7MGTE cams - when to and when not to replace the stock bump sticks?

[whatthe?]

Yeah, but stock 7M exhaust ports flow like a broken nose

[andrew_mx83]

then there is the much nicer port angle of the 2j head...

[boxh34d]

Awesome replies gents, thanks.

Morgo: Interesting the 8mm on stock ports. When my head was rebuilt they did some minor port work, but at that stage I was much more of a noob and didn't really take it all in. I seem to think he only cleaned and matched the inlet ports, but did more work on the exhaust side. Not sure how serious though. I'll be catching up with him again soon so I'll have to find out if he can remember exactly how much was taken out of the exhaust.

Black supra: Yeah, turbo selection will be catered very much in the mid range to top out at around 500 engine HP or a bit less.
Interesting, I did see some head flowbench figures a while back comparing stock vs ported 7M's and 2JZ's. Little bit disheartening when you see the amount of work required for a 7M exhaust port to compare with a stock 2JZ.

Anyone have any thoughts on what kind of duration figures are appropriate for what level, and where the power curve starts tilting rather than gaining overall?

[MorGo]

Yeah,the port intake area is huge but the actual limiting area is at/near the valve seat.Now I don't have the flow numbers to post but tomorrow I can get them from flowbench computer.
It is interesting to see how practically all japanese cams(HKS/TRD/### as well the stock) are designed for stock heads;one wonders what was first in the design (from factory),the cam lift or head flow? "we have 7,3 mm lift cams;design head for them!" Or was it just the other way??
The 4A-GE/7M-GE just stop flowing at 8 mm and how it happens that there is no lift more than 7,3 or something like that..
And same for those aftermaket tuning cams:there is maybe 9 mm lift but usually very close the factory lift.
Sensibly ported 4A-GE/7M-GE head will flow up to 12 mm lift with stock valves (benefit after 10 mm is small but is there) and race ported NEED the high lift to be effective.Then we come to question of bigger valves..

[andrew_mx83]

a couple of views of the seats and bowls









heaps more at:
http://www.toymods.org.au/forums/sho...61#post1240061

[boxh34d]

Ha Ha, Andrew, I can almost hear your drop saws cries of pain every time I see those profiles!!!! Never ceases to amaze me when I see them.

[andrew_mx83]

haha i got a new blade for it, they call it a "rage blade"

cuts through 80mm solid ally bar in under a minute

[MorGo]

Stock vs. ported head flow numbers @10" depression.%DIF column is the presentage differense between the numbers.Actual depression was bigger but since almost everyone here uses the 10" I use it too.Multiply by 1,67 to get 28" numbers.

CFM % DIF
LIFT No. 1 No. 2 No. 1 No. 2
--------- ----- ----- ----- -----
1,0 19,7 19,9 0,0 1,0
2,0 37,5 38,4 0,0 2,6
3,0 55,3 57,9 0,0 4,8
4,0 73,7 75,2 0,0 2,0
5,0 89,5 90,4 0,0 0,9
6,0 102,2 101,4 0,0 -0,8
7,0 110,0 111,4 0,0 1,3
8,0 114,6 118,9 0,0 3,7
9,0 117,5 126,2 0,0 7,3
10,0 118,7 133,1 0,0 12,1
11,0 118,9 138,3 0,0 16,3
12,0 119,7 142,5 0,0 19,1
13,0 --- --- --- ---

[oldeskewltoy]

OH MY LORD........ those exhaust ports are horrible!!! The amount of intrustion by the splitter alone is atorcious. Andrew... do you have a view cut through the ports parallel to heads surface?



I'm wondering how much room on the outer port walls is available for exhaust port re-taper????


example of what I mean - taken from a 4AGE

[boxh34d]

From my very (very) brief discussions with my machinist early this morning, he knows he did the quick work of: port match, polished, shaped the divider, and worked the short radius a bit, but he can't remember exactly how much work he did around the bowel area. And like I said, when the head was done, I new all of about 1/5th of f*ck all about ports and cams, so I didn't really look too hard to be honest. I think I'm probably up to around 3 or 4/5th of f*ck all, so I'm still a noob.
Given the quality of his work generally, his knowledge base, and the amount of performance stuff he does do, it would have only been a question of my story and his interprepation of goal / requirement vs $ that would have sacrificed in doing a really good job with them.
So I guess, the long and the short of it is, I'll have to wait till I pull the exhaust manifold off and have a proper look in there, and see what I got, and start making some calls from there.

MorGo: very interesting flow numbers. I'm curious to know how far you went with the porting to get those? From your previous posts regarding lift numbers vs flow, I'm guessing quite serious.

OST: Nice work on the 4AG. Also, further to your earlier post re: web cams that I previously skipped over, I have previously looked at a few suppliers, but I don't think Web was one of them.

