Looking for some help from all of you folks who are smarter than I am out there.

Just wrapped up installing a new motor in my 1985 IROC. Was a 305 TPI car originally. It could be all in my head, but I just do not think it is right, and am looking for some advice on whether I am just expecting too much from the car, or if I am on the right path with my assumptions here.

Engine- 5.7 Vortec out of 97 Sierra. Re-worked heads for screw in studs, LT4 Hot Cam, 1.6 rockers, Holley Stealth Ram, 24 lb hour injectors running at 40 PSI currently, and a custom tune. 2500 stall convertor, built 700R4, and 10 bolt with 3.73's in it. Hooker shorty headers, and a y-pipe directly into muffler (waiting on my exhaust guy to get time in the shop to run new pipes on it).

Issues/Concerns
- Vacuum is one issue I have. It has enough to run the brakes and stop, but not enough to hold the car when I stand on the brakes and load the car up to either do a burnout or launch the car.
- Power- the car is definitely stronger than the 350 with the TPI setup on it, but still is not making the power I anticipated. It almost feels "hollow" pulling through the power band (I am running it up to around 6500k before shifting, it may have a little more left in her, but I am afraid to spin it too hard until I know its right).

My first thought is perhaps I have a miss due to valve adjustment issues. It is hard to tell due to how hard the car cam's, and I do not have a ton of experience troubleshooting this. My first thought was to go ahead and check compression on all cylinders, assuming this will tell me if I have a valve hung open (it does have a high volume oil pump, and my understanding is that this creates much more sensitivity to adjustment). If that checks out without issue, was going to move to spark next.

It does have brand new 24 lb/hr Accel injectors, so I am leaving fuel until last.

I guess my real question is, has anyone done this and had vacuum issues? Or for those who have done it, did you have plenty of brakes and power to boil the tires down low? Am I expecting too much or not understanding the setup I built well enough, and I need to stop chasing bugs that are not there, or do you think I have an issue and need to keep digging.

Thanks in advance for any help!

 

Sounds like 2 problems:

Not enough ignition advance
Tuning

Might both be part of #2 actually.

First thing to do would be to MAKE DOUBLE DAMN CERTAIN that wherever you THINK 0° BTDC (exact TDC IOW) is, is REALLY exact TDC, by some method involving observing the piston. Back in the day we used to use things like, a tie-wrap stuck in the #1 or #6 (they come to TDC exactly together) spark plug hole; in 2021, a cheeeep USB borescope is the better deal.

 

Brakes may not be a vaccum issue, stock brakes usually suck imo. Did brakes work before? What is your vacuum? You can try revving car up high in neutral then standing on brakes, then putting into drive to do a burn out. But converter and more power it may just want to push thru brakes regardless.

last hotcam afr 180 head car i did had plenty of vacuum.

how was the tune done? Was it on a dyno? Was it tuned with wideband o2 on street? What is the air fuel and timing? 6500 is likely way to high for stock vortec head deal, but wont know til you dyno to see the power curve. Usually i would see that being done closer to 6000-6200

 

Tune was done blind, based on engine setup ahead of it being built, by Brian Harris with Harris tuning. I will be candid, I did not get too far into the specifics of the tune, but he as aware of the exact setup. It is probably due to a more formal tune now that it is up and running.

And brakes were fine before, no issues. I will stick a vacuum gauge on the car this week and see what I am pulling on it to get a true number.

But, even if the brakes stink, I would think that car should damn near boil the back tires off with the amount of power it "should" have, coupled with 3.73 gears and the steep first gear in that 700R4. Would you agree, or am I being ambitious? I know with the old setup it would boil them, but I am sure I had a lot more torque with the original TPI base and the 4x4 comp cams cam I had in it.

I will double check the timing and check compression to ensure the valves are all closing as they should, and search out a more local option for prom tuning. I have a buddy with a dyno I can get some time on, just don't want to waste the time or money until I feel the car is running well. The lack of brakes really makes me think I have an issue causing it to run poorly and not generate enough vacuum, since everything I read says it should be fine with this setup.

Thank you both for your time and knowledge!

 

You definitely should have plenty of vacuum, might consider the 870 to 165 ecm upgrade.
the 870 is slow baud and uses a 2732a prom but can be upgraded to use a flash eeprom.
you can time he 870 but it’s more difficult than the 165 ecm.

 

I would get into datalogging and tuning yourself. I have never seen a mail order tune run perfect. Some work good enough but hard to tell how good it was until you sit down on the dyno or track and really work it out. Or even street tuning with wideband to verify afr and timing values. Im gonna guess thats a big part of your problem.

also make sure you dont have bad distributor cap and or arcing wires. Plugs i would keep at a .035” gap and dont run multiple ground strap plugs like e3’s. That be a good place to start to make sure ignition is functioning well

edit: good point on the 85 ecm. Def consider later model swap

 

Doesn't matter how much you know about a combo, the engine has to be tuned after it's running and together. There's no replacement for that. I would suggest ditching the stock ecm altogether and getting something more modern, but having the car retuned would suffice.
Stock TPI makes a ton of torque very quickly because of its runner length. Your new engine's characteristics with the stealth ram are going to be very different, but it should be making nearly as much torque a little higher up in the rpms and way more hp. It does sound like you're down on power.

Definitely double check the timing situation. You could also pull the plugs and get a read on what they're doing, a misfire or poor running condition would be noticeable there I would think.