sohc 4g63 rebuild advice

oggy · Post by **oggy** » Tue Jun 27, 2006 1:08 pm

hey guys
i'm about to start the rebuild on my SOHC 4g63, just wanting some advice.
:D

i read that some of you guys are using vr4 forged pistons in the SOHC engine, and that this causes it to become an interferance engine. do you guys use a decompression plate of sorts? i'm going to be using a camtech stage 3 or 4 cam (hoping for a 7,500 - 8,000 rpm rev limit) do you think i'll run into any problems with this setup?

what do you guys reckon about keeping the balance shafts in or not?

cheers

:beer

jakobsladderz · Post by **jakobsladderz** » Tue Jun 27, 2006 1:16 pm

If you plan on hitting 7 or 8KRPM I'd definately remove the balance shafts. you may also need to get some tougher rods and certainly tougher big end bolts (factory redline is ~6K and at 8K you'll be putting nearly twice the load on all the moving bits). Check that the valve springs will provide enough force and allow for enough displacement, they may bind if they get pushed too far.

There are people out there who have done it though, so I might leave it to them to confirm or deny what's required..

Duncan

oggy · Post by **oggy** » Tue Jun 27, 2006 1:18 pm

thanks for the reply mate :)
eagle h-beam rods will be used

kit · Post by **kit** » Wed Jun 28, 2006 5:56 pm

i get 286 bhp @ the wheels holding power to 7,000 revs with balance shafts in place with higher octaine feul and more timming i can get over 300 at the wheels balance shafts are good contact redzone for information pm him

flav · Post by **flav** » Wed Jun 28, 2006 6:19 pm

The balance shafts are not an item i would spin to those rpm levels. If this is a full custom rebuild, which it is to achieve these revs and high output then this is all going to require rebalancing. The balance shafts are a waste of power and will fail under that load. You will also require a decent set of valves and springs and retainers and collets. We use Incanol or Stainless valves all custom made. The installed hight of your top end set up will depend on alot of factors including your camshaft. I could go on for pages and pages but im guessing you already have some kind of goal in mind or some purpose that is intended for this engine. I am more than happy to give you absolute professional advice i have gained in a lifetime of motor racing.
My email is evident and a more personal approach awaits if needed.

Mick · Post by **Mick** » Wed Jun 28, 2006 6:44 pm

pro-fessional flav... real smooth LOL

flav · Post by **flav** » Wed Jun 28, 2006 8:30 pm

I am also a man whore........cheap too!

boosted88 · Post by **boosted88** » Wed Jun 28, 2006 9:31 pm

I'm also installing Wiseco's (9.0:1) with Eagle rods, are ther any top end clearance issues with a standard lift cam? Also fitting a Cometic MLS head gasket not sure that there much difference in gasket thickness what's your thoughts Flav???

toysrus · Post by **toysrus** » Wed Jun 28, 2006 10:06 pm

boosted88 wrote:I'm also installing Wiseco's (9.0:1) with Eagle rods, are ther any top end clearance issues with a standard lift cam? Also fitting a Cometic MLS head gasket not sure that there much difference in gasket thickness what's your thoughts Flav???

No issues with a standard lift camshaft

The cometic head gasket is a little thicker (0.19mm), there are two thicknesses available but I'm assuming you went with the standard size which most people get. Static CR will drop a little, maybe 0.05 or so......

Note, running VR4 Spec pistons on the SOHC will drop your static CR by a large amount, around 0.4, which is actually a good thing when chasing more power before 'knock, knock, detonation :D

Ok, now for the interesting bit, you will eventually need to switch camshafts, so while you have the cylinder head off, go and buy two metal rulers that have accurate 0.5mm increments on the edges. Turn the cylinder head on its side. Now, get a 17mm socket & ratchet combo, and turn the camshaft, after a could of full revolutions you will get a good feel for when the valves are opened at their maximum lift. So stop where you think the exhaust & inlet valve are at max lift and then use the straight edge of one ruler to run over the Cylinder head surface perfectly so that you can measure with the other ruler how much clearance the valve has before coming into line with the surface of the cylinder head. Remember you will have to do this process seperately for both inlet and exhaust valves, and to get an accurate reading, double check your figures on each cylinder.

You know the cometic Head gasket has a thickness of (0.51") 1.295mm or (0.54") 1.372mm, so at the min 1.295mm, you should also know that the Wiseco pistons run 0.3mm piston-deck clearance and you should now have the min valve-cylinder Head surface clearance, which the total of all of this lets you know how much extra valve lift you can run before you smash your valves onto the pistons

I think there is a saftey margin of 3mm recomended, so taking 3mm of the total current valve-piston clearance will give you how much extra lift you can run :)

Now the thing to be wary of is that the rocker ratio is 1.5x, meaning your extra cam-lift value is 0.66 x possible extra valve lift, i.e. always a lower value.

Anyhow, thats ^ is what I would do if I were you, enjoy :beer

oggy · Post by **oggy** » Wed Jun 28, 2006 10:20 pm

pro-fessional flav... real smooth

LOL

I am also a man whore........cheap too!

i was actually going to PM you about getting some head......errr headwork done

i'll shoot you an email or a PM on the weekend sometime :)

flav · Post by **flav** » Thu Jun 29, 2006 4:45 am

Toys seems to have been there. Follow that info, it's pretty good.

Austarion

sohc 4g63 rebuild advice

sohc 4g63 rebuild advice

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