2925 vs Modified 2925 on dyno.

Chad Speier · Joined: 12 Nov 2007 Posts: 1088 Location: Hays, Kansas

OK guys, here is the scoop. I've been working with Chris Cobb at DynoTune Engineering, www.dynotuneengineering.com in Paris Tennessee. First, one nice guy! Anyone who needs dyno service, fabrication, engine assembly, needs to check him out!!

To make this a fair test, the manifolds and engine were tuned to a 13.2 AFR.

The engine that was used as a test mule is a UMP Dirt Modified. Here is the breakdown.

414 cid
3.875/4.125
6.0 rod
13.02 compression
Dart Pro 1 227cc CNC heads
264/270 106 LSA installed at 103
.670/.679 lift
1.750 headers
12" long collectors
35º timing
4150 gas 950 Ultra HP

The dyno session was to compare a box stock 2925 vs a Modified Plenum 2925. Other manifolds were tested, we will get to them.

Results:

STOCK 2925:
594.4 hp at 6300 rpm
564.6 tq at 4700 rpm
Average: 560.3/505.5

MODIFIED 2925:
616.9 hp at 6600 rpm
571.9 tq at 4900 rpm
Average: 580.0/522.6

Note: Chris said it accelerated .10 faster than the stock manifold! I'll have more info as we go. He is testing spacers tonight..

DynoTune Engineering
3745 HWY 79 S
Paris, Tennessee 38242
731-336-6899

This IS the manifold:

_________________
Speier Racing Heads
420 East 8th
Hays, KS. 67601
785 628-6673
cell 785 623-0963

Pro-Filer AIR Wolf, Pro-Filer Performance, REV Valves, GRP Rods, Probe Industries, Innovators West, Ferrea Components, Comp Cams, RHS Heads, Victory Valves

358T · Joined: 14 Nov 2007 Posts: 149 Location: Illinois

Thanks for sharing.

Are those corrected hp/trq #'s? I'd be dissapointed if I bought dart cnc'd heads and bolted them on a 414 and only made 600hp... not slamming the engine, just thinking outloud. Maybe it is just because it is set up for dirt racing, but I think 1/7/8 or 2" headers and a bigger cam would wake that engine up.
_________________
Scott

2007 & 2009 Gateway S/Pro Champion

420 SBC 1.092, 3.124, 4.860@140.5

Chad Speier · Joined: 12 Nov 2007 Posts: 1088 Location: Hays, Kansas

Chris was disappointed with the heads also. His thoughts also. Just cuz they are CNC.... Sad

_________________
Speier Racing Heads
420 East 8th
Hays, KS. 67601
785 628-6673
cell 785 623-0963

Pro-Filer AIR Wolf, Pro-Filer Performance, REV Valves, GRP Rods, Probe Industries, Innovators West, Ferrea Components, Comp Cams, RHS Heads, Victory Valves

Supernova · Joined: 13 Nov 2007 Posts: 242 Location: Mayfield Kentucky

Paris Tennessee is only about 50 miles from me. Dang! I didn't know that there was a Dyno that close.
_________________

David Clapp

Chris Cobb · Joined: 19 Mar 2009 Posts: 22 Location: Paris, TN

First of all, I would like to thank Chad for the great work on the manifold and working with us.

The engine is a local dirt modified racers' that had Dart Iron Eagle 215 (Cast Iron Heads) that were unported when it was delivered to us. We baselined the engine with those heads and the Brodix HV1000 manifold prior to the head and cam change.

It made the following peak numbers.

552 hp @ 6,000 rpm
541 lb-ft @ 4800 rpm

The planned changes were to change to the customer supplied heads (Dart Pro 1 227 CNC) and to change the camshaft to broaden the power band of the engine.

Old Cam - Bullet
255/263 .625/.625 106 ICL / 106 LSA

New Cam - Comp Cams
264/270 .670/.679 103 ICL / 106 LSA

After the changes (head & cam) we determined the baseline power curve before we started the manifold testing. We tested the following manifolds:

Brodix HV1000 - semi-ported (Customer Supplied)
Edelbrock Super Victor 2925 - Non Ported
World Motown 061040 - Non Ported
Hurricane - Fully Ported
Edelbrock Super Victor 2925 - Plenum Modified / Port Matched

We will be providing a full report to Chad with all the test data for his review and publication.

Thanks,
_________________
Chris Cobb
DynoTune Engineering
"Engineered Power to Win !!"
www.dynotuneengineering.com
731-336-6899
731-697-4913

airflowdevelop · Joined: 21 Dec 2008 Posts: 59

I am curious how the motown did against the 2925 unported.

imakehp · Joined: 29 Dec 2007 Posts: 74 Location: Reseda CA

Hi Chad

Milling the carb opening bigger :

Exposes more of the 4 middle ports opening or line of sight

Increases the plenum volume

By milling the plenum wall back it in effect extends the dividers farther into the plenum

Is one more benefit then the others? Or for that matter am I even understanding what's happening correctly?