Interesting that compared to the factory cams (and the likes of BC etc), their profiles are so short in the advertised duration, yet so much larger in the 50thou duration with modest increases in lift. From my limited understanding it makes complete sense to increase the duration where it matters by steepening the ramp rate, but to be honest, I really don't understand the relationship between duration vs lift vs powerband.
I've had a look around the net to try and learn some more, but most of the readily available info is for detroit V8's so I don't really think it's appropriate.

What I'm highly interested in is how different cam profiles would compare with the stockers in terms of power band. My thick noggin says that added cam lift should add power everywhere (provided that the package can breathe), whilst my very limited understanding says that longer duration = more top end power at the possible expense of low end. However, for instance with the web cam profiles, with less total duration, and more duration @50thou, would I be right in assuming that the cam would allow far greater average power, without sacrificing too much bottom end?

How much duration is too much duration?
I know most of this is likely to be very generalised and how long is a piece of string type stuff, but at this stage, I'm after all I can get.

[BlackSupra]

Exhaust port on the Megap00

[oldeskewltoy]

OST: Nice work on the 4AG. Also, further to your earlier post re: web cams that I previously skipped over, I have previously looked at a few suppliers, but I don't think Web was one of them.

Interesting that compared to the factory cams (and the likes of BC etc), their profiles are so short in the advertised duration, yet so much larger in the 50thou duration with modest increases in lift. From my limited understanding it makes complete sense to increase the duration where it matters by steepening the ramp rate, but to be honest, I really don't understand the relationship between duration vs lift vs powerband.
I've had a look around the net to try and learn some more, but most of the readily available info is for detroit V8's so I don't really think it's appropriate.

What I'm highly interested in is how different cam profiles would compare with the stockers in terms of power band. My thick noggin says that added cam lift should add power everywhere (provided that the package can breathe), whilst my very limited understanding says that longer duration = more top end power at the possible expense of low end. However, for instance with the web cam profiles, with less total duration, and more duration @50thou, would I be right in assuming that the cam would allow far greater average power, without sacrificing too much bottom end?

How much duration is too much duration?
I know most of this is likely to be very generalised and how long is a piece of string type stuff, but at this stage, I'm after all I can get.

From my understanding(allowing dissent, or others opinions.... )

The big negative to higher ramp rates is more stress on the valvetrain. Ideally then... you have accounted for the added stress (valve springs mostly...) and so you have now accounted for the higher ramp rates.

more lift = good all the time...... not always... if the port is not properly prepared, a higher lift cam adds stress but doesn't substantially allow more air to pass. A properly ported head will allow more volume to pass.


Duration... in a boosted engines case... the discussion should be adjusted to "Overlap" instead.

Concerning Web camshafts.... I've now had 2 4AGE engines using them. Engine #1 was a largeport TVIS rwd, using Web's 294 grind. It had only seat and bowl work... no other porting (no exhaust re-taper) it planted 112whp and 89 wheel #/ft. Engine #2 uses Webs 577, it is a smallport 4AGE with EXTENSIVE port work it plants 145 whp and 112 wheel #/ft.

I've been satisfied with Web, although the 577 grind came damaged, but they were quickly warranteed.

[MorGo]

Well,you can think the 7M-G(T)E as a 4A-GE with added 2 cylinders.Sure,the 7M have 32 mm intakes vs. 4A-GE 30,5 but the stock flow is not much different.
The 7M-GTE have about same cams as a 4A-F(E).230º duration with 7,3 mm lift is not a performance cam..
Treat 7M-GE like 4A-GE and you get similar results in rpm range and power.
The 7M-GE is flawed by design;it started from early 60's in 2 litre form.Expanding it to 3 litres resulted small bore and due that small valves.
Sure,it could be made to make big power but it is not the best plant to build up.

[andrew_mx83]

sorry oldeskewltoy i didnt do a cut that way

i know nothing about cams in a boosted application (as opposed to almost nothing NA) but overlap can still be adjusted to an extent on a fixed duration by playing with the timing. steeper ramp rates will cause the valve to slam shut much harder so puts stress on the valve and seat as well as the spring. old school engines had issues of pounding the seats out or bending the valve head slightly (tulip shaped) when at the limit but im not sure its that much of an issue on these beasts.
on a side note, these comp cams springs really DONT "drop in" to the 7m head like everyone says they do. the spring seat ID is too small for the OD of the chevvy springs without having to mash them in and have it machine itself away everytime to spring compresses. i tried boring a few out but they end up about 0.2mm thick and just fall apart. hmm, what to do now...

[boxh34d]

Andrew, a while ago I saw performance springs in qld? was advertising direct fit upgraded springs for the 7M on ebay. About 50 to 60lb from memory. Can't remember the cost, but I don't recall choking on anything when I read it.

How have all the US guys been banging on about the comp springs if they don't really fit?