Mechanical engineer anyone?

Tweety · Post by **Tweety** » Thu Aug 28, 2014 8:55 pm

Most of you know the plan.

Stock ea81 (with broken ring in one piston and two blown head gaskets) to be rebored and comp ratio raised to 9.0:1. Heads slight polish. Cam 16/56 with .235" lift as per Steptoes experiments that found it was more suitable for towing/low down torque which I'm seeking.

I want to know what the benefits the larger SPFI manifold and the larger than common weber 38/38 synchronic carb will give the engine.

The SPFI manifold has 25% extra volume (6mm larger in diameter). The ends of the manifold where they bolt onto the heads are the same size as the stock ea81.

I've read up heaps on the 38/38. Many people think it is too big for this engine but this extract and numerous 4 cylinder owners swear by this carbie for low down power.

Can anyone tell me the benefits of the larger manifold and larger carbie combined?

Silverbullet · Post by **Silverbullet** » Thu Aug 28, 2014 9:08 pm

It will breathe better, which I think is hugely important with the EA81. From my experiences so far if you can remove some restrictions on the air getting in and out it makes alot more power over more rev ranges. With the engine in my ute I had it running perfectly with the stock Hitachi and stock exhaust and it ran pretty good. Upgrading to a 2" higher flow exhaust, EA82 intake manifold and Weber 32/36 has made it much much better. Doesn't rev out as quickly and has more torque over a wider range, higher top speed in every gear.

Tweety · Post by **Tweety** » Thu Aug 28, 2014 10:34 pm

Yes SB, I'm hoping the breathing will improve its power and torque.

This site is for MGB owners. The 1979 model had a 1798cc engine. The 38/38 has made much improvement in performance. Comments from many owners, http://www.mgexp.com/phorum/read.php?1,1083844

steptoe · Post by **steptoe** » Fri Aug 29, 2014 8:36 am

ask too many people, too many questions, and you get too many views, ideas and opinions

then where are you gonna be ?? I like to think the greater volume of the spfi manifold will give slicker response, maybe no more torque or horsies. Greater volume should also work higher up the rev range, screaming the gizzards out of the auto ! Still to drive my spfi inlet manifold, and will be too long ago to compare the original inlet set up

for fair comparison (I'll likely wanna jump back in my torquey EA82M in the other Brumby )

Just bloody hurry up

Tweety · Post by **Tweety** » Fri Aug 29, 2014 4:50 pm

too many people too many questions? the more the merrier then I can sift through them to find someone that actually know what they are talkin' bout!!

yeh, better response. Should be interesting on the dyno with correct jetting

Engine builder has been held up. whats new. lol

Subydoug · Post by **Subydoug** » Fri Aug 29, 2014 7:51 pm

Well Tweety my new efi manifold has a ID of 1 1/2 inchs. Pretty sure it pulls a decent bit harder in the low end. Also with a static comp ratio of around 9.5 -1. The single 50mm throttle body is on the large side for the motor though as I have to use stupendous amounts of acceleration enrichment. My hunch would be that your carby may be on the big side for the motor. You wont really know until you tune it. If it tunes up fine and still idles normally your probably laughing.

Regards

Doug

Post by **TOONGA** » Fri Aug 29, 2014 8:04 pm

When you bought the carby you said it was jetted to suit a 1.8 litre motor didn't you?

If so then it will work

Remember that I have a carby that was designed for a 4.1 litre motor on a 2.2 litre motor. My carby uses the same jets a 32/36 would on a 1.8 litre motor or a 2.2 litre motor. Datsun 1600 owners swear by the 34 ADM so do I

The biggest problem I have is when the second barrel opens and all economy goes out the window

TOONGA

Tweety · Post by **Tweety** » Fri Aug 29, 2014 8:04 pm

Doug, (thanks) ....thats why I've searched the net for 4 cylinder owners that have gone the 38/38 to find their results.

I'm a little apprehensive and will only know when its running and more so- tuned and jetted right. I suppose I'm after the engineering side of things, the way the manifold works, if the larger carbie and larger manifold will suit each other. I'm hoping it will. Logic tells me it should but logic and engineering might not always match.

With all the engine bits being new and with better breathing and exhaust than stock I'd be happy with 80hp. More importantly I'm after low down torque, as much improvement as possible out of a 1800cc engine.

As far as it being too large, after reading lots of owners from Datsun 1200's to Jeeps size doesnt matter. The guy at Weber that sold me the carbie told me that idle jets are more critical than other carbs but thats for the dyno guy to establish.

Subydoug · Post by **Subydoug** » Fri Aug 29, 2014 8:51 pm

Well yeah tweety, thats mostly what I mean by too large. Once the petal is on the floor The flow is going to be fine. The biggest issue with running a largish carby on a small motor is poor driveability and poor engine response. You end up jetting to a tiny idle jet to get your mixture right, but then they struggle to supply fuel for the progression from idle to go. All that being said I doubt your going to have any troubles. Not like the carby is made for a big block chev

. My hunch is that you could get better throttle response and engine pickup with a slightly smaller carb. That being said, with an ea81, you probably wouldnt notice it without a dyno.

Regards

Doug

Tweety · Post by **Tweety** » Fri Aug 29, 2014 11:59 pm

Thanks again Doug,

Actually this short write up is exactly what I was after. It distinuishes between the 32/36 and the 38 for various applications. Please read. http://www.ebay.com.au/gds/Weber-32-36- ... 751/g.html

eg The 38mm DGAS carb should be the only
consideration if the engine is in the future or currently going to have
any level of additional engine modification. Such as headers, free
flowing exhaust, a cam, or rebuilt engine. Usually these motors will be
improved over stock with oversize pistons and towing cam. The 38 will
enhance the improvements of any of these items.

steptoe · Post by **steptoe** » Sat Aug 30, 2014 8:31 am

thinking back - a long way - I had mostly doubters when I whittled away at things to shove a 465 cfm 4 barrel Holley on a 250 ci I6. It ran, took a bit of fiddling to make the lightest of light vacuum secondary spring yet turned out a bloody beautiful sight, idled well, pulled well and even gave 27 and 30 mpg on highway runs ....awesome and doubters kept quiet. Gees, half tempted to dig it out and shove it back on !

What ever you do Tony , it will be a suck it and see. You might even need to play with levers, smoke and mirrors to alter the cable pull on the pedal - sorry - throttle - to make it less sensitive

Tweety · Post by **Tweety** » Sat Aug 30, 2014 10:43 am

I'm a bit of a worrier. Its my nature.

Many have said the carbie is "too big" and have hoped with the larger manifold it wont be. But I know now it isnt, in fact it is recommended over the 32/36 for fully recoed engines with "towing cam" as the article says.

Weber guy told me that the carbie is jetted for around 2 litre capacity already and its the idle jets that might need tweeking. So at the time purchased two other jets might be smaller ones. So can play a little.

I've been solely preoccupied with getting lots of torque down low in the rev range without squeezing the throttle heaps. Some family laugh when I say this engine could last me out but many Subie engines last 30 years or 400,000 kms if well looked after and that will make me 88yo

. By then a future grandson might be riding it....with me on a rocking chair on the roof ala beverley hill billy style.