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madkaw

Comparing triples to plenum induction

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Wasn't sure how to title this thread - but here it goes ,

Just swapped out my triple Mikunis 40's for MS controlled N42 intake. Why? because ready to move on.

Basic engine parameters haven't changed much. Head was shaved another .020 to bump CR.

Characteristics of my performance have changed in the way the engine pulls. Triples hit hard and performance thru rpms seemed pretty linear . Engine pulled hard all the way to redline ,7000 from as low as 3000.

N42 is more turbo effect or non linear and pulls hard later .

I have a little stretch of road that I've done many hard runs on 0-100mph, and comparing the two I would say that that the two different set ups get to 100mph about the same time, but the N42 seems less torquey? I would thought of just the opposite thinking about the engine it was designed for, but I realize it's about the complete package.

I had my isky 490/290 on #2 cam hole to get intake closing correct , but now I am on #3 now. With a total of + .055 head shave , maybe I need more cam advance to bring my power band down , or maybe the reality is that I will never get the same performance curve between these two induction systems.

I did NOT degree my cam second time around . I shaved another .020 off head to bump ,,CR and thought it would need another bump in advance valve timing.

I have a Nismo gear on there which would give me #4 or 8 degrees before I would need to advance a whole tooth??

Edited by madkaw

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Independant runner manifolds tend to give more Torque down low than plenum manifolds. You can get the same effect with EFI. You just have to go with ITB's. 

 

On small block Chevies , changing over from a a Plenum manifold to Weber 48 IDA downdrafts can yield an incredible bump in low end Torque. Top end Power is about the same. 

 

And the stock Nissan plenum manifolds are far from being optimised for a " high performance " motor.

 

 

Now if you want a really good Plenum manifold... give these guys a call. 

 

https://www.facebook.com/customplenumcreations

 

For ITB's Jenvey make some nice stuff.

 

http://www.jenvey.co.uk/products2/throttle-body-kits

 

Be prepared to work some overtime!! $$$$

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Would be great to see comparison dyno sheet. Do you have any sheets available from before you switched?

The nice thing about EFI is that you can optimize AFR over the whole RPM range. Tuning is much easier also due to just changing some digits in the computer vs. swapping out jets and such. I agree with the statement above, the Stock N42 manifold is far from optimized, and will not flow nearly as much as your Tripple carb setup. The ideal way to go would be ITB like the ones from Jenvey.

I would expect the Carb setup to have less torque down low but more power up top where as the stock manifold to be great until about 4k rpm and then start dropping off.

Just in terms of open area at full throttle if you are running a 60mm TB compared to 6*40mm TB that's a 62% reduction in area...

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I will add that my 40's had 32 chokes compared to the 31mm runners on the N42.

I actually thought the plenum would feel more torquey down low and Peter out higher rpm , but it seems just the opposite . Maybe apples to orange comparison , since I don't have a cam to optimize the N42.

I also can't say that I have the tune on the N42 optimized, but WOT AFR is very consistent ( beauty of MS).

So I am considering bumping the cam advance some more , though I will be getting close to a whole tooth :0.

I do plan on getting to the dyno, but want to work some more with my tune. I know my accel enrichment might need some work, but at WOT that shouldn't be a factor .

I have another plenum that I need to complete that will be completely different - tapered runners and a bigger plenum, that should change things up some more.

Do I expect the N42 to run the same as the triples , not really . But I think I should be able to get close with the tuning advantage I have with MS .

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I saw that- very nice. I was contemplating the same project - with TIG now in hand it would be fun to be creative like that. I've been holding on to some old intakes for practice . Not done messing with plenum style intakes yet.

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Actually, the easy way would be To take a Carb Manifold and either add ITB's or a Plenum to that. There are companies that sell Plenum kits. Design and taper of Plenum is critical, but the good vendors have that sussed out. 

 

I'm sure I have a few kinks buried in my Audi archives. 

 

Ross Machine Works has parts for making DIY intake Plenums.

 

http://www.rossmachineracing.com/intakepartspage.html

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I had my isky 490/290 on #2 cam hole to get intake closing correct , but now I am on #3 now. With a total of + .055 head shave , maybe I need more cam advance to bring my power band down , or maybe the reality is that I will never get the same performance curve between these two induction systems.

 

You changed at least two variables at the same time.  Going back to #2 will move the power up the RPM curve.  And you're tuning by ear and butt.  You've lost the honk of the triples so it will sound less powerful, of course.

 

Without numbers though, you're really just guessing, and any suggestions are mostly bench-racing.  Unless they have numbers to compare.  No offense intended to the prior suggesters but the comments seem to be about expectations, with no measurements.

 

Also noticed this - "WOT AFR is very consistent ( beauty of MS).", and remembered that you want to be rich when you're around the torquey part of the power band.  You didn't give the numbers though.  So maybe there are still some tuning gains to be gained.

 

How do your ignition timing advance curves compare?  Another variable.

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You changed at least two variables at the same time.  Going back to #2 will move the power up the RPM curve.  And you're tuning by ear and butt.  You've lost the honk of the triples so it will sound less powerful, of course.

