Tighe Cams 708x 805c

[discopotato03]

One for Cubes or Simonr32 , these Tigh cams you've got - can I have some details about them as I couldn't see them under Nissan in that link .

From what I can see they must have reasonably aggressive ramps to have the duration at 50 thou lift mentioned .

I have to look into 33 25DET cams in the next few months and the price is looking good compared to Poncams .

Cheers A .

[Cubes]

Simon had to really push some overlap in to it to work good the size cams are really better suited to the rb30 that essentially soak up the cams.

Unless that is you like the lopy idle then they are worth it.

rbman has had some good results with his 254 8.5mm lift cams. 214duration @ 0.050" still quite an aggressive ramp rate. Exhaust centreline is slightly different that aids top end.

Mine at 115degree's has pushed peak power to the same 6000rpm and drops ~10rwkw by 7000rpm. BUT its not a true indication as mine is showing an inlet restriction issue.

Std airbox/filter combined with 2" fmic piping.

I am absolutely wrapped with mine to be honest. It has really free'd up the motor feels so much more alive.

Rolling on the throttle in third gear at 60km/h.. by 70km/h its pulling so hard and pushing the nose in to the air I feel like its going to break something.

[discopotato03]

Ok so if I read the data correctly and the cams are timed correctly the valve timing/duration/lift/LCA should read :

708 = 4-61 63-11 In Dur 244.61/In lift 8.515 on 112 ATDC LCA , Ex Dur 254.23/Ex lift 8.510 on 117 BTDC LCA .

805 = 21-65 65-19 In Dur 265.38/In lift 8.913 on 110 ATDC LCA , Ex Dur 263.73/Ex lift 8.902 on 115 BTDC LCA .

This probably begs another thread but it does still relate to the 30 series turbos and the difference with 20% extra capacity ie RB30 bottom end .

Cubes I'd expect the extra capacity to tone everything down (maybe 20% ?) given the 20% increase in capacity but without 20% more port and valve area . So you could use the extra valve timing (duration) to fill the larger cylinders .

I had to go back and check the 708 inlet cams opening time before top dead center (BTDC) because it looked very short .

I'm guessing they made the inlet cam a shorter ~ 245 deg duration because customers may put those cams on engines with factory turbos and cop a fair bit of restriction and reversion . I suppose one way to have reasonable trapping efficiency and not too much charge pollution (from high exhaust manifold pressure) is to keep the inlet short and advance it up to keep the overlap short - 15 degrees .

The situation would change with a larger turbine and housing (eg 3071R) , lower exhaust mani pressure I reckon would mean the engine could scavange a bit more effectively and possibly get away with the inlet valves opening earlier and the valve open period or duration a little longer .

The thing I know nothing about ATM is how much an R33 RB25's VCT changes the inlet cams phasing .

To the Mods , if this is getting too OT should I start a cam thread and maybe transsfer this post there ?

Cheers A .

Edited July 25, 2008 by discopotato03

[Cubes]

Ok so if I read the data correctly and the cams are timed correctly the valve timing/duration/lift/LCA should read :

708 = 4-61 63-11 In Dur 244.61/In lift 8.515 on 112 ATDC LCA , Ex Dur 254.23/Ex lift 8.510 on 117 BTDC LCA .

805 = 21-65 65-19 In Dur 265.38/In lift 8.913 on 110 ATDC LCA , Ex Dur 263.73/Ex lift 8.902 on 115 BTDC LCA .

I had to go back and check the 708 inlet cams opening time before top dead center (BTDC) because it looked very short .

I'm guessing they made the inlet cam a shorter ~ 245 deg duration because customers may put those cams on engines with factory turbos and cop a fair bit of restriction and reversion . I suppose one way to have reasonable trapping efficiency and not too much charge pollution (from high exhaust manifold pressure) is to keep the inlet short and advance it up to keep the overlap short - 15 degrees .

The situation would change with a larger turbine and housing (eg 3071R) , lower exhaust mani pressure I reckon would mean the engine could scavange a bit more effectively and possibly get away with the inlet valves opening earlier and the valve open period or duration a little longer .

Where do you get 244duration? IVO of 14.06 & IVC of 60.55 gives you 254 duration?

When rbman ran those cams he picked up 26rwkw on around the same boost, peak power rose by 400rpm and it held on to that power until close to 7500rpm.

Even though my cams are larger the lca's shift the power considerably to the left.

[discopotato03]

Sorry Cubes my mistake , on the left sheet its 14 not 4 BTDC on the inlet cam . Just not a great printout .

Will edit my previous post .

Back in a sec .

[discopotato03]

Ok so if I read the data correctly and the cams are timed correctly the valve timing/duration/lift/LCA should read :

708 = 14-61 63-11 In Dur 244.61/In lift 8.515 on 112 ATDC LCA , Ex Dur 254.23/Ex lift 8.510 on 117 BTDC LCA .

