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I know this issue has come up before but I am just checking to confirm, I do not want to screw anything up on this possible mod. I have a set of oem intake and exhaust cams in good condition from a stock na 7rib 1987 4age Largeport engine. I am doing a headgasket job on a 4age SMALLPORT engine installed in a 1987 Mk1. The Smallport is a stock NA motor running all Smallport electronics! I have heard that a nice upgrade on this engine is to switch out the SMALLPORT intake and exhaust cams and replace/install the 1987 4age LARGEPORT CAMS (more lift/duration) in their place. Is this a good idea, and if so, will I notice any overall improvement in performance on the Smallport? Can a percentage be attached to this performance gain (seat of the pants)...i.e. 10% overall improvement...15% overall performance gain...? Also, very important..... do the valve shim adjustment measurements per the BGB stay the same on the 4age Smallport when changing out to the Largeport Cams? Thks for any experience/insight into this issue.
 

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You are pretty much on point with most of what you mention but, the thing to remember is that not all largeport cams are created equal.

The early pre 87 3-rib cams in the "bluetop" 4age are the ones with the higher lift and longer duration. Even then its only just a tad more, you would hardly notice.

The 7-rib "redtop" largeport cams that you have would be the "milder" of the two.

Not sure on the cam specs of the small port, I dont think they got bigger when the smallport came out. I would guess they are the same as the 87 7-ribs cams but you may want to verify that.

The shim clearance would be the same as factory if you did swap the cams.

It would be some what time consuming to swap the cams and you wouldn't see a whole lot of gain with such a small increase in lift/duration for the effort spent.
 

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Basic differences between small port cams and big port cams. Big port cams have 4 degrees longer duration and .46mm more lift. Your valve clearances would be the same with either cam. You would get a mild increase over the small port cams over the RPM band. One of my favorite combos is the WEBcams 294 grind on the intake and the small port cam on the exhaust. I got basically the same power band as stock with a noticeable bump in torque.
The small port set will work well with the big port cams I'm sure. Just don't expect big increases though.
 

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Maybe try changing just the intake cam to a big port cam. Changing the exhaust cam at this minor increment really wouldn't do much. The WEBcams 294 is 246*(advertised) at 8.2mm lift, it would give a 10* split with 1mm extra lift. Or look for basically the same grind. Makes for a smooth power band while staying with a pretty much stock feel.
 

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I know this issue has come up before but I am just checking to confirm, I do not want to screw anything up on this possible mod. I have a set of oem intake and exhaust cams in good condition from a stock na 7rib 1987 4age Largeport engine. I am doing a headgasket job on a 4age SMALLPORT engine installed in a 1987 Mk1. The Smallport is a stock NA motor running all Smallport electronics! I have heard that a nice upgrade on this engine is to switch out the SMALLPORT intake and exhaust cams and replace/install the 1987 4age LARGEPORT CAMS (more lift/duration) in their place. Is this a good idea, and if so, will I notice any overall improvement in performance on the Smallport? Can a percentage be attached to this performance gain (seat of the pants)...i.e. 10% overall improvement...15% overall performance gain...? Also, very important..... do the valve shim adjustment measurements per the BGB stay the same on the 4age Smallport when changing out to the Largeport Cams? Thks for any experience/insight into this issue.
The difference is going to be very small. I would guess hard to quantify on a dyno.
264 poncams are lucky to get you a 15% power gain at redline.
This dyno is of a smallport with stock vs poncams vs poncams with a compression bump.
Personally I think the gen 1 cam is a waste of time but if you are already in there it won't hurt.
As mentioned though it is only the early gen 1 largeport that had the bigger cams. Otherwise they will be identical to yours.

A real cam like the poncams can get you gains worth caring about. Combined with compression can really get you somewhere but then we are talking about a completely different ballpark.
 

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Yoshi, clarifying that statement on the power band. The engine felt the same throughout the power band, just pulled the hills better than stock. So, same power band just better power. Toss the math!
 

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The cam timing chart you see below is the duration, and timing difference between early, and later cams. These are TOTAL degrees.