 

Without numbers though, you're really just guessing, and any suggestions are mostly bench-racing.  Unless they have numbers to compare.  No offense intended to the prior suggesters but the comments seem to be about expectations, with no measurements.

 

Also noticed this - "WOT AFR is very consistent ( beauty of MS).", and remembered that you want to be rich when you're around the torquey part of the power band.  You didn't give the numbers though.  So maybe there are still some tuning gains to be gained.

 

How do your ignition timing advance curves compare?  Another variable.

Sound is a mute point- I ran the CAI so there was no induction noise. Ignition was previously run by MS-so that has not changed. Cam timing I did change but I believe not enough. It seems power comes on around 4K instead of 3K+ previously-very  distinctive on the butt dyno. I believe with the additional cut on the head I have retarded timing beyond where I was, but I didn't degree cam this time around. The head shave of .020 I thought I would notice, and maybe I do at the higher RPM. It seems what I lost at lower rpm the engine makes up for now at higher rpm. It pulls hard right to rev limiter-6900rpm.

Tuning make play out more power since I have lots to learn  

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I stand 100% by my statements about IR manifolds with independant throttles  having more overall torque than a Plenum manifold with a single Throttel. Lots of technical information on it if you do your research.

 

One prime example is in Vizard's book. How to Build Horsepower Volume 2. " Carburetors and Intake Manifolds. Turn to page 99 and start reading on the results of testing a mildly modified shop truck engine ( Vizard's personal truck )  with four 48 downdraft Dellorto's  Nothing changed other than IR Intake and carbs

 

350 ci SBC,  9.5 CR,  mildly ported heads, 1 5/8" headers, 256 Intake duration and 262 Exhaust duration at .050" . This mild 350 pulled 445 ft lbs of Torque with a big fat and flat  Torque curve.  That is impressive if you know SBC... and I do. 

 

Tests done with a back to back comparison on a higher output engine revealed:

 

Page 100.

 

 " Changing from a 750 Holley on an Edelbrock Performer, a known functional combination, especially at lower rpm, to the Dellorto setup seen her produced an almost constant 45 ft/lbs throughout the the rev range on this 350ci SBC. At the Top end this produced a 50 HP increase. Along with this increase came reduced part throttle consumption, a glass smooth 400 RPM idle and Sprint Car like throttle response. On the down side, calibration takes more than just a casual knowledge of Carburetor function  

 

 

On Page 101 there is a further comparison, with Dyno charts of a IR Dellorto setup on a 350 ci SBC with 10.5 CR, AFR aluminum heads, Street roller cam and 1 3/4 headers. This engine made 518 HP and 469 ft/lbs on Torque with the IR Manifold. On 92 Chevron Pump gas.

 

Further comparisons were made between a 650 Holley DP and an 850 Holley DP. The IR manifold with Dellorto's made significantly higher horsepower and torque figures than any of the Plenum manifold. The Dyno plots are shown on page 101 in figures 9-12

 

This is not a one off example either. Anyone who does some proper research will find that IR manifolds are superior to Plenum manifolds in making HP and Torque in almost every single High Performance engine application. This has been covered in dozens ( if not hundreds )  of technical articles from Race Car Engineering, Race Engine Tech and SAE white papers.   Carburation is particularly effective, because of the strong booster signal and lack of restriction. But similar results carry over to EFI.

 

Unless restricted by rules ( and many racing classes are ),  EFI independant runners with independant throttles are used by almost all major Racing Engine manufacturers. F1, WEC, LMP , Indy car, NHRA Pro Stock etc, etc. The improvements in Torque, HP , BSFC have been proven for well  over 50 years ( IR manifold vs Plenum style manifold ) .   

 

The biggest drawback to IR manifolds is cost and complexity. There the Plenum style manifold wins every time. Cost is the biggets factor as to why you don't see them on evry day Econo cars. 

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madkaw's talking about the shape of the curve, less so the max number.  Still no numbers. not even measured times, so it's all sensation.  The same power curve with a bump at the top might feel less torquey than an engine with less max power.  

 

I remember getting beat by my friend on his boring old XL125, against my peaky two stroke 125.  He had power everywhere, I had to wait on mine.  Mine felt faster, but his was faster  Plus he outweighed my by 20 lbs.  Very frustrating.

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New Zed is correct in that the thread was about discussing my butt feel of the power curve.

And for reference I was running the shorty Mikuni intake so runner length is pretty close.

 

If I was to guess what the outcome of this switch of induction system I would have guessed more torque down low and running out of steam higher rpm- but really seems opposite . Not that I knew what I was talking about , but I thought it would make for good discussion.

 

I will be advancing the cam timing to see what affect that has on things. I'd like to get the engine to where it seems to be tapering on power towards red line- but now it seems to wake up later then the Mikunis and pull harder the further into the rpms.

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It does make for a  a good discussion. But there is a lot more than just runner length involved. It gets really, really complicated with stuff like runner resonances and helmholtz frequencies involved from what I've read. Way above my pay scale. In a simplistic manner, I think the plenum volume dampens the intake pulses that you see in the runners as compared to the IR design. The strong intake pulses combined with resonances adds to the Ram tuning effect of the IR runner design.