805 = 21-65 65-19 In Dur 265.38/In lift 8.913 on 110 ATDC LCA , Ex Dur 263.73/Ex lift 8.902 on 115 BTDC LCA .

This probably begs another thread but it does still relate to the 30 series turbos and the difference with 20% extra capacity ie RB30 bottom end .

Cubes I'd expect the extra capacity to tone everything down (maybe 20% ?) given the 20% increase in capacity but without 20% more port and valve area . So you could use the extra valve timing (duration) to fill the larger cylinders .

The thing I know nothing about ATM is how much an R33 RB25's VCT changes the inlet cams phasing .

To the Mods , if this is getting too OT should I start a cam thread and maybe transsfer this post there ?

Cheers A .

No edit function so this is best I could do .

I guess another thing is how cam duration relates to compression ratio , I have to wonder if something like 9.3-9.5:1 and a good inlet manifold/multi throttle system would allow the use of the warmer cams in an RB25DET . It would have to have low restriction on the exhaust side to achieve anything worthwhile .

Also I might contact Tighe to see if they are interested in doing a hybrid of the 805's ramps on the 708's centers and timing numbers , may be a bit noisy though and need good springs .

While I'm here to what extent was your 32 25 head ported and does it use std sized valves ?

Cheers A .

Edited July 26, 2008 by discopotato03

[skylinecouple]

Something I am very interested in right now. Increase overlap and compression is essentially dropped right ? At what point does the cam become too much for the lifters and springs on a standard head ?

[discopotato03]

Someone else would need to chime in about std springs but I think the things to look out for are spring coil bind and not being too over the top rate wise .

IMO the valve overlap period has a lot to do with trapping efficiency particularly at pedestrian engine revs .

When you build an engine the CR figure given is the measured or "static" compression ratio , it assumes no inlet restriction (at all) so 100% volumetric efficiency .

It doesn't work like this in the real world where you do have restrictions and the throttle/s are usually the greatest restriction - its how we control the engines speed/load - by strangling it .

Anything that limits the cylinder filling itself on the inlet stroke governs how much air we have to compress on the compression stroke . What you get is a "dynamic" or effective compression ratio and the greater the inlet restriction (throttle/s etc) the greater the difference will be in static and dynamic compression ratios .

At idle the throttle/s are making a huge restriction so less air reaches the cylinders so with less to compress the effective or dynamic CR will be quite low .

Multi throttle inlet systems are a huge bonus because when fully open they allow whatever pressure ahead of them to reach the inlet ports/valves so the dynamic CR shoots up faster than a single throttle would allow .

Cams with longer overlap periods tend to give that "lope" or what I call brittle idle and it's much more pronounced on a single throttle plenum type inlet manifold . The reason being that all inlet ports/cylinder can communicate with a single plenum manifold so pressure fluctuations do weird things to adjacent cylinders .

To my way of thinking what the individual (per cylinder) throttles do is mostly block the pressure reversion waves in the cylinders (caused by earlier opening inlet vales) from spitting back into the manifolds plenum and doing weird things to the plenums air conditions .

So in other words the long overlap cams designed to breathe and scavange at higher revs can have the chaff cutter effect reduced by using individual throttle type manifolds .

If you have to use a single throttle manifold the engines low down manners are not going to be good with wide overlap cam profiles , as SK said the cam (valve timing) should be set to suit the engines desired usable rev range so if you don't need telephone number revs you don't need wide overlap cams .

Nissan was obviously looking for more serious power from homologation engines like the RB26 and GTiR spec SR20 , both hade individual throttle per cylinder inlet systems and no doubt warmer cam profiles than the more mundane (single throttle plenum) RB and SR spec engines . This not doubt had a win win with performance and emissions in mind for road registered cars .

I've always wondered about RB26 cams in RB20's/RB25's and hydraulic buckets aside its quite possible that more overlap in a single throttle engine caused them to lose out low down .

My opinions only , cheers A .

[Cubes]

While I'm here to what extent was your 32 25 head ported and does it use std sized valves ?

Cheers A .

It was lightly tidied up.. Rebuilt + port polish and valve deshroud set me back 1k.

Standard valves.

Feeling the port inside especially the exhaust side was quite noticeable around the bowl area. It was what they considered a stage 2. They said the next step you spend more $$ for little gains.

Seems to have worked well as its always made decent power vs boost on the same dyno compared to other rb25det's and rb30det's.

Economy has improved clocked up a heap of km's on the weekend and pulled 480km's out of 52litres.

[discopotato03]

I got an E-mail back from Tighe cams about what is suitable for RB25DET's , they said look under Ford Sierra because the lobe disign must be similar to the Ford ones .

I was wrong about the 805's valve timing , it's bugger all longer than the 708 . It must have more agressive ramps to have the bit longer duration at 50 though lift and a little more total lift .

The REAL interesting grind is the Ford Sierra one below the 805 one - very similar but ~ 10.2mm lift on from memory 254 deg duration .

Very interesting , cheers A .