Toyota 7M-GE head work questions

[amichie]

Hi Guy

I have a spare cylinder head and I am aiming at improving the general performance in the 5000 -7000 rpm rev range through improvements in volumetric efficiency.

The engine is from the early 90s and is a non turbo 4V twin cam 3 litre inline 6.

Firstly, in the following pic the intake valves seems to shrouded by the chamber walls to a greater extent than many of the more modern heads seen on this forum.
Would you recomend deshrouding/opening up the chamber slightly. The clearance between the edge of the valve and the chamber wall is never more than about 3mm regardless of lift. I realise this will reduce my compression ratio but do you think the improved cylinder filling make up for it?



The follwing image shows the whole chamber. You can see it has 4 squish areas.



The last image shows the depth of the chamber and the closeness of the chamber wall to the edge of the valve regardless of lift. The wall is virtually parallel with the valve stem.



Any suggestions would be welcomed.

[Guy Croft]

See photo.

Get rid of all the L&R squish regions (left one shown red - be careful not to undercut support for the gasket) and where I've marked yellow - adjacent inlet valves - you should put a progressive taper/ramp on those squish bands.

Yes the CR will drop measureably unless you use replacement forged pistons suited to the new chamber volume. Depending on the boost on the new engine that might be a good thing. For 15-20psi boost I'd run 7.5/1 and 25-30 psi 7.2/1

GC

[amichie]

Thanks Guy

Would you give the same advice for a non turbo engine??

Andrew.

[Guy Croft]

Sorry!

Yes I would - and now I see yours is not actually turbocharged!

However, since I design my own pistons I leave that till the head prep is done and I've cc'd the chamber. Then I can configure dome and setup height.

If you have to use the original pistons I might be slightly less 'radical' with the removal.

G

[amichie]

I guess a good place to start would be to measure the chamber volume accurately. The pistons are dished but I can still work out the compression ratio change if I remove material from the head. I estimate that if I reomove the 2 side squish pads I will lose about 1.5 to 2 cc of material from the chamber. This will drop the stock compression ratio from 9.2 to 8.95 to 1. Given that I have slighly longer duration cams than stock and run premium unleaded a compression ratio closer to 10 to 1 would be ideal.

[4v6]

That chamber in the photo looks very very similar to the ones ive been working on with another of Toyotas engines, the big bruiser V6 camry engine.

Guy's indicated modification to the chamber is precisely what i do myself, although i tend to leave the side squish areas pretty much alone, i blend the radius in the corner out into the chamber so there is less of an "edge" to it, in the photo thats indicated in red.
The other part shown in yellow, i also modify it as Guy has indicated but i have to be careful as the gasket cuts across so its not possble to relieve the area as fully as desired.

Please see the photo below for a comparison with your 7Mgte head.

Standard V6 chamber.

S8002772 (816 x 612).jpg (125.28 KiB) Viewed 8237 times

[amichie]

Many thanks for the pics. I know the camry vz engines love to rev.

How would you describe the performance benefits from this modified chamber?

Are you getting better cylinder filing at high rpm and a corresponding high rpm torque increase?

Andrew.

[4v6]

Im afraid dyno data is a little thin on the ground regarding these as i do them very intermittently.
The only (and best so far) result to date I have feedback on is 215.8 bhp, where the standard engine was making 185bhp i believe, with a fairly substantial 25 foot pounds of extra torque present at 3000 rpm dropping off approximately 10 foot pounds at 5500rpm, but still far better than stock levels.
The engine certainly revs much more freely when the ports are improved on these.

I find that the bare port flow of these Vz heads ( i cannot speak for yours as i have not worked on one) is fairly easily improved upon, with the resulting valve in flow also improving quite markedly and i hasten to add that i owe much of that to Mr Croft pointing me in the right direction at various times.

I dont think im at a sufficiently advanced technical level at the moment to be able to comment on the advantages of the chamber shape alterations, (mans gotta know his limitations) but i can say i have seen a definite improvement in flow at low valve lifts when the chamber is modified in the fashion described.
Im sorry i cannot be more helpful on that question.

I havn't experimented with valve seats and shape to any degree as of yet either but i'm certain after reading Guys various articles on the site that improvements are there waiting to be discovered in that aspect also.

[amichie]

Here is a quick photo update.

I have done my best to follow the advice given and at the same time not remove too much material. I really don't want to reduce my static compression ratio particularly because I have cams with slightly longer duration.

I have 5 chambers looking like the one on the left and one original unmodified chamber (shown on the right). I now have a couple of mm extra clearance around the edges of both the intake valves, nearest to the cylinder walls.

I have only removed about 1 - 1.5 cc of material which I should get back with a very minor shave of the head.

I am building a home made flow bench and will atleast be able to make some relative measurements on the modified chambers versus the untouched original chamber.

I will post results as soon as they become available.