Forced Induction Custom FI Setup Questions

Rear Mount Advice...

Old 11-12-2014, 07:10 AM
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Hello,
I'm new but I need your thoughts. I have a 69 Mustang 371cid 8.5:1 built with too much money designed for a supercharged application - even gas ports..

Originally I was going with a Paxton centrifugal.. Technology has caught up with me.

Now I'm thinking Turbo - Comp Turbo the oil-less (water cooled) but in a rear mount.

Why a rear mount - no engine bay room - seriously. I do need help in determining the right turbo. I'm thinking two more than one - but that's not 100% firm at this point.

I've read several books on Turbocharging but it seems to leave real world experience short - seems they all discuss it in the same "theory" language.

The engine will utilize a FAST 2.0 throttle body (the one that supports 1200hp N/A) and the FAST 2.0 XFI ECU.

My goal is 600hp area, but I'm not about peak performance numbers, my choice is a strong throw you in the back seat street car that's quick and fast. Not interested in being "John Force or Mario Andretti" but an off combination of both.. The kind of attitude that makes a car fun to drive across country..

Got any advice ?
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Old 11-12-2014, 10:27 AM
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I would probably talk to Comp about this as they should have the most information about what their turbos work best on.

I'd be a bit concerned about fuel distribution issues if using throttle body injection on a turbo. Port injection will make it less likely that you'll have one of your cylinders running lean.
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Old 11-12-2014, 01:15 PM
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Thanks..
I thought there might be issues but the throttle body flows enough that it will safely support 700ish boosted pressure (FAST/ Comp Cams info) that's why I'm really happy for 600hp target..

Anyways don't want to sound like a comp cams info-merical I truly appreciate the information..
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Old 11-13-2014, 09:30 AM
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Just because it flows enough fuel and air doesn't mean it's all going down the right cylinders. I haven't tried using a TBI on a forced induction application, but I've seen cylinder by cylinder EGT readings with several four barrel throttle bodies on naturally aspirated motors and have yet to see one where all the cylinders are running the same air/fuel ratio. Some motors were to the point that you'd have four red header tubes and four black ones at full throttle. I would not like to see what that would do with a turbo. Unless you've got data from a similar turbo build with the exact same throttle body and manifold combination, I'd strongly advise going port injected.
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Old 11-13-2014, 11:02 AM
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Thanks for your concern - are you aware of a 4 pattern camshaft ? (Comp Cams) This should reduce the condition in which you describe.

I've been using them for years in the N/A engines and they are actually worth the cost.. The best way to describe it is a camshaft (for a V- 8 ) that the grind is in such manner that it takes account for the different runner length - this problem occurs in standard engines because the shape of the intake - the only exception is individual runner which is more difficult concerning for aftermarket efi..

Please don't take this as being as a "jerk" in reply - I'm addressing the topic just in case someone is reading the thread and in current build process - I want everyone to get the most from their build/project ..

Again thanks..
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Old 11-14-2014, 08:20 AM
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It can be useful for equalizing the volumetric efficiency. The problem with a TBI is that the fuel charge is not uniformly distributed throughout the air mixture. So if one of the runners happens to draw air from a spot that doesn't get as much fuel in it as the others, you get a lean cylinder. It's similar to what happens if you have a manifold optimized for a Holley and try to put a Predator carb on it.

Have you used a TBI setup with one of these cams before? If so, what did plug reading or EGT tell you about the fuel distribution?
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Old 11-14-2014, 09:58 AM
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Matt in the honesty I've never supercharged, but in communication with FAST techs and B. Macey (The efi store/horsepower connection & efi fast xfi instructor - whose car score # 9 in hot rods drag week) this is very very do-able because the throttle body (please check it out) will flow enough volume with a finer (way more than better) atomization than a Holley - really at this point a C&S Specialties carb. The only hold back if more power desire then get another throttle body and manifold and have two throttle bodies which the FAST XFI can support - but I only want 600hp.. thing is good for 700-ish (math- the class I always hate) then utilize bank to bank because their is 8 - 76lbs injectors and it will reduce dwell time.. Yes got the Holley Twin Dominator fuel pump and depending on fuel pressure at the body - the ecu will bring the other pump on and then regulator will adjust based on intake manifold pressure.. Set initially for 46psi and rise in boost then second pump not to exceed 60psi (on Dyno this number may change to lower) and cycle pump (second on & off) according to boost psi..

