how can twin port EA81 be so much better?

steptoe · Post by **steptoe** » Thu Mar 07, 2013 6:59 am

Just wondering why those who have had or still got an EA81S or the twin port with twin carbs say they are so much better...... the secret yeah, partly in the twin carbs, got those and yeah made a nice difference to the way the power came on and stayed (there ^ goes^ the prices^ again^

)

Is the fun factor above the 5000rpm mark, somewhere a normal EA81 should not go ?

Surely, it is not in the valve placement with the exhausts on the outer edges of the head, so inlet just drops straight in on down the middle ?

Coz if you look at an EA82 - they already have the inlets in the middle ! ?

Given I think I tossed ( I did ) my carb EA82 heads, I am not gonna experience a twin carb EA82 anytime soon . ( so that is why I kept them ?

)

velocityboy · Post by **velocityboy** » Thu Mar 07, 2013 7:44 am

I'm not familiar with the EA81S heads, I have seen EA81 heads with a divider in the exhaust port (is the dual port you mean?) and I haven't seen EA81 heads that have intake valves in the middle of the heads (if they exsist I WANT THEM

). There are 2 problems in my view with stock EA81 heads, Siamesed intake causes a lot of flow problems and the exhaust is very restricted by the contorted track it has to take to get around water jackets and the push rod casting etc.
It's just a bit of fun mucking around with an '81 engine because the difference between stock and "tuned" engine is academic, but some of us get our jollys in the strangest ways.

Silverbullet · Post by **Silverbullet** » Thu Mar 07, 2013 5:07 pm

I dunno Jonno, I'll let you know when my car is done

On my twin port engine the actual exhaust outlets on the bottom of each head are larger than a normal 81. I.e you need the Y pipe from the car or a custom one made because the regular Y pipe isn't big enough diameter wise. Then the two larger pipes join into a larger pipe again. This would no doubt aid the engine's breathing. Twin carbies gives it the extra fuel it needs and the reversed intakes aid air flow yet again. All this must add up to some awesome revving capability

tambox · Post by **tambox** » Thu Mar 07, 2013 5:19 pm

I have never worried about the "technical" explanation as to why they go better Jonno, as you said the carbs had a bit to do with it. My one was always more responsive than the single carb and loved to rrrrrev.
Then I lightend the flywheel, made it even more responsive and nicer to rev:D, but 4wdriving with 195/75/14's, lightend flywheel caused a noticable loss of tourque

Matt · Post by **Matt** » Thu Mar 07, 2013 9:15 pm

The are way more fun to drive i have driven both back to back so to speak. It has to do with the flow. The intake and exhaust are about 25% bigger atleast. Roughly the standard EA81 is under 40mm where as a EA81S or dual port head is around 50mm. So therefore more air and fuel in and burnt stuff out quicker. Thus they rev quicker and harder. The same reason a ported and polished head will be more responsive, etc.

YouTube · Post by **El_Freddo** » Wed Mar 13, 2013 6:24 pm

steptoe wrote:Surely, it is not in the valve placement with the exhausts on the outer edges of the head, so inlet just drops straight in on down the middle ?

That'd be part of it. Then there's the already mentioned exhaust ports, the twin carbs and the next thing I'd be looking at would be the cam profile. All of these things would add up.

steptoe wrote:if you look at an EA82 - they already have the inlets in the middle ! ?

Yep, but what came first? It's a development move on the EA82. I think you'll also find that the shorter in take to the inlet valve would reduce induction temps too - less time moving around the water jacket area.

My thoughts anyway

Cheers

Bennie