pellmanm

iTrader: (1)

This last weekend I was finally able to run my new engine for the first time, take it out and break it in a little, along with my rebuilt trans and new rear end. The car is an 89 GTA that has been converted to speed density. I am running an AUJP bin and have only changed a few of the constants such as injector flow rate and a fan controls. After emulating the bin, and setting the timing i took the car down the road, and it wasn't running well. I know its not going to be great since it will need to be tuned properly, but it barely had half of the near 500 horses that it should. Next i hooked up a vacuum gauge and i only have 9 inches of vacuum at idle, and i think it should be twice that. Another thing is that i had to turn out the idle speed screw as far as it would go in order to have the car idle at 700 rpms. That makes me think that it might not be running on all cylinders. Next weekend i am going to use an infared temp sensor and check the headers and make sure they are all warming up, but i wanted to see if you guys had any thoughts. By the way i have degreed the cam, so i am sure that the cam timing is correct as well.

Here is some of the specs on my engine:
-383 short block 10:1 compression
-Trickflow 195 cc heads
-Cam Specs comp cams 280xfi:
Operating Range: 2000-6000 RPM
Duration Advertised: 280° Intake / 288° Exhaust
Duration @ .050'' Lift: 230° Intake / 236° Exhaust
Valve Lift w/1.6 Rockers: .576'' Intake / .570'' Exhaust
Lobe Separation Angle: 113°
-superram intake-gasket ported
-58mm holley throttle body, holley fuel pump, holley afpr
-30 lb-hr. injectors
-slp 1.75 headers

pellmanm

iTrader: (1)

Does anyone have a similiar set-up or have an idea of about how much vacuum this engine combination should pull at idle?

Mkos1980

iTrader: (8)

I ran the same motor and heads but with an LPE 219/219 560 560 112 cam and I was around 14 inches at idle. I ran this combo with stock injectors on a stock 89 bin and power was awesome and knocked down some good numbers and MPG. But I've since moved onto tuning.

pellmanm

iTrader: (1)

Is it possible that my vacuum is normal then? I still think i should have more vacuum, my cam should not have that much valve overlap that it would cause the vacuum to be that low. I know a healthy stock engine should pull around 20 inches, i am getting less than half of that.

brutalform

That cam is a nice size cam, but I would think your wide 113*LSA would yield better vacuum. Is the gauge reading steady, or moving slightly, up, and down. If it is, could be an A/F ratio thing. Also, a low vacuum reading could indicate, a bad intake valve, (which I doubt), or a leaky intake, runner, or plenum. It might be leaking, and you wont necessarily hear it. Check all you vacuum sources, dont forget the brake booster either. You might have to spray the areas to find if the engine raises RPM, to find a leak.

One more thing, that engine will probably LOVE more spark advance. I hope you are ready to really dive in the tuning process.

pellmanm

iTrader: (1)

The vacuum gauge is steady at about 9".

I am armed with my Autoprom and TunerPro for the tuning process, this weekend i will check the headers for similiar temps, and also spray for leaks. I really don't think there are any leaks as far as the intake manifold and vacuum lines are concerned.

One of my friends had a similiar problem when he rebuilt his engine. He put it all together and he around 10" of vacuum, maybe a little less. He did a compression test and found that one or two of the cylinders did not have any compression. He took the heads off, inspected them, found nothing wrong, so he put the engine back together. This time when he tightened down the rocker arms, he only went a 1/2 turn past zero lash instead of 3/4, and the vacuum was fine. I don't know if the lifter adjustment is what fixed the problem, or if that was just a coincidence.

Because of this, i am a little suspicious of this with my engine, since i used 3/4 of a turn past zero lash, which i have done for many older engines and never had a problem. Could 3/4 of a turn past zero lash cause the valve to stay open?

brutalform

Well thats a good reason to suspect it. Not too hard to check either. I never go more than 1/2 turn on the adjustment, or less for that matter. That cam, even with the 113 LSA, still might give low vacuum.

Cats, and exhaust system not plugged, or crimped?

pellmanm

iTrader: (1)

Right now i have an open SLP y-pipe attached to my1 3/4 headers. But i can just pop off my valve covers and check recheck the rockers. I will have to do alot of troubleshooting this weekend, but i wanted to see if i can narrow it down a little bit during the week.

pellmanm

iTrader: (1)

So I went to my shop today and i took off my valve covers and re-adjusted the valve lash to 1/2 turn past zero lash. I hooked up the vacuum gauge, and i still only have 9" of vacuum. The reading is fairly steady and only fluctuates between 8.5" and 9.5".

Is my next step to take off the headers and do a compression test? Or is it possible that the cam is really taking that much vacuum combined with a non-tuned bin. I have only changed some of the constants such as injector flow but haven't done anything with any with the tables.

I really don't think the cam should give a vacuum level much below stock with the wide LSA and mild duration that it has. I also do not think that it is an intake gasked leak. Does anyone have any more ideas?

