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Mailbag: fuel injection ahead of supercharger?


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Gene wrote:

Hi Bruce, I have read a few of your posts on a Cadillac forum about the 4.4L super charged engines. I have a series of rather offbeat questions. Do you suppose this engine  could run with the EFI injectors running on the input side of the super charger? I am not trying to achieve greater HP. I am wanting the Super Charger to act upon the A/F mixture to increase vaporization.  
A penny for your thoughts.
Thanks!
Gene
 

Bruce

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It is possible, but it might not be ideal.  The supercharger gets hot from the compression of the intake air, so you could actually have detonation in the blower.  The supercharger blades and seals would degrade from passing more than air.   Gas doesn't compress as well as air, and compression of the fuel air mixture might also cause detonation (dieseling).

Bruce

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Gene wrote:

 

Do you have any idea how hot the SC might get? I am shooting for 300F in the intake. Is this intake plastic or aluminum or?

I would elevate the A/F mixture in temperature to arrive at the intake of the SC at about 200F. This should make compression easier/less risky.

Bruce

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The lc3 intake tubing from filter to s/c is metal; then the supercharger sits on top of the block. The supercharger is aluminum I suppose. The MAT can be over 212F but I sustect the s/c itself (not the air flowing through) is 240+ but yes under 300F.   The reason people avoid meth thru the blower is to protect the blower so I do think that is a concern.

What is the application? In an sts-v or another platform?

Bruce

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Gene wrote:

Just as a potential test mule at this point. You are the first person I have known who understands these engines.

The Meth would be a cold mist right? My plan is for an interheater between the injectors and the SC intake to bring the A/F up to around 200F is so. Final heating would be done with the engines normal intercooler. Dimensions might have to be adjusted to accommodate the thermal expansions.

Bruce

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Yes the meth is used to reduce intake temps and richen fuel air. The more heat the less power.  My intuition is you lose much more by injecting fuel ahead of the blower than you can gain in mixture quality but keep me posted on your project.  

Bruce

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Gene wrote:

The plan is to have a very low heating capacity that is overwhelmed as throttle is applied and flow increases  allowing for good power, though somewhat less, when the foot is put into it.

Working out these thermal time constants and heat transfer rates is the fun part.

Bruce

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I'm not even close to Bruce when it comes to familiarity with the engine but I am curious how pre SC fuel injection would be possible. 

THERE IS ALWAYS ENOUGH TIME TO DO THE JOB RIGHT - THERE IS NEVER ENOUGH TIME TO DO THE JOB AGAIN !!!

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18 hours ago, OldCadTech said:

I'm not even close to Bruce when it comes to familiarity with the engine but I am curious how pre SC fuel injection would be possible. 

Many old school street SC engines ran Roots style blowers with the carburetors on top of the blower. Newer engines put EFI injectors (Pro-Jection, etc) on top of the blower in place of the carbs. Serious racers who want even more power, cooler Air/Fuel, will put the injection under the SC. In my case, I am not trying to cool the fuel, actually the opposite. I want to transfer engine heat, water heat, oil heat, exhaust heat if needed, to the intake charge. But, I only want to have enough heating capacity to affect the lower RPMs. As my foot goes into it, I want the added fuel to cool the intake and start cooling the A/F mixture to make more power. My question to Bruce was whether the engine components, the intake manifold, the SC, the intercooler, could withstand the added heat as opposed to the normal chilling effect. 

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Thanks,

I was familiar with the old school SC and the EFI under the SC but I must have been locked in the closet on the FI on top of the SC. I was trying to picture Port FI. :wacko: Throttle body perhaps...

Quite a project from the sounds of it.  Good luck :)

 

THERE IS ALWAYS ENOUGH TIME TO DO THE JOB RIGHT - THERE IS NEVER ENOUGH TIME TO DO THE JOB AGAIN !!!

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