Mine's a BBC Victor on a 540 and I'm wondering about milling mine.

Dave

Chris Cobb · Joined: 19 Mar 2009 Posts: 22 Location: Paris, TN

banjo · Joined: 15 Nov 2007 Posts: 357

Great results! They pretty much confirms what I saw on the track.

Chad, I think there may be a few more ponies in that intake mod. I have an idea about and additional mod. I want to take some pic and see what you think.

Dave, I am speaking only for the SBC intake. Not sure the the BBC intake has the same issue. If you look at the untouched manifold. The area that actually feeds both center cylinders isn't much bigger then one runner. The two center cylinders rob each others air and fuel. I could see with my logger that that center cylinder egts where different and since the mod they have evened up. On my engine, I also saw an increase in plenum vacuum after chad did this mod. It went from 1.3 to 1.6. This really confirms this because this allows each cylinder to pull on the plenum equally.
Here is a pick of the stock manifold

Chris, Did you happen to monitor plenum vacuum for the pulls? I am curious if you saw the same thing as I did.

I betcha chad could wake those heads up Wink

Just goes to show, just because it it is cnc, doesn't mean it is all that.
_________________
Bill Simpkins
Empty Pockets Racing
74 Chevy Nova
smallblock 406
1/8 6.42@106.5
1/4 10.15@130.5
Fourtenposi@yahoo.com

nomad · Posted: Sun Mar 22, 2009 7:27 am Post subject:

What's the purpose of cutting that carb pad back that much? And does cutting it back leave excess material to shape those runner "ears" to the desired shape?

banjo · Joined: 15 Nov 2007 Posts: 357

The reason in my eyes is it makes the transition into the runner alot smoother.. The turn into the runner is not as abrupt. Consider this and someone correct me if I am wrong on it, Air and Fuel have different masses. Traveling in a straight line,the air and fuel stay mixed. Now try to make the same mixture make a 90 degree turn. The air makes the transistion pretty easy, Now the fuel because it has more mass tends to want to continue to travel in a straight line and splats against the outside wall. This is why air speed is critical. To fast going around the corners and the fuel seperates power goes down. This is why lower valve angle heads can tolerate more air speed. Air does not have to turn as much to get to the cylinder.
_________________
Bill Simpkins
Empty Pockets Racing
74 Chevy Nova
smallblock 406
1/8 6.42@106.5
1/4 10.15@130.5
Fourtenposi@yahoo.com

Jason G · Joined: 29 Dec 2008 Posts: 27

The other reason is to be able to increase the cross sectional area of the interface between the plenum and the intake area. There is an optimal area here depending on the combination.

Jason G.

DW · Joined: 20 Mar 2009 Posts: 5

STOCK 2925:
594.4 hp at 6300 rpm
564.6 tq at 4700 rpm
Average: 560.3/505.5

MODIFIED 2925:
616.9 hp at 6600 rpm
571.9 tq at 4900 rpm
Average: 580.0/522.6

Just curious as to why the engine gained rpm. Possible the cross section change on the short runner.

Rickp · Joined: 19 Dec 2007 Posts: 74 Location: Fremont Oh.

Hi Chad.
After reading through these comparisons there's something i don't quite Understand in the Opening statement it states the Outa-Box 2925 Made 594.4HP at 6300 along with 564.6 Ftlbs. at 4700.
Now if you read what Chris Cobb says he states it made them #'s with a 1In. open spacer as a Outa-box 2925 with no spacer the Intake/Engine only made 586HP and 557 Ftlbs.

Question with that being the case was the ported manifold tested with the same 1In. open spacer in the Initial testing in the comparison #'s?
If they weren't then you'd be giving up 8HP in your test comparison #'s.

What i mean is if you didn't use a 1In. open spacer in the testing with the Ported SV then you have to compare it to the unported SV without a spacer which infact made 8Hp less then what you Initially listed.

Meaning this:
Unported SV
586 HP 557 ft.lbs.

Ported SV
617 HP 572 ft. lbs.

Diff. of 31HP and 15 ft. lbs. from the porting.
_________________
Rick

Chad Speier · Joined: 12 Nov 2007 Posts: 1088 Location: Hays, Kansas

The purpose is to open up the two middle runners, opening up the CSA. The CSA is just too restricted stock. Yes, it gained RPM due to this.

Yes Rick, I see that also. However, the purpose of this exercise was to make as much power as possible, while tuning to a 13.2 AFR. I talked with Chris Saturday and the 1" milled spacer matched to the opening made the same power as a 2" Super Sucker..
I think it's safe to say that a 1" spacer and the mod is worth 20-30 hp.

Another thing of interest. I wanted a back to back test. I feel there is even more hp in the mod with sizing the runners to the combo.
_________________
Speier Racing Heads
420 East 8th
Hays, KS. 67601
785 628-6673
cell 785 623-0963

Pro-Filer AIR Wolf, Pro-Filer Performance, REV Valves, GRP Rods, Probe Industries, Innovators West, Ferrea Components, Comp Cams, RHS Heads, Victory Valves