 

The increase in Torque is not in just one area either. It covers the whole Torque curve of the engine and is significant.  That is why you can feel such a big difference in the old " Butt " dyno.

 

I'll see if I can take a scans of the Dyno plots from Vizards carb comparison of 650, 85 Holley DP'ds and the 4 x 48 IDA Dellorto's. It will be later as I'm going out for dinner right now

 

It's interesting to note that many aftermarket Plenum manifolds for both NA and Turbo charged cars use huge Plenums in comparison to the stock size. VW/Audi aftermarket Plenums for 1.8/2.0 Turbo motors are close to twice the volume of the factory Plenums. Dyno plots show no loss in Torque( in fact gains in Torque ) at low RPM's even on stock motors. 

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I did NOT degree my cam second time around . I shaved another .020 off head to bump ,,CR and thought it would need another bump in advance valve timing.

 

Degree your cam! Judging from the results I have gotten it is very much worth it. Actually retarded it 4 degrees from cam card and made a WORLD of difference. Especially at top end.

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Found a couple of articles that explain in Laymen's terms why ITB's give better throttle response and efficiency  over  a Plenum design with a single throttle body. Dyno plots aren't shown. but they are in other examples.

 

As I surmised earlier, the Plenum design with a single TB dampens the acceleration of the air column. This is because of the lowered atmospheric pressure in the Plenum.  This reduces instantaneous Torque and that " snappy " feeling of ITB's .

 

This video pops up quite a lot, and effectively gives a layman's description of why ITB's have a much better response than a Plenum design.  

 

http://www.motorauthority.com/news/1109383_the-benefits-of-individual-throttle-bodies-vs-a-single-throttle-body 

 

A short article from Jenvy UK on ITB's vs single TB with Plenum. A bit too simplistic, but essentially true.

 

http://www.jenvey.co.uk/faq/big-single

Edited by Chickenman

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Steve, what size TB are you using on the Z right now? I found my car was much more responsive with the TWM  Big Bore TB ( 60mm ) than the stock size... which I think is 52mm? 240SX TB  is 65 mm I believe.

 

Integrated Engineering did some comparisons on TB size for the VW/Audi 1.8/2.0 Turbo engines. Stock TB is 60 mm. They found that the best results for driveability and HP/Torque gains was 70mm. Anything bigger than that and the gains were minimal, but low RPM driveability became worse. It became  hard to modulate the throttle at low RPM's.  

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I wish I did or could have degree'd the cam, but the motor was in the car which makes it really hard to do. I think I have a good idea how close I am the numbers since I did previously did a proper degreeing of the cam.

i'd be curious of others that have shaved a head this much with NO shims and how far off the timing was .  

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Well sometimes you just wing it, but advancing the cam woke this engine up -earlier- .

Now at 9 degrees advance I probably made up for chain slack , head shave .

Yes it's a butt dyno, but with the cam retarded I couldn't chirp the tires thru the gears , but now I can - just like I did with the triples .

I did notice that my AFRs went lean after the cam adjustment, so that is a good thing. Added more fuel (point and click) and power with higher VEs .

So though there is a bit of difference between triples and this plenum , it is negligible by the butt dyno.

I know - put it on the dyno- I'm close

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It bears repeating my DCOE N42 experience with the butt dyno...
With the 40 DCOE's and header it sounded great, FELT fast as hell, but dynoed at 87RWHP
Changing ignition leads, putting an all stock 76 EFI system onto the car (including stock exhaust manifold with MSA downpipe to the same 2.5" Crush-Bent Exhaust) and changing plug wires with the stock air box and K&N filter in it had EVERYBODY saying the car was "torquey at the bottom end" and "fell off up top"...
Consensus from multiple Butt Dynos was the car was more tractable due to the torque, but wasn't as 'fast'...

Of course, it also Dynoed at 147 RWHP at the same shop and same dyno the DCOES were set up... 

Now, the DCOE's were NOT optimized. But the sounds and the WAY they seemed to have an "on-off" switch throttle response convinced EVERYBODY including me that they had gobs of power over a stock setup. Of course, and properly set up DCOE set should make more...but the point of this post was the butt dyno was worthless in any manner of empirical evaluation and gave universal 100% incorrect feedback.
:

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New Zed is correct in that the thread was about discussing my butt feel of the power curve.

And for reference I was running the shorty Mikuni intake so runner length is pretty close.

 

If I was to guess what the outcome of this switch of induction system I would have guessed more torque down low and running out of steam higher rpm- but really seems opposite . Not that I knew what I was talking about , but I thought it would make for good discussion.

 

I will be advancing the cam timing to see what affect that has on things. I'd like to get the engine to where it seems to be tapering on power towards red line- but now it seems to wake up later then the Mikunis and pull harder the further into the rpms.

I am having the opposite problem.  

 

Oh and my tuner kept putting in more Advance and the engine kept liking it...  

 

I am thinking that I will be popping in an adjustable cam pulley soon...

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