scott13676

iTrader: (1)

I just got my motor broke in and finally pushed it hard and im not impressed on the low end. its a 383, crower 225/232@50 and .535/.550" cam, 2v flat tops, 70cc brodix ik200cc heads port matched to a performer rpm. holley 750hp, blueprinted hei dist. It has a th400 with 3,000 stall with a 3.42 rear gears. when I hammer it off the line it just doesn't seem to pull like it should, but when im doing 50 or so and hit it, the car goes like crazy. Could this be a timing issue? Thanks.

Jorlain

iTrader: (4)

What timing are your running at idle and all in? With a 3000 stall you should be pretty much be all in right off the bat. How much vacuum are you pulling? Any idea what your AFR is? How about your compression ratio?

The more info you can give us the better.

Piston454

Could also be off a tooth on your cam to crank timing chain (or gear depending on what your setups is). Might be retarding your cam just a hair to give it more so of a top end cam and you end up loosing more of that bottom end. Just a thought....

scott13676

iTrader: (1)

Im not sure on what the timing is set at. the engine builder did it, he also told me that there wasnt much timing in it. on the initial timing it was pinging under load, so we retarded the timing just enough to stop the pinging. i figure the static compression to be around 10.4. it almost seems like theres not enough timing.

scott13676

iTrader: (1)

would changing out the springs on the advance help me any?

fasteddi

iTrader: (2)

Is this just a street car or a street strip set up? I have a feeling you need to get into the timing curve faster. Personally I have mine locked at 34 degrees. But if you are using it on the street alot and use the springs and eights I would have it with full timing 33-36 degrees by the stall....3000 rpm on your case. Also is the carbed tuned well... what squirters are you running... power valve in front? In the back or blocked off?

I have a 385 with similar heads, cam exc. 200cc intake runner dart heads. Although your cam is a touch bigger then the one I currently use. Mines 226/230 dur. I can jank 1.58 60 foots at the track on drag radials. Its a tq monster for sure. I have 3.23 gears and a 3500 tq converter. 11.1 compression helps me.

btw I run 11.60s at 114-115mph in the 1/4. Its still a street car as well.

86LG4Bird

iTrader: (1)

That's a pretty small cam for a 383 with 10.4 SCR.
Are you running 93 octane? If not, I don't think you'll ever get a timing curve that will give decent low end power.

pancherj

Without knowing your base timing, total advance and vacuum advance, there is no real way to help you.

scott13676

iTrader: (1)

its just a street driven car. i run 91 ethanol free gas, thats the highest ive seen without ethanol anyway.

fasteddi

iTrader: (2)

I personally think your cam is just fine for a street driven car. Its matched well with the performer rpm intake, the stall/ Its about the same as mine and granted my car is gutless over 5300rpm... you can clearly feel it fall off, its a ton of fun on the road. Instant tire shreading power.

I think you need to work on your timing badly, and also is the carb tuned good? No stumbling? You arent running out of fuel or loading up when you stomp it?


Mechanical or vaccum secondarys? Also any idea what power valve is in the secondarys?

I run 93 octane with mine and i have iron heads...darts currently with no spark knock at all. Like i said its locked to 34 degrees of timing. I drive it arround a little bit here and there and ive never had a issue with detonation. And you have slightly less compression so even with 91 you shouldnt be having spark knock unless you are running rediculus timing. I still use my 7730 ecm so i have a knock sensor, wideband o2 exc... and datalog so that helps.

Here is a vid of mine leaving the line... clearly it leaves just fine. Or look at my sig video. I did have alot of issues with it when i first swapped it but it was all carburator related. It was a dog when i first got it.

scott13676

iTrader: (1)

the carb is a 750dp with a hp main body. throttle response is excellent. 6.5 power valve. idles nice. its when i hammer it off the line. if im going 50, hit it, it really comes alive. its a summit blueprint hei dist. with a med weight spring. ive got the vac line running to full vacuum off the carb base. the fuel pump is a carter mechanical that seems to stay around 6.5-7. i know when i had the 350 in it with the orig dist and pertronix upgrade it was a lot more responsive. could my advance be coming in too early or too late? im running out of ideas.

scott13676

iTrader: (1)

i can only hope mine launches like that,lol

NoEmissions84TA

iTrader: (1)

Block off the vacuum advance completely and then work on your timing curve.
Start at 12 degrees INITIAL.

scott13676

iTrader: (1)

thanks, ill give a try tommorow! scott

scott13676

iTrader: (1)

i forgot to mention in the beginning that on the initial timing when i first got it, it would ping. so we backed off the timing. scott

fasteddi

iTrader: (2)

Yea I never expected this engine to perform like it does but it was just great set up from 3k-5k rpm. I put the engine in last spring hoping for 12.50s or so in the 1/4 mile... Now from tuning and such it's a 11.60 car and 60s awsome.

I just still find it hard to believe you had to back out the timing since I run locked 34 degrees all the time and do drive it on the road exc and i even have iron heads and more comoression. Both our cams though dont blead off alot of compression so our dynamic compression isnt too good. But anyways I would do like they say above. Your timing is probly the issue but once you work on that, if you still feel is lazy out of the hole it may be something else.

Jorlain

iTrader: (4)

Is it hesitating or stumbling off the line, or is the acceleration just flat?

