7A Exhaust Cam

[desmo888]

I have heard so much about the use of the 7A exhaust cam on the 3B and I wanted to get more info on this mod.

Are there dyno results showing increased power?

Have piston to valve clearances been checked?

Thanks!

[Mihnea]

Re: 7A Exhaust Cam

Originally posted by desmo888
I have heard so much about the use of the 7A exhaust cam on the 3B and I wanted to get more info on this mod.

Are there dyno results showing increased power?

No, only assumptions based on facts such as increased timing and more lift. Should only be about 5-10 HP but the fact is that you can feel the difference in terms of breathability at high RPMs.

Have piston to valve clearances been checked?

Yes, no interference and still far from it.

[90quattrocoupe]

I have another question about the 7A exhaust cam. Specs show that the exhaust valve is still open, overlap, when the intake starts to open on a S2.

I know this is good for NA motors, because it draws more mixture into the cylinder. But you also get a little unburnt fuel in the exhaust.

It seems like with a turbo, you would want the exhaust slammed shut, so you don't have fuel going out the exhaust.

What are the thoughts on this? Do you put an adjustable cam gear on the exhaust and retard it a couple of degrees to insure it is closed? You would shorten the duration a little, but you would still have the lift?

Thank you,
Greg

[Mihnea]

Greg, this works like this and some people even use both 7A cams, so I wouldn't say it's THAT bad.... the overlap is minimal and having cams with 0 overlap is virtually impossible... also, don't forget that once the engine is at high RPMs and also due to lifter clearances, the static duration/lift are a bit messed up....

[Josh-stateside]

I'm curious about this too.


The idea is that the 7a cam will push more exhaust gasses through which will spool the turbo faster. Isn't it like having more displacement? I am thinking for this applications something like a k26#8 hotside housing with this cam will make it feel more like a k26#6 with stock cams?

Lately that's the direction I am thinking of heading.

Seemingly this cam is not necessary with stock applications or a k26#6 in my opinion.

It's not a matter of how much horsepower it can produce but rather how much it can compensate for the slow spool of a larger exhaust hot side housing and turbine?

Not to get too technical. But it's nice to say the actual reasons it might help vs just saying it will add more hp.

I don't know.. Still learning but thats how it makes sense to me.

Cheers
Josh

[Mihnea]

Originally posted by Josh-stateside
I'm curious about this too.


The idea is that the 7a cam will push more exhaust gasses through which will spool the turbo faster. Isn't it like having more displacement? I am thinking for this applications something like a k26#8 hotside housing with this cam will make it feel more like a k26#6 with stock cams?

Lately that's the direction I am thinking of heading.

Seemingly this cam is not necessary with stock applications or a k26#6 in my opinion.

It's not a matter of how much horsepower it can produce but rather how much it can compensate for the slow spool of a larger exhaust hot side housing and turbine?

Not to get too technical. But it's nice to say the actual reasons it might help vs just saying it will add more hp.

I don't know.. Still learning but thats how it makes sense to me.

Cheers
Josh

Josh,

A K26#8 turbine will still remain a #8 turbine and won't make much boost below 4k RPM. Ask Doug, his was only working from 4.2k and I hope the 7A exhaust cam will reduce this a bit to about 4k.... the #6 turbine makes good boost at 3.3k and full boost from about 3.5k RPM-on.

So, if you're after pre-4k performance, definitely go for a #6 hot side, if not, #8 is for you


Cheers,


Mihnea

[desmo888]

On the subject...

I have a K24 with 235k miles on it (or at least on the car it was removed from).
There was no problems with it when it was removed removed from the 200TQ. The orevious owner had the car for 3 years in which time he had NOT had the turbo rebuilt.

The shaft is very tight and everything seems to be fine. I am not sure which direction to go when I install my 3B engine in my Coupe.



1. Put the K24 on as is

2. Have the K24 rebuild and install it ($350-$400 quoted)

3. Buy a lower mileage K24 ($125 quoted)

4. Buy a lower mileage different turbo (K26???)

I am going for a daily driver with about 300 hp. Upgrades later are possible (to 370 hp or so).

Any suggestions would be appreciated.

[desmo888]

What about this unit?

http://cgi.ebay.com/ebaymotors/ws/eB...category=33742

[Mihnea]

Dave,


Don't, I'm saying don't ever put a K26 on your engine. a K26 can only do about 290 HP with MUCH MUCH MUCH more lag than a K24, thus it's not really worth it.

Depending on the octane rating that's available where you live, 300 HP is more or less a dream on a K24. Personally, I've never done more than 280 HP on a K24, and that was already running pretty close to its reliability limits, but not beyond. My advice: use the stock turbo for now, then when you have the dough, get yourself either an RS2 (370 HP are possible) or a K26/27 or K26/27/29.


HTH,

Mihnea

[Mihnea]

Originally posted by desmo888
What about this unit?

http://cgi.ebay.com/ebaymotors/ws/eB...category=33742

********e, it has an integral wastegate and thus you can't use it on your 3B. Chances are also that it might even give less HP than the stock unit!!

[desmo888]

Originally posted by Mihnea
Dave,


Don't, I'm saying don't ever put a K26 on your engine. a K26 can only do about 290 HP with MUCH MUCH MUCH more lag than a K24, thus it's not really worth it.

Depending on the octane rating that's available where you live, 300 HP is more or less a dream on a K24. Personally, I've never done more than 280 HP on a K24, and that was already running pretty close to its reliability limits, but not beyond. My advice: use the stock turbo for now, then when you have the dough, get yourself either an RS2 (370 HP are possible) or a K26/27 or K26/27/29.


HTH,

Mihnea

THANKS Mihnea!!


That is what I needed to know. Of course I do not understand the designations of the turbos you described but I will when the time comes.

[Josh-stateside]

Thanks Mihnea


So much to learn!

Cheers
Josh

at least I am on the right track

[Mark Halligan]

Gents,

I know that this started off about the 7A cam, but its sort of turned into a turbo discussion.
I feel I must point out that it IS possible to get a relatively quick spool up with less lag using the #8 hotside.
The turbonetics T3/T4/KKK hybrid fitted to mine has the ceramic ball bearing option and I have 1 bar at 3k rpm and a mentally fast spool up from then on, I believe this is a good part of the reason why the power delivery has been described as 'brutal' by a few people before, this is quick, especially because I am also using a large turbine at 63mm (turbine housing reworked to take it) which you would think would slow it down even more?

I suppose what I am trying to say is that there is more to life than the KKK, nowadays there really is so much available, that we are not so limited in our choices of turbo.

Josh said:

So much to learn!

Too right brother , there definately is, but its fun doing it (if not a bit expensive ).

It's too soon for me to comment upon the longevity of the ceramic bearings, but but if you want a quick and hard spooling turbo, they'll do it for you.
Like I said I am still learning, so if I'm talking ******** please tell me, but be kind when doing it...........its Christmas .

Regards,

Mark.

[Mihnea]

Mark, you're cheating man your exducer bore is as big as a KKK27 #7 hotside, same as the one used in sport quattros

but yes, ball bearings are cool, but beware of the big bad surge line!!!

[Mark Halligan]

Mihnea,

help me out here, what size is the exducer bore on the K26 #8 hotside?

Mark.