HP woes with Sniper Sytem

[Stang_1973]

So Im feeling pretty defeated becuase as we all have found ourselves scratching our head with a decision we made that didnt end up as we thought. But I dont want to give up, just gotta find the right way to turn this around.

Basically the shorter version of this story is when I switched over to a 351 roller cam engine and AOD, i was pretty happy with my results. For a couple weeks until i twisted the input shaft on the AOD. At that time my setup was a 351W, GT40 tubular intake, RPM heads, X Cam, longtubes, Xpipe, and 2.5" straight through exhaust. Car made 305HP/360TQ to the wheels after being tuned. Again after 2 weeks, the input shaft twisted.

I got the AOD rebuilt for an Edge Racing Non Lock Up style converter and upgraded clutches, servo, etc. However after this numbers dropped to 290HP/355TQ to the wheels. Also, felt like the car lost alot of pull.

Was that way for a looooong time. I had been having trouble with the car running right for a couple years and decided to go towards the simpler holley sniper EFI. I had been told that my engine would actually do way better with better airflow since the GT40 intake was fairly restricted compared to aftermarket stuff.

Switched over to an AirGap intake and the sniper system with full electronic timing control. Had the car tuned by the same guy who tuned it before and sadly the numbers are WORSE! Came in at 284HP/315TQ to the wheels. And yes you can really feel the difference. car feels sluggish low, and at higher speeds as well, no pull really. Heck my 2017 F150 5.0 feels more fun to drive right now.

I started looking up top end packages form edllebrock and comparing my setup to theirs and even their 400HP package, the only difference is my cam. they use the RPM cam while i have the X-303 cam. Im not sure what my commpression ratio is tho, while eddie advertises their setups as used on a 9.5:1 compression ratio. The 450 HP package uses the ECNC heads and rolling thunder cam.

thinking at this point to change out my cam, and possibly switch back to the Lock up style AOD, and hopefully a hardened input shaft will be enough to not break.

Any info/advice/encouragement is appreciated.

 

[limp]

For all out horsepower at top end RPM carbs will out perform FI......
For street manners, better fuel mileage, and LESS Polutants out the tail pipe, Fuel Injection is better

 

[Stang_1973]

For all out horsepower at top end RPM carbs will out perform FI......
For street manners, better fuel mileage, and LESS Polutants out the tail pipe, Fuel Injection is better

My GT40 setup was FI

 

[General karthief]

T

For all out horsepower at top end RPM carbs will out perform FI......
For street manners, better fuel mileage, and LESS Polutants out the tail pipe, Fuel Injection is better

This is subjective at best, some combinations of fuel atomization work better than others, EFI can and does out preform a carb in some instances and a carb will work better on other setups, not going to get into the 'which is better' explanation but to say research and planning are key.
The member in this instance has miss-matched engine/trans setup and the changes they made went (obviously) in the wrong direction.

 

[Stang_1973]

T

This is subjective at best, some combinations of fuel atomization work better than others, EFI can and does out preform a carb in some instances and a carb will work better on other setups, not going to get into the 'which is better' explanation but to say research and planning are key.
The member in this instance has miss-matched engine/trans setup and the changes they made went (obviously) in the wrong direction.

Thanks. I didnt wanna get into a carb vs FI debate.

hoepfully someone on here has done similar changes and had better outcomes or discovered better setups with parts similar to what i have going on. Maybe even something ive missed.

The tuner is adamant that his tune is good, says he feels there is something going on internally with either the engine or the transmission. We were expecting to be about 320-330 HP at the wheels. And especially not a decrease in overall power.

 

[TOOLOW91]

You were steered wrong in opinion , if you needed a better system they should’ve kept you multiport fuel injection with a different style Holley controlling it. Or the stock ecu at those type of modifications is still very resilient to working

I’d guarantee the converter isn’t right either by the sounds of it. I also run a non lockup aod in my car and have had a Holley HP efi unit in my car since 2017-18 - but it’s still multiport fuel injection

 

[Noobz347]

T

This is subjective at best, some combinations of fuel atomization work better than others, EFI can and does out preform a carb in some instances and a carb will work better on other setups, not going to get into the 'which is better' explanation but to say research and planning are key.
The member in this instance has miss-matched engine/trans setup and the changes they made went (obviously) in the wrong direction.

This is why I moved it out of [Tuning] section.

I don't think it's a tuning issue at all. It's a [less than ideal] engine combo issue.

 

[General karthief]

Single plain intake?
What rear gear?
My opinion, either match up a cam and heads for the intake or swap back to the tubular setup that was there.
Just a thought.....

 

[AeroCoupe]

You need to get a hold of TMoss and have him port the GT40 lower and put them back on the motor. The heads will fine but I am thinking that you have a lot more to gain in a better cam for that combo.

 

[Stang_1973]

Single plain intake?
What rear gear?
My opinion, either match up a cam and heads for the intake or swap back to the tubular setup that was there.
Just a thought.....

its a dual plane intake but has a 1" spacer.

rear end is a 9" 3.5 posi.

 

[General karthief]

Why do I have a feeling this is not in a fox body mustang?

 

[Stang_1973]

So after doing a bit more research. I found that the RPM heads come in 2 version. both with 60cc chamber yet one has 2.02/1.60 valves and 190 cc runners, while the other has 1.90/1.60 valves and 170 cc runners.

looking at the heads on the car, i dont see any identifying numbers.

 

[Stang_1973]

Why do I have a feeling this is not in a fox body mustang?

LOL, check my signature, its a '73 but all the engine parts are essentially based off a fox setup.

 

[Bullitt347]

Duel plane intake manifolds do not work well with throttle body FI systems like the Sniper.
An open spacer under the Sniper would help,
But the best driveability/power would be with an Single plane Intake manifold.
T-body injection and duel plane manifolds have huge distribution problems.

 

[Stang_1973]

Duel plane intake manifolds do not work well with throttle body FI systems like the Sniper.
An open spacer under the Sniper would help,
But the best driveability/power would be with an Single plane Intake manifold.
T-body injection and duel plane manifolds have huge distribution problems.

I do have a 1" spacer

 

[TOOLOW91]

Duel plane intake manifolds do not work well with throttle body FI systems like the Sniper.
An open spacer under the Sniper would help,
But the best driveability/power would be with an Single plane Intake manifold.
T-body injection and duel plane manifolds have huge distribution problems.

This !!!

 

[revhead347]

Live and learn. The Sniper system is designed to make an easy EFI conversion for a carb engine. My friend used one on his old Pontiac and it got fooled by the air filter setup. I'd go back to the GT40 intake, and get rid of the alphabet cam. Another +1 for TMoss. Great guy to do business with.

Kurt