Was the carburetor modified at all? You are feeding more engine now than you were before. If it hasn't been tuned to this motor you might be leaning out a bit, which would cause a predisposition towards pinging. This would be less likely if it were out of the box and never tuned for the 350 it was on before. Were you getting the ping at all RPMs under load?

scott13676

iTrader: (1)

there is no stumble, i launched it today from a dead stop, shifted it manually and it goes a hell of a lot better than leaving it in drive thats for sure, but i think part of the problem is the secondary jetting is too fat. it has 84's. i still have to fine tune the initial timing. i think its getting too much too quick and wonder if thats part of the pinging problem.

scott13676

iTrader: (1)

on the adjustment thru the vacuum cansister, when they are shipped from the factory, is the setting anywere near right?

Jorlain

iTrader: (4)

It really depends. Every manufacturer seems to be different as far as what the stock curve is, along with what the vacuum can adds. Once you hammer the throttle though, you should lose most, if not all, of the vacuum advance. It should definitely have no vacuum advance at WOT if it's setup right. The only way to know for sure is to hook up a timing light and verify it with your own eyes rather than guessing this that or the other thing.

I'd go through Sofa's thread on tuning the Holley, too. I thoroughly recommend borrowing or purchasing a Wideband AFR kit. While your AFR is not the end-all\be-all of tuning, it's a very useful tool.

scott13676

iTrader: (1)

Thanks, ill give it a try. im sure sooner or later it will get there.

fasteddi

iTrader: (2)

Secondary's are 84? Is the rear power valve plugged and the front is 6.5? Man Id like to see what vacuum you are pulling at a hot idle. IMO 84s in the rear is way fatter then what i run on mine. And i would think you are in the same ball park as me...sorta 79 in back 73 in front. 5.5 power valve in front the rear is plugged. Squirters are 35 in front 33 in the back. But regardless I would also look at the fueling, check the plugs, exc.

Take it out. DO a WOT pull from 30 to say 70ish and then just shut off the engine. Pull off the side of the road and check the plugs. Check as many as you can although they all should be relatively the same. This should help you know if your fat or not under WOT and my guess is the secondary's....since you dont complain about the richness at idle or are fouling plugs.

Personally i use both a wideband 02 sensor and the plugs reading method to tune. Both have there benifits as using both is better then one or the other in my opinion.

scott13676

iTrader: (1)

sorry the secondary jets are 82's, 31 nozzle front and rear, no rear power valve.

pancherj

Do not mess with the carb before the timing curve is set. Otherwise, you will be chasing your tail.

scott13676

iTrader: (1)

Thanks, ill will do that. scott

NoEmissions84TA

iTrader: (1)

fasteddi

iTrader: (2)

I agree. But setting the timing up shouldn't take too.much time.... 15 minuets? Max even with a vac secondary

a timing light is your friend to make sure it's doing what it's suppose to and the base is set right.

pancherj

I agree fasteddie, but it sounds like he doesn't know where his is even at...just that there was some pinging (maybe). When working on an unknown engine, I first find TDC and make sure the damper and timing mark are correct. Then, set the base advance to 12 degrees as a starting point. See what the max centrifugal is and the max vacuum advance (using a hand pump) and then go from there.

NoEmissions84TA

iTrader: (1)

Did everyone miss this?

skinny z

Nothing wrong with running full manifold vacuum for the advance. In fact, it's often the only way to get enough timing into a big cammed engine and have it idle at a reasonable RPM (not saying the OP has big cammed engine, just saying). Problem is that it takes quite a bit if work to get it dialed in. A combination of an adjustable vacuum advance can (for the set point) as well as advance limiter will do the job.

As for the OP, the first thing I will ask is: Have you done a compression test? The cranking pressure will provide a reasonable clue as to what your compression ratio really is. You might be dealing with too high a SCR to go with that cam or it could be the other way around. Do a test a work from there.
Do you have the engine details? Piston to deck clearance. Head gasket thickness. We can guess that the 2V pistons will have about a 6-7 cc volume. You've quoted 70 cc combustion chambers. I've worked out to be somewhere in the 9.7:1 range with a piston that's .020" down and .039" gasket. There should be plenty of room for a decent timing curve.
What would also be helpful are the full specs on the cam. Advertised duration, LSA and ICL. Or the cam part number.

sofakingdom

iTrader: (1)

That thing ought to be able to light up the tires at will in low gears at any time for any reason (or no reason at all) no matter what.

Once it's established that the motor is mechanically assembled properly (cam timing and valve adjustment), I'd be looking at TUNING, in all its forms.

It will probably want about 36° of "total" timing, with 18 - 20° of "static" and the curve starting just off idle (1200 or so, for stability at idle) and "all in" by around 2800; then about 12 - 15° of vac adv on top of that. Getting the vac right will be kinda tough since the vac will be so high to begin with, with that small of a cam; if I were the guessing kind I'd expect it would want to go from full adv to no adv when the vac drops below around 14".

Someone wrote up a step-by-step process for tuning a Holley carb, on the carb board. One of the moderators thought it was so good he turned it into one of the "sticky" threads at the top of the page. Once you install a timing curve somewhat as I just described, you should take a look at that, and follow it from start to finish, in order, skipping no steps, not starting in the middle, not jumping around in any other order let alone no particular order at all, START TO FINISH, IN ORDER. I've tried it myself, more than once in fact, and I can assure you with 100% confidence that if your carb is in good working condition to begin with, IT WORKS.

Put that curve in your dist, go through the Holley tuning procedure in that post, then come back and tell us how many sets of tires you've already roasted just test-driving it.