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View Full Version : Difference in Cams Lift and Duration for BP/BPT


project.r.racing
31-12-2007, 07:47 AM
BP-05 inlet cams have 233 degree and 8.0mm Lift
BP-26 inlet cams have 233 degree and 8.0mm lift

BP-05 exhaust cams have 250 degree and 8.5mm lift
BP-26 exhaust cams have 248 degress and 8.5mm lift

Differences are in when the cams opens from TDC to BDC thus affecting overlapDave or anyone else,

Do you/anyone know how much degrees before and after TDC and BDC are?

The reason I ask:-
Is that it seems like if you got a inlet cam reground to 250d + 8.5mm lift, (same as exhaust cam,) and have the extra duration added only after TDC, you'd come out with a cost effective N/A mod by only regrinding 1 cam? And by adding the extra duration only after TDC on the intake cam, thus limiting the overlap where the inlet valves are opening and the exhaust valves are closing, so it shouldn't idle like a piggy or race car style idling. But still achieve a decent power gain.

Thoughts??? Ideas??? Flaming???

Ryan

zappy65
31-12-2007, 08:13 AM
According to my mazda manual:
Intake Open for: 231 degree's after TDC
Exhaust Open: 113 After TDC and is open for 247 degrees
Exhaust has 8 dgree's of overlap after TDC
correct me if im wrong plz....im still new to all of the cam grinding math...

project.r.racing
31-12-2007, 08:20 AM
Hi John,

So intake = 233d total, so 2d before TDC, 231d after TDC

Exhaust must be wrong tho? If intake is 231d after TDC and exhaust is 113d after TDC, then thats a minimum of 113d overlap, I don't see an engine running with that much overlap when the intake valves are opening. Then i could be wrong also...

That was for BPT right? Know what BP is at all?
Intake Open for: 231 degree's after TDC
Exhaust Open: 113 After TDC and is open for 247 degrees
Exhaust has 8 degree's of overlap after TDCIf we just take out what i have in italics - using those other pieces of information, it would mean a 10 degree overlap near TDC, which seems more realistic to me. Maybe?

Confused,
Ryan

BigMal
31-12-2007, 11:18 AM
Why regrind a intake cam to exhaust specs instead of using the exhaust cam
with adjustable cam gears. Isn't that the mod that ROBBOE tried on his turbo
without success ???

zappy65
31-12-2007, 12:04 PM
yeah its called the exintake mod....i think its basically using specs from the exhaust cam on the intake cam, didnt do anything for him i dont think...ill recheck my specs, but yeah thats for the BPT, the Mazda Manual has nothing about cam duration or anything and its straight from mazda..useless they are...

project.r.racing
31-12-2007, 03:38 PM
yeah but both you guys are referring to a turbo application where boosted air go thru the inlet valve, but out the exhaust valves at normal engine compression, hence the difference before and after TDC?

but for a n/a, that has normal compression air going thru both inlet and outlet valve. couldn't they be the same duration and lift? I know that B-Spec Miata cams are both 255degree duration and 8.8mm lift. so they could be the same, but just not a aggressive?

ryan

dave0r
31-12-2007, 04:26 PM
Valve Timing BP-ZE
Intake cam duration
233° @ 0.003"
Intake cam opening
5° BTDC
Intake cam closing
48° ABDC
Intake cam lobe height
44.094mm (1.7360")
Intake cam base circle
35.941mm (1.415")
Intake valve lift
8.1534mm (0.321")
Exhaust cam duration
250° @ 0.003"
Exhaust cam opening
56° BBDC
Exhaust cam closing
14° ATDC
Exhaust cam lobe height
44.600mm (1.7560")
Exhaust cam base circle
35.941mm (1.415")
Exhaust valve lift
8.6614mm (0.341")
Valve overlap
19°


GTX/Turbo is different again
*stolen from here http://www.protegefaq.net/

*Edit* They dont even list my engine on the site (BP22) and it has 2xx degree and 8.5mm lift on the INLET SIDE different cams again, pistons CR. so dont take it as to heart. its just the US/Jap Specs.... OZ and NZ specs could be different

project.r.racing
31-12-2007, 04:42 PM
So this is what I would be trying to achieve:-

