Why does my power drop off so sharply at 6700 rpm - B18c1 block + B16a1 head
 

I went to the dyno yesterday and did a few runs with my road race car. My setup is the following: B18c1 block, b16a head and cams, head is ported and polished. After playing with the timing, we managed to get the hp up to 141 hp, but that was it. At 6600-6700, it starts to drop off very sharply. We didn't have time to setup my exhaust to accept the wide-band before the cat, so that's all the info I have for now. Does anyone have any idea what could be causing this? One of the mechanics at the shop suspected I might have cams from an automatic B16a. I wonder if the air-fuel ratio could affect high rpm hp so much or am I somehow at the limit of these cams. Any ideas?

sounds like the air fuel ratio is way off up top

Re: (ea_hatch)
 

Off in which direction?

Re: (Civic44)
 

eeww why are you even using b16 cams? its ok to use a b16 head but at least get some gsr cams in there, b16s are too weaksauce, about your power dropping off that sounds weird should climb to at least 7800, any dyno charts?

Re: Why does my power drop off so sharply at 6700 rpm - B18c1 block + B16a1 head (Civic44)
 

no way to really know without your a/f curve. Get it straightened out and go back.

s

Re: Why does my power drop off so sharply at 6700 rpm - B18c1 block + B16a1 head (stevel)
 

I didn't get the charts printed out, I'll try to get them. I only used B16 cams because that's what I had. I didn't know that they would hinder performance...

Re: Why does my power drop off so sharply at 6700 rpm - B18c1 block + B16a1 head (Civic44)
 

The B16 cams aren't any worse than the GSR cams for power. Virtually the same profile I thought.

Re: Why does my power drop off so sharply at 6700 rpm - B18c1 block + B16a1 head (HondaBullSQ)
 

if he has the obd0 first gen b16 cams then its a different story, especially when its automatic (yes they are different specs).

who ported the head? did he provide you with a cfm chart before and after?

Re: Why does my power drop off so sharply at 6700 rpm - B18c1 block + B16a1 head (c17r15)
 

please post the dyno chart because if it is dropping off as violently as it sound then the car may be falling out of vtec due to an oil problem ..

Re: Why does my power drop off so sharply at 6700 rpm - B18c1 block + B16a1 head (HOOKUPS)
 

Like Hookups said ^. Stock b16 cams stop making power at 7600 and b16 and gsr cams are almost virtually identical their is no noticable hp increase between the two of them. You might have automatic b16 cams though. Need to post the chart up or let us know what the air fuel was across the board. Might have to bust out microsoft paint and get creative. https://honda-tech.com/forums/images...s/emsmilep.gif

Re: Why does my power drop off so sharply at 6700 rpm - B18c1 block + B16a1 head (goforbroke)
 

Yeah, I guess I have to do some more runs with the wideband, we didn't have time to set it up. I'll also try to get them to email me the chart. Thanks for the ideas so far.

Re: Why does my power drop off so sharply at 6700 rpm - B18c1 block + B16a1 head (Civic44)
 

Here's the dyno chart. As you can see, after 6500, it's all downhill:

http://www.we-todd-did-racing.com/we...ZmQzMXk1NDE%3D

Re: Why does my power drop off so sharply at 6700 rpm - B18c1 block + B16a1 head (Civic44)
 

whoa.....that doesn't look right, I've seen 2L blocks on a stock auto pr3 head, the power doesn't "drop" per se instead it sort of flatten itself out and drops.

it sure could be a dirty head where the engine can't breath past 6700 rpm.

https://honda-tech.com/forums/images...es/emdgust.gif

Re: Why does my power drop off so sharply at 6700 rpm - B18c1 block + B16a1 head (Civic44)
 

might be the header you're using. I've seen dyno charts that show a DC JDM 4-1 fall flat on its face after 6500.

Re: Why does my power drop off so sharply at 6700 rpm - B18c1 block + B16a1 head (DavidR)
 

Could it be my "high flow" aftermarket catalytic converter then? I have a JASMA 4-2-1 header (don't know the brand) with a 2.25" exit, 2.5" piping, high flow cat and Cherry Bomb Turbo muffler.

Re: Why does my power drop off so sharply at 6700 rpm - B18c1 block + B16a1 head (Civic44)
 

Check A/F ratio, then I would opt for a different header.

Re: Why does my power drop off so sharply at 6700 rpm - B18c1 block + B16a1 head (DavidR)
 

correct me if i am wrong but that dyno plot is not in RPM it is in "SPEED" https://honda-tech.com/forums/images...es/emsmile.gif

Re: Why does my power drop off so sharply at 6700 rpm - B18c1 block + B16a1 head (HOOKUPS)
 

Haha that would be even worse !! Than power drops at 65 km/h.

Re: Why does my power drop off so sharply at 6700 rpm - B18c1 block + B16a1 head (rev limiter)
 

this is a very odd looking dyno plot i dont think i have ever seen this type of dyno

Re: Why does my power drop off so sharply at 6700 rpm - B18c1 block + B16a1 head (HOOKUPS)
 

i'm so supprise that no one mentioned that his vtec is not working thats why his power falls to a dead stop at around 7 grand. plus that graph makes no sense

Re: Why does my power drop off so sharply at 6700 rpm - B18c1 block + B16a1 head (street dreams)
 

The vtec is coming on, I can hear it and I have the runs on video and I can hear it when I watch the video too.

Re: Why does my power drop off so sharply at 6700 rpm - B18c1 block + B16a1 head (Civic44)
 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Civic44 &raquo;</TD></TR><TR><TD CLASS="quote">The vtec is coming on, I can hear it and I have the runs on video and I can hear it when I watch the video too.</TD></TR></TABLE>
i dont think so buddy low fuel pressure is not going to make your power fall off at 6700 rpms u have no vtec

Re: Why does my power drop off so sharply at 6700 rpm - B18c1 block + B16a1 head (street dreams)
 

https://i2.photobucket.com/albums/y4.../Scan10002.bmp

my b16 drops liek that too, 6800 rpm, hmmmm

Re: Why does my power drop off so sharply at 6700 rpm - B18c1 block + B16a1 head (EFB16ACRX)
 

You might have auto-b16 cams, which are rated at around 150hp stock (instead of 160 for the 5spd).

Re: Why does my power drop off so sharply at 6700 rpm - B18c1 block + B16a1 head (92TypeR)
 

whatever that shit sucks


as most will say theres some sort of "breathing"or fuel problem withthe motor.


list out all your mods so we might be able to help u figure it out, and also try a normal dyno next time https://honda-tech.com/forums/images/smilies/emthup.gif


i made 157whp with a bone stock internals b16 so u definatly have an issue