My big issue is which Turbo and people (such as you) experience. I prefer your experience concerning the turbo from brand to performance - need on inter-cooler or not.. Road issues etc Do you have a preference.

I like Comp Turbo and would like a water-cooled turbo.. easier to plumb from radiator (supply & return/stand alone pump) and since I use evans coolant - the BTU removal will be greater and no carbon issues that exist with oil feed turbos.. Also doing more research about the oil-less claim.. What is your beliefs, thoughts...
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Old 11-17-2014, 09:22 AM
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I would be interested in seeing the measurements they used to check the fuel distribution. Can you post them? I have seen the FAST throttle bodies in person, but there is nothing visible about them that would imply their fuel distribution is any different than their competition, and I have not tested one on an engine myself.
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Old 11-18-2014, 10:03 AM
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Just checking .. The FAST Throttle-body is the 2.0 that has all eight 76 lbs injectors incorporated into the throttle body also the air temp sensor, Throttle position, Idle air, there is a 1 bar map but in this case buy a two bar and relocate..

I'm using it as a "high tech" Dominator - it flows enough cfm to support 1200hp in N/A..

The thinking is the understanding of "intake runners" in a carb set up runner allows time for a better atomization of fuel before it enters the cylinder..

Port Injection - it was discovered early into fuel injection that atomization was just as critical. However runners were configured to provide a charge of air that would crash into the cylinder and assist in the atomization from the injector. The optimum cylinder length is between 12" - 14" and the injector to be placed in that range. This provides ideal atomization for the fuel... But this type of design also has a hood clearance issue and practically isn't a marketable aspect to sell a car.. So the engineers have kept port injection but increased in their understanding of runner length and design - LS series is a great example of excellent design.. Good visual is the 86-93 mustang and then compare today's mustang intake.. change but now longer runners designed to flow more with more aggressive action inside the cylinder..

Going back to carb.. Open plenum sucked through the curve but was excellent at WOT.. Then came open plenum with runners that individualized and power increased, better fuel atomization and designed to crash inside the cylinders

Dual planes - better through the curve. Designed to atomize better before the cylinder and then came the "Air-Gap" which maintained the philosophy but also brought the individual runner from the open plenum - which allowed the crash inside the cylinder.. (a plus was the lifted space for a cooler denser charge..)

(Crash is my words for extreme mixing of fuel and air molecules for the better bang)

So what I'm doing here is the exact carb proven theory with a throttle-body that will atomize fuel better than any carburetor and provide better control for a boosted environment..
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Old 11-19-2014, 08:28 AM
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Virtually every OEM intake I've seen has the injectors located as close to the ports as possible. The further upstream the injector is, the more room for the fuel to contact the walls and stick to it. About the only exception I've seen is high RPM engines with straight runners and injectors firing straight down the runners, and even those tend to use a low RPM injector stage at the ports to get good atomization at low air flow numbers.

NASCAR engines put the injectors high and upstream, but not for any performance advantage - every article I've seen on the new EFI intake manifolds state this was done to prevent teams from getting an advantage by fine tuning injector placement, and they wanted all teams to be equally handicapped by this.

Typical results from dyno testing a TBI at our shop produced runs where you'd have something like the coldest cylinder's EGT at 1300 and the hottest at 1650. Sometimes the ------ was even worse, with nearly 300 degrees difference between the hottest and coldest.

Do you have any measurements with the FAST TBI that indicated it did better than the ones we tested?
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