View Full Version : SOHC headwork
Ok, approaching headwork time on the KA24E. I plan on doing:
-match porting: intake manifold to head, plenum to intake manifold and plenum to TB
-perhaps solid lifters
-268deg inlet 272deg exhaust cam (.441 intake lift .447 exhaust lift)
-Thinking about HPC coating on the valves/combustion chamber
-3 or 5 angle valve job
My budget is about $1000 and all work (except valve job) will be done by me. What should i do? Ideas? Criticisms?
Car already has extractors (genie, 4,2,1) and will most likely be getting forced induction in about a yr.
If you are going to go to forced induction later, don't modify the engine as a NA unit now. Optimum specs for a turbo engine are different to those of a NA engine. For a start the proposed cam possibly has more overlap than you would want in a turbo engine. To make that cam work well in a NA engine you would increase the CR. When you later go to turbo it you'll have to lower it again. The proposed headwork would be worthwhile in either application.
What I'm trying to say is if you turbo it later, you'll end up redoing a lot of the work you want to do now.
Just a few thoughts off the top of my head.
You will go close to breaking your budget just doing a couple of those. HPC a full set of valves and pistons will not be cheap....ditto a set of solid lifters.
But otherwise I echo what Hamish said. The cam is a bit big for later turbo, and also a bit big for standard compression N/A. You will lose a lot of bottom end unless you pick up some compression.
the std cam is 240 inlet 248 exhaust, would kind of duration should i be aiming for?
You probably wont go to far wrong if you keep it close to std. See if you can get a grind that has extra lift.
You would really need to speak to an expert on cam grinds to suit turbos. Crow or Ivan Tighe may be able to help.
Originally posted by hamish
If you are going to go to forced induction later, don't modify the engine as a NA unit now. Optimum specs for a turbo engine are different to those of a NA engine.
It depends on what sort of car you're after. One of the guys on the TurboBricks mailing list ("fast" Volvos), who's involved in racing the things in Sweden, reckons that for a fast road car you're best to get really good n/a performance going, and then when you add a turbo you multiply your performance by the boost level a lot more.
ie. he says it's better to have a really responsive lower-boost engine than a high-boost motor that might be OK on a race-track or a dyno shoot-out, but is a pig to drive around (& is slow until you really push it as a result). The example he gives is that if you get ~200hp out of a 2.3L 4cyl volvo motor in n/a form, adding a turbo to that exact motor & running only 7.5psi gets close to 1.5x the power, or close to 300hp ... yet leaving it standard at 130hp, dropping the C/R so you can handle big boost & lowering power to 115hp, and then putting boost in to get 300hp means you need ( ( 300/115 * 14.7 ) - 14.7 ) = 23.5psi (this obviously assumes certain inefficiencies aren't there; the reality is probably worse). And yet the 23.5psi motor is much more doughy off-boost.
Obviously it's different for different motors, and it depends on what sort of power you're after.
If you are going the turbo route,you will want a cam with less exhaust duaration than the inlet (every cam specs for turbos i have seen have a retarded exhaust duaration).Also isn`t polishing street heads a no no as they will only slow the mixture down as a polished surface is more "sticky" than a rough surface and will not provide any useful gains until you rev the ring out of the motor (very top of the rev range).
Just a thought
I will be doing a finer (hence more polished finished) on the exhaust ports, and a rougher finish on the intake ports.
Don't a lot of performance companies offer 272deg exhaust duration cams for turbo engines?
18-05-02, 09:25 PM
The HK$ cams for the 4G63 come as 264/264 264/272 or 272/272 (in/ex) (I know it's not single cam, I telling ya what I know)
The biggest I found was max duration of 310 on both cams! (powerband of 4500-9000)
Those big cams are more intended for drag racing, or close ratio gearbox circuit racing....basically only useful at full throttle full revs. For street driving you need to set up your lobe centres to kill some of the big cam effect. And that reduces the top end benefit of having such a big cam.
As someone else has already mentioned, more lift is more worthwhile.
So 260 inlet 268 exhaust would be the way to go then? 20deg more duration than std.
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