New dyno result..... :-(

Well, after my tuning of the carb and ignition this winter winter, I decided to check the result.
I also tested the car last summer and the result was quite ok, 440 hp at 5700 rpm.
(Drivetrain losses was calculated to 25%)

According to Desktop Dyno , the CS XR280 cam should give its max power at 6000-6100 rpm, upon that I also have installed the cam 4 degrees retarded, (to prevent engine ping and get a little more hp at the top rpm) so the top hp should be at 6200-6300 rpm.

What have been done since last pull is a swap from a Holley 650 dp to a HP750 with quite larger jets. (I'm right on spot when checking air/fuel ratio with a narrow lambda)

Here is the result:
Got a difference of 40 hp between the two pulls ???
And I also think the losses in drivetrain is calculated to 10% this time ????
What is your comment on this graphs?

This is a pull at third gear, HP on crank:


Same graph but HP on rear wheel:



Pull on 1st gear: (second gear went in at 4800 rpm)


The pull:
[ame]http://s236.photobucket.com/albums/ff28/gbak/Corvette%20-71/?action=view&current=CIMG2127.flv[/ame]

Good to hear from you again, you have been quiet for a while. :smash:

I thought that engine made peak HP at 5500rpm or so, the first graph shows 4200 rpm???

How does it 'feel' compared to last year ?

25%? A bit optimistic don't you think?

MYBAD79 said:

Good to hear from you again, you have been quiet for a while. :smash:

I thought that engine made peak HP at 5500rpm or so, the first graph shows 4200 rpm???

How does it 'feel' compared to last year ?

Click to expand...

Have other things (building a new house) to focus on right now, so I have been away from all forums for a while.

What is fact is that the HP on rear wheels now are 384, it was 340 Hp last year. So I should have 44 more this year if the dynos just are correct callibrated.
I thought I could pick up maby 20-25Hp with the tuning I did under the winter, (swapped to a Holley 750 HP mainbody, increased the jets (with a lambda), changed the ignition timing a little bit)
But the different is when calculating the engine HP

enkeivette said:

25%? A bit optimistic don't you think?

Click to expand...

I don't really know what the drivetrain (alternator, pumps?) losses is supposed to be, 10 or 25% ?? or something between?
What is your experience?

Anyway, the maximum power should be around 6000-6300 rpm.
There must be some restriction somewhere.....where should I look?

gbak said:

Anyway, the maximum power should be around 6000-6300 rpm.
There must be some restriction somewhere.....where should I look?

Click to expand...

Look under the car, maybe somebody installed a catalytic converter :lol::lol:

Seriously: yes, with that cam and your AFR heads you should see more power at 6000rpm..... something isn't right....

I've always gone by 15% manual 20% max for an auto, add 2% for IRS.

Post yours specs so we can spot the restriction. Not familair with the XR280 cam. And I don't know which AFR heads you have.

ENGINE:
Block: 010 , +.060", decked to 9.015"
Heads: Trick Flow 64cc/195 cc #TFS-30400003-CNC
Headgasket: Mr Gasket 0.028 (quench dist 0.043") #MRG-1134
Pistons: Probe SRS 11.3 comp, forged for 6" rod, #12337-060
Rings: Perfect Circle plasma/moly #315-0033.065
Rods: Manley streetmaster 6" forged (weight matched to pistons)
Crank: Eagle ESP cast int balanced (rebalanced) #103503750I
Camshaft: CC Advertised Duration 280/ 286, Lift .570/.576, 242/248 at 0.050", #CCA-12-771-8
Manifold: Performance Products Typhoon (same as RPM, but will fit under my hood, matchported) #52020
Carb: Holley HP750 Carb: jets 72/84, Pw #6,5, shooters #31.
Lifters: CC Super roller #CCA-818-16
Roller rockers: Crane #CRN-11745-16
Push rods: CC Hi-Tech length 7.700" #CCA-7963-15
Timing kit: Cloyes Hex-A-Just #CLO-9-3100A

The rest:
Fuelpump/fuel lines: stock.
Exhaust: 2 1/2" - 3" "straight through" muffler.
Ignition: MSD dist, black bushing, 18* pre, 36* total timing, all in at 2500 rpm. Holley Anihilator 75 ign box, Accel coil.
Vacuum: 7 InHg/800rpm

Gearbox:
TH400, with modified governor, and adjustable modulator.

Rear ratio: 3.39

Drivetrain losses:
I guess the 25% measured last yer did included all losses, such as steering pump, alternator, fan.
Then it can be in the 25% area.

On the dyno last weekend the calculated losses can be seen at the bottom of the graphs, which is around 9% at top HP.

But as said before, the good thing is that I have 44 more HP on the rear wheels this time.

Can it be the dualplane manifold that is the bottleneck, it's rated up to 6000 rpm, Maby a Victor Jr would be a better alternative in my case?

What is the duration at .05? ...And the 20% includes accessory loss.

Still confused about your exhaust system. Do you have one single 3" pipe? Do you have equal length long tubes? How big are the primaries? High flow cat?

The RPM manifold is rated to 6K but I'd knock a few hundred off that realistically. Never heard of the typhoon manifold, if it's a cheap chinese knock off... well, enough said. The carb is kind of small too. You should have a 750cfm carb, if the 650 made more power, I would attribute that to tuning.

Camshaft: Duration at 0.050, 242 int./248 exh.

Carb:
Holley HP750, (was wrong in my spec)

Exhaust:
1 5/8" headers.
3" collector.
Dual 2 1/2" pipes.
3" muffler.
No cat.

Manifold:
Yes is a Chinese RPM copy, it's a "exact" copy of the Edelbrock RPM, just 1/2" lower.

Funny, when showing specs, the important ones are always missing. What is your ignition timing curve, and what is your a/f ratio plot?

Don't have any a/f ratio plot, I just can read the led's on my (homebuild) display.

The only thing I can observe is that the engine is running a little bit lean under hard acceleration, (shooters should be increased to 33 or 35) otherwise it's right on