What camshaft

lmcchesney · Post by **lmcchesney** » Thu Jan 15, 2004 5:42 pm

Any input from our cam gurus? I have not seen an end to what cam would be best. Do we need a custom grind?
We are port and polishing the heads now and will need to decide on a cam shortly. Presently, we have a Web Cam #73 in the shop but I'm still not convienced that a #73 is the optimal grind.

L. McChesney

Hot Wheels · Post by **Hot Wheels** » Fri Jan 23, 2004 5:28 am

Honestly you guys are way over my head on the d-jet stuff, but wasnt shad running some modified stock injection system with an aftermarket computer controll and fabbed plenume? useful thought to the creative process?

lmcchesney · Post by **lmcchesney** » Sun Jan 25, 2004 1:38 pm

Thanks Sean,
I did send a PM to Charles regarding the combination used for his setup, but I have not recieved back information.
I continue to think about this. We know we can provide a altered relationship between the sensors (MPS, CHT) and the ECU. One point of concern is the intake signature as read by the MPS. Increasing the intake valve curtain allows for an increased volumetric effiency thus decreasing the work of the intake stroke. The next factor will be the adjustment of the combination of cylinder head flow and induction tunning as matched to the exhaust tuning. I beleive the setup for the D-jet represents an individual runner with port injection. I need to predict what the best combination of runner length combined with some porting of the intake ports with the increased valve size to achieve the 700 FPS velocity of the intake ports to allow for the harmonic ram.
The other side of this, we are designing a combination to match the SCCA/PCA rulings on modifications. This combination will be for compitetion. Thus, the combination can be optimized for racing and not for street use. It came to me this weekend that for this purpose, drivability/idle is of little concern. For use of the car for street driving, I am not restricted by the SCCA/PCA rulings and can thus utilize a Megasquirt modification for street use. The key will be to have quick disconnects for the changes.
L. McChesney

larryM · Post by **larryM** » Mon Jan 26, 2004 9:43 pm

i'm adding some comments at L. McChesney's invitation:
...based on my own experiences with Webcam 73, 91H and Elgin 6408 on stock 2.0's with euro pistons & CR's from 8.2 to 8.8, i agree with the guys who say the djet will not handle the low vacuum caused by the overlap; the 73 is a nice streetable setup that comes on around 3500; the 91H pulls like a runaway horse but is very bad on the street (trailerhitching, low fuel economy, etc) but will rev easy to 6800 (but i always tossed the fan belt at that point); the Elgin & Webcam and other sales reps have all said "it'll run with FI", but you'll discover they are talking about VW BUS L-jet which is where they sell most of the cams, and they really have little experience with Djet; most admit that anything wilder than the 73 grind should be run with carbs; check the cam specs on Elgin's site.

And do consult the airflow charts in Tomlin's Dellorto book & compare that data to your oversize ports vs the stock manifold & ports. I think that you can use DeskTop Dyno to calculate the airflow requirements based on your planned mods

my question to all you guys is WHY? This ain't a streetability issue here. What is the rationale for trying to tweak a Djet to fit this monster motor? Second: why even worry about streetability given the intended use of this motor? Get some Delorto 44's or bump the fuel psi &/or at least get the later 2L "blue-gray" injectors (which i've tested to have a bit fatter flow than the green o38's); Finally, ya do realize you are going to be running $5/gal 110 race gas when you go over 9:1 CR don't you???

Bleyseng · Post by **Bleyseng** » Mon Jan 26, 2004 9:59 pm

Sounds like he is trying to stay in a certain class that requires the use of the stock injection system. So IF he goes with Webbers, bam out of that class to another where he won't be competitive.

Geoff

raygreenwood · Post by **raygreenwood** » Tue Jan 27, 2004 5:49 am

Actually, the# 73 IS built for D-jet. Incidentally...L-jet used the same cam as D-jet...so its actually for both. Ther was only one type 4 cam after the 411,412's arrived on this continent. Tha cam was also in the 2.0/914, the 1.8 914 and the 411/412 1.7 and 1.8. The relevent aspect was the intake valve timing and absolutely nothing else. Check the book. The #73 has as nearly exact timing to the late 411 injection cam...as you can get... and still have more lift and duration.
L-jet itself has a few...but very few...problems cams, as long as the lift does not get too high. This is because its injection sequence is fully banked (all four inject simultaneously). D-jet on the other hand has actually more timing issues than vacum issues ( it has no more vacumeissues than CIS)....within the stock rate of tune that is. It's not that D-jet cannot support larger engines....thats no problem. The runners and manifolds are the parts that cannot support too much larger engines

Adding larger injectors to D-jet will net you little. In fact..adding larger injectors generally nets less hp without serious adjustment (unless slight changes in displacement like 1.7-2.0 warrants a change)...as the ECU has no idea you added larger injectors and therefore has no idea anything has changed. Fuel flow ability is not the problem.
The problem is when the engine displacement, in contrast to manifold flow ability....and/or cam changes....upset the fuel map...by upsetting the ability of the MPS to meter along the lines it was set up at the factory. That ...and a few changes necessary to the CHT and the fuel supply system to keep up with the extra heat range created by changes to the engine. A chunk of these problems can be adjusted for.

