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5th Gen Engine Modifications


sa1713

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Craig thought the exhaust ports were poorly designed as they do not exit in a straight line from the chamber. If he had the shop he would redesign the ports.

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Yep, all stock internals. I proposed to get lighter rods/pistons/etc... but Craig went through all of it and said Honda had everything just about light as can be. He said he could add lighter components but I would never know the difference. The gain only would be useful on the track/real racer....

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So basically there will be reground cams, intake fidgeting with some porting, headers/exhaust and custom map?

A new in box TBR stainless header was sourced a few years ago and I have a PCV with autotune. I've modified a K&N filter that now takes up almost the entire OEM filter plate. I'm also looking into adding a scoop to add airflow into the airbox.

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The journalist that had the BioBlade done told me, that some mild head work (suspect HRC RC45 mods) some cams, new exhaust one off by Arkropovic & an aftermarket airfilter gave it 124rwhp, 130 on methanol. It retained the standard airbox, as they had to pass noise tests !

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I am getting ready to do an overbore on the throttle bodies. Not worried about noise tests ;)

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Edited by CandyRedRC46
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What size are the throttle bodies on an RC45?

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46mm, according to a magazine road test from back in the day.

36mm for the VFR800 5th gen, again, from a magazine test.

Hope that's right, I didn't cross-check it to anything else.

Edit: I just google searched "RC45 46mm throttle bodies" and got a ton of exact hits.

Same for "VFR800 36mm throttle bodies".

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Yup that's what my research shows too. I know 46mm is way too large to run with out smaller velocity stacks, unless you are running the hrc race kit cams, pistons etc. but I would like to have mine bored out to about 40mm.

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The RC45 has the same inlet track as the 800, the 45 as standard has a 46mm TB, but with a 40mm velocity stack. The 45 race kit opens this by replacing the VS with full width ones. The man Larry, made a replica set, spent ages on it & LOST power everywhere. Without the race kit, it's a bad idea. My modified VS are 40mm diameter & 30mm shorter, but I've not got round to dynoing them yet.

The idea is they should move torque higher up the rev range & thus increase HP. We will see ;)

Edited by Mohawk
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Yup that's what my research shows too. I know 46mm is way too large to run with out smaller velocity stacks, unless you are running the hrc race kit cams, pistons etc. but I would like to have mine bored out to about 40mm.

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This may be a silly question, you being an engineer wannabee soontabee... is there enough metal in the throttle bodies to remove 2 mm from the walls without compromising integrity? Do you have 40mm Honda parts bin throttle plates lined up? If so, please share the model :beer:

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yeah been there done that & 30mm is the most length you can lose & still have a good VS entry. You could radius the airbox mouths & shorten by another 10mm, but not sure if it would flow as much air. The TB's are good for 1mm increase to 38mm, but as per Bioblade testing, they are NOT the restrictive area. Making them bigger will achieve nothing, but messing up the fuelling. Cam lift & duration limit the breathing of this engine. It lacks compression which is easily fixed on the 6th Gen, but much harder on the 5th gen, but can be done.

Edited by Mohawk
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here is one idea from a pal in school.. mind you this done on VMAX..

my roomie made a 2000 cc vmax. be bored the cylinder until it was gone!!!!!

then he ran sleeves running directly in the coolant!! :blink::blink::blink:

yep he modded the cams and other stuff. :comp13:

when you have your machine shop you can do what you want. :beer:

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Couple of guys here built the crap out of the Vmax's and all have suffered the same fate, motor's were great but shredded the rear gear ...

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Couple of guys here built the crap out of the Vmax's and all have suffered the same fate, motor's were great but shredded the rear gear ...

my pal threw away the drive shaft. installed a chain. that simple :beer:

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  • 2 months later...

Yup that's what my research shows too. I know 46mm is way too large to run with out smaller velocity stacks, unless you are running the hrc race kit cams, pistons etc. but I would like to have mine bored out to about 40mm.

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This may be a silly question, you being an engineer wannabee soontabee... is there enough metal in the throttle bodies to remove 2 mm from the walls without compromising integrity? Do you have 40mm Honda parts bin throttle plates lined up? If so, please share the model :beer:

Honestly I was just going to buy a clean used set and send them away to maxbore.com and let them work their magic. If they can only get them to 38mm that's fine. Just smoothing out all the casting marks and knife edging the butterfly's and and pins should work wonders.

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