7age blacktop..vvti possible??

[Mooro]

Sorry if its an old question but I haven't been able to get a definitive answer in my searches.

From what I have read when doing a blacktop 7age conversion you can use the stock 16V cambelt because the 20V cams are closer which absorbs the difference on block heights.

Also from what I have read a big problem with doing a 16V 7age is getting the cam timing right and some of the under-performing 7ages are due to the cam timing being off. An obvious solution is adjustable cam gears but with a blacktop 7age this means losing vvti.

So my question is, due to the 20V cams being closer is it possible to get the cam timing correct by just using the 16V cam belt and hence allowing vvti to operate or will it still be off and therefore require adjustable cam gears and losing vvti???

[Mr Revhead]

20vs run vvt, not vvti

and theres no reason you cant use it.

[DX20VT]

Ok been thru this al all sitting wiating for some rods and assembly.

Use the 7A block and Blacktop head.

To get the cams to line up and keep VVT you will need

- Blacktop oil pump assembly which holds the cambelt tensioner which on a BT is the Hydraulic type.
-To run the BT tensioner and get the cambelt covers to ( nearly ) fit you will need the blacktop water pump.
- Run a 4AGE cambelt drive pulley on the 7A crank
- Use a 4AGE 16V cambelt.

As long as you dont have to plain too much off the head or block to get a decent compression ratio the marks will be so close to lining up that you will need bloody good measuring gear to tell if it's out or not, because as good as your eye can look it will line up fine.

[skiddz]

is that using the 7a or 20v pistons? is the pin height different? how much does the block need to be shaved to give decent compression?

[Mooro]

DX20VT...thanks for the help...exactly the info I was after. Where I'm heading is that if the cam timing is right, vvti (my understanding is that silvertops are only vvt and blacktops are vvti) is maintained, then I could potentially run the standard ecu with maybe a basic piggyback to enrich the fueling abit as necessary. Probably not the best solution but as a budget job it could work OK.

As far as machining the block, my understanding is that if I use the blacktop pistons with the 7afe HG the compression ratio will be quite high...only problem is it might be too high . DO you know what the CR will be using blacktop pistons and a 4age gasket, and also using blacktop pistons and 7afe gasket?

[Mr Revhead]

no, all 2vs are VVT. they are basiclly a 2 position switch. VVT-i is variable anywhere between to set points.
the black top does have different settngs to the silvertop though

[Mooro]

Yeh you are right, I just did some searching. The silvertop switches at a set rpm, whereas the blacktop can switch at anywhere between 1800rpm and 6800rpm, but still technically vvt.

Vvvti can dynamically change the valve timing throughout the rev range.

[johnny]

Sorry if its an old question but I haven't been able to get a definitive answer in my searches.

From what I have read when doing a blacktop 7age conversion you can use the stock 16V cambelt because the 20V cams are closer which absorbs the difference on block heights.

Also from what I have read a big problem with doing a 16V 7age is getting the cam timing right and some of the under-performing 7ages are due to the cam timing being off. An obvious solution is adjustable cam gears but with a blacktop 7age this means losing vvti.

So my question is, due to the 20V cams being closer is it possible to get the cam timing correct by just using the 16V cam belt and hence allowing vvti to operate or will it still be off and therefore require adjustable cam gears and losing vvti???

Yes, but you'll need to seperate the cam lobe by about 10 degree to get the correct timing (done by running a cam gear on the exhaust-> a normal 4age 100kw will fit). The only time you'll need to remove the VVT is if you go above a 265+ cam since valves will start hitting pistons when the the cam moves. You can limit the movement with some creative techinques, so it doesn't move all the way, this does allow some moderate bonuses. As for pistons, you need to use the the 20V pistons.

[- Use a 4AGE 16V cambelt.

hmm porsche 944 fits perfectly, that's why you need to move the lobe centres apart ten degrees

so far the record for a blacktop 7AGE stands at 220 whp (164kw) this was in a front wheel drive starlet circuit racer

[thu187]

Yeh you are right, I just did some searching. The silvertop switches at a set rpm, whereas the blacktop can switch at anywhere between 1800rpm and 6800rpm, but still technically vvt.

Vvvti can dynamically change the valve timing throughout the rev range.

