[gearbanger]

I took the GTO to the dyno this weekend and learned some intreresting stuff. First of all was that there is definitely alot of horsepower to be found with tuning. I made 395 rwhp to begin with and I thought that was going to be about all she wrote because it ran so well, I thought the tune up was pretty good. Not!! we picked up 60 hp and there is more left. 454 rwhp is not too bad though for a 10:1 461 I didn;t think. I want more though!

We started with a first pull afr of 11/1 and we reduced the jets from 76P to 71P and 84S to 78S over the course of 17 pulls or so. That only got us to 12/1. The dyno guys seemed puzzled as to why the jets weren't making more difference.

Why would a Quick Fuel 850 annular require so much reduction in jet to give a good afr? We didn't reduce the pvcr any but I am going to tackle that soon. I thought about just blocking it and jetting sqaure to see what happens first. Any ideas?

I am tuning with a LM-1

[shaker455]

Gear,
The QF/Pro-Form stuff can be very difficult stuff to tune...

Lets start by asking you what cam and exhaust?

What do you have for airbleeds in the carb now?

Check your booster and see if you can wiggle them around.

[gearbanger]

It has a 242/250 .600 lift hydraulic roller
2" headers 3" exhaust with x-pipe
the boosters are tight
The carb has billet blocks and the a/f was steady and pretty flat across the revs
Everything seemed fine except it seemed like alot of jet changes for a small change in a/f

Only other strange thing I found was the motor wanted to stop pulling at about 5700-5800 rpm. It would actually start popping and missing like the lifters were floating. I had a 6000 rpm chip in the msd box. I changed that to a 7000 and am going to test it out tonight to see if that was what was doin it.

It made 454 rwhp so that seems about right for the combo, but I think there may be more in it.

[harry k]

"I took the GTO to the dyno this weekend and learned some intreresting stuff. First of all was that there is definitely alot of horsepower to be found with tuning."
aint that the truth

"I made 395 rwhp to begin with and I thought that was going to be about all she wrote because it ran so well, I thought the tune up was pretty good"
i always make 3 BASELINE PULLS AS ARRIVED , so we have a solid baseline to start with to compare ,how they leave at the end before&after.


" Not!! we picked up 60 hp and there is more left. 454 rwhp is not too bad though for a 10:1 461 I didn;t think. I want more though!"
sure thing when people have their car dialed in ,by so called "seat of the pants" tune ,ofcourse there is a hidden HP to be found with a use of valueble tool as Dynojet Chassis dyno-end user/ NOT ENGINE DYNO , and then people will still want more

"We started with a first pull afr of 11/1 and we reduced the jets from 76P to 71P and 84S to 78S over the course of 17 pulls or so. That only got us to 12/1. The dyno guys seemed puzzled as to why the jets weren't making more difference"
almost all Holley carbs are caliberated "TOO FAT" to start with (but thats a whole different subject to go in now) so there isn't anything to be wondering for !my Holley jet box always lacks of the smaller jets .

"Why would a Quick Fuel 850 annular require so much reduction in jet to give a good afr?"
it has to do with few things,such as your engine's combinations demand of BSFC ,so there is no specific numbers for an engine like this , this is not a stock production engine .
could be due to fuel delivery and exhuast as well

"I am tuning with a LM-1"
what was the dynoshop's wide band data log used ? were you the only one in car with your LM-1 or the shop had wide band hooked with his dyno software ?
and being very very familiar with a 461 combos , the HP numbers with the BIG cam used ,sounds lil bit on the high side ,but that could be due to different dyno than what i own& use.
was it Dynojet dyno ?

www.HKMotorsportsDynoShop.com

[gearbanger]

I think they made two or three pulls to begin with, and they usually made two pulls with each round of modifications. I guess that was to verify a good number.

The wideband was the shops equipment connected to the dyno. I verified the info with my LM-1 after I was back home so I could have a comparison to the dyno widband.

The dyno was a superflow WinDyn, I think that is what it said.

I was more interested in the amount of gain in the tune up because I don't have alot of confidence in chassis dyno numbers. I believe we gained 60 hp but I don;t have alot of confidence in the 454 rwhp number. It could very well be less than that.

So what do you think about the carb jetting issue harry?

[77TA]

Was that all gained with just carb jetting ?
Dang nice man congrats...

[gearbanger]

On one run in particular, we went up on timing from 26 to 30. I thought I had the timing on 30 but my timing light must be wrong or I screwed up somehow. I verified that later as well with a buddies timing light. So a 2 size drop in jet front and rear and a 4 degree increase in timing netted 25 hp. Then more jetting got us the additional 35.

