1.6 on a carb will be fine, that's what I'm doing. It's just how you sort the manifold out that's the difficult part.

If you get an earlyish 1.6 you can fit the pickup from a 1.3/1.4 and use the smaller sump. Won't hold as much oil obviously so you might want to consider more frequent changes or possibly even an oil cooler. I'm going to keep an eye on my temps anyway.

Oh cool, let me know how you get on! Think I'll just get the manifold modified to fit, be easier that way using the original sump.

Manifold, I'm thinking TIG welding and redrilling will work?? If not welding a new flange to the GK manny is an option...

Mine is now in and running! A noticable improvement over the 3F block in terms of torque, so it's been worth it in my opinion.

Just found this thread on a search. Has anyone decked the ABD block to increase the CR to that of the original 3F? I've just been looking at the numbers, based on the following info:

3F is 75mm bore x 72mm stroke and is 11:1 CR

ABD is 75mm bore x 78.7mm stroke and is 9.5:1 CR

Using this info you need to deck the block between 40 and 45 thou or 1 and 1.15mm in new money (depends on what your machineshop works in ). This gives 10.8:1 and 11.0:1 respectively.

This assumes that the 3F and ABD head gaskets are the same thinckness.

This woud need to be checked for valve and piston clearance using some plastacine and turing the engine over by hand and would more than likely cause problems on high lift cams with minimal valve clearance, although as previously mentioned pocketing the pistons would solve this if there's material (and i'd hope that 1mm off the piston would be possible otherwise reliability would be a serious issue!).

There are other options like custom pistons, conrods etc. that would give the same results but that's £££s.

I can't attach my Excel ramblings for some reason. If anyone has HG thicknesses of ABD and 3F or info on combustion pockets in the pistons, piston to deck gap at TDC etc. then that will add meat to the calculations.

Edited 14 June, 200818 yr by Andy_Casey

The pistons stick out of the block so you can't deck it without modifying the pistons. You don't really need to deck it once you've modified the pistons either, as you can just fit a thinner metal headgasket.

3F is 10:1 BTW

Sorry, slightly confused, if the pistons stick out of the 1.4 block then how can you use the 3F (flat) head, surely this would give you no combustion chamber whatsoever?

Decking the block would have the same effect as a thinner headgasket though, both bring the head closer to the pistons and this increase CR. With 10:1 compression ratio, decking the block 0.70 to 0.75mm / 25 to 30 thou would do the trick from my calcs and give you around 11:1 CR. I take it that due to the flat cylinder heaqd on the ABD, the combustion chamber in the piston? If it is then you don't really want to skim the pistons as it'll cause all sorts of fun with re-pocketing them...

Then again, 10:1 really isn't that bad

10:1 on the 3f, not on the ABD :(

compression ratio for an ABD is 9.5:1. mines having the block decked, pistons skimmed, valves recessed in the head to accomodate the reprofiled cam and then the head skimmed to keep the compression up. brothers a race engine builder, dimensions and reprofiling is left to him. according to the guy at kent cams the camshafts cam be reprofiled by up to 40thou/1mm before you have to modify the oil galleries for the hydrop buckets.

anybody know the lift of a GT cam as opposed to the 2G/ABD cams i have already? gaz?

The standard headgasket takes up the extra block height required by the stuck out pistons.

The pistons and valves practically touch at TDC, on both the 3F and the ABD, which both have the same "pistons stick out of the block a bit at TDC" design. Yes the combustion chamber is virtually all in the piston. Decking the block is a waste of time on these engines unless the block is no longer true. It just means you have to take more out of the pistons. As I said before, you can't deck the block without modifying the pistons unless you fit a thicker headgasket, which defeats the object. Overall, piston modification with a thinner metal headgasket seems to me to be the more straightforward and cost effective option to what you're suggesting.

Of course, if you get different pistons it's a whole different ball game. Decking the block is not necessary here either though if you can get some that give a nice compression ratio at standard height. It's just you can't get high compression pistons for the 1.4 (As far as I know, and low compression 1.3 ones don't fit) and there are already 11:1 pistons available for the 1.3s with no decking required.

So what about the AEE, what's the standard compression on that? I take it that the CR on the 1.6 lump can be raised by skimming the head as it is not completely flat?

Not sure on the AEE's CR but you can fit a mk4 polo head gasket i believe to raise the CR abit.

Ah I see, that's clever. How's your AEE project going anyway Carver?

Not too bad thanks, theres a thread in the photo bit floating around.

Not got very far with the engine to be honest, been rebuilding the knackered brakes for the last few days but I'm hoping to get the engine in next week :)

There are three 1.6 engines, the early one (ABU) is similar to the 1.3/1.4 in that the pistons stick out of the block and the headgasket is very thick. I looked into a thinner headgasket on one of these but decided it was easier to change to AEE pistons (which don't stick out of the block) so I could increase compression and fit a metal headgasket. The easyest way to up the compression on any of the later engines is to skim the head, cos like you say, they have combustion chambers in them.

AEE/AEA is usually quoted as 9.8:1 and ABU is 9.3:1

Ah right, changing 9.5:1 to 10:1 isn't really worth the effort of machining as you say, I was under the misguided impression that eth 3F was 11:1.

Thinner HG makes sense in this case, what options are there? Do any of the VAG HGs fit or is it custom stuff?

1.6 must give the light Polo3 a real kick to it I'll ahve a look at the threads on the subject...

The thinner head gasket on the ABD takes the compression up to around 10.5. When you machine the piston down to keep the distance to the head the same, you'll have reduced the compression volume in the piston, so the compresson will be up around 11:1. Far cheaper than custom pistons, but I don't know what the long term reliabilty issues are particularly at high rpm.

He's right, Yeha just solved the best thing to do, skim the pistons to lower the chamber volume and sorted the valve clerance in one move!! Respect!

by skiming the pistons your increase the chamber volume not reduce it, which will in turn reduce he compression ratio

whats the thiner metal headgasket off??

by skiming the pistons your increase the chamber volume not reduce it, which will in turn reduce he compression ratio

whats the thiner metal headgasket off??

Yeah if you keep the original gasket, the compression ratio goes down. Fitting the metal headgasket from a mk4 polo will correct this.

I've just done the ABD conversion to my Gt lump in the mk1, only gone for a quick run but feels more torque; the Gt distributor packed up though so I'm running the ABD one do you think this would affect performance?

might try fitting the golf AFM again now its a 1.4 might run better!?

rich

I ran my Gt for abit on a spi dizzy, idled quite low but ran fine, i didnt notice any better performance although on a rolling road graph theres a little dip in the curve i think. So there might be some slight power increase but not much.

an ABD dizzy will work, but the trigger wheel profile is different, which means the ecu gets incorrect engine position/ignition timing information. It's ok as a backup but try and get hold of a GT/G40/Mk4 MPI dizzy asap. More info here

I ran a golf AFM on mine no problem but it required setting up.

The AEE and alike don't rev like the GT topped 1.4

The best N/A mk3 i had was a GT on FZS 600 Fazer carbs on a Bogg Bros custom inlet manifold, Piper and vernier, 4-2-1, ported head, it was a screamer, and i reckon that little lot on the 1.4 ABD will make a blinding mk3

You can make them rev very nicely. But you're forever increasing the risk of getting it to throw a rod. Aftermarket ones are available for about £500.