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Posted by: Dan (Almaden Valley) Sep 20 2006, 11:28 PM

anybody out there using them on a stock D-jet FI system?
I am just about to start my motor rebuild and will be keeping my stock FI.
Wanted to know if anyone is using currently, or has used, enlarged throttle body on their stock injection.

If so, how did it work?
notice any power increase? If any where in the rpm range?
tuning issues?
other motor mods along with the throttle body change.

Posted by: trekkor Sep 21 2006, 12:20 AM

Andy Brian from RR-PCA uses a larger TB from a Volvo I believe.


KT

Posted by: Joe Ricard Sep 21 2006, 05:07 AM

What 44 IDF's are not big enough?

Oh, D-jet. Didn't Jake say that there isn't much to be gained? Stock stuff flows enough for much more HP. Something like that.
Well except getting drop kicked to a higher racing class.

Posted by: Mark Henry Sep 21 2006, 07:51 AM

Yep, no gain...save your money

Posted by: Bleyseng Sep 21 2006, 08:20 AM

I bored my out to 50mm and had shaft bushing installed.

I think I get more outta the shaft bushings than the boring.

Brad said once he tried both out on a dyno and the difference was 1 hp.

Posted by: Jake Raby Sep 21 2006, 08:26 AM

Most of the time POWER WILL BE LOST!

Bigger isn't better- never, ever make that mistake!

all the larger T/B will do on a stock engine is make the car drive worse!

Posted by: pbanders Sep 21 2006, 10:44 AM

Even if boring the TB improved the volumetric efficiency (VE) curve, with stock D-Jet, unless the engine speed mixture correction circuits in the ECU are modified for the new VE curve, you won't get any improvement in power or torque.

Posted by: gregrobbins Sep 21 2006, 11:07 AM

Brad, good to see your recent post on the D-jet throttle body. I have appreciated your work and web page. Thanks for the effort.

I still hope to meet you in person some time.

Do I recall from the bird board you are having your motor rebuilt. Is that being done here in the valley? If yes, whom did you select to do the work. Jack?

Tried to PM you, but got a message the box was closed/full

Greg Robbins
Glendale
602-291-3525

Posted by: pbanders Sep 22 2006, 11:37 AM

Greg, yeah, Jack's doing the rebuild. Let's just say its proceeding at a "leisurely" pace (i.e. the car went in the shop in mid-April), but the work so far has been excellent. It's supposed to go back into the car this weekend, but I'm expecting it to take a few more weeks before I get the car back.

As soon as I have the car back together, I'll take it out to one of the local 914 runs. I did one a few years ago up to Sendona that was a lot of fun. Hope to see you there.

Posted by: Brad Roberts Sep 22 2006, 11:52 AM

Thanks for posting Brad

Havent seen you here in awhile.

No gain with larger TB/waste of time/money


B

Posted by: Dan (Almaden Valley) Sep 22 2006, 05:39 PM

That is a surprise to me since several of the old time BP racers said it seemed to make quite a bit of differnce on their 2.0L cars.

Posted by: bd1308 Sep 22 2006, 06:42 PM

The deal with bigger TBs and not having the VE or the engine designed to take advantage of this, you'll find that the engine will have a higher value of high-rpm zip but lack very big in the low-end torque value.

MPGs will suffer as well too.

Ive personally done some experiments on this very thing.

It 'feels' faster, simply because the low-end grunt sucks so much, that people get all excited when it finally starts going...

b

Posted by: Dave_Darling Sep 22 2006, 11:41 PM

Charlie Davis bored his stock TB and made a new throttle plate. He claimed some "seat of the pants" improvement, once some tuning had been done to the D-jet. He even went so far as to fab up a throttle body of his own at one point! Sounds like the improvement from that last one was marginal or nonexistent.

No dyno runs that I know of.

--DD

Posted by: bd1308 Sep 22 2006, 11:42 PM

I wouldnt be surprised to see less low-end power than stock and a bit more high-speed power than stock.

The seat of the pants factor is from the 'difference' between these two spectrums.

Posted by: Rand Sep 22 2006, 11:50 PM

Made me think of http://www.shoptalkforums.com/viewtopic.php?t=102542. Interesting reading at least.

Posted by: bd1308 Sep 22 2006, 11:58 PM

exactly, its like taking 40IDFs and putting 48 velocity stacks on them or something.

It just doesnt work, most people prefer 32s or 38s i believe

and it shows, our engines like more air velocity and the only way to do that is choke down the TB.

Posted by: Dan (Almaden Valley) Sep 23 2006, 12:08 AM

so the moral of this story is that a 2.0L needs a smaller TB and/or plenum?

Hmmmm

How about some sort of pyramid in the plenum under the TB?

IF a stock TB and plenum was too large for a 2056 then it must be way too big for a stockish 2.0L.

Posted by: tradisrad Sep 23 2006, 10:11 AM

I thought of buying a T/B from high performance house that has been enlarged but I figured it was a waste of $250 as the performance would not be improved that much.
My T/B did not have the vacuume advance port on it, last night I added the vaccume advance port to my T/B. I do not feel any improvement in power however the car has smoother acceleration. So maybe if your T/B does not have the vacuume advance that may be worth adding.
We bought a .157" brass tube from the local hobby shop and drilled a .154" hole in the port area, we went .4" deep and then finished off the hole with a .040" hole that went all the way into the T/B. We measuerd the stock hole (from a friends '73 2.0) and it was .040". At one point some one said that we should drill a .030" hole but that was smaller than the stock hole.

Posted by: pbanders Sep 23 2006, 04:40 PM

Yeah, but racers aren't streeters. A race car is operated closer to WOT and in high engine speed ranges continuously. With a larger TB and a richer mixture you can probably extract a few more HP, at a loss of low-end torque and some drivability - but on a race car, who cares?

Posted by: Jake Raby Sep 23 2006, 04:57 PM

The key is increased runner and plenum development. The throttle body seems to have the least impact on the engines I have tested.

Recently we outperformed a stock (large volume) 2.0L 914 plenum by using a stock 2.0 bus plenum with the stock throttle body being used on both. That arrangement tested back to back provided 153HP from a 2270cc engine, 13HP more than the larger volume 2.0 plenum.

When my new dyno gets here I will be doing more of this development as I plan a new single T/B development for my DTM outfitted engines.

Posted by: gregrobbins Sep 23 2006, 05:22 PM

Jake, is this something your working of for SDS FI motors? Problem with the dual Jenveys?