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Styp

RB25 stock head flow figures

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Hey,

I am looking for STOCK RB25DET head flow figures. The best would be in small increments, as I need it for a model.
Have searched the internet up and down and it seems to me that somebody in here could help me with some good numbers.

Thanks guys!
Cheers
Martin

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I dont know em exact but off the top of my head somthing like :

rb20 and rb30 2000cfm

Rb25 2500cfm

Rb26 2600cfm

 

As i stated unsure on the figures and ill add even the terminology used.

 

Maybe someone will pop in!

 

Or research.

 

 

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Figure I have is 265 cfm but I can't remember where i got that from.

(Its written in my notebook so it must be true!)

OK so I looked it up: stock is 234 cfm the above number is a ported head from Lewis engines.

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2500 cfm = 70792.11 l/m

70792.11 litters per minute

Depending on your project and if the figures are close or you get em...

How and why do you need them in increments, increments of and for what?

The engine running ? At wot ? Removed ?
Zorst on? Vs temp? Or maybe the redneck in me is missing somthing here ?

Gts boy ? Are you telling him how to scale it or apply math to figures?

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Yer id say i powerD it up

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7503 l/m sounds better

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59 minutes ago, Slap said:

2500 cfm = 70792.11 l/m

Gts boy ? Are you telling him how to scale it or apply math to figures? emoji3166.pngemoji856.pngemoji51.png

No, I was telling him that your numbers were approximately 10 times higher than they should be.

Heads are flowed on a flow bench with a certain suction pressure applied. 10 inches of water, or 25, or 28. Head flow is not expressed in an engine running configuration. It is always on a flow bench at a certain depression. The depression used is important, because, of course, the measured flow will be a lot higher at 28" than at 10".

"Increments" refers to increments of valve lift. It is important to flow a head at various valve lifts so that you can see what it does in the cam lift period where the head is close to the seat, and in mid lift, and at max lift. It's a bit like a dyno sheet where area under the curve can tell you things that the peak number alone can't.

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So apply math.

 

Wich was figured.

 

Good info.

 

Got the ball rollin atleast.

 

Can you help him with the increments and different flow rates?

 

 

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No, because I don't have any flowbench numbers for an RB head. The only head I've ever ported and done before & afters on was my Alfa twincam.

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14 hours ago, Slap said:

rb20 and rb30 2000cfm

Rb25 2500cfm

Rb26 2600cfm

Those figures are sky high, F1 motor flows less lol

 

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Hey,
I am looking for STOCK RB25DET head flow figures. The best would be in small increments, as I need it for a model.
Have searched the internet up and down and it seems to me that somebody in here could help me with some good numbers.
Thanks guys!
Cheers
Martin


IMG_1560228132.293586.jpg
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On 6/11/2019 at 6:43 AM, t_revz said:

IMG_1560228202.217199.jpg

Thanks! Was looking for this for a long time!

Am I right in the assumption that Cyl 2 is stock and Cyl 1 is ported?
The gains are impressive, especially the low lift area is really nice. I think you a very torquey engine there!

Cheers!
Martin

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Thanks! Was looking for this for a long time!
Am I right in the assumption that Cyl 2 is stock and Cyl 1 is ported?
The gains are impressive, especially the low lift area is really nice. I think you a very torquey engine there!
Cheers!
Martin


Correct cyl2 was stock. I spent a fortune on the head but have never had the rest of the engine 100% right since building and it’s never been much of a priority to rectify.

Can’t tell with results so far if it was worth the money getting it done. One day I’ll finish it off

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Can you detail the extent of the porting and the cost? Also the intent of the build, power target, expected rev range, any of those things if you had them when you went into it?

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Can you detail the extent of the porting and the cost? Also the intent of the build, power target, expected rev range, any of those things if you had them when you went into it?

 

So I was initially aiming for 420-440rwhp with a hypergear SS2 on ported factory manifold, Poncams/gears. The guys doing the head recommended removing all quench areas and looking at the Det damage visible on them it made sense at the time. I spent probably 40 hours porting it myself but when I went to flow test they said I was too aggressive in some areas and not enough in others. So I bought another head and let them do it all. Never intended to go above 7200. It was more a learning project than going all out.

 

I asked them to remove quench areas and $1000 worth of porting. Bought poncams, new valves, springs, lifters and external VCT feed in case I got a 30 block down the track. I traded in standard stem seals and guides for a discount on custom ones they made for me. Oil drains enlarged.

 

So I guess I spent a bit over 5k on the head. When I said it’s never been 100% it’s because it’s had fuel dilution since initial tune. I’ve found multiple small issues which have improved the engine/response but the samples have never improved . I now have found compression on #3 changes regularly especially when cold. It has forged JE pistons/Hastings rings. I’m unsure if a ringland or ring got damaged on first tune, or something wasn’t set correctly? Leak down test was 9% all cylinders but maybe it seals better due to being stationary? I hope to remove pistons over winter and find something.

 

I’ll upload head photos after lunch IMG_1297.thumb.jpg.0eec4a73f801677fe9e43f94a9e70a7b.jpg

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That's quality information. The kernel is probably that ~$1000 of porting work gained a pretty good 20 - 25 cfm across the lift range.

An important thing for readers to keep in mind is that the peak numbers on your table/chart are at 1/2" lift and there has probably never been an RB with that much lift. 9-10mm being most common, 10-11 mm being on the extreme side. Doesn't affect the exhaust side so much, but it nibbles away at the cfm number for the inlet by about 10-15 cfm.

Question: "Race Seats" on the scanned paperwork. Implies they were set up properly, multi-angle or radiused or similar? The seats can have a huge impact on the flow - more than the port itself, especially at low lifts.

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That's quality information. The kernel is probably that ~$1000 of porting work gained a pretty good 20 - 25 cfm across the lift range.
An important thing for readers to keep in mind is that the peak numbers on your table/chart are at 1/2" lift and there has probably never been an RB with that much lift. 9-10mm being most common, 10-11 mm being on the extreme side. Doesn't affect the exhaust side so much, but it nibbles away at the cfm number for the inlet by about 10-15 cfm.
Question: "Race Seats" on the scanned paperwork. Implies they were set up properly, multi-angle or radiused or similar? The seats can have a huge impact on the flow - more than the port itself, especially at low lifts.


agreed the lift has raised using poncams over standard but they tested at a much higher lift. About 0.350” column is probably closest at ~235cfm

As for the question about seats I can’t answer it. It was done in 2012 and I can’t remember what we agreed on. Not sure if I have any close up photos that might reveal an answer. I’ll check soon
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