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 Post subject: Headwork for turbo discussion
PostPosted: Thu May 22, 2008 1:38 pm 
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Giggety! :P

I read alot of things in this forum about modifications to GTI's when turboing them.... and it is great stuff! =D>

But I always seem to hear the same thing about vitara bottom ends, turbo sizes, management etc..... but never alot about the head :roll:

I know that people have their little secrets about headwork and cam grinds and that..... but for those that know a bit about it through experience, could you please share your expertise and advice to the rest of us travelling down this path.....

I mean stuff like valve sizeing, lifters, porting etc.... [-o<

Just want to throw some ideas around to get the best bang for buck when getting the head done.... :mrgreen:

Cheers! 8)

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 Post subject: Re: Headwork for turbo discussion
PostPosted: Thu May 22, 2008 4:57 pm 
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Adapt a 20v head :lol:

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 Post subject: Re: Headwork for turbo discussion
PostPosted: Fri May 23, 2008 8:03 am 
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Headwork is very important in getting good hp figures in the turbo g13b,in std form the exhaust valves are way too small and the exhaust ports very restrictive,so these are the first areas for modification.
Be aware that unlike the bottom end of the engine (to a large degree)that money/time spent on improving the flow of the head will give you hp results, if you get it wrong it will cost hp ,if you get it right then the gains are instant, or course you need a good bottom end to handle the hp ,but even cheapo vitara piston engines will see results from a good flowing head.
Its also a waste of time having a good flowing head if you dont have a good inlet/ex manifold, the std gti inlet manifold seems to become restrictive around 180hp,fitting a cultus inlet made an instant gain of almost 20hp at these levels.Of course you can get more than 180hp through a std inlet manifold by upping the boost ,but its not as efficient.
Basically thats what it comes down to, make everything as efficient as possible or give it more boost!!,if you spend enough money/time you can do both!!

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 Post subject: Re: Headwork for turbo discussion
PostPosted: Fri May 23, 2008 8:43 am 
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Thankyou for that Dave 8)

Is there anybody else that would like to add some more technical information or ask any questions?

Now is the time so we dont get ppl saying "FFS! SEARCH!!! WE HAD THIS THREAD LAST WEEK!!!!" :lol: :lol: :lol:

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 Post subject: Re: Headwork for turbo discussion
PostPosted: Fri May 23, 2008 10:57 am 
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About the only thing Dave didn't mention was cams. The general view is that Cultus-spec cams are the best for turbo applications, anything more aggressive is counter-productive. (Of course this isn't true for ALL engine configurations.)

A set of adjustable cam gears is a given too, especially handy for tweaking the exhaust timing if you're fitting larger valves and a different profile cam.

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 Post subject: Re: Headwork for turbo discussion
PostPosted: Fri May 23, 2008 11:27 am 
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I'm glad you mentioned the cams YLD80Y. I can't seem to get my head around something. I'll try and explain what I am thinking. Say if you have a turbo that kicks in at around 3500-4000 rpm, wouldnt it be best to have some cams that work with the turbo from that rev range onward? So the likes of BD10's or 14's for example (not saying they are the ones to use though). Or will this make the bottom end really sluggish until boost comes on :-k Arent cultus cams just a fly sh!t better then standard GTi ones?

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 Post subject: Re: Headwork for turbo discussion
PostPosted: Fri May 23, 2008 12:02 pm 
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I probably won't be able to explain this 100% accurately, but more aggressive cams will create too much valve overlap, so with a boosted motor you can end up squeezing air straight out though the exhaust valves during the start of the intake stroke -bad news!

The slight extra lift of the Cultus cams allow more air into the combustion chamber than with standard cams, without creating an overlap issue.

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 Post subject: Re: Headwork for turbo discussion
PostPosted: Fri May 23, 2008 12:29 pm 
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I see your point. Understood :lol:. Thanks mate

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 Post subject: Re: Headwork for turbo discussion
PostPosted: Fri May 23, 2008 12:49 pm 
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As YLD80Y stated.... more aggressive cams will create too much valve overlap, so with a boosted motor you can end up squeezing air straight out though the exhaust valves during the start of the intake stroke -bad news!

When this happens you get into the realm of also needing the best aftermarket ECU's that money will buy.
You need ones that have adjustable start / end of injection time to better cope with lots of overlap.
The ONLY ones that I know of which have this are MoTeC and Autronic.

Most aftermarket ECU's only inject fuel at a fixed reference point (crank / valve angle) which is ok most of the time... This can become an issue with high RPM and or big cams.
Even the factory Baleno ECU injected the fuel at different crank / valve angles as per MoTeC / Autronic style.

Cheers,
Damian


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 Post subject: Re: Headwork for turbo discussion
PostPosted: Fri May 23, 2008 5:08 pm 
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I understand this point about larger camshafts also...... but could somebody explain why for example a GTR Skyline that runs a huge turbo like a T51RSPL is always complimented by quite a large set of camshaft to shift the cams where the turbo is.....? :roll:

Why does this theory not apply to G13B's? :?

