I am helping out a buddy of mine with a small block Mopar making 940 Hp in a 3070 lb car. Car has a 727 with 2.45 first and 4.57 rear. Tires are short at 30". Guy who built the motor has done a few and all are running strong. Car has run a best of 9.22 @146. Should be running 8's. Motor has been leaked down, compression tests and springs test all good. Motor has a 1150 Dale Cubic carb I believe. Floats were high and reset using 7/16 bit. Jetting tried and we can certainly lose mph and ET stays about the same. Even when we worked on the launch and picked up a tenth, we saw nothing on the top end. Looking at the race pak data on the O2 sensors, at launch we see once on the 2 step, the engine goes really rich ( 10.2) and struggles to recover. The
rest of the run it stays around 12.7 or so. We just confirmed fuel pressure with a snap on gauge and saw 8 pounds. Did a free flow test at the regulator outputs and saw about 1.9 gallons in 1 min. Dropped the pressure to 6.5 pounds and saw 2.1 gallons in 1 minute. Magnafuel says this is on the edge but OK. I have always thought you needed to pump a gallon in 18 seconds or less to feed this kind of power. I found a few links on line to confirm this. L am looking for a smoking gun on this combination. The difference on the car from the dyno is the fuel system and he is using the grid and grid ignition. No timing retards at this time and confirmed on the racepak. Thoughts?

have you looked at the plugs?
What was the A/F when it was on the dyno?

you say that the ignition system was changed from the dyno (not going to ask why you didn't use your system) what system was on the dyno? the grid has a compensation system built in, most boxes do not. you may be running into detonation.
let me give you a example, a 7AL3 set with 34 degrees at 3000 rpm may have only 30 degrees at 7000. a grid will have 34 degrees at 7000.

in addition if you have a forward facing hood scoop you will increase the volumetric efficiency which will require less timing.

So other then the fuel, ignition and air supply it's the same as the dyno.


Joe

Fuel is the same as dyno. Hood scoop is rear facing. Plugs were checked. I did not know what ignition was used so the information you provided is good to know. Will need to look into that. Also found some more information from my friend and he is upgrading fuel system after his discussion with Magnafuel. The A/F ratio on the dyno was 12.7 as well.

AFR just after the hit usually goes rich for a bit due to fuel slosh in the bowls, and no, adding a crossover tube to the front a rear vent tubes won't stop it. I have found that this is not a problem when all else is good in the carb. 8 psi is too much,, the lower the better, I only run 5.75 on a 1200hp plus BBC with no supply issues.

If you O2 is at 12.7 or close after the launch then I'd say you are not having a fuel supply problem so look elsewhere.

Tuning he car to launch better and run quicker will do nothing for top end MPH. Top end MPH is the best indicator of HP the motor is making.

9.22 @ 146 are matching and only showing close to 800 HP so your missing a bunch if the motor made 940.

Post the Racepak graphs

Top38 or anyone else . What would be the lost of HP from the dyno 940 HP calculated to rear wheel HP with his combo, I've been told its close to 15%. Did not mean to derail OP post. Just wondering ...

Is corrected dyno HP being compared to real time HP?
If so 940 vs 800 sounds about right to me.

TOP38- We did have a crossover tube already. The funny thing is when we dropped the floats to where they should be, we did lose some mph. Maybe the fuel upgrade will help some but I don't believe it will create 100 more HP. As far as top end HP, I agree with you on that. I will see if I can get a copy of his racepak file. Even took the hood off for 1 run with nothing gained.
Just an FYI, my smaller 383 W8 motor makes 834 on VP C16 and 863 on Q16 and is much crisper than his. My et in good air matches my Hp. You should know my car from Rick Jamieson.

quote:

Originally posted by J178RED:
Top38 or anyone else . What would be the lost of HP from the dyno 940 HP calculated to rear wheel HP with his combo, I've been told its close to 15%. Did not mean to derail OP post. Just wondering ...

I figured his HP based on flywheel HP(from his et and speed) not rear wheels. It's off or the dyno is!

quote:

Originally posted by J Olejniczak:
TOP38- We did have a crossover tube already. The funny thing is when we dropped the floats to where they should be, we did lose some mph. Maybe the fuel upgrade will help some but I don't believe it will create 100 more HP. As far as top end HP, I agree with you on that. I will see if I can get a copy of his racepak file. Even took the hood off for 1 run with nothing gained.
Just an FYI, my smaller 383 W8 motor makes 834 on VP C16 and 863 on Q16 and is much crisper than his. My et in good air matches my Hp. You should know my car from Rick Jamieson.

First, listen to the time slips before any other data! Lowering the floats leans the motor. If all else was the same and you lost MPH then I'd richen the carb up and see what results you get from that.

When you took the hood off, did you use an air filter?


What size are the needle and seats in the carb?
I assume this is gas and not alky. They need to be at least .130". If they are smaller your likely draining the bowls.

940HP uses about a gallon per minute of fuel so I would say you want about double that from your fuel system to supply adequate fuel to the motor. So 2 gallons per minute should be good.

We did richen up the carb 2 jet sizes and lost some mph and et if I remember correctly. Doesn't add up. When we took the hood off, we did have a filter on it. Don't know the needle and seat size at this time. Will check it out.
This may be what it is going to run regardless of Dyno HP. Like they say sometimes, it is what it is.