20V 7AGE parts and compression numbers validation?

[ns270r]

Hello,

Goal is to build a 20V 7AGE using factory parts.

Can anyone verify/vouch for these numbers? I've searched many resources to find conflicting information, but I believe these to be accurate:

Parts
7AFE Block, Crank, Rods, Oil Pan.
7AFE Headgasket (0.4 mm).
Silvertop 20V Pistons.
Blacktop 20V Head, ITBs, Oil Pump, ECU.

Numbers for Compression Calculation
7a Bore: 81 mm
7a Stroke: 85.5 mm
ST Dome: -1.1 cc
BT Chamber: 37.8 cc
7a Deck Clearance: 0.6 mm (assuming piston height is the same for 7AFE and 20V, 30.5 mm)
7a HG Thickness: 0.4 mm

Using these numbers, assuming they are valid, I come up with 11.0:1 CR.

Any help in verifying these numbers will be greatly appreciated.

[yoshimitsuspeed]

Why use ST pistons on the BT head?

It would be easier to make calculations if you used the BT pistons.
They would get you over 12:1 but with some cams that wouldn't be a bad thing.

Most of your numbers look good but for the piston dome and chamber volume I don't trust any of the numbers I have seen out there. Most of them don't add up when you crunch the numbers.
If you do want to go that route I would measure what you have to be sure.
I keep forgetting to measure my ST head I have here. Maybe I'll try to remember to do that. Unfortunately I don't have any ST pistons but if we can get down to one unknown we could solve for it and assume it should be correct.

I will have rods out in about a month that will be floating wrist pin for 4AGE rods and .6mm longer to give you zero deck like the 4A motors.
I also broach timing gears and have belts and most anything else you need for a 7A build.
http://www.matrixgarage.com/store/7a-fe ... components

Personally I would go with a 16v/ST oil pump and tensioner. They are cheaper and easier to find in the US.
http://www.matrixgarage.com/products/ga ... alve-7a-ge
and
http://www.matrixgarage.com/products/ai ... -silvertop

[ns270r]

Thanks for the help. if you get more info on chamber/dome measurements, please post them.

I've got a blacktop that could use some new rings. If I'm going to tear it down I'd like to get a little more out of the little guy without going Standalone. Hence the goal of a stock-ecu-manageable 11.0:1 CR.
More importantly, I not going to break the bank for it. It wouldn't be much to convert it aside from $100 for a 7afe and about $200 in new head gasket, timing belt, timing gear, and rings. I have the rest of hard parts (minus ST pistons).

100% not buying cams, cam gears, high comp pistons, forged rods, standalone, turbo, or naws.

edit: Cool stuff on your site. I'll probably look into some of those parts. I was previously looking at MRP, but shipping..

[Duy-]

quick stupid question:
what's good about the 7AGE route? I'm not quite sure I see the appeal + cost vs a standard 4AGE.
I'm currently in the middle of rebuilding my blacktop with silvertop rods and deciding on low comp pistons from a GZE or an off the shelf set, I tossed the idea of 7agte around and it seems like a lot of hassle.
also I have some stock silvertop pistons if you want me to ship those your way yoshimitsuspeed

[yoshimitsuspeed]

quick stupid question:
what's good about the 7AGE route? I'm not quite sure I see the appeal + cost vs a standard 4AGE.
I'm currently in the middle of rebuilding my blacktop with silvertop rods and deciding on low comp pistons from a GZE or an off the shelf set, I tossed the idea of 7agte around and it seems like a lot of hassle.
also I have some stock silvertop pistons if you want me to ship those your way yoshimitsuspeed

What's good is that you gain .2 liters. It's not a lot but with our little motors it can help. It will allow you to make more power at a more reasonable RPM with less stress and wear to most of the motor.
It's not really a lot of hassle assuming you can easily source a healthy 7A block. They are common so that shouldn't be hard.
Then you need to compensate for the cam timing change, get a different timing belt and a couple other things but overall it's not a lot more work.

I wrote this up last night so it needs more detail and editing and stuff but it gives a decent breakdown of the big items that need to be addressed.
http://www.matrixgarage.com/content/get ... brid-build

[Duy-]

that's a very helpful read.
so my main concern is since I'm boosting, will I need to be looking for custom forged rods and pistons? I heard the 7a crank is weaker than the 4a, is there any truth to that? what pistons will I need to achieve 9:1 or 8.6:1 compression

[oldeskewltoy]

that's a very helpful read.
so my main concern is since I'm boosting, will I need to be looking for custom forged rods and pistons? I heard the 7a crank is weaker than the 4a, is there any truth to that? what pistons will I need to achieve 9:1 or 8.6:1 compression

"weak" rods... and turbos usually mix ok... what doesn't mix with "weak" rods is ever increasing rpm. If you keep the redline @ 7000... you can use a complete 7A bottom end, if you want to go higher, its best to source aftermarket rods.


Pistons are another story, you might want to research it... but I'm pretty sure the best OEM piston for boost is the last gen 4AGZE piston, and in your application it might work - providing adequate static compression

[yoshimitsuspeed]

that's a very helpful read.
so my main concern is since I'm boosting, will I need to be looking for custom forged rods and pistons? I heard the 7a crank is weaker than the 4a, is there any truth to that? what pistons will I need to achieve 9:1 or 8.6:1 compression

There are shelf options of both available so custom is pushing it. Although a custom piston tailored specifically for your build would be optimal it's much less of a concern with lower compression and flatter designs.
Oldskewltoy summed it up pretty well. Reasonable amounts of boost are not a significant strain on rods. This might change once you start going crazy with boost but it takes a lot to overcome the tensile stresses at TDC. If you want to know more about what I am talking about read the first chapter of Maximum Boost.
Now on the other hand the rods that I link to in that article do have some other notable advantages. They should be lighter and stronger although I am still waiting to hear back on exact numbers. They are also already designed for the 4AGE floating pin. So you could run stock rods and get them modified for 4AGE pins, or you could get custom pistons designed for the stock rods, or you could get those rods and run any 4AGE piston you like.
The 7A crank is supposedly weaker than the 4A crank however failures are pretty unheard of. I have had a hard time determining it's limitations because I have had a hard time finding enough similar failures to build any valid data points. If you are going for any sort of moderate build I am confident it will be a non issue. If you are going for crazy numbers that may be different.
That brings us to that point on your build. I don't remember if you told me or if you have posted it elsewhere but what are your power goals?

[Duy-]

no I haven't gone into much detail about anything lol. I lost my password for club4ag and I'm working off my mobile so it makes me sort of lazy to type out a build thread. the lost password system sucks, still hast sent me an email.
but again, I have those silvertop pistons if you want them for research purposes

[yoshimitsuspeed]

no I haven't gone into much detail about anything lol. I lost my password for club4ag and I'm working off my mobile so it makes me sort of lazy to type out a build thread. the lost password system sucks, still hast sent me an email.
but again, I have those silvertop pistons if you want them for research purposes

I would love them. I could pay shipping but probably not much more. Money is tight right now with those 7A rods I just dropped a bunch of coin on.

[ns270r]

I wrote this up last night so it needs more detail and editing and stuff but it gives a decent breakdown of the big items that need to be addressed.
http://www.matrixgarage.com/content/get ... brid-build

Thanks for all the input. It's nice to see information being shared so openly.