To find out the placement of performance cams, you would take ramp (duration between total and measured) and add it to the beginning and end of the listed figures.


There are 2 advantages (less overlap, and sooner IVCE) that Toyota brought to the table with the 2nd gen cams, while losing about 4/10mm of lift. The lift loss turns out to be a bit less significant due to stock port flow capability, where as the IVCE being 7 degrees different allow more time for the intake charge to be compressed.


So... in an otherwise stock engine(same short block, same pistons)... you'll have a bit "fatter" mid range(3000-6000) using the later cams, while you might make 1 or 2 hp more with the early cams(5500 - 6600).



For a moment think about the basic parameters... the later engine, utilizing a knock sensor, used a .9 point compression bump, AND shortened the duration. So, taking that into account, a static compression of about 10.5 to 10.8 would begin to allow the early cams to be fully realized.
 

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The cam timing chart you see below is the duration, and timing difference between early, and later cams. These are TOTAL degrees.





To find out the placement of performance cams, you would take ramp (duration between total and measured) and add it to the beginning and end of the listed figures.


There are 2 advantages (less overlap, and sooner IVCE) that Toyota brought to the table with the 2nd gen cams, while losing about 4/10mm of lift. The lift loss turns out to be a bit less significant due to stock port flow capability, where as the IVCE being 7 degrees different allow more time for the intake charge to be compressed.


So... in an otherwise stock engine(same short block, same pistons)... you'll have a bit "fatter" mid range(3000-6000) using the later cams, while you might make 1 or 2 hp more with the early cams(5500 - 6600).



For a moment think about the basic parameters... the later engine, utilizing a knock sensor, used a .9 point compression bump, AND shortened the duration. So, taking that into account, a static compression of about 10.5 to 10.8 would begin to allow the early cams to be fully realized.
I think both early and late largeports and smallports are starving for more cam. Especially the smallports. Talking with Bill Strong several years ago right after I installed my smallport, he said that smallports really come alive with bigger cams. More so than largeports. The smallports have all the supporting cast members to make the power. Just not cams. Better flowing head, manifold, higher compression, knock sensor, etc. But smaller cams AND make more power.
 

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I think both early and late largeports and smallports are starving for more cam. Especially the smallports. Talking with Bill Strong several years ago right after I installed my smallport, he said that smallports really come alive with bigger cams. More so than largeports. The smallports have all the supporting cast members to make the power. Just not cams. Better flowing head, manifold, higher compression, knock sensor, etc. But smaller cams AND make more power.
higher... yes... but not high enough :eek:

ever heard of Keiichi Tsuchiya??? His old "street" AE86, built by TRD legend Sakurai, used STOCK CAMS..... :banana

Lots of headwork, lots of compression... lots of tuning... but STOCK CAMS

But smaller cams AND make more power.
yes... if there is too little compression for the cam... or too much duration for the compression... a "smaller" cam (more appropriate for the compression) will make more power
 

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Gotta address cams and compression together to get the most out of a build.
LP compression is sad by todays standards even on the stock cams. SP isn't bad with the stock cams but should really get more to get the most out of a bigger cam.
 

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Yes, I said toss the math. In a case where we're just talking about playing with a generally unmodified engine and just changing the cams by a few degrees. Without doing any supporting mods not much will come of it. So, toss the math.
 

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Discussion Starter · #16 ·
Thanks guys.....but back to my questions above ( for Scottgas, Oldskool and Yoshi) and let's stay on point here....so the general consensus, unless putting in AFTERMARKET performance CAMS on the Smallport, then there is no real gain (seat of the pants) by installing the 1987 7 rib Largeport cams on the NA Smallport, is that correct guys?
 

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Thanks guys.....but back to my questions above ( for Scottgas, Oldskool and Yoshi) and let's stay on point here....so the general consensus, unless putting in AFTERMARKET performance CAMS on the Smallport, then there is no real gain (seat of the pants) by installing the 1987 7 rib Largeport cams on the NA Smallport, is that correct guys?
not likely to feel or measure the differences... get clearances on the tight side of tolerance.
 
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