Weak part throttle performance

[PRH]

If the converter flashes to 3200....... imo, it’s too loose.

For “truck” type duty, I think both the heads and cam are a tad too big.

I wouldn’t think a combo like that would be all that happy at part throttle cruise with mid-high 14’s AF ratios.

I’d go up in jets a bit and gauge the effectiveness of that strictly based off the seat of the pants feel...... at least initially.

[David Redszus]

What is your part throttle Lambda reading?

Even with dyno tuned race engines we frequently find incorrect partial and transitional throttle mixture settings.

[travis]

One of the greatest things about the Edelbrock carbs IMO is the ability to quickly change the part throttle mixture over a pretty considerable range with a quick metering rod change. I’ve tried them everywhere from a bit lean to quite rich...it doesn’t seem to care as long as you don’t get too far one way or the other. It is much more sensitive to timing though...the difference between 38 total and 32 total is about 600-800 rpms on top. At 32 total mechanical it pulls cleanly to 5800, which should be a few hundred rpm past peak.

I don’t really think the cam is too big, but maybe it is. I’ve used a million cams in the 260 to 270 seat duration range in builds like this...but never on a 112 lsa (always 108-110), never a hydraulic roller, never with this much compression, and never with heads this size or with this flow capability. And...never in anything quite this heavy.

I think the real answer here may be 2 things...more cubes, and less converter.

I’ve lost most of the truck functionality. I hooked my 16’ trailer to it today, and even at about 1900 pounds empty it really takes an excessive amount of throttle to get it moving. So...lesson learned I guess. I’ll be pulling the engine out next week, and coming up with a new plan

[Tuner]

Since building this new engine for my heavy weight ‘83 F150 extended cab, I haven’t been very happy with its performance, especially in part throttle stop and go traffic situations. To recap...

.030 over 351w, 10:1 compression, promaxx 180cc heads (flow 262@.550”, 266@.600”), Jones hydraulic roller (264/268@.006, 218/222@.050, .544/.544 lift, 112 lsa, 109 ica), weiand 8016 dual plane, 650 vacuum secondary Edelbrock carb, 1 5/8” long tube headers, dual 2 1/2” exhaust. 2500 stall, 3.55 gears.

I built this thing for good low end and a super strong midrange...you know, the things that a 4900 pound truck NEEDS. And I thought I had accomplished that. Throttle response is absolutely amazing right off idle, but the truck feels sluggish at part throttle, and the fuel economy is absolutely terrible.

Today I put a fresh set of plugs in it and changed the oil, and went over the tune again. A/F’s are good, plugs look good, nothing seems out of whack. One thing I hadn’t checked was the converters flash stall. I tried a couple different scenarios...and I’m seeing around 3200 rpms flash, even at 3/4 throttle.

How much more cam do I need to need to make this right?

This head is the "fast burn" type and is more sensitive to timing than most people think. Soggy feeling part throttle is as likely from too much timing as too little. Chambers like this are sensitive at part throttle just as they are at WOT. A couple degrees off the sweet spot can be a deal breaker. Some engines are numb to timing at part throttle, other than lower EGT, but fast burn chambers are usually picky.



More SBF ignition timing rambling here viewtopic.php?p=880342#p880342

[dfarr67]

Since building this new engine for my heavy weight ‘83 F150 extended cab, I haven’t been very happy with its performance, especially in part throttle stop and go traffic situations. To recap...

.030 over 351w, 10:1 compression, promaxx 180cc heads (flow 262@.550”, 266@.600”), Jones hydraulic roller (264/268@.006, 218/222@.050, .544/.544 lift, 112 lsa, 109 ica), weiand 8016 dual plane, 650 vacuum secondary Edelbrock carb, 1 5/8” long tube headers, dual 2 1/2” exhaust. 2500 stall, 3.55 gears.

I built this thing for good low end and a super strong midrange...you know, the things that a 4900 pound truck NEEDS. And I thought I had accomplished that. Throttle response is absolutely amazing right off idle, but the truck feels sluggish at part throttle, and the fuel economy is absolutely terrible.

Today I put a fresh set of plugs in it and changed the oil, and went over the tune again. A/F’s are good, plugs look good, nothing seems out of whack. One thing I hadn’t checked was the converters flash stall. I tried a couple different scenarios...and I’m seeing around 3200 rpms flash, even at 3/4 throttle.

How much more cam do I need to need to make this right?

