Was testing on the dyno this weekend and noticed that one of the cars being tested (All motor drag civic H22 revving to 10,000rpm) had a wierd issue of generating manifold vacuum towards redline. So this was not noticable before as redline was 9400rpm and due to a change of cams we moved the redline up to 10000rpm. The drop in manifold pressure from 9400 (-0.2psi) to 10000 (-1.1psi) is large.

What is causing the negative pressure in the intake manifold close to redline? Usually we see a flat -0.2psi all the way to redline. Thoughts that came to mind are 1. Throttle body too small (currently 74mm) 2. Intake manifold runners to short (Skunk 2 pro series H22) 3. Intake piping length (Currently 3" exiting right headline).

I guess the main question would be if it is normal to see a drop in manifold pressure towards redline?

 

Whats the overall build consist of?

I'm leaning towards Throttle opening is too small.. have you tried another manifold to see if this does it? Reving a h22 out to 10grand, you must be a really nice setup.

On alot of na car's that i tune, including my own that are really efficent you tend to see alot of positive manifold pressure.. whats the cam setups and how are they setup now? Whats the exhaust setup?

 

what is the exact engine setup? what size tb? sounds like 70mm tb if using 3" pipe. need to know what the setup is...and how much power on what type of dyno?

intake runners definitely not to short, if anything they are to long on that manifold.

 

was going to say that, but redited because i didn't wanna jump to more then one conclusion lmao..

 

more information is required.

 

You can see pressure at the valve not at the throttle body where a map sensor is located..... Unless you have come up with some way of measuring close to the valve you are not seeing actual positive pressure.

 

This is just how i have it setup on my own car..as i'm assuming your asking about my personal car.

Map is tapped into a vac setup, that has the nipples placed roughly 1-2''s away from the entrance of the head. vac lines run to a box, that the map is reading off of. I've seen a good bit of positive pressure on mild days, on really cold nights, it sees a good bit more.

More or less on most cars that i've tuned, really nice setups do get around 980+mbar and can really get higher.. i've had cars that go high on low cam and then fall lower on high cam..showing there's some type of distorting in the intake or something of that nature.

 

Do you think this is happening before it after the valve closes?

 

I'm assuming an ITB setup? If that is the case, using a vacuume block seeing positive pressure is even less likely, with one cylinder filling at a time and 3 open to atmosphere to bleed any pressure out of your vac manifold.

 

I think this is happening after its closing.. I say this because the OP seems to have a serious setup going on, i dont know all the details but what its sounding like, is he has a really efficent setup for the lower side of things.

Once the air speeds up, its coming in at a force to where its hitting the back of the valve and possibly bouncing back and causing some type of disruption in the cycle..

Now, whether or not his cam timing needs to be adjusted, runners on the manifold need to be shorter, or possible the allowance of more air i dont know. I'm not there, i dont have logs and i can't see whats actually happening on the dyno. I can only throw out some educated guesses. I experinced this once on my setup for a few days, and i ended up having to advance the intake alittle bit to get it to clear up.. This is all just ..speculation really, without knowing everything its hard to really idenitify

 

After reading a few articles since i'm trying to kill time, and some other things i think the OP might find this statement helpful

"In a naturally aspirated engine, on the intake stroke, the piston
drops creating an area of low pressure in the combustion chamber that is less than atmospheric pressure and as the intake valve opens, the air from the outside is set in motion down the IM runner.

Once air (as a sound wave) has been set into motion down an IM runner, it does NOT simply stop when the intake valve is closed and wait for the intake valve to re-open.


Instead, when the intake valve closes shut, this air sound wave bounces off the backface of the valve and travels at the speed of sound back up towards the IM plenum (rarefaction wave). This reflected wave has a frequency, amplitude, and negative pressure associated with it."

Taken from Team-integra.net, found it in google, its a pretty good logic and does confirm the ops problems.

SO, to go any futher, we need a very big break down of the setup, when its happening, how its happening and where. Dyno graph would be awesome too.

 

Team Integra is an excellent old resource.

 

I'll list the old build and highlight the parts changed that led to the issue we are having.

-H22A motor 90mmx99mm compression close to 15:1
-2" 4-1 header of long tube design (collector below the steering rack) into merge then out into taper 7deg then into 3" diameter 14" length exit (exits under the car)
-Head is ported by us and retains the stock valve size but has the squish pads welded, it is also skimmed around 0.5mm.
-Intake manifold is Skunk Pro port matched to the head with a 74mm throttle body (We tried dual 90mm throttles on a custom intake and made the same peak power but lost a lot of midrange power)
-Intake is 3" pipe to the front headlight area (increase in size did not add power or fix the issue)
- Cams are Skunk Pro3 (we degree on the dyno for maximum power)

This setup made 297whp peak at around 8900rpm (ill try and get a dyno graph soon). The car has run 10.8@122mph.

The change was going from the Skunk2 Pro 3 to a more aggressive two lobe setup with ferrea rockers and increasing redline from 9400 to 10000. With these cams peak power moved up by about 300rpm but remained the same around 297whp.

 

Just curious, whats your valve seat pressure set to? And what valvetrain?

 

Sounds like a combo of problems, Cam timing possible off, not enough air, too long of runners. lets see the dyno graph if u can get it. I'm assuming the reason u wanted to rev so high was because of gearing?
So which 2 lobes did you go to?

