OK I have a 92 GMC Sierra reg cab stepside. Forged 370 , 233/236 619/578 111+3 cam, Edelbrock dual plane intake, quick fuel vac secondaries 750 carb, 1 3/4" headers, th 350 with tight converter stock 10 bolt open diff 3.42 gears, heavy *** 15x10 all around and 28" mickey drag radials. Truck ran a best 12.88 109.06 mph first time at track. New mods: I just put a circle d 3800 stall and am doing a ford 9" 3.89 gears, caltracs, racestar darkstars bigs and skinnies in front, adjustable shocks. Will the new mods get me in the 11s? Is there anything else I should do? Nitrous is in future but want 11s NA

 

Bump!

 

What cylinder heads you running?

 

317 milled .020" 10.5:1 comp ratio

 

Anyone else?

 

Bump$

 

I'm gonna say no, those mods alone pick it up that much. The switch to a 9" from a 10 bolt will probably be a wash even with the better gears. The converter could help some.

What was the 60' on the 12.8 pass? Are you fixing a major traction issue? If so, then maybe yes. But the 109 mph trap seems to slow for 11's.

 

You need start with a better head. Look into a prc/afr/TFS......

 

What converter was in it before the circle D ?
what was your 60 time on the 12.8 run ?

Post your 12.8 slip

 

Well, for the $6k you just spent on all of that, you could have bought a 2500lb rolling chassis and been well into the 11's!

Don't feel like I'm singling you out here, but what's your end goal? I mean this is a pretty wild mish mash of parts, and I'm not surprised at all that it under performs. Here is my thinking

1. First thing that sticks out like a sore thumb is that cam. Who spec'd it with that god awful exhaust lift? If you want to make a lot of power, that's not the right cam. If you want to make a ton of noise, then don't change a thing, cause I bet it sounds choppy as hell.

2. Do you need to run the dual plane? Hot Rod/Motor Trend's David Freiburger just posted a newer video on youtube comparing dual plane/short ram/tall ram setups, and picked up 50 fwhp going to the tall ram/dual carb setup. Video is here if you're interested.
3. Heads. With a 4+ inch bore, why not LS3 style heads? They flow more out of the box than any stock LS1 style.

4. Headers. Again, why the compromise of 1 3/4 headers? Big motor's gotta breathe. 1 7/8 would help, but I bet 2 inch wouldn't hurt and would let you grow with the nitrous. What is the rest of the exhaust? Does it go into some janky *** y-pipe and then a 2 inch pipe to the bumper or is it true dual? We need some more info here.

5. Might it be under carb'd? Carbs really aren't my thing, but I understand CFM, and a stock LS1 78mm throttle body will flow over 700cfm. More airflow means more boom.. Speaking of which, what is the AFR? Is the carb jetted properly? That low MPH makes me think not, and probably not enough advance either.

That should be a good start on getting things figured out. I vote to spray the rods out of it asap.

 

Thanks for the comments

60ft- 1.999
1/8- 8.38
1/8 mph - 86.6

Converter was a jw flashing around 2,800. Truck was lugging on launch

1. Martin Smallwood specd the cam.

2. I will be changing to Vic Jr single plane soon. I went with dual plane at the time as it was mostly street

3. As far as heads I was running low on $ at the time of the motor build and just stuck with them

4. Schoenfeld made a set of headers for ls swap in 88-98 model trucks so I used them. Only came in 1 3/4 primaries. Exhaust is a true dual 3" into spintech mufflers. I know these are probably choking it some

5. I have thought of changing the carb. Afr was low to mid 13s during the run so it was running a little lean I need to jet up. Timing is at 32*.

 

I have no idea who Martin Smallwood is? Might be from TICK? What was the compromise you needed to make with that cam?

You need to figure the AFR out for sure. That's probably your MPH right there. Timing seems super high for pump gas. Have you pulled plugs to check the fuel ring and timing mark on the strap?

