fungus mungus

So, here's my build info:

B18C1 block/P72 head
PR3 pistons (stock size, I think, but not 100% sure as I didn't build the motor)
PnP head by JG, later redone by DNR
S2 Pro intake port matched to head and 70 ml. BBK TB
Supertech valves, titanium retainers, and dual springs
S2 Tuner Stage 2 cams
Comptech intake+icebox
DTR 4-2-1 header w/2.5" collector connected directly to 60mm Apexi WS2
Tuned on Hondata S300

The build put down 200 whp/130tq on DNR's dynojet, but the VTEC crossover has been set to 6700, which is higher than I'm comfortable with. The reason they set it there is that when it was set at 6000, there was a 15 whp/tq drop at the VTEC crossover. Said it's the only way they could clean that area up. Hondata specifically advises against setting the crossover higher than 6500.

The guy at DNR speculated that there's restriction in the exhaust that is shocking VTEC. I'm surprised by this as there is no cat...only a resonator and muffler, and there's no way I'm losing those. In fact, I'm planning on putting on a real high-flow cat.

Before I put the DTR header on, I was running a JDM ITR 4-1 header and a cat, putting down 175whp/118tq on Blacktrax' dyno (which reads about 4-5% lower than DNR's). VTEC was set at 6000 RPM and the curve was perfect...no dips at the VTEC crossover whatsoever.

Any ideas why VTEC has to be set this high? Or how I may get that crossover set lower without losing a bunch of hp/tq at the crossover?

fm

92cxturbo

4-2-1 headers are known to cause a dip in that area, and that exhaust is known to be restrictive which probly makes it worse for you. Did they adjust the cam gears at all?

fungus mungus

Cam gears were adjusted before the DTR header went on, but not after. Not swapping the exhaust at this point...it's only got about 3000 miles on it.

fm

Honda Bull

4-2-1 is slightly an odd choice of header for an engine of that sort. Not sure if it would make THAT much of a difference though.

Do you have a pic of the dyno graph? I'd like to see the curve prior to the VTEC crossover.

Also, what reason did Hondata give for avoiding the crossover above 6500 rpm?

4g hatch

drop the exhaust and make a pull on open header and see what happens?

fungus mungus

Why is a 4-2-1 header an odd choice? From what I understand, 4-2-1s are supposedly better for low-mid end hp gains while the 4-1s are good for top end. The DTR made 10 whp more on the top than the JDM ITR 4-1, although I'm sure losing the cat had something to do with that gain. But I read on a header shootout on this forum where the DTR header gained about 5whp over the JDM 4-1.

As far as dropping the exhaust on the dyno, are you suggesting that the drop in HP and TQ may still be present with that header after the exhaust is dropped? Or that maybe my 2.35" exhaust is to blame? I thought about doing this, but dyno time is expensive. Before going through the process of elimination, I wanted to get peoples' thoughts on ways I may get around this without resorting to leaving the VTEC crossover so high.

As to why it's not good to have it that high, HONDATA says:

Do not set the VTEC point too high as the high speed cam rocker arm may float on the lost motion assembly, damaging the valve spring retainers. It is not recommended to set the VTEC point over 6500 rpm.

fm

fm

fungus mungus

Dyno graphs. The first dyno is with the JDM ITR 4-1 and an OEM cat. The green line is the final tune that day. Note the smooth transition at the VTEC crossover at 6000 RPM. Peak HP was almost 175whp/117 tq.



This is after the DTR header was put on and the cat deleted...the yellow line is the final tune. About 10whp gain at the top, only about 3 tq, but note the huge drop in torque (15 ft lbs) and whp at just over 6000 rpm.



Here is the dyno run 2 days later on DNR's dynojet. The yellow lines are the exact same setup as the previous dyno graph...yeah, it reads higher than Blacktrax's dynapak, but the curve is still the same. The tan line is after DNR raised the VTEC crossover to 6700. Unfortunately, I don't have the AFR graphs from DNR as they didn't record them.



fm

92cxturbo

If you worried about the high vtec for now just put it at 6500 tell you figure out the problem. If you cant get a graph of the a/f then ask your tuner to see the graph on his laptop yourself to atleast verify its good. What are your cam gears set at?

fungus mungus

The tuner just plugged an AEM wideband in to monitor it live...the dyno's wideband is broken, so there are no graphs to go on. I know, fail.