Lo-tec

700rpms is a little low for idle, I have a similar comp cam (230/236) on a 110 LSA that idles at 800 with 13" of vacuum in neutral (stick). Sounds like you need to do some tuning; yours should pull 14"-15" of vacuum with the wider LSA at a slighter higher idle (800-850??) pretty easily.

pellmanm

iTrader: (1)

So are you saying you think it is tuning related, or do you think it is something more serious. Now that i have converted to MAP, it is probably initially worse than maf because the lower vacuum reading is throwing it more off. If it is tuning related, can i really make up 6" of vacuum through tuning it at idle? It just doesn't make sense that it only has 60% of the vacuum it should. Plus when i took it out on the road, it just fell on its face, although that could be tuning as well i imagine. It is just hard to tell because this is my first heavily built up fuel injected engine, so it is difficult to tell whether it is ecm related or mechanically related.

Lo-tec

If you have a stock speed density chip for a stock TPI engine with just the injector constant changed, you will need alot of tuning. I looked at your laundry list for your engine (nice setup), and I would be happy that it runs and drives with the stock chip. If it makes you feel better you can do a compression test, but I wouldn't worry about it right now. Another possibility could be a vacuum leak as brutalform posted earlier and super-rams are famous for.

brutalform

BTW, your engine is going to make the vacuum it makes, I would not worry about it. As long as its steady, and there is no exhaust restrictions, etc, you should be fine. I only pull 11 inches at idle, and my cam has a 114* LSA. Whatever my guage reads...so be it.

Also, Ive picked up quite a bit of power through tuning.

pellmanm

iTrader: (1)

This weekend i did a compression test....175 psi on all cylinders. So i know everything up to the manifold is good. Then i put a sealed plated behind the throttle body and plugged all the vacuum lines. I put a vacuum pump on the plenum and found a vacuum leak in the PCV hose where it attaches to the hose barb (crappy hose=sloppy fit). Im not sure if that could be the sole cause of my low vacuum. Could that affect it that much? After putting a new hose on, the intake holds vacuum. I don't have the engine running yet to see if the vacuum is better or not. How much could this possible raise my vacuum?

vernw

iTrader: (2)

When you did that vac test, was the plenum off the motor? Seems like it would have had to be for the manifold to hold vac (unless all the rockers were off so that all the valves were closed). IF the plenum was off, check the runners to intake manifold fit and sealing. Speaking from experience, my 383 had lots of vac sealing problems that took a while to sort out. Check the overlap on your runner to intake junction. If you have the older style gaskets there can be as little as a 32nd of an inchof gasket to try and seal those runners. Also (sad to admit this) but make sure none of your lower runner bolts are bottoming out in the intake before totally compressing the gasket. You shouldn't have to ask me why I know of that potential problem - but in fairness the SR/Accel lower intake manifold is not threaded very deep. At least mine isn't. You might check that all the threads go all the way into the hole, and there are no thread mismatches (metric as opposed to SAE). My 218/224 duration 112LSA cam pulls about 16.5 to 17.0 in my 383 SR setup. My compression is a lot higher than yours though, mines supposed to be 10.5:1 and a compression guage on mine shows more like 230-245 PSI cranking it over with the throttle blades open.

pellmanm

iTrader: (1)

I did the vacuum test with the rockers backed off (valves closed). I am not sure exactly what my compression is, but it is supposed to be around 9.5:1 to 10:1. I am pretty sure my superram is sealing fine now. I am a little curious as to why my compression is only 175 cranking it over with the throttle blades open, but all the cylinders are equal. I am using dished pistons, but my deck has been milled down a bit, i am also using 64 cc heads.

vernw

iTrader: (2)

How long did you let it crank before reading the compression gauge (or were you turning it over by hand)? I was cranking mine with the starter until I saw the oil pressure guage come up (about 6 - 8 seconds for each reading). That's when the readings would max out and stabilize as well. My SP2 heads are 64cc as well.

I may have to try your vac test method on the SR (never thought of that one). That would definitely let you know if there is still a vac leak somewhere. Sounds like you don't, and that's GOOD!!! I may just have to try that one this weekend, been debating on changing out my aluminum 1.6 intake and 1.5 exhaust RRs for a full set of Comp Pro Mag SS 1.6 RRs anyway, so that would be the time to probably do it.

Guest

I have that cam with a 350, ported AFR 190's, and TPI and it pulls about that much vacuum at idle, a little more when warmed up.

I think you have a different issue if you have to open the throttle plates up all the way (that is what you did, right?) to get it to run. I didnt have to do that. Sounds like you need to get into the chip and raise the idle, the throttle blades are not the way to do that. The ECM controls the idle speed. Likely the TPS is way off, among other things. Start there, the rest should fall into place.

pellmanm

iTrader: (1)

Thanks, that is what i wanted to hear, someone with the same cam. my vacuum should be a little better now since i found the leaky pcv hose. my throttle blades are not cracked open that much after adjusting the air/fuel and the timing. I think the rest of it is tuning now. I did notice that my spark plugs look like they are brand new still, so it must be running lean.

vernw

iTrader: (2)

Or just about right.....

pellmanm

iTrader: (1)

This is an old thread, but i found the problem with the vacuum to be a cracked pcv hose and the lack of tuning. After installing a new hose and with a little bit of tuning the vacuum reading went up to 11 in hg. If i still had the engine together and did more tuning that number might go up a little more.

brutalform

Even though its old, its still good to have post what you found.

vernw

iTrader: (2)

Sure is!

Zipdrive

Well what happened to the motor?

pellmanm

iTrader: (1)

Its being machined at the moment because of a cylinder (oversized) to piston clearance issue. After that im getting a few higher perf. parts. Then we'll see what kind of power it makes.