4A-GE engine mix - question

[Uzelac]

ur right, head was cut 1mm.
will measure chambers, than i will see if any grinding will be done.

[Uzelac]

Continued


Measured my chamber cylinder 1, only 32cc!
I'm sure head was cut 1mm, but measuring was done good, friend who is a professional engine builder did it.
It is a smallport head, 100% no porting/enlarging chamber.

Does it make sense ?
Where would i end up, 13+ CR zone ?

[Bean]

Uzelac Wrote:Continued


Measured my chamber cylinder 1, only 32cc!
I'm sure head was cut 1mm, but measuring was done good, friend who is a professional engine builder did it.
It is a smallport head, 100% no porting/enlarging chamber.

Does it make sense ?
Where would i end up, 13+ CR zone ?

with a 1.2 HG shy over 12.6:1 (static)CR
a nice and easy (allows metric or imperial) CR calculator you can find here: http://www.csgnetwork.com/compcalc.html

when you say no porting at all, does that mean the hotspots in the combustion chamber are still there? if yes in combination with the wiseco pistons you'll be in big trouble.

Also although a lot of people choose the HG simply to get their desired CR, they often forget that, in combination with the deck height, the choice influences the effectiveness of the squish area (this should be idealy some where ~1mm on a high CR engine, run too low and your pstons will hit the head, when the rods/rodbolts stretch, piston expands; too big and the effect will suffer)

At the end of the day SCR is only half the story - what you want to know is DynamicCR to calculate that I would need to know at what ° ABDC (AfterBottomDeadCenter) your intake valves fully close, as only then the engine will start compressing. with your wild cams it'll be fairly late so you will need a higher SCR but mind you, depending on fuel quality and engine running temps you wouldn't want to run much above 9:1 DCR


just as a guideline - oh and if your oil gets easily to 100°C+ on track forget about the lower two lines

[Uzelac]

http://www.pipercams.co.uk/pipercams/www...OY16VBP300

[Uzelac]

Bean Bandit Wrote:with a 1.2 HG shy over 12.6:1 (static)CR
a nice and easy (allows metric or imperial) CR calculator you can find here: http://www.csgnetwork.com/compcalc.html

when you say no porting at all, does that mean the hotspots in the combustion chamber are still there? if yes in combination with the wiseco pistons you'll be in big trouble.

12.6:1 sounds great, i had 13-14:1 figures in my mind .
Chambers can be done, ported, removed hotspots, whatever, no problem, if that is reasonable, if at the end i can end up with low 1.something HG and CR at ~11.5-12 with Wisecos.

I'm aware about importance of squish, that's the reason I don't want to go with larger HG.

If not, then i will continue to use bigport head, and keep the smallport for some other times or other engine which doesn't have Wisecos.
BTW. for what i know now, i would never again by pistons made like these, flat surface is the way to go for pistons.

[Bean]

Ok, so your dynamic stroke using the figures above 76° (this only applies if you time it at 106°) is *drumroll* 53.67mm (53.673989256 to be exact )

using that info in the CR calculator gives not much joy to be honest. You would need to use race fuel for sure and try to get engine temps as low as you can.
Going from the following givens:
Dome CC = 5.9; Deck height = 0.4 (this might be different and only you can tell/measure what it is exactly with the Wisecos); HG bore = 82mm (most are); Dynamic stroke = 53.67mm
this will result in the following combos:
[code:1:c3348415d2][Head CC;HG thickness] = DCR
[32;0.8] = 9.64 [32;1.0] = 9.36 [32;1.2] = 9.11
[33;0.8] = 9.38 [33;1.0] = 9.12 [33;1.2] = 8.88
[34;0.8] = 9.10 [34;1.0] = 8.90 [34;1.2] = 8.67
[35;0.8] = 8.90 [35;1.0] = 8.68 [35;1.2] = 8.46
[/code:1:c3348415d2]
I'm not sure how much you can increase the head CC (oldeskewltoy might) without taking too much off the squish shoulders.
Personally I would go for the [35;0.8] combo if possible as this has 1.2mm squish which is ok-ish and use fuel as close to race fuel as you can (min. 100) and fit a big ass radiator and oil cooler (with good ducting to force as much air through it as you can). If you still need to get valves get some dished (like the Supertech) ones as I think in your case every little increase helps

looking at those figures I'm glad my head is a virgin and has 37cc after porting (thanks Dan )

[NoHachi]

Bean Bandit Wrote:I'm not sure how much you can increase the head CC (oldeskewltoy might) without taking too much off the squish shoulders.

You can go quite far by sinking the valveseats and deshrouding them afterwards. Every mm is 2.5cc or so. Don't have to come anywhere near the quench-pads.

[Uzelac]

Thank you very much, this is great.
I will measure everything once more, but looks to me that "good old bigport" will have to do the job .
Or maybe, put this head to a stock blue top 3rib engine, it has only 150k km beside 25years, could be fine actually

[Bean]

Uzelac Wrote:Thank you very much, this is great.
I will measure everything once more, but looks to me that "good old bigport" will have to do the job .
Or maybe, put this head to a stock blue top 3rib engine, it has only 150k km beside 25years, could be fine actually

That would give in the regions of 10.5:1 with a stock HG and the 9.4 pistons. So would go niceish with cams around 272 +/- 10 depending on how they are timed

[Uzelac]

What is better?

1. Take bigport head, skim it as necessary clear hotspots.

or

2. Take this already-pretty-skimmed-now-32cc-per-chamber smallport head find a way to enlarge chamber to 34+ cc (hotspots, sink/deshroud valves), maybe even go with 1.5mm HG

In both cases, i wouldn't like to pass 12:1 CR mark. If that ain't possible with smallport head, than bigport is only choice.

Why i keep insisting on smallport? It should be better choice for 150-200 hp and have better low/mid range. Beside cams are already seated in it.
Since Piper market this cams as Rally with power band in 3000-8000 rpm it seems smallport is better in all aspects.