The cam gears were supposedly set to +4 intake and +3 exhaust.

fm

fungus mungus

Let me clarify, the cam gears were set to +4 i +3 e before the DTR header was put on. The final dyno was after the ported-matched intake and 70ml TB were put on and tuned. No changes were made to the cam gears after the header/tb were installed.

fm

bsmith100

I was going to suggest the same thing.

fungus mungus

Yeah, I installed Windows 7 on my Macbook today just so I could do this. I'll change the VTEC crossover this weekend and have it tuned again once I get the high-flow cat on.

fm

vteczone

may be the NEW B Series LMA (may be not so..NEW) could solve this problem. that's if u still need to set the VTEC point that high. idk. may be.
https://honda-tech.com/forums/all-motor-naturally-aspirated-44/%2Anew%2A-b-series-lma-info-2312727/

vidanator

Bump for more info. I have the same issue with vtec at 7200!! With almost the identical setup.

DDTECH

s2s2's dont normally like the exhaust advanced..

infact a pretty good universally settings is +3 intake / -2 exhaust.

vtec on the s2s2's like 5400-5800range..
usually high vtec points are a sign of shitty exhausting.

vidanator

Not trying to thread jack but i think the op and i can use this info. I have a hytech 4-2-1 replica header, smsp high flow cat, and a 2.36inch rsr exmag. I was thinking of changing to 2.5inch piping with my exmag muffler...i can post my dyno graph also if anyone is interested.

fungus mungus

Please do. Some people have told me to increase the size of the exhaust, but I'm doubtful that this will make that big a difference. Just got back from the tuner a couple of days ago...he smoothed it out some on a Dynapak, but didn't eliminate it...still about a 10whp drop. He said he thinks the car isn't making enough compression to carry it through the crossover gracefully. It's at about 11:1 right now.

fm

fungus mungus

BTW, the cam gears were set at where they made the most power before I swapped out the stock cat/JDM 4-1 header. They tried negative on the exhaust side and it didn't like it. They considered playing with the cam gears but they didn't think that it would make a difference.

fm

slowcrx954

[QUOTE=fungus mungus;43050543]BTW, the cam gears were set at where they made the most power before I swapped out the stock cat/JDM 4-1 header. They tried negative on the exhaust side and it didn't like it. They considered playing with the cam gears but they didn't think that it would make a difference.

fm;
im having the same problem,but i got a fully build gsr on pro 2 cams,anything below 6800 crossover i loose 15whp in a dip before vtec..moving cam gears helped out any?also i herd people saying 421 is not good,thats why there is a dip.but seeing you got a 4to1 im starting to think exhaust for sure.open header dyno?

slowcrx954

im almost sure its header design,but im trying 3in exhaust before i buy another header.check my build.
https://honda-tech.com/forums/all-motor-naturally-aspirated-44/help-me-make-more-power-dyno-inside-2796992/

conertedrange

spray it and see what happens lol jk

DDTECH

High vtec crossover isn't necessarly bad.. if the springs can support the life of the cams. thats not always true what hondata said.. and believe me, they have been very wrong in the past.

fungus mungus

Good point about the high vtec crossover...I read Hondata's advice and didn't consider they were probably talking about running a stock valve train.

To be clear, I am running a 4-2-1 header myself...big tube, but 4-2-1. My JDM ITR header was 4-1, but that was before I swapped it for the 4-2-1.

As for redynoing, I've spent plenty on the car the past couple of months...time to take a break. I don't feel like springing for a cut valve cover and another hour of tuning. Especially since I'm probably going to save up to have my bottom end sleeved and bored over to 84mm.

fm

1.5Slowmatic

its the exhaust and muffler most likely. To restrictive. quiet but restritive

00Red_SiR

I just noticed something, if I understand you correctly, that dip appeared AFTER you installed that DTR header correct? In your last post above, you said the header is a big tube. A big tube header is meant for a 2L+ sized engine in general and is probably why it falls flat on its face until you raise VTEC up a lot higher. That header is meant for your future build, not your current one. That header with your current small/restrictive exhaust will not make your engine happy.