rodhay

Firstly I should say I'm trying to find out how to make power with a lower VTEC engagement point on a fully built motor with Neptune RTP.

I've got a recently built H22 with JUN cams/springs, ti retainers, adj cams, mahle hi comp pistons, Euro R IM, K&N intake/filter, DC header (got a HyTech to replace it which I'm fitting on Sunday).

The cams have been dialed in by checking peak lift & duration of the primary lobe, and I'm running at IN +4.5/EX +7.5. That sounds like a lot I know but I've checked many many times and it's right (at least to what JUN say it should be in relation to BTDC and ATDC). Also triple checked the cambelt is on properly (not slipped a tooth). I tried running at 0/+1 and had NO power at all, then at +3/+5, and finally at my measured settings as above and it definitely makes the most power with that setting (have to keep EX at least +1 of IN for v2v clearance). Compression is excellent and even.

My AFR is as best as I can get from probably 100+ hrs of street tuning. I'm within a couple of percent of my targrt AFR's across the board. I've worked a fair bit on the low RPM timing, read/replaced plugs, listened for knock/chirp and retarded, etc. It's running very smooth and fast now up to VTEC.

Here's the thing. If I set VTEC to engage at anything less than 5600, there's a VERY noticable dip in power. At 5800 there's still a dip in power in 2nd gear and higher. The power comes back in once I'm over 6K, and screams up to 8K quite well, although I'm sure there's a lot more power to be had up in the high rev range. But I'll wait till I'm on the dyno before I mess about with timing too much at the very high RPM's.

I've tried many different settings, AFR's, timing, basemaps etc. But I just can't make any power below that engagement point.

I think it's way to high for a H22, even though the low cams make excellent power right up to 6/7K (if I disable VTEC).

If you've ever watched the JUN prelude on youtube that has an almost identical setup to me, JUN run VTEC at around 4800 - 5000, right about where I feel it should be.

I should mention there is about a 1mm square hole in the flexi pipe of my DC header, and I still have the CAT on. CAT back is an aftermarket free flowing exhaust. Could these be causing MASSIVE power losses in VTEC? I mean massive power loss but only when in VTEC.

So I wanted to get some idea if anyone could shed some light now how they've retuned to lower their VTEC engagement point before I hit the dyno. I mean I've read some people are engaging at 3K. I tried tuning for a 3K engagement and it felt like my engine was a 1 litre, no matter what AFR/timing I tried!!

likwidchz

I'm not sure I can really add to this, but from my understanding aftermarket cams generally will have a higher vtec crossover "depending on how agressive they are" I have never really heard of anyone wanting to make vtec switch over lower.. ... Maybe for a turbo... But I dont hear about people doing turbo vtec and changing the switch over for lower/higher that's kind of another topic...

mouab18c1

iTrader: (5)

With the h22 block you should have all the low end torque you need already. I say its the tune!

likwidchz

This is my dyno sheet, its neptune tuned by me, headers aren't the best ... dc sports crappo's and 3 inch intake, no filter "long story" apexi ws2 exaust for the quietness, also has a cat.

internals are all stock, no IAB's butterflies removed...

from the looks of things, its more then stock but not all that great in the power department from what others make with stock stuff.

mouab18c1

iTrader: (5)

Your numbers look really low, or is it just me. I know numbers are just numbers but....

likwidchz

No you are probably right! the headers kill it.
Btw that phantom looking line where hp starts to fall off is where I want hp to be! hahah

josephcmiller2

Have you searched for other dyno sheets for people with your cams? What do their torque curves look like compared to yours? Yours peaks at about 5200 RPMs which is really low for making any power. I don't know those cams, but for your RPM range, I don't think 5800 VTEC engagement is low.

ddd4114

Maybe I'm missing something, but why do you want to tune for a different VTEC engagement point? What's wrong with just setting the engagement point for whatever gives you the best torque curve and calling it a day?

DDTECH

leave vtec along.

rodhay

Thx for the advice guys...

Yeah I've searched and searched but no one with these cams seems to say much about how they got on! All I really know is the JUN Prelude is making power at 4800 ish but mine won't until another 1K.

Good point! I guess it's because I'm thinking there's something wrong with it being so high, and maybe I could make more power at lower RPM's. I just have no idea how some tuners have managed to set VTEC so low and make any power.

Maybe it is the crappy header and standard CAT causing big restrictions. I'm all set for a day on the ramp tomorrow and hope to fit the hytech rep. Will see how it goes.

rodhay

So I didn't get as far as actually fitting my hytech header on Sunday, after notching the chassis (it's a very tight fit), repainting/rustproofing the cuts etc. and doing a few other things I needed to do on the car, I ran out of time and had to refit the DC.

But I did manage to swap out the CAT for a straight through 'test pipe'. I checked the CAT and although it's very old, it doesn't look blocked at all and I can see light through all of the mesh.

On the way back home I noticed the dip in power seemed to have disappeared. And today I had a chance to plug the laptop in. I went straight for it and dropped the VTEC engagement to 4600 (1K less than before). All of a sudden I have power in VTEC!

So it's conclusive for me. Having the restriction of the standard CAT in the exhaust meant that the big JUN cams couldn't breathe on the VTEC lobe. It made a huge difference - and I haven't even started to tune afr/ign with the lower engagement point.

For anyone else with big cams, it goes to show how important it is to have a completely free flowing exhaust. Big cams put a lot more air into the chambers, hence a lot more exhaust gas is produced. Anything standard in the exhaust system can cause huge restrictions and harm power significantly.

I can't wait to see what difference the hytech will make now...

xbigpitax

change those dc headers there crap there holding back alot of power