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 Post subject: Re: Headwork for turbo discussion
PostPosted: Fri May 23, 2008 6:55 pm 
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Ive messed about a fair bit with cams in my turbo engines and if you want a dyno pony engine then there are big gains (top end power wise)to be had by fitting bigger cams,but this comes at a cost,basically you lose out down low and when the cams come in late the effect on the turbo makes it all or nothing,which is pretty useless on the street!! instant wheelspin.
Now I know there will be some guys out there who have fitted bd14s to their turbo cars and think that they are wonderful but I would have to question whether they ever tried dialing in both cultus cams then back to backing the bd14s, I have been there and done that and I took the bd14s out straight away and sold them!!.
I have been using a cam for the past two years that is based on the cultus profile but with an extra 1mm of lift,so 1.5mm more lift than std but a very mild cam ,this gives the best of both worlds if you have the head flow to go with them.
It is relatively easy to make 250+hp from a turbo g13b (and thats plenty for on the street)so it then comes down to getting the nicest power delivery possible,a flat tourque curve and hp figure that stays constantly high from 4000 to 8500, what you get with big cams or big turbos is a very short tourque curve and a peaky hp curve which is only good for dyno runs. :lol:

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 Post subject: Re: Headwork for turbo discussion
PostPosted: Fri May 23, 2008 7:04 pm 
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Sorry K star I didnt answer your question regarding skylines and big cams ,I would put it down to the fact a lot of hype is created by the workshops regarding power figures,putting big cams and big turboes in is an easy way to make an impressive hp figure(bragging rights)but if youve been out in one of these cars its pretty clear they are a dog to drive down low and have such a small power band that they are slower than a properly set up lower hp car.Ive seen plenty of hi hp skylines on the dyno and thats about the only thing they are good for!!

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 Post subject: Re: Headwork for turbo discussion
PostPosted: Fri May 23, 2008 7:29 pm 
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Geez Dave! :shock:
Your being very informative and educational 2nite!! :o
If I didnt know any better, Id say somebody was glowing from some action last nite or something... :lol: :lol: :lol: hahahhahaha

But thankyou for your warm advice all the same Dave =D>

Anybody else got any questions/advice?

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 Post subject: Re: Headwork for turbo discussion
PostPosted: Sat May 24, 2008 8:05 am 
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I think Dave has pretty much summed it all for what I was curious about. Cheers Dave.

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 Post subject: Re: Headwork for turbo discussion
PostPosted: Sat May 24, 2008 1:24 pm 
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Would it be possible for some of the people in the know to lay down some measurements of head components etc? I know Dave has given us a bit of insight into cam sizing that he uses but not in much detail. Same story with valve and port sizing and the like. What about valve spings?

I know that some of you may have secrets in regards to some of these details, I understand fully that you wish to keep it this way. But it would be greatly appreciated by myself, and I'm sure many others if we could get some more details.

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 Post subject: Re: Headwork for turbo discussion
PostPosted: Sat May 24, 2008 11:00 pm 
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The "under the curve" comments Dave has made are very important. I mean just look at the consistantly high power being produced from 5750 to 7250 on the graph below

Image

There are a few other power graphs I have seen where the power is extremely peaky. I would love to see a torque curve from your car Dave (without having to back calculate the hp curve - cos I'm lazy..)

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 Post subject: Re: Headwork for turbo discussion
PostPosted: Sun May 25, 2008 12:03 am 
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This is a better dyno sheet to have a look at, for how quick daves engines and setups come on boost, and how long they stay in the power band. This is my car when i got it done a few years ago, with dave new turbos he is running it comes on quicker again.

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 Post subject: Re: Headwork for turbo discussion
PostPosted: Mon May 26, 2008 10:26 am 
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Just touching on the camshaft thing here.

While you should choose camshafts to match your turbo size/power band, you would be surprised at how much midrange you will gain with the correctly selected camshafts. Stock, BD10, BD14 and cultus cams are all poor in comparison to something designed specifically for a turbo application.

One of the biggest misperceptions in turbo charged engines is that the air is forced into the cylinders. While yes, the air is compressed, the engine is still breathing the air in. A good NA engine will always make a good turbocharged engine.

If you have the supporting mods - ported head(stock head cannot flow that well even with big cams), an intake manifold, not the cultus or stock(yes there are gains from the cultus over stock, but its not the best manifold, thats for sure), preferrably a straight runner with correctly sized runners, bellmouths and plenum, you will gain a hell of alot of midrange/topend with the appropriate cams. Lets be serious here, its a small engine, its not going to make good bottom end regardless. Having a powerband from 4k+ isnt hard to drive with, you just adjust your driving habits, to be in different gears to suit.

If you have the supporting mods, this is where I'd be looking for cams ... total duration around the 270-280 degree area, 230+@1mm, lift would be determined by the head work as there is a choke area if you go too large on the stock valves/porting. The duration@1mm is the most critical part and most often overlooked by the total duration, which really doesnt give any idea of what the cam can do. With advances in cam manufacturing, you can get very radical ramp rates that wont harm the valve train, huge gains to be had here.

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 Post subject: Re: Headwork for turbo discussion
PostPosted: Tue May 27, 2008 11:57 am 
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Very nice thread guys... well done! =D>

But now the question of how much would it approximately cost to get a head tricked up a bit for turbo?

Most of us are penny pinchers :lol: and choose the best bang for buck ie. vitara pistons, turbo chips etc..... to get the best power vs $$$..... so what is a rough price to make a good positive improvement in a head without breaking the bank?

Cheers! 8)

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 Post subject: Re: Headwork for turbo discussion
PostPosted: Wed May 28, 2008 9:13 pm 
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Regarding cams and mainly directed at dave

Im currently running bd10s in my current turbo setup (td04l) and is yet to be tuned. I also have access to a set of cultus cams. From your experience bd10 would still be to lumpy? Im tempted to put the cultus ones in now before the tune. I also have adjustable cam gears

Dave

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