Ok so I have a wideband hooked up to my car and at idle she reads fine. Right around 14.3 to 14.7 I would say. Then I get on the gas and she is still fine when going slow. If I lay on it HARD she is still pretty much fine, the car stumbles a little, but pulls hard.

Problem is part throttle. If I give it like 30%-50% of the throttle. She bogs and the O2 reads like 19 and up to 21 or so but is jumping around like crazy. I just had the car dyno tunned at the end of the summer so I thought the the jets were right.

I have a jet kit, should I toss in some slightly larger jets on the primary side and see what happens?

(PS, I am new to tunning carbs, thats why I got the dyno tune. I have read the Holley carb book and stuff, but am def no expert)

 

dont know about you but its getting cold where i am.... cold air = denser air charge = more air then fuel on the same jets.
id throw some larger primary jets in should clear the problem up.

 

Leave the jets alone. They're not the problem.

What's happening, is that the power valve is not opening soon enough. The vacuum has to drop TOO MUCH before the carb goes into power enrichment. In between the point at which the vacuum has dropped enough to where the engine wants power enrichment because of throttle opening, and the point a which the vacuum has dropped far enough to actually allow enrichment, you have this llllooooonnnnnnngggggg flat spot. Pretty familiar.

Put a higher # PV in the primaries. Stock, it's probably a 65 (vacuum has to fall to 6.5" for enrichment to occur); try a 85. See what happens. If it gets better but not perfect, try a 95. Etc.

 

Well, guess I will go back to stock then cuz I have a 45 in there now. Before they car was tunned a different way and was bouncing around with 6.5" of vacuum all the time and I the power valve was opening and shutting all the time making the car run rich, just at idle. Now with the new tune it pulls 9" at ilde, so I will toss the 65 back in and see if it helps.

I will do it tonight and report back tomorrow morning.

sofakingdom: Thanks for your help. I will closely monitor how the change helps or hurts and let you know. You seem to have good advice. Thx.

later

 

What jets are in it now? I agree the overall jetting is probably right, given that you have it dyno-tuned, but you could be lean on the primary side/fat on the secondary side. Works just fine at WOT, but might be squaky-lean at part throttle running on primaries only with the power valve closed.

 

Before you change anything check the float level. If it's wrong everything will be a little off, esp. if its low. Check it in both the front and the rear. If it pulls 9" vacuum at idle then you should need a 65 or 75 power valve. Also check your accelerator pumps for proper operation, esp. the rear.

Did they change the jets when it was dyno tuned? If so how much?

 

yes they did. A lot. They had it on the dyno for 4 hours trying to get it to smooth out. Crazy. It has big jets in it now. I forget what they are, but they said they were way bigger than they thought it would want.

I can call and see if they remember. But I am 90% sure my floats are great. I checked them a couple days ago. The linkage is all good too. It must be the 45 PV I am running.

If thats not it, i will check jets.

 

your combo was abit mismatched to begin with so its gonna be harder to tune that thing perfectly

 

Yeah, i know that now. Which is a bit gay since I bought the combo from trickflow as a set that is supposed to push out almost 500 fly HP!!!!

I would have never done it unless if I knew it was a lie!!

I have no idea what the deal is with this motor. I paid so much for it and it is pissing me off. I wish I could go back and change get a crate motor instead of just getting a head/cam kit and hoping for the advertised power.

I just wanted forged parts since I am very "into" having strong parts.

Now it kinda seems like wasted $. If I spray a lot of go turbo in the future at least I know my bottom end can take it.

 

This is typically a sign that the fuel delivery to the carb is dropping off.

RBob.

 

Yeah, except I have 2 fuel pressure gauges that don't move a pinch even when shooting a 100 shot of N20.

The pump pumps a TON of fuel, has a nice areomotive FPR and all 8 -AN lines with a 8-AN return.

I am positive the flow is good and that the floats are full. It has to be the PV or the jest, or a little bit of both.

 

What carb's on it now?

Jets being "a lot different than stock" is not usually a good sign. Usually means something else is out of whack either in the carb's basic functioning or elsewhere in the motor.

 

a 750 holley DP. It had to be changed quite a bit cuz the cam is so big and they were also tunning the air bleeds at the same time. I will need another dyno tune again once the new intake and cam are in. I will change that PV now when I go home.

 

sofakingdom: I think you are entirely right. i swaped out the 45 for the 65 and with the initial test drive last night i couldn't get the problem to come back.

I think you fixed it. I am getting a new computer over the weekend and will be able to data log again. I am going to go data log me accelerating slowly, moderatly and heavily to see if I can find any lean spots.

