1.8 valve sizes...

[calipornya]

Are 39x33 valves OK for a carbed 1.8 configuration with a Web 86 cam? What kind of breathing issues, if any, am I running into here? This question is for you very experienced head/engine builders, obviously.

[calipornya]

bump

[dstar5000]

NEVER cheap out on Type IV heads.....


You might as well go with 42X36's.

Don

[HAM Inc]

The combination your thinking of running will do fine up to around 4000-4500rpm's. At that speed the restrictive exhaust port will limit torque, though the engine will continue to rev. Aside from being the most reliable of the type IV heads (in stock form) the 1.7 heads (39.3mmx33) are nicely responsive at lower speeds. They are good candidates for budget street engines. Look for castings with a 'Q' at the end of the casting #. If 'Q' heads are not available, don't lose any sleep over it, all 1.7's are pretty dependable. The 'Q' heads are a little beefier around the exhaust port. It isn't much of an issue though if the head won't be ported.
Len Hoffman

[Plastermaster]

It is common on both T1 and T4 to have the exhaust valve be 5 or 6mm smaller than the intake. On the T4 which has such lame exhaust issues, why not go 39 39 or 42 42, 42 40 maybe? I know the port is more the problem than the valve, but I am assuming the valves are sized to the port and vica versa, at least in stock form. You can open up the port but the valve seat can only be as large as the valve will allow. So, what if you took a set of heads and improved the flow on the intake side, but kept the valve the same (39), and really worked the exhaust and increased its size as much as reasonable for optimum performance.


Ron

[MASSIVE TYPE IV]

Lately I have been using 44x40 valves in some combos with some new cams and making the same power as with other cams that had more lift, nastier ramps and required dual springs..

Its all in the combo.

[Plastermaster]

That's interesting. Theres more than one way to skin a cat (personally I like cats), The bigger valve has more mometum and can require more springs, but if the cam is milder and the valve not moved so violently it sounds like you can get better flow and be easier on the valve train. I guess its a fine balance and has to be done just right. less cam usually means less power. Bigger valves often need stronger springs, BUT allow for a more open port. You found an optimum!

Ron

[MASSIVE TYPE IV]

I have dropped our spring tension 80 pounds by doing this... and adding ceramic lifters

[HAM Inc]

Ron's using his head. The greater the efficiency of the intake the more efficient the exhaust must be. I have set up 1.7 heads for engines up to 1.8l with intake ports polished and blended to oversize valve seats that were as big as a 39mm valve can plug, which means no reshaping of the port and only a slight reshaping of the bowl area directly beneath the seat. The exhaust port is reworked to 2.0l specs with a 34mm valve. The only difference between the finished port and a 2.0 914 port is the I.D. of the 34mm seat is 1.25mm smaller than the stock 2.0l seat.

My customers that have used this combo report tremendous low speed torque and responce, but that the engine continued to pull up to 6500.

I've said this before about 1.7 heads (see the Jan'04 post) being great candidates for smaller engines because the intake port is 2.5mm smaller that the 1.8 & 2.0. This is not what you want for an engine that will see sustained high RPM's but for street cars, even with high redlines, the low speed responce makes these heads a good choice, autocrossers take note. Because the port is smaller than its 1.8 & 2.0 counterparts the port can be cleaned up without getting to large for lowend torgue.

Remember that every "improvement" mod performed on any engine has a compromise or down side. With bigger valves it's increased shrouding issues and motion control because bigger is heavier, as Ron pointed out.
Len

For larger engines with higher redlines I love the 42x36, 42x38, 44x40 valve sizes depending on the size and intended use.
Len

[Plastermaster]

Len, so in in the end what is the difference in diameter of the intake and exhaust ports with your approach? What I was originally getting at was the possibility of doing something weird like making them close or equal in size to compensate for detrimental position of the exhaust port. So far we have done this with the split cams, and now Jake has done this to some extent with the exhaust valve/port size and an easier cam. I guess I am asking how far you can go before making the exhaust flow excessivly compared to the intake.

Thanks
Ron

[MASSIVE TYPE IV]

You'll never over do it on the exhaust port! With a TIV its near impossible.

[HAM Inc]

Ron with the set-up I described the intake seat I.D. is 36mm and the exhaust I.D. is 30.7mm. Compared to 33.5 & 28 O.E. The intake port dimensions stay pretty much the same as stock except for port matching, polishing and blending the bowl area into the seat. The exhaust port gets major attention. I machine the floor of the port down 6mm to the 2.0l 914 spec. and open it up.
Engine designers got a handle pretty quick on the relationship between intake and exhaust. On engines with design potential to have ports of identical efficiency (such as hemi's and pentroof's) the exhaust is typically around 90% the size of the intake. 2.0l Alfa's are an example of this. A hemi head with 44mm intakes and 40mm exhaust and nearly identical port shapes and shrouding factors intake to exhaust. (Peugeot came up with this design in the first decade of the 1900's)
Offenhauser copied this design but fitted many engines with identical intake and exhaust ports so innovative car builders in the 50's could mount the intake and exhaust on either side of the car. Turbocharged and blown engines tend to benefit from identical port efficiency.
The 2.0l 914 with its efficient intake has a 42x36, the exhaust is 86% the size of the intake. I tend to work with configurations that follow these numbers as the intake is not as efficient as a hemi or pentroof design which justifies a higher %.
Jake is right that you won't be able to over do it on the type IV. Mainly because the port won't support a valve big enough to reach the kind of efficiency of the intake. Good thing the right cam can help the balance.
Was that to much info?
Len

[Plastermaster]

Was that to much info?
Len

No, I think I handled it pretty well.

I didn't know that the port could not be improved to accomodate a valve (valve opening) to reach the efficiency of the intake. It sounds like there is only so much you can do to it. However if I can make a yeahbuttle, You are still making improvements and enlarging the intake as well as the exhaust. I think the intake could be left alone and the exhaust could then be made as efficient. If the 2.0 is 42X36 and can be opened to 38 or more on the exhaust, why not apply that to a 1.8 with a 39 intake. I suppose if you did, then you might as well improve the intake as well, and then add a suitable cam, but at this point the question is more hypothetical. If I understand correctly, the exhaust can not be made to equal the efficiency of the intake PROVIDING you have also made the improvements to the intake. Is that right?

Thanks
Ron

[MASSIVE TYPE IV]

The intakes don't need improving... The more you do to the intakes the more it hurts your ratio of flow!

Most of my heads have nothing done to the intakes except smoothing

[Plastermaster]

On your 44X40 you must be doing a little? You are starting with a 42X36, right? I'm totally green on all this. I am guessing that the port on a 42 intake is already not up to snuff for the size of the valve. To go to a 44 intake it must take some work to make the size increase on the valve worth the trouble.

On another subject, what engine are you putting your first set of Lens heads on? {this weekend }

Ron