 

This is the dyno before the cam. This setup ran 10.8.

- don't know seat pressures. Old setup was with skunk2 pro 3 cam and skunk2 valve spring and retainers. New setup is what came with the cams.
- The 2 lobe cams came with their own springs and retainers. (Also I said before ferrea rockers but it turns out the rockers are from somewhere else) will try and find more info on the cams later.
- reason to rev so high is to make more power. We make 360whp in our K motors (thanks Drag Cartel!) and those we rev to 10500.


Edit: I mentioned earlier a higher peak power. Was wrong. This is the pro3 graph. The new cams moved everything to the right by about 300rpm

 

Are these shelf cams? Have a part #?

I know Ferrea has a shelf cam thats advertised a little bigger than the Pro3, when actually they are smaller.

I also dont know of any other roller rocker out there besides Ferrea. Any more info? Degree settings? Measured lift of cams?

 

They are bigger, lift wise i believe, not duration wise. However, this is only from memory..

The only roller rocker arms that come right to mind are crane and ferrea.

I'm thinking its cam timing right now, also, just for what its worth to me i dont think the switch was warrented.. if anything you should have went to a custom camshaft instead of another "shelf" profile.

It actually could be both, too long of a runner and cam timing slighty off..i'd like to hear some more specs on the cams before we start throwing out ideas..

OP also, have you tried different gear settings?

 

The Pro3's are hard to beat, but I am also for testing out new things. Wether its warranted or not, you never know till you try.

If its the cams I am thinking of they are smaller in both ways. I am currently running them also switching from Pro3's. I believe they were supposed to be around .525" on the intake lift, mine came out to be around .495". My Pro3's degreed in at .505" also with more duration.

In my case I gained power anyways, but cams werent the only thing I changed. If this guy went from Pro3's to the Ferreas I am thinking of, with no other changes, this is probably what I'd expect to happen.

A custom cam is probably whats needed here to make more power. It was the avenue I was going down until the cam manufacturer ground and H series profile on a B series core. That deffinately wasnt going to work. In a pinch I went the shelf route, but it wasnt what I was building around.

 

There was another guy making them at one time it seemed, but I dont know if he ever got past prototyping them. He used to have them on a website and they were to be used with a Ferrea/Crane roller cam. Thats the only other one I can think of and its very doubtful the OP has a set of those, I dont think they ever got past prototypes.

 

There's no doubt, the pro3's are probably one of the BEST shelf profiles out. With that said, to beat it, on a 3 lobe type camshaft, you'll have to go custom.

We'll need to wait for the OP to chime in with more info on the cams used, and if he's moved the gears..

 

I vaguely, remember hearing something.. but not sure.

Alot of my customers who do have my roller cams, do run ferrea rockers however, its all i've recommended for my roller cams.

 

Did some digging, the guys name was Joe McCarthy and his company was called Prototype Racing. Seems they are long gone. I Googled and came up with a post about them on team-integra but it was some 10+ years old haha.

Derek on your customers cars how do those rocker arms hold up? Anyone using them in a street driven application where they would see alot of miles? I've notived the tappet adjusters are fairly soft compared to stock adjusters.

Sorry to the OP for going off topic!

 

None of my roller customers are street driving cars, only track driven. :-\ sorry.

Joe mccarthy, i was reading about his manifold stuff in the k series forum and on facbeook.. he's still around i believe?? ..

Rocker arms hold up fine.. I got alot of guys who went the entire season last year without a hiccup.

 

ok you have several problems with this setup. everything is so restrictive the engine cant breath properly.

first you need to get rid of the intake manifold, tb and intake tube. the plenum is too small, the runners are too long, the tb is too small and the intake tube is not only too small but its a restriction in itself (yes you tried removing it but you wont see any change when the intake and tb are still restricting the engine). assuming your looking to make the most power possible with the best powerband for drag application you will need to go with either a custom manifold and SINGLE 90mm tb and 4" intake tube opening up to as wide as you can get it @ the headlight or for better results put the tb through the hood. OR you need a good set of itb's and air box/inlet and a lot of testing to dial it in properly.

next you need to get rid of the header. if the collector is truly under the steering rack then the primaries are WAY to long. you want a 4-1 header with either 1 step or straight 2" into the collector directly under the oil pan. keep the beginning of the collector towards the front of the pan and the primaries as short as possible around 23.5" or you can do a side exit to get the primaries shorter and gain ground clearance but you will lose a lot of scavenging so id stay under the pan, it works. either way use a good quality collector with a choke size between 2 3/8" to 2 1/2" then bring it out to 3.5 inch exit then back down to 3" using whichever size meg you have room for. DO NOT add any length of pipe after the meg/rev cone. DO NOT use a bend after the collector for any reason.

next two things to look at are the cams and portwork. the cams you have are questionable and its gonna be extremely hard to get a set of cams to perform better than the pro 3s. if they are kelford cams definitely go back to the pro 3s but either way swap them on the dyno after fixing the intake and exhaust issues. if your not seeing noticeable differences on the dyno when swapping parts after fixing the intake end exhaust properly then the head is the problem.

follow those steps and it should make close to 350whp (dynojet) on the pro3s assuming the head flows