. I did not account for any evaporation since there is high humidity here anyway.

With the supercharger removed, there are no IAT issues.

I have a blow off valve and can feel the hot air come out of it when I manually rev the engine, and feel the bypass air. Also, the high IAT lingers for a few minutes which I believe is due to the response time of the “fast acting” GM IAT sensor. I took out the sensor to check that it is operating well and saw that the plastic protector at the tip of the sensor was curved. When I touched it, it came apart. The sensor though seems to work well, responds to temp changes and is close to coolant temperature and ambient temperature when first started.

So, based on the experience of others, are the IATs too high?

Any suggestions? An intercooler would be difficult since the supercharger takes 1/3 of engine bay, I have an AC compressor and a mounting platform for other sensors near the throttle on the passenger side.

Supercharger is a whipple twin screw. There is no intercooler. Water injection nozzle flows 350 cc/min though I can lower it to 170 by PWM the pump. This data was obtained via testing. The air intake is through cylindrical K&N filter close to the firewall.

[Dr J]

Some pics of filter placement



Water injection detail:



Deformed sensor tip

[RarlyL8]

Do you think the supercharger is getting heat soaked? I've seen tiny air/water intercoolers for superchargers that are simply a plate that bolts to the SC outlet. You probably have room for one of those but then there is the plumbing and radiator.

[patkeefe]

Dr J, what sort of induction system are you using on the converted SC, and where are you measuring the intake air temperature? In my turbo SC, I had two temperature sensors; one at the intake of the air filter, and the other inside the airbox plenum. I rarely saw inlet temperatures at the plenum sensor above 200F, and my water injection cooed this down almost instantly to just above the airbox plenum temperature, which always seemed to be around 150F, no mater what.

[Porsche 935]

Are you running just water or methanol and water. The methanol will help cool the charge.

[Tippy]

Yes, those temps are super high.

Under 1.4 bar of boost, I don't see more than 10-15 degrees over ambient with a full width IC (I have the same fast response GM IAT). In my case, I have the Treadstone TRST9 intercooler:

https://www.maperformance.com/products/treadstone-performance-trst9-series-intercooler-trstp9

[Dr J]

Thanks guys for the replies.

RarlyL8
I haven’t run it enough to get heat soak. The temp changes are seen when I press the throttle even when the car is relatively cold.

Pat
The induction is SC but I use a metal version of the airbox. The temps are taken post Supercharger, pre throttle body, in the tube connecting the two.

Porsche935
So far using just water. Methanol should help due to the lower boiling point. Am having some difficulty finding -20 deg washer fluid in Miami. May have to mix my own.

Tippy
Thanks on the heads up wih the treadstone. I have seen someone’s neat install with fan and all here on pelican, but it may be a nightmare with the space. Maybe the water air RarlyL8 was mentioning.

For now I am going to use a thermocouple and independently get some charge temps. Can’t get to it this week so I will post next week with results.

[MikeD930]

Dr J...I'm confused here...are you getting high intake temp with a blower belt on but currently running low boost (or none) by having a BOV bypassing the boost? If yes then perhaps it's the blower that is heating up the intake charge even though there's no boost to the engine. Also, maybe the blower speed is too high.

[Dr J]

The BOV lets the air out at idle, where there is no heating issue. As soon as manifold pressure values increase by accelerating, the BOV shuts the flow to atmosphere allowing the air from the blower to go to the intake only. That is when the IAT increases.

[kuehl]

Intercoolers make a world of difference, and the bigger the better to some extent. You can see this when you have air temp sensors on both ends and record the data in the AEM or toss it up on a gauge.

In the meantime, make sure your BOV is venting outside of the engine bay rather than dumping all that heated air in the bay. On my 87 cab we ran a pipe out through the grommet hole in the RH inner fender wall that was used for the carbon canister hoses.

[spence88mph]

Can you fit a water to air in there? I think it will be your best bet. Congrats on getting EFI running, to be honest I would switch to turbo, I think supercharging just over complicates boost on a 911, I've been on this forum for a long time and never seen any compelling reason to go super, quite the opposite. A turbo and set of 930 headers is not a big $ switch and will rid of these headaches.

[Tippy]

Originally Posted by kuehl

Intercoolers make a world of difference, and the bigger the better to some extent.

Couldn't have been said any better..

