Built VVTi head - stock ECU

Am just about to get my head built - 272/9.9 cams, stock valves with spring upgrades. Am I ok to drive this, until I can get Ryan to map this all in? I think the cams are my main worry and with it being the VVTi too.

Any help appreciated

Am just about to get my head built - 272/9.9 cams, stock valves with spring upgrades. Am I ok to drive this, until I can get Ryan to map this all in? I think the cams are my main worry and with it being the VVTi too.

 

Any help appreciated

Should be fine dude, I think you will be running an interferance engine with those cams so an uprated cam belt would be nice.

It will probably be very rich if your going from standard to these. Is the Syvecs setup with O2 feedback? If so it will be fine.

It will probably be very rich if your going from standard to these. Is the Syvecs setup with O2 feedback? If so it will be fine.

The Syvecs isn't fitted yet, Paul - It'll be to drive to/from the garage to home - no more than 20 miles really.

I'll just be tootling on 30mph zones

The Syvecs isn't fitted yet, Paul - It'll be to drive to/from the garage to home - no more than 20 miles really.

I'll just be tootling on 30mph zones

I thought you meant drive it to Ryan, do you have an AFR guage to check mixture??

The Syvecs isn't fitted yet, Paul - It'll be to drive to/from the garage to home - no more than 20 miles really.

I'll just be tootling on 30mph zones

I'd stick an AFR gauge on there just in case as its a big change from stock cams to these.

I thought you meant drive it to Ryan, do you have an AFR guage to check mixture??

I'd stick an AFR gauge on there just in case as its a big change from stock cams to these.

Yep - I've got an AEM UEGO in there (along with Boost and EGT).

Should be fine dude, I think you will be running an interferance engine with those cams so an uprated cam belt would be nice.

Not sure I follow the logic there dude!

Yep - I've got an AEM UEGO in there (along with Boost and EGT).

See what its like in that case.

Not sure I follow the logic there dude!

An updated belt because if it snaps the pistons and valves will smash into each other and make a mess,an uprated one could help avoid that

Lol. How thick am I? Actually I never think of belt life in terms of interference versus non interference engines as so many engines are interference these days, but it still wouldn't be acceptable to have a short belt life even if it wasn't.

With cams that long it would be interesting to know if the valve accelerations and loads were much higher than stock.

With cams that long it would be interesting to know if the valve accelerations and loads were much higher than stock.

Funny you should bring that up as ive always wonder why people go for such high lift cams? Even with some careful porting on the exhaust ports themselves, from my understanding and conversations with some well known names in the supra world, they fail to flow much more past 8mm of lift aswel as premote valve spring failure

An updated belt because if it snaps the pistons and valves will smash into each other and make a mess,an uprated one could help avoid that

Exactly , Paul Whiffin sells the Gates racing belt, great value and plenty good enough, in fact PW seems to be my new one stop shop for Supra bits, great prices and quick delivery.

Funny you should bring that up as ive always wonder why people go for such high lift cams? Even with some careful porting on the exhaust ports themselves, from my understanding and conversations with some well known names in the supra world, they fail to flow much more past 8mm of lift aswel as premote valve spring failure

Well, that's not really where I was coming from. Just thinking aloud that a higher lift spread over a longer duration might give similar valve accelerations as stock - and hence similar belt loads. The static spring load at MOP would be higher because of the increased spring compression but that would be low compared to the peak loads due to inertia.

I know it wasnt i just always wondered thats all

10 mm lift is nowt, that's not very high lift! Over 12 mm from a direct acting cam is getting something like THEN you need good valves, springs and retainers and an excellent cam profile.

That clears that up then

Very different logic the yanks have when it comes to built heads/engines.

I suppose the main worry is if VVTi control is enabled and set to allow too much cam movement for the newly changed piston to valve clearances. Ideally you need to furnish the mapper with a data sheet show allowable cam VVti movement that maintains safe piston to valve clearances throughout. This obviously needs to be done at the assembly stage with cam and crank degree wheels, some soft test springs, and a dial gauge. It can take ages. I would THINK you will still have plenty of scope for VVTi cam movement, but it may well be considerably less than on stock cams.

Did some very rough calcs today using cam profiles automatically generated from max lift and duration figures.

*Disclaimer* These results serve to illustrate a point. Because I do not have the actual cam profiles I can't claim that these results are applicable in the real world.

First I generated a profile for the stock intake cam (224x7.8). I then set the spring rate to only just cover the valve at its maximum opening point. The spring is purely fictitious but the cover curve shows that the valve would be just under control for this cam profile. I also generated the drive torque curve for a single cam. This peaked at just over 12000N.mm

I then changed the profile to the one mentioned in this thread (272x9.9) and left everything else unchanged. Note the following:

a) The inertia force curve has dropped from about 350N to 300N at MOP because the cam profile has got less aggressive because of the longer duration despite the higher lift.

b) The spring cover curve has gone up because of the higher spring compression. This means that you could actually run lighter springs in this setup and still get adequate spring cover.

c) The peak drive torque has dropped to well below 12000N.mm. The drive torque as the cam reaches MOP has gone up significantly, indicating that friction has increased (probably because of the increased spring loads).

In the first case, the fictitious spring had a preload of 150N and a rate of 30N/mm and was initially the same for both cam profiles. Without publishing the results in full, I then changed this spring to 150N preload and 20N/mm rate. This brought the spring cover curve back to just sufficient for the 272x9.9 cam inertia, and correspondingly reduced the friction torque at MOP to almost zero.

All calculations were done at an engine speed of 6000RPM.

So it goes to prove that in theory the cam drive might not be having such a bad time of it with aftermarket cams.

Did some very rough calcs today .......

Nice info - thanks. That'll set a few cogs churning

I think I'll wait before driving and let Ryan install the Syvecs

Definitely the best idea. I never even start an engine without the mapper present, unless the changes are ones I know won't cause any risk at all.

Definitely the best idea. I never even start an engine without the mapper present, unless the changes are ones I know won't cause any risk at all.

If it was non-VVTi, I'd be ok - but the VVTi bit scares the b'jesus out of me