Intake cam duration
250° @ 0.003"
Intake cam opening
5° BTDC
Intake cam closing
65° ABDC
Intake cam lobe height
44.600mm (1.7560")
Intake cam base circle
35.941mm (1.415")
Intake valve lift
8.6614mm (0.341")

Exhaust cam duration
250° @ 0.003"
Exhaust cam opening
56° BBDC
Exhaust cam closing
14° ATDC
Exhaust cam lobe height
44.600mm (1.7560")
Exhaust cam base circle
35.941mm (1.415")
Exhaust valve lift
8.6614mm (0.341")

Valve overlap
19°

That way, the overlap near ignition / TBC is still the same, but the inlet is open a little longer and the idle should be close to factry idle. Workable or not? Worth it or not? Or just go out and buy 2x new billet cams from supplier?

Ryan

bourbon
01-01-2008, 09:40 AM
just go buy 2 billet cams...less stuffin around...but you might need headwork to match...i know when i had my new ones in anda bit gruntier (custom made from a guy in sydney) they neeeded to do headwork for it to work properly... im getting extra lift out of mine and more torque...

project.r.racing
02-01-2008, 07:14 AM
yeah i'm aware of that, hence the reason for this thread. 2x billet cams cost $800. i was trying to get a tight-ass option of doing 1 cam until i fit bigger cams in.

since starting this thread, i called a few people in the indrustry that kinda know about this stuff. just getting the intake cams up to the same specs as the exhaust will gain little if any hp and torque at all! same as ROBs then i guess. they said that throttle responce and lower end would be better, but you'd probably not realize the changes.

bourbs - what did you get?

BigMal
02-01-2008, 08:00 AM
Have a read on solomiata.com The 99 cams are larger than any of the earlier
ones if you can find them.

bourbon
02-01-2008, 09:57 AM
they just got me new billet ones, and then reground them...gun performance in stafford have the contact in sydney...he does them to what ever specification you want...

dave0r
02-01-2008, 12:49 PM
the US boys seem to have good results when doing the cam swaps. most N/A get 6-9 WHP ,most turbo get 20-28 WHP jump
this being 250d and 8.5mm lift on the inlet side

no idea why robs results where so low

same thing happened to mate in NZ
swapped from a GTX head to N/A head, using GTX cams
car made no power, wouldnt boost past 12psi!! anymore..really strange, swapped it back to the GTX head..no problems

i did the headswap. no problems..but havent done the cam swap yet..its in the N/A motor but not running <--few weeks away

project.r.racing
02-01-2008, 04:50 PM
most N/A get 6-9 WHPi guess 4-6kW isn't too bad for spending $300 on a cam??? you'd spend 2x or 3x that on a full exhaust and only get the same power gains...

project.r.racing
02-01-2008, 06:11 PM
Found this:-

264d - 272d Advertised Duration
210d - 225d .050" Duration

This range is designed more for the midrange, smooth cruise and slightly lopy idle. This is still suitable for automatic transmission using standard stall converter. Modified Distributor and exhaust systems are recommended. This is good for towing in larger capacity engines. Higher compression ratio is not required, larger valves are not recommended. A typical lobe separation is 108d - 112d.

Power range:
Small capacity 2000 - 5800 R.P.M
Large capacity 1500 - 5000 R.P.M

---

272d - 290d Advertised Duration
225d - 245d .050" Duration
This range is for modified street, limited modification race or speedway. Used for single carburetor (350 Holley) and 6 cylinder engines. Twin carburetors are recommended for 4 cylinder engines. For road application suggest ported cylinder head, bigger valves, balancing and higher compression ratio (9 or 10:1). The distributor also requires regraphing. Lopy idle, if automatic transmission is used a higher stall will be required. A wide area of camshaft selection, different duration's and lobe centers used are to give different power ranges. Lower rear axle ratio may be required to achieve the best result from these modifications. Typical lobe separation of 106d - 110d.

Power range:
Small capacity 2600 - 6500 R.P.M
Large capacity 2200 - 6000 R.P.M

Ryan