This head is the "fast burn" type and is more sensitive to timing than most people think. Soggy feeling part throttle is as likely from too much timing as too little. Chambers like this are sensitive at part throttle just as they are at WOT. A couple degrees off the sweet spot can be a deal breaker. Some engines are numb to timing at part throttle, other than lower EGT, but fast burn chambers are usually picky.



More SBF ignition timing rambling here viewtopic.php?p=880342#p880342

Makes sense I have a TPI 383 with AFR version of the GM vortec fast burn, I have a ping I'm having a hard time tuning out mid throttle area even with 91 octane.

[PRH]

To put the cam size into perspective....... for something that will need to retain its truck worthiness ........
I have a 2004 Silverado 2500HD 4wd, listed as having a curb weight of 5400lbs.
6.0, 4.10’s, factory converter stalls 2500........the stock cam is 196/207.
This is pre-mds and pre-vvt.

For all around driving, the truck is actually pretty “lively”.
No, it doesn’t really spin the tires, or rev to the moon........ but the motor’s responsiveness around the part throttle cruising range area, I feel is pretty good.

Mixed driving mileage is about 13.5-14mpg.

What is your hot rodded 351 getting for mileage?
You said it’s bad....... how bad?

If I were trying to improve it without redoing the whole combo I’d say...... put a stock converter in it for a 351w truck....... and then a cam that’s in line with whatever it ends up having for a stall speed.
For reference as to how much you’ve strayed from the factory, a stock HR cam in a truck 351w was 176/197@.050

[travis]

It’s getting 6-7 mpg right now. On all fairness though, there has been a lot of heavy throttle testing and tuning.

I chose the converter primarily because I was worried about having pinging issues under load at low speeds. I just didn’t expect or want it this loose.

I also think some 4.10’s would make a big difference. However they would absolutely suck for highway driving with no overdrive. It already cruises at 3200+ at 65mph.

The current compression worries me with trying to go smaller on the cam. Without changing heads and/or pistons, I might be able to go a little smaller on the cam, but only if I widen the lsa even further. But I think that is the same approach used on the 6.0 you have...small wide lsa cam, with good flowing heads.

[F-BIRD'88]

Check for front and rear wheel/axle FRICTION.. brakes too.
The modified torque converter may have been a big mistake for a heavy truck (other than WOT blasts). (internal design)
You may be able to send it back to be re-tweeked, re-tuned.

(too much mushy "dynoing effect" at your specific speed,rpm,load,throttle position)

How a converter actually dynamicly functions is quite adjustable.. Drive and turbine fin angle, fin to fin blade clearance. Stator blade shape, angle etc..

[F-BIRD'88]

Kep in mind that a high perf engine makes more power by BURNING MORE FUEL. so... if when you use the throttle to make more power to accelerate quicker to do that REQUIRES BURNING MORE FUEL..
A high perf engine makes more power by burning more FUEL.. You won't save gas. X2 in a big 5000 lbs brick truck.

[Jeff Lee]

Being local, I’ve had Hughes street, street / strip, and SUV converters, and every single time, I’ve kicked my self in the butt and asked “when will I ever learn” ?
I’ve seen Hughes sponsored super class race cars pick 12 MPH by changing to a different brand.
I don’t know if that’s your problem but based on my own experiences, it’s worth investigating. Sounds like it’s flashing a little to high. I would think a 2200 stall / 2600-2800 flash.

[bobmc]

the gearing, tire size, rpm calculation at 65 mph indicates more than 15% converter slip, do I have those figures correct?

[My427stang]

It just doesn't sound that wild to me for that combo, have you tried pulling it into 1st instead of D? Are you feeling it shift twice when driving?

[travis]

the gearing, tire size, rpm calculation at 65 mph indicates more than 15% converter slip, do I have those figures correct?

I don’t remember the exact numbers at the moment. If I get a chance later today I’ll go double check.

[travis]

It just doesn't sound that wild to me for that combo, have you tried pulling it into 1st instead of D? Are you feeling it shift twice when driving?

It shifts through all the gears, but I do have to drive it shifting manually. The trans is calibrated for the factory engine that peaked at like 3600 rpms, so it shifts much too soon. I haven’t got to that issue yet...there is almost no info out there that I have found yet on modifying the C-6’s shift points

[norm]

It shifts through all the gears, but I do have to drive it shifting manually. The trans is calibrated for the factory engine that peaked at like 3600 rpms, so it shifts much too soon. I haven’t got to that issue yet...there is almost no info out there that I have found yet on modifying the C-6’s shift points

Look in the modulator nipple that the hose goes on. Most likely you will see a screw in there that you can turn to adjust the too early shift issue.

Makes quite a difference