An engine with VVT is dyno'd with VVT completely off and with it enabled permanently. There'll be a point where power will be identical for both cam settings and this is where VVT kicks in.
I don't get what you mean by still technically VVT. It's VVT-i because it is able to be engaged based on a position sensor at the back of the head on the camshaft rather than at a set rpm.

[Mooro]

Haha Johnny, I just sent you an email thinking you might be a useful source of info.

Thats interesting, I thought the 944 belt was for 16V 7age, and the 16V belt worked well for 20V 7ages, I've also been in contact with a guy in NZ who has a 7age AW11 MR2 and he uses a Fiat QTB178 cam belt. Seems like there are various options available...I guess it comes down to what accessories you use in terms of oil pumps, water pumps, cam wheels etc.

So is the cam duration problem an issue with normal 4age 20V's or jus tthe 7age variety??

Also do you know what CR you would achieve with blacktop pistons and the 4age or 7afe headgasket combinations. I would want something around the 11:1 mark...I figure anything higher is getting dicy on a street motor?

I guess that is the Loftus car...that would be nice but I don't think I going to be quite in that league

[Mooro]

An engine with VVT is dyno'd with VVT completely off and with it enabled permanently. There'll be a point where power will be identical for both cam settings and this is where VVT kicks in.
I don't get what you mean by still technically VVT. It's VVT-i because it is able to be engaged based on a position sensor at the back of the head on the camshaft rather than at a set rpm.

No my understanding (I'm no expert) is that vvti is a continuously dynamic valve timing, whereas vvt is basically on on/off type thing that switches between two valve timings...

With both the silvertop and the blacktop the valve timing essentially changes between two settings, so it is on and off, it's just that the blacktop is a little more intelligent in determining when to change over.

With vvti the valve timing can vary over a continuous range to suit the breathing requirements of the engine through the rev range.

Like I said I'm not an expert, this is just my understanding from reading various stuff on the web which is not always the most reliable way of doing things .

[Mr Revhead]

yes thats right.. the 20Vs are VVT. NOT VVT-i

[DX20VT]

Yes all 20V are VVT. The cam timing is either in normal position or is 15 degress advanced. It is not possible to run it at 7 degree's advanced, because

a, the solenoid is on or off and does not get duty cycle controlled,

b, to run VVTi which is continously variable cam timing you must have a sensor to tell the ECU what the actual cam timing is at so it knows weather it needs more or less advance,
and the is no sensor on the intake cam at all on a 4age.



As a reply to compression ratio's it's all dependant on what configuration you want to run.

I am doing a turbo version so will be using GZE pistons and getting custom length con-rods made to raise the pistons further up the bore to get better compression.

[johnny]

headgasket combinations. I would want something around the 11:1 mark...I figure anything higher is getting dicy on a street motor?

I'm going to have a guess at that, but my gut feeling it's goning to be up a little higher than that, possible closer to 12:1, but that shouldn't be a huge issue, Since this is comp I run in my Rally car's 20V which has to run on BP ultimate 98 and didn't miss a beat or pinked once at ROC.

[Mooro]

Hmmm this is the info I have on CR's...but nothing on the blacktop

With the BT the higher CR is achieved via the pistons right? as opposed to the silvertop where it is the combustion chamber, so therefore the blacktop 7age is going to be higher than the silvertop 7age and I guess even with 4age HG still upwards of 12:1 which is getting pretty high for a daily driver.

7A-G, bigport pistons, stock deck height, 7A-FE head gasket = 10.3:1
7A-G, bigport pistons, block decked .024" (0.6mm), 4A-GE HG = 10.3:1
7A-G, bigport pistons, stock deck height, 4A-GE head gasket = 9.7:1

7A-G, smallport pistons, stock deck height, 7A-FE head gasket = 11.3:1
7A-G, smallport pistons, block decked .024" (0.6mm), 4A-GE HG = 11.3:1
7A-G, smallport pistons, stock deck height, 4A-GE head gasket = 10.6:1

7A-G, 8.0:1 early GZE pistons, stock deck height, 7A-FE head gasket = 8.8:1
7A-G, 8.9:1 early GZE pistons, stock deck height, 7A-FE head gasket = 9.8:1

7A-GE with stock 7A block, silvertop pistons and head, 7A 0.6mm HG = 11.55:1
7A-GE with stock 7A block, silvertop pistons and head, TRD 0.8mm HG = 11.48:1
7A-GE with stock 7A block, silvertop pistons and head, 4A 1.2mm HG = 11.35:1