Why do we play with D-jet? Why not? Its a very smooth system when tuned properly. Its original...so its got a bit of fun nostalgia. It can be adjusted to make much better HP than stock, it has throttle repsonse that L-jet and carbs cannot touch....and I have always liked the challenge of tuning it. As simple as it is, some of its problems are actually quite complex. A 100 hp 1.7 is simple to get. Simple....but not easy. Ray

Bleyseng · Post by **Bleyseng** » Tue Jan 27, 2004 8:08 am

Some 914 guys have figured the 2.0L Djet setup intake setup would work to a 2.4L.
How do you figure it won't?
I am not a mathguy so I won't be trying to calulate this. I have heard of people trying to run 48mm intakes before and that didn't work with Djet.

Geoff

raygreenwood · Post by **raygreenwood** » Tue Jan 27, 2004 10:22 am

Bleyseng, D-jet could work fine on a V-8...but not with the 2.0 runners and manifold. A 2.4 type 4 should be no problem. But the manifolds will be a problem. It will still run...but how good? and in what powerband? At that rate...what you get trying to cram 2.0 runners and plenum onto a 2.4 wngine would probably not worth the expense of building a reliable 2.4....which I doubt most of them are reliable when used in this manner.
But...yes, generally, If you builddifferent runners and plenum...properly sized, there is no reason why D-jet could not work on any size engine. Ray

Bleyseng · Post by **Bleyseng** » Tue Jan 27, 2004 8:12 pm

I am going by what some other guys said that the Djet is sized so that it "could" run upto a 2.4l. I know it ran on V8's, German ones at that!
Just looking at the intake manifold of a 1.7 vs a 2.0l and they adjusted them a few mm's, its not like double in size. The intake valve went from 39mm to 42mm.

Geoff

raygreenwood · Post by **raygreenwood** » Tue Jan 27, 2004 9:15 pm

Yes, the runners only moved a couple of mm...but the plenum of the 2.0 moved about a 1/2 liter larger. A 2.0 runner and plenum set up should be good I think..to about a 2.2...no prob. I think a 2.4 may be pushing it...but hey...if they have done it...and its driveable....cool! The 1.7 is very well sized. I think the 1.8 could do better with the 2.0 plenum and TB. In fact, the larger TB of the L-jet 1.8 makes 1.7 run better. I have installed D-jet on a 1.8 in place of L-jet. I tried the 1.7 TB..and thats a serious restriction point on the 1.8...being that the plenum is the same as 1.7...and is a hair restrictive. Ray

Bleyseng · Post by **Bleyseng** » Tue Jan 27, 2004 9:42 pm

I do know it works great on a 2.1L, mine! 95hp at the rear wheels is ok by me.

Geoff

raygreenwood · Post by **raygreenwood** » Tue Jan 27, 2004 10:53 pm

I always tell people that D-jet is a lot more tunable than they think. I get tired of trying sometimes. A lot of people lack creativity when thinking about the D-jet system. 95 HP is what...about 115+ on the engine dyno as compared to the chassis dyno with tranny and tires attached?

Bleyseng · Post by **Bleyseng** » Wed Jan 28, 2004 9:22 am

Yes, 115hp is about right. I can get more if I install a header maybe 120hp with it. Course, then I need heavier valves springs to help at high rpms. This is with a stock cam too and idles like a kitten.
I have seen oil temps of 230 degrees when AXing thou so I would love a cam with more exhaust duration to help cool it off some.

Hey, I enjoy reading all your posts even if I don't always agree or understand what you are saying!

Geoff

Dave_Darling · Post by **Dave_Darling** » Wed Jan 28, 2004 10:12 am

Bleyseng wrote:Hey, I enjoy reading all your posts even if I don't always agree or understand what you are saying!

Ay-men to that!!

Besides, if we never disagreed then nobody would do the interesting stuff that's never been done before! Anyone remember, "You can't turbo a 914"?

--DD

Bleyseng · Post by **Bleyseng** » Wed Jan 28, 2004 2:39 pm

Amen to that DD!

Also "Toss that POS Djet and get some Webbers for some real hp!"

Tossing ideas and beers is always a good way to learn something new.

Geoff

Still waiting for Ray to send me a new diaphram to test out!

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What camshaft

djet & cams