Ok so I'm still beating my head against a wall trying to figure out why my car isn't fast. I've come up with 2 final theories....either I have something wrong in the shortblock that is really killing power (I'll be doing compression and leakdown tests when it's not sub zero outside) OR the fact that I'm still using the bone stock airboxes and inlet hoses is choking my engine out.

What are all of you guys that are making atleast 350 rwhp using as far as filters and ducting into your throttle bodies? I mean the stock airbox gets really thin/narrow where it passes over the radiator support. I'm hoping maybe this is corking up my intake and power potential?? I know this is a very bad idea for a few reasons, but once the ground clears here I was thinking of taking the car for a very short ride on a very clean road with the intake box removed and just the MAF open to see if I feel any major difference. This way if I do I can design something new or look into an aftermarket kit.

Any input would be highly appreciated.

 

Cut off the bottoms of the airboxes & add a TB foil


See if you notice any major difference. I can imagine the stock airboxes left uncut would really restrict some air. Cutting the bottoms off was one of the first things I did immediatley after purchase!

 

Have you descreened your MAF sensor? That will increase air flow from about 529 cfm to 711 cfm freeing up some cfm's to feed that 383 the air it needs.

 

The airbox mod, tb foil, and descreened MAF should help.

Seems to me tho, that you have a serious bottleneck somewhere if you're feelings are accurate. I'd find someone with a wideband O2 sensor to see if you're leaning out and/or running rich in different areas of the powerband. Your sig doesn't show a custom chip... I seriously hope you have one, if you don't that'd be next on my priority list. With your combo, a stocker chip would hold you back a TON.

 

I have seen 2 z28's collapse the factory tube in-between the tb and the airbox. Both cars were miniram'ed. Cut out the bottom of your airbox and put in some k&n filters, and run some tubing from the bottom of the airbox to the air damn openings next to the license plate. You will need to reinforce the area between the tb and the airbox with something metal, so it does not collapse.

Don't fall in love with dyno numbers. The cut out air box and cold air ducting won't show a benefit on the dyno because there is no air moving over it.

Take it to the track, that is the only way to know what you've got.

 

I am replacing the stock TB bellows tube.

Not because I think it will collapse but for a few upper RPM horsepower. My materials:

(1) 4" hump hose - silicone
(1) 3.5" to 4" transition hose - silicone
(2) 3" plastic couplers from home depot
(1) 3" diameter pvc pipe section

So... starting from the air box. The 3.5" end of the transition hose goes over airlid outlet. The 4" end of transition hose goes over a 3" plastic coupler. That same plastic coupler goes over the PVC. PVC runs into other 3" plastic coupler. 4" hump hose connects over the 3" coupler over the PVC and to the TB.

The biggest expense for me was the silicone hose stuffs. I am sure other materials can be used to success like traffic cone. The reason for chucking the stock bellows is because it contains way to many ribs to turbulize airflow. These materials add up to a much smoother air transition from airlid to TB.

 

Sorry for the confusion. I do have a custom chip that was done by SkiDwnIt a few months ago. Also I already have K&N filters and the MAF screens have been removed. I think I'll try my idea of removing everything infront of the MAF for a short drive when the weather finally breaks and if it works out I'll devise a new system.

I was hoping for some better answers from anyone else who may have tried using the stock factory setup with their new engine and then modified it after.

 

Paul, hook a vacuum guage up to a port on your plenum and mount it so you can see the guage while you take second gear up to your max RPM. Let us know how many inches of vacuum you are generating at WOT & max RPM. This will show how much actual restriction the engine is seeing up to the plenum area. Then we can go from there.

 

Sorry Paul, but you have something more than an air problem.
We have have two cars out here making more than 325(both 350's) to the rear wheels with the stock air boxes (thin thing) one has the SR and one is a long tube (AS&M runners). You need to get in to it more to find whats wrong, I don't think it's air.

 

Here ya go:

 

and this:

 

Yeah I'm worried I have something else wrong too, but at this point it has to be in the shortblock because I've checked everything else. I guess I'll have to pull the headers so I can get a compression and leakdown tester in there on each cylinder. Other than some bad rings what could be killing so much power??

 

Maybe I'm coming in on this thread too late but, have you checked your knock counts?

When tuning my 383, I found that the ecm was pulling out 12 degs of ignition timing. We disconnected the ESC and found new power. I am using a DFI and have permanently disconnected the ESC.

My car ran 12.0@113.5 with pretty much your same setup.

Good luck!


www.geocities.com/dzperf

 

I had a few knock counts at very sporradic RPM's so the chip I'm running now actually has the knock retard disabled. This is only temporary until I find what's rattling, banging, etc. to cause the knock condition.

 

Got proper clearance between rotating assembly and block, cam, oil pan?

Maybe you are bouncing your crank off the oil pan, this happens sometimes in 383s.

What are your 02 voltages at WOT?

What does your WOT spark curve look like? If your timing is off you will be down on power if it pings or not.

Got proper sized gaskets? Port mismatch, reversion?

Clogged exhaust?

Is there audible ping?

What voltage does PE come in at? What is your WOT TPS voltage? Is your TB opening all the way?