[kuehl]

Fun to play with
Relative Horsepower Calculator Relative Humidity Factors


Comparisons
The Effects Of Temperature On Horsepower


reading to put you asleep:
Comparison of Engine Power
Correction Factors for Varying
Atmospheric Conditions

[Dr J]

Originally Posted by kuehl

In the meantime, make sure your BOV is venting outside of the engine bay rather than dumping all that heated air in the bay.

Good point. Currently venting to engine compartment though far from the air filter. I can easily port it out the hole previously used for the air injection to the exhaust. I was hoping to recirculate for noise reduction but not until I have a good handle on the temp issue.

Spence88:
I'm already all set up for the supercharger. Going turbo will be another couple of grand when I'm so close here with all of the engineering done. If the supercharger dies, then I will reconsider it. I think I would try intercooler first since I would most likely need if I went turbo.

Thanks Kuehl for the links. Will be reviewing them.

[kuehl]

Heat going into the engine bay from the BOV also enters the engine cooling fan which passes it on to the cylinders and the oil cooler. So we did not use a 'whistling' vent on the BOV and chose the straight snorkel which made it easy to attach a reasonable size high temp hose to it and route it out through the inner fender on the right side; this also cut down on a noise you'd hear through the rear plastic window on the cab top; making driving more relaxing; you don't want loud mufflers either.

So ya kinda want to ensure you section in where the air is going using baffles.
We wanted to keep the stock decklid look, try to get as much air through the intercooler rather than around it, and provide a separate entrance for the air we burn and use to cool the motor. Had to put on and take off the wing quite a few times, drive it for a few days in between to see what works and what does not work. And, naturally, when you got "stuff" in odd places on a motor you end up spending more time doing more 'stuff'. But, its a lot of fun.

Thinking back, would I do a turbo rather than a supercharger? Maybe, however, the instant linear torque is satisfying.

Oh. Yeah. That's one busy engine bay. I never get bored looking at it.

[dannobee]

Way back when, I used to drag race with some guys who used air to liquid intercoolers. Their cooling medium was isopropyl alcohol and dry ice, recirculated through some kind of small electric pump. That mixture is good for about -110 deg F, IIRC. The outside of the intercooler would be a big ball of ice after the runs.

[Dr J]

Ok. Took a while but finally got back to this and managed to find the problem so I am posting to show the resolution.

The root cause of the high IATs was the blowoff/bypass valve plumbing. In my configuration with EFI in speed-density configuration I did not need to recirculate the air so I used the valve in a blow-off configuration. In a turbo setup the blowoff valve operates when there is hard vacuum such as when you get off of the throttle. However, in a supercharger setup, the blowoff valve should be operating during idle and part throttle. It should only shut down on hard acceleration.

When I plumbed the blow off valve I plumbed it off the bottom port in the front of the throttle body. In that configuration the blow off valve would shut down as soon as you go off idle. Because the twin screw supercharger compresses the air whenever it is spinning, the air to the intake would heat up even though the engine was still operating in vacuum.

The solution was to plumb the blow off valve from the back of the throttle body, where the old decel valve used to be. Now it gets good vacuum signal all the time that the manifold is at vacuum so air intake temps increase only slightly during idle and cruise. Of course, the IATs should increase on boost but that is expected. Moreover, once off high load, the IATs will quickly cool back down. Now I can finally drive the car with the supercharger on.

Another suggestion I followed is moving the bypass air out of the engine compartment. I used the empty hole in the engine tin that was used to recirculate air to the exhaust. Now the air comes out of the engine bay. The hole was the right side when using 1in silicone tubing. Another plus was toning down the “noise” inside the cockpit.

Now that that issue is solved I can continue mapping the VE table on boost. With the Infinity ECU I can set engine protect at whatever boost level I want so that I can safely map that region of the VE table.

Thanks to all for your suggestions. I think I will keep the water methanol setup and not use the intercooler. For my setup the only reasonable intercooler I could fit was an air/water unit.

[Dr J]

The cable coming off the supercharger out the engine bay to the left was a thermocouple I used to verify the IATs of the IAT sensor.

[Black_Hat]

https://www.amazon.com/Torco-Nitro-100-Methanol-gallon/dp/B0065630E6/ref=sr_1_1?dchild=1&keywords=methanol&qid=1586910510&sr=8-1

[Fever]

Intercooling is a must have!, for lower iat’s!, Rigo.