 

Yes he is from TICK. Yeh I didn't have any jets with me when I went. Plugs look good. Have tried down to 27-28 * but this was just on the street using the *** dyno and didn't really feel a difference. Thanks for response

 

What stall speed did you put in the spec sheet, do you remember? I don't have access to any of the old camshaft specification sheets I use to give out unfortunately. I would of most likely recommended at least a 3500-3700rpm converter for that cam. A 2800 converter is not going to perform well with that combination and will hold it back as you're seeing. A looser converter will help the E.T. on the launch and smaller shift extensions. The RPM the engine crosses the finish line at and the change in rear gear ratio should also help as well.

Do you know how much the truck weighs Baron? Just doing a little research it looks like most weigh 4000lbs. so it's not a featherweight by any means. That said it will need more stall speed and gear to get it moving.

The exhaust port on an engine cares a lot less about lift than it does timing events. Opening and closing events pertaining to the exhaust port are much more important than curtain area. Although important in its own right, curtain is just not as important when it comes to the exhaust port.

The pressure differential between the cylinder on the power stroke and the exhaust port before the valve opens is so great that nearly 50% or more of the cylinder's contents are evacuated during blow down by the time the piston reaches BDC.

If the exhaust center line on the cam is 114* BTDC, then what good is adding more lift 66* ABDC going to help with if 50% or more of the exhaust gas is already gone 66 crank degrees before that? By that time during the exhaust stroke scavenging and pressure wave tuning will start to kick in and help pull the remaining spent gasses from the cylinder as the piston travels to TDC.

The only time you run even close to, the same amount, or more exhaust lift than intake lift is when you have to sacrifice exhaust valve diameter for intake valve diameter. Such as on a high RPM N/A engine where maximum bore diameter and maximum intake valve diameter is desired. To effectively center the intake valve the exhaust valve must be made smaller and shoved up against the cylinder wall. Thus more lift is needed to make up for the loss in curtain area.

The small amount of change from .578" lift to .600" lift would show no gain whatsoever on the dyno. Especially on a cathedral port head that has better intake to exhaust flow bias than other LS cylinder heads.

The single plane victor intake will want even more stall speed. At least 4400rpm and it will prefer 4600-5000rpm. The single plane will move the power curve up and really would also require a camshaft with an earlier intake valve closing event to optimize the shorter runner.

Usually carb motors due to poorer fuel atomization will want slightly more timing than EFI motors. Since there isn't a finely atomized stream of fuel spraying on the back of the intake valve, combustion isn't quite as efficient and usually will want a few more degrees to help make up for the differences.

 

You're right Martin you did suggest a 3,500-3,700 stall I just had that 2,800 one laying around and used it. The truck has always pulled good when I get the rpm up I think the cam is great. The circle d converter I put in has made the truck a totally different animal its a 3,800 but flashes around 4,000. I'm not dissatisfied with the performance of the truck like you said she's on the heavy side. I was just curious to find out if the changes I made would net a much lower E.T. like I said the new converter has really woke it up! I think Martin is one of the top guys as far as knowledge of these motors and creating a custom spec'd cam and will always have my business. I am actually going to start on a turbo build soon and will be getting another cam from him.

 

I believe that stall will get you close to where you want to be. The other was just to tight

 

The Circle D converter you have now will really wake the truck up on the track. I can imagine the difference in performance between a stall that flashed to 2800 versus your current converter that is flashing to 4000rpm now. It will be an entirely different animal on the track.

It may even cause traction issues from hitting the tire harder with more power which will present a whole different set of challenges. That said, with the adjustable shocks, cal tracs and big and littles I think you'll be just fine.

The change from heavier wheels and tires to the smaller skinnies up front and lighter wheels out back will also help drop the E.T. and gain MPH.

With all the changes you made you have a good recipe to get this truck into the 11.90 zone.

 

Update, got everything done and took truck to bracket race this weekend. 1/8 mile only it ran 7.81 at 90 mph in 107* heat index! That's .6 and 4 mph faster than when I ran in November in 70* weather. Overall I'm happy with it. Getting a new pro systems carb this week. I did go 4 rounds at the race, truck is deadly consistent. Looking at some prc heads now

 

Single plane intake and maybe some 4:10 gears on a 28" tire.. That should help..