Who built the motor?

 

Properly adjusted valves?

Valve float?

Poor valve job? Valves not seating properly.
We had to send a set of Pro 1s back to Dart with a buddys buildup as the valve job sucked and the vlaves wouldnt seal right. This was before we put the motor together though

 

I'll have to admit....I built the engine and didn't use plastigauge at all to measure the clearances. (Young and stupid is my only excuse on that one).

I know the crank shouldn't be hitting the oil pan because I did clearance that.

Exhaust is definately not clogged, especially since I recently had an electric cutout installed right before the cat.

My TPS voltages are fine and the throttle body is opening all the way.

I have a meter wired directly into my O2 sensor and I'll have to double check the voltage at WOT, but SkiDwnIt said it was damned near perfect.

No audible ping, gaskets are all good, and the valves were adjusted by a friend of mine who's a professional mechanic and works for a race team so I'll trust him on that one.

 

Can you describe your exhaust system? Was the cam installed straight up? Is your TB atleast a 52mm or bigger? What's your fuel pressure?

KM

 

The cam is straight up. I didn't degree it though (once again young and stupid and rushing to get things done.)

The exhaust is as follows: SLP 1 5/8 headers and y-pipe, 3in. electric cut-out, high flow 3in cat (single), Flowmaster American Thunder Series cat-back.

My fuel pressure it set at 48psi currently. I have tried adjusting it up and down with no results.

I am running a 58mm Edelbrock/BBK throttle body

 

vacuum at WOT?

 

If you show any vacuum at Wide Open Throttle then you have some type of restriction meaning your eng wants more air but something is restricting air flow before the manifold.

 

Paul,

Do the mod that 1bad91Z shows above. Its really awesome. I did this to my IROCZ about 5 years ago. Truely, the best ram air for our cars.

You remove your fog lamps and cut out the bottom of the boxes just below the two air filters. Now fill in the passage from where the fog lamps were and the filters with some kind of ducting. I could tell an immediate pickup in HP.

I actually bought what might have been the last molded ram air piece that some guy manufactured. But you can use air conditioning duct work or plumping, just look around for some thing thats you can bend 90* and is about 4" in diameter.

It looks like 1bad91z has a fabricated metal ducting, his mod looks great!

BTW: I'm biulding a 395 cu in motor right now, so I will find out this Spring if I have a major air feed problem too. My best trap speed with the current 350 was about 105mph.

 

Came across this and remembered your problem:

http://www.chevyhiperformance.com/techarticles/49161/

 

Fevre thanks for the link. While that is a useful article for some it doesn't have any relevance to my problem I don't think. My block is a stock roller cam block and therefore has the plate that bolts right over the end of the cam to keep if from walking.

I definately appreciate the research though. Hopefully somebody can be an in depth in their search as you and help me find a lead on this problem.

 

Assuming since you did not check the other clearences then the cam endplay is also in question. Just because it should be fine you will never know until you check it, cam could be a few 100'ths of an inch short giving you lots of play. Guy over at my vette forum is putting together a 383 like yours, newer block with a thrust plate, and found his end play to be out of spec, his was too tight so he had to shim to allow the .004-.006 end play. I have done my fair share of 'it should be fine' eng building so I am not trying to knock you. Keep looking you'll find the cause, doing that right now with my Formula, won't start.

 

\

one more time...

 

Do a diffrential compression test on the motor or have one done for you. This should set you at ease with the short block as long as your oil filter isn't trapping metal or some crap like that. Cut your filter open and examine for signs of trouble.

Have you had a wideband on this setup yet? Unplug your knock sensor and take it for a ride. You'll know right away if that was the problem. Maybe try wrapping the threads of the knock sensor with some teflon tape (alot).

How confident are you that you got your timming pointer zeroed correctly? Try playing with your base slightly and see if things start to improve (be very attentive here).

Borrow a scanner (Diacom etc..) and send Ski_Down a trace to look at. Borrow a wideband, build a wideband, or go see a shop with a wideband. Every car's tune comes in differently and yours may just need a little more!

Let us know what you find
Good Luck!

KM

 

1bad91Z
I love the way you did this ram air. I did the same thing but with plastic sheets it works very well but isn't as pretty as yours. Probably lighter though.

 

My metal boxes weigh less than 1 pound per box.

 

Definately haven't had a wideband on it yet. Right now it's just way too cold to be even thinking about working on the car. Probably will start some serious searching come April. Definately keep the ideas coming though.

I'll try to get that vac reading this week if possible.

 

You need some insight into what the engine's actually doing. Using a scanner or datalogging will give you that.

Not to mention the key to getting the most out of an engine is proper tuning. ie chip work.

 

Granted I didn't have a wideband hooked up, but when I went out to SkiDwnIt's place he said that my chip was pretty close to begin with. We made a few minor changes and that was it. I didn't gain any power out of them, just some driveability.

 

ttt

 

Sorry for no updates but I"ve been busy repainting my truck the last few weekends so I haven't touched the car really. I took it out for a ride last night but that was it.

The car is very sluggish all the way up to like 3500 or 4000 then it takes off like a bat out of hell, but it shifts around 5000 or 5,500 so it doesn't have much time to run that way.

