4AGE Timing. Slightly raised compression.

[justin_es]

Good day people's.
I have a slight head gasket leak so i am about to do a HG change.
Im going to go with standard gasket as i will get the head shaved anyway. 1 to smooth it out if any warping is present. 2. to slightly raise compression.
I was told .5 is safe for a stock motor so im going to go standard size HG with a .5 shave. (only more if more NEEDS to come off obviously)

Now
What timing should my motor be running at?
Is different to stock timing required with a compression raise?

I was going to do a timing check on it soon anyway just to make sure its spot on.

Cheers.

[mattysshop]

run 98 RON fuel, and 15-18 BTDC with T1 & E1 bridged (or TE1 & E1)

as the smallports run a knock sensor, and were designed in the 80's to run on kerosene (91).. this should be a walk in the park..

to answer your question though... no nothing really needs to change, you can run the factory 10 deg BTDC if you wish.. but i always run a couple degrees more.. does it make a difference? probly not.. but i like to think so!

[SHEPPO3930]

may i ask what bridging t1-e1 does?

[Hiro]

may i ask what bridging t1-e1 does?

Puts the ECU into diagnostics mode (allowing error codes to be read via the CEL) and locks the advance on distributor allowing you to set base ignition timing.

[justin_es]

yeah i always new that people often advance it a little more than factory i just wasnt sure exactly what by.
So to set the timing properly the diagnostics mode has to be on hey?

ive seen it done without it but at the time i was actually thinking something doesnt seem right here when they were doing it as timing kept changing itself back after they turned the dizzy manually?

i have no idea if thats right or not but they were having trouble getting it right anyway haha.

[TERRA Operative]

Yep, you need to bridge the terminals. Otherwise the ECU bounces around the place adjusting at the same time you do.

I set my 4A's to 12 degrees, my freshly rebuilt 4AGE 20v silvertop is at 12 degrees with a TRD head gasket and a slightly shaved block (just enough to make it flat). The engine is designed to be run on 100 octane but BP Ultimate will do the trick.

[justin_es]

ah so when i said hey guys im pretty sure your doing something wrong here i was right LOL.
i just wasnt sure what it was they were doing wrong haha.

I was thinking about 12 degrees too. it seems to be the common adjustment from stock.
Might try slightly higher. If i get no knocking or ping then im laughing. :-)

[oldeskewltoy]

.5 what?

I'll assume you mean 1/2mm. A 1/2mm cut(.020") will shrink the combustion chamber by about 1cc to 1.5cc. So the combustion chamber will go from about 36cc, to somewhere between 35 and 34.5cc.

You static compression is only going to change by a few tenths of a point.(35cc chamber = 9.58 to 1, 34.5cc chamber = 9.67 to 1). To be honest... the changes is minimal... set up timing as you would any other time

[justin_es]

The reason I'm thinking 1/2mm is because I was advised by a few people that, that is the safest to assure I don't have issue's with ping etc.

What do you recommend so that I will notice a slight gain but won't have too high a risk of ping?
And with what timing?

Cheers.

I was originally going to go 0.8mm trd gasket down from 1.3 or 1.2 whatever stock is. So thought cheaper to get a full stock head gasket kit and just get head shaved instead as its going.to need shaving anyway?

Are my thoughts on the right track or way off?

[jondee86]

run 98 RON fuel, and 15-18 BTDC with T1 & E1 bridged (or TE1 & E1)

I would be careful about running that much more advance than stock. 15-18 deg is what you would normally set the engine without putting the engine into diagnostic mode. Better to go with the 10 deg base setting, or up it to 12 deg if you like. FWIW when my basically stock smallport was on the dyno, we tried a couple more degrees advance over stock, and lost power

Cheers... jondee86

[MorGo]

Well,if my 4A-F runs well at 11,5:1 with Russian 95 octane and +5º advance I don't see how 0,5 mm in 4A-GE could be a problem.
(0,4 mm from block,0,8 mm HG and 1,4 mm from head)

[justin_es]

I'm going to be running stock hg. Nit shaving the block at all. Just smoothing and shaving the head. Was considering taking more than .5mm and advancing to 12-13

How do the valves sit in the head. Will they need adjusting if you shave too much?

[maj]

TBH given the small increments we are dealing with by shaving, I wouldn't bother trying via that method, you could just be potentially ruining a good head, especially if the shop doing it bodges it up.

Sorry if I may be glancing over here a bit, but did you mention if you were running bigport/smallport? Not too sure in the NA world but GZE smallports ran a higher compression than bigport and this had nothing to do with the HG or volumes. It was all done properly via piston design. Surely there is aftermarket support for pistons to raise CR.

If you are doing the HG and are talking about raising compression then why not do it this way? You'll be able to give your block a minor refresh and know that you are building an engine that can handle even a 0.9:1 jump in compression all day, every day.

If your HG is leaking there's a chance your block needs a rehone anyway, my GZE is apart for the exact same reason, HG did not blow completely but it's confirmed there's coolant damage to cyl #3, so I'm doing a complete block refresh but keeping everything to factory spec.

[justin_es]

Well I'm hoping it doesn't come to that.
I don't have the money for a rebuild.
Realistically I'm just trying to find out how much I can remove safely while its off that's all.
If I need to rehone the block and pull motor completely apart I'm going to have problems.

I'm lucky enough I have a mate who is going to do it for me. Just gotta pay for machining and gasket kit.

[maj]

Fair enough, I'd use caution then increasing CR whilst doing it on the cheap.
My original intentions for mine were just a head recondition (stem seals mainly) as it's cheap enough while the head is off. Turned out a lot worse than that; I *could* put my engine back together without touching the block, but likely evening everything factory I was bound to drop a piston sooner or later.