But the way it drove last night was a dream. Pulled hard, no flats spots really. With this cam, when the RPM are low it syumbles over itself a little, but after 3000 it pulls hard and keeps pulling harder and harder till you let off. I think the 4.11 make the car feel a lot more powerfull than it is.

Anyways, I am happy and thanks for not having change the jets around, that would have been a nightmare.

 

what did that thing dyno and at what rpm's?

 

I have the dyno sheet and home and it got a little wet b4 I was able to post pics of it, but the max TQ was 340 at around 3500 and max HP was 344 at around 6500 (I think) I will post a pic of it over the weekend.

The nice part is that the TQ stays above 300 All the way to redline. And is above 300 at right about 3000. The HP I don't remember as well. All I know is that the dyno guys say it seemed strong so that was nice, but i bet they say that to everyone.

I asked them what a C5 ZO6 puts down and he said that it puts down 350, so only 10 more HP than me. Different RPMs I bet but whatever. Nice to know where I stand. Now i just want to see the dyno sheet with the 200 shot on there.

 

cool. The torque seems a little low for a 383ci. I would like to see where the peaks are and how the entire curve looks for that cam. If you get it posted, cool. Depending on weight of the car, you may have a mid-high 11 second car....11.75 ish @ 114ish on SLICKS with a 5500rpm launch and a 1.55 60'.

 

yeah TQ is a bit low but I think thats cuz I am running 2" worth of spacers ontop of the Vic jr. Without those I think those #s would look better.

I am going to swap the cam, intake, ditch the 1" spacer and keep the N20 plate and get another dyno tune with the 200 shot as well as N/A.

I mean it is fast for me. The only other car I have to drive is my moms 95 Carolla wagon.

With the TQ curve moved down, it will feel even better. Also with the N20 dialed in, it will be tons of fun since around here it is not uncommon for me to drive to the movies or soemthing and find myself totally alone at night on the highway. I just with that Mustangs would pull up on me, but with a 4" catback, a 6 point, 315s, 3" cowl, ZO6 brakes and a Choooopy idle, they ALLWAYS stay away.

 

I just have never understood why anyone would want to the Curve moved down. I couldnt care less how it feels at low rpm as long as it gets out of its own way and isnt a total dog....Like say a 4 cylinder with a huge turbo making 500hp....Hell Im not sure that would bother me. Hell that helps keep ya outta trouble because your not moving so quickly with minimal throttle.
I just LOVE the feeling when the power comes on a 4500, KICKS you in The ***, and screams upward of 6500rpm. Who cares how fast it is when your foot isnt on the floor....I know I dont. Its like ride a 1450cc Softail Harley and then ride a 600cc sportbike like a ZX-6R or GSX-R 600, or a YZF-R6. There is just no comparison in fun factor there. Like when the tach swings past 10,000rpm and the front tire shoots for the sky in 1st gear.

 

I see what you are saying. i like it too. I like how it SCREAMS up to 5000 and pins you. But after a second I have to let off cuz there is traffic or something else. I just don't like having to rev up to the power. I want it to be where I am driving so I have it all the time. I want the car to be fun MOST of the time and 90% of the time I am between idle and 3000, when having fun I am between 3000 and 5500. I just want a cam that can pull hard then and not at 6800 like i have now. There are just too many cops and too little road to have something that needs to have that high a rev. Also I want to have more vacuum and better MPG. Since with the cam and therefor motor now wanting to be anything less than 3000 it is very inefficient down there. Maybe with EFI it is better and able to tune, but with a carb it wants to run rich down low and pull hard up high. I want to run perfect down low and maybe a hair rich up high. I can't do that with the cam I have now, I the 00468 cam brings the power down about a grand and will make my brakes work better. I think it is def worth the hasslte of the swap.

But thats just me and to each his own.

 

I still would go NO LESS than the comp XE282hr 230/236.

 

z28freak84: You and my dyno guy think the same thing. I was on the phone with him for about 1/2 hour and his first recomendation was the comp XE282hr 230/236. He likes it due to the lower lift and better duration than some others. He made some good points. The inpuls momentum of the cam hitting the springs would be much higher due to the less duration and still comprable lift if I went with the 00468. he says I should go with a little less lift and only a little less duration. Stick with the 1.5s and be done with it. Slap on the RPM ari-gap and call it a day. Makes sense. He also talked about many other cams that GM used to use back in the day to make power on motors that need to last 100,000 miles. They had low low lift but very long duration so that the springs didn't go get put under a lot of stress. From a mechanical stand point I like it a lot. I will ask my dyno guy what he thinks about needing a small base circle. I still don't see why I would need one since I don't have one now, but oh well....

So the XE282???? Going once....