Like I said, the afr was under 11 to begin with and we went to just over 12. I am dying to know what would have happened if we would have kept going to see where the breakover point was.

[harry k]

"It has a 242/250 .600 lift hydraulic roller
2" headers 3" exhaust with x-pipe"
i assume E-head as well with these numbers ? you didnt specify that earlier.


"The carb has billet blocks and the a/f was steady and pretty flat across the revs
Everything seemed fine except it seemed like alot of jet changes for a small change in a/f"
like i said previously , i pull jets out all the time !almost allways the menatlity of the "bigger the better" exists with hotrod'ers ways of doing things!
was this "out of the box" Holley HP carb or Modified specialty carb?
the reason i am asking that is ,if it is out of the box stock Holley or Proform carb ,like i said they come too fat to start with ,if it is modified carb , then i can't speak much more than what i said about BSFC and what not ! check with carb builder,they have their way seeing things with "wetflow" bench's and what not .

"Only other strange thing I found was the motor wanted to stop pulling at about 5700-5800 rpm. It would actually start popping and missing like the lifters were floating."
well that all your going to get with your assuming not Exotic Hyd-roller valvetrain ,see that all the time normal.

"I had a 6000 rpm chip in the msd box. I changed that to a 7000 and am going to test it out tonight to see if that was what was doin it"
do you have a graph to display ? is it still pulling at 5800rpm climbing on the power curve ?if not , the max you wantto shift this at 5800 to 6000 rpm, just ask our friend Cliff ,hes done all the Hyd roller track tests

"made 454 rwhp so that seems about right for the combo, but I think there may be more in it"
you wanna eat the whole cake huh

www.HKMotorsportsDynoShop.com

[gearbanger]

"Quick Fuel 850 annular"

I wondered about the heavy hydraulic roller lifters and possiblly not staying on the cam at high rpm. If it still does it with the 7000 chip in it, I am going to be very suspicious of that. Although, I don't think it did this the first two years on the motor. I experimented with shifting at 6000 at the track and I never remember it doing this.

What is BSFC?

Yes I want the entire cake.

[ponjohn]

gearbanger- what cylinder heads?

[gearbanger]

KRE d-ports with 310cfm port.

[Probird]

It may be time for a new set of valve springs if the MSD chip isn't the problem.

[GOAT8U2]

12:1 on straight gas is safe but you could get greedy and move it up around 12:5 and probably notice another gain in HP and maybe TQ.

What I'd do next is with that 12:1 go back and add more timing in increments of 2. Do another base pull at 30 ( hopefully 12:1 AF ) and then add 2 more degrees and see what happens. It should make more power and lean out a tad at the same time making even more power etc.

I wouldn't be surprised if around 33 degrees and 12:5 AF you gained another 30whp.

Missing up top could be valve springs or plug gap etc, hard to say.

[gearbanger]

I ran it last night with the 7000 MSD chip in it. No Change.

I am thinking valve springs too because it didn't do this at the last two trips to the drag strip because I experimented with shifting at 5500 and 6000 to see if there was a difference in et. There wasn't but I did notice that I thought the car didn't pull as hard after it got above 5500. The dyno seemed to show different though as it made its peak power right before it started the popping and cutting out.

I am going to throw on the old carb tonight and run it again, if it still does it and am pretty sure it will get a set of valve springs.

How long does a set usually last? These have been on since sept 05. I wonder if they were ever really strong enough because of the way it stopped pulling hard above 5500.

[gearbanger]

Well after talking to JK, it appears the general consensus is valve springs. He is sending me a set of .060 shims to bring the seat pressure up. That should definitely tell me if that was the problem.

[440GP69]

if ya don't mind me asking, where did you get 2" primary headers?

[gearbanger]

The headers were made by MadDog. They had to be installed and sent back twice to make them fit and I still have a little trouble with really good clearange with the steering shaft. They install in four pieces and the drivers side rear tube goes outside the frame rail.

Otherwise they are a pretty good piece. They hang a little low but I don't think you could really do any better without modifications to the crossmember and custom making them on the car. They have adapter plates that allow for wider bolt spacing and that makes for even less clearance between the head flange and the frame.

Headers on a A-body are such a PITA.

I have about $1200 in the headers including shipping them back and forth and sending them off to Airborn Coatings for ceraminc coating.