 

Geez, Paul still haven't figured it out? That sucks. Forget the compression test do a leakdown test even though it's a PITA. I did the same thing with my iroc a year ago, I had it tuned perfectly and w/ my SR/AFR/219 setup and only ran 13.3 at 101 or close to that. I ended up having 25% leakage in my 8 and 4 cylinders. I'm guessing broken rings but the engine was never taken out to verify it. I was losing about 90hp that's for sure.

Oh yeah I own one of the cars that 89gta383 was talking about with the intake problem.

 

Yeah as soon as the weather gets tolerable I'm planning on pulling the headers off to do a full leakdown and compression test. Unfortunately I can't get either tester in atleast half the plug holes with the headers on.

There is definately something wrong. I just took the car out for a ride tonight and I swear it sounded like it had the death rattle while I was driving it. When I got home though and popped the hood I couldn't hear anything abnormal. Also it is definately burning oil. I can see it big time when I'm decelerating and a little on acceleration. The engine only has about 7k miles on it but it didn't smoke this bad when it was first built.

This may sound stupid, but at this point I'm almost hoping there are some broken rings because I feel like I've been chasing a ghost all this time.

Opinions are welcomed

 

I would just rip the topend off and do a visual after the leakdown.

 

That's a possibility, although the Super Ram is a total PITA to remove and install, even if it will be my 5th time.

What would I want to look for? Scored cylinder walls?

 

I also have a SR.

Sure, just a general look over everything. Scored walls, broken rings, broke pistons, just check it all out.

I would be unsettled if I was in your position and would tear it down for piece of mind.

 

Good call

 

Ski who used to post here had the same problem that I was experiencing w/ my Iroc. His times were just a little quicker than mine with the exact setup of course his was a vette. The difference was his was a worn out stock bottom end and mine was freshly rebuilt. I'm pretty sure I grernaded some rings from detonation when I first started that 383 up and broke it in. Ski had the broken rings and similar leakdown readings that's why I always assumed my rings were bad. Plus that Iroc had severe blowby from the PCV valves.

I love the miniram on my 91, 12 bolts and that's it. It makes life so much easier. I also thought I never would want or need a 6500+ shift point, but now I love it, wouldn't want anything else.

 

Sorry to say it, but if you degreed the cam correctly, don't have any vacuum leaks, and are sure about the state of the tune, then you will probably have to tear it down for inspection. Have you pulled the valve covers to see if anything is out of whack? I used to get vacuum leaks on my old superram. You always have to go back over the bolts when the intake cools down, even though taking off the valve covers is a pain.

 

Paul just so you know, I had my old 383/SR/AFR/219 combo on the chasis dyno with about 20percent leakdown on four cylinders and gess what? 256 laughable rwhp and 318rwtq on an engine that shoulda made 330+hp and 350+rwtq. The rings are shot on this engine from detonation or whatever and although it runs decent it's a joke at least to me and my new engine.

 

Yeah I think my current performance level is pretty poor to say the least. I am planning on pulling my headers in another week or two for a full leakdown and compression test (can't get the tester in with the headers on).
At this point I'm actually hoping I find some problems with the rings because if not I'm going to just grenade the engine and start new anyway!
Now if money wasn't so tight right now I could think about rebuilding it better.

 

Paul- this sounds a lot like ignition timing. Easy to check also.

It's a 383, so you had to replace the harmonic balancer. You probably re-used your old timing tab. If so, you have no way of knowing that the tab is scaled right for the new balancer.

I've seen instances of different 350 balancers having the TDC pointer in different locations...owner had same problems as you, down on power, but the timing light showed 6deg BTDC...in reality, we found it was over 8deg ATDC.

The ECM masks some of this problem, as it starts adding timing at the higher rev/load coordinates of the spark map.

So...go check your timing. Pull your old balancer out of storage if you have it, and compare the location of the TDC line relative to the crank keyway against your new balancer.

If you don't have the old balancer, you could probably carefully start adding advance in small increments and re-testing while watching the knock retard.

 

PS: not using Plastigage or mics was definitely a bad move, but if you're not knocking and it holds oil pressure you're in OK shape for now. It's more of a longevity issue.

 

Yeah definately dropped the ball with the plastigauge and mics.

I don't have my old balancer however I have experimented with my timing a few times with no change. I've added up to 8* above where I am now with no changes...actually ran into some detonation so I dropped it back down.

 

About all I'm left with is cylinder pressure leakage and/or cam degree error.

A leakdown tester (not compression tester) will diagnose or rule out the first one, the cam error will require a degree wheel and a lot of engine disassembly.

Good luck dude.

 

I have to raise an eyebrow to the fact that your stock chip wasn't that far off with your pretty wild setup. It should have been pretty far off. After tuning my tbi setup to a much tamer setup I have to wounder how close your car really is tune wise. By the way washing down your cylinder walls with fuel will make it burn oil like no tomarrow.

 

I didn't use my stock chip at all on this engine. The first chip I used in it was custom burnt by Ed Wright then SkiDwnIt helped me tweak it a little more but the numbers were already pretty close with Ed's chip.