Hi all,

I have had my 1991 Prelude Si-4WS mt professionally rebuilt with darton sleeves (bored to 84mm), JE 12:1 pistons, Colt Cams Tri-Flow cams, converted to OBD1 and professionally tuned with
Hondata ECU. Also has Hurricane 2 1/4 headers with mandrel bent system hi flo cat etc. I was hoping for a few more HP that I got, 135 at the wheels. I know this is a nice increase over stock, but TBH the headers and exhaust made as much difference as all the rest put together (I had them on prior to engine rebuild).

The noob question I have is...with significantly more displacement with the bore, I would have thought that the speedo should be showing higher speed at the same revs and gear as previously? It is definitely not...

I am wondering if the cams might have too high a powerband for my engine which doesn't love to rev too high...??

Anyway any advice as to how I could unlock the 'hidden' power which SHOULD be somewhere there, would be much appreciated!!

 

Displacement (bore size) has nothing to do with rpm and speed. That is going to be a matter of gearing in the transmission.

It looks like the power is nosing over at the top so it makes sense for the tuner to stop at that RPM. I don't know much about your cam selection but if it is designed to make power up top that is not what your graph shows. Your intake could be the limit in your current configuration.

 

Thanks for the reply mate and clearing up bore vs speed at certain revs question.

The cams are made with the same grind for a few different vtec Honda engines. Given that the b20a in 3rd gen Preludes is the lowest revving and just can't make any power up top (as evidenced by the chart) is why I was thinking different cams that are designed to make power a bit lower where the b20a6 likes to be might produce a better result?

Re the intake, the tuner actually did a run with the intake off (no flow restrictions) and produced the same result, so that is not the bottleneck.

 

I was thinking the intake manifold and throttle body are your limit. Perhaps even the intake ports on the head. Or that cam is pretty mild and just doesn't make power beyond the stock rev range. I did a quick search for that cam and didn't find any details on it.

Your power gain may seem small but for not really adding any RPM it is pretty decent.

Oh wow! Does that engine really have a 95mm stroke?! That is nearly K24 stroke! Yeah it probably won't like to rev. Mid range torque is going to be the name of the game with a stroke of that magnitude.

 

Yeah the gain is definitely significant but not what had been predicted for the full build I had done...

Thanks, I'll see who can take a look at throttle body and intake manifold and what can be done there.

Yeah 95mm stroke..it's a kinda strange engine. Not easy to get much power from N/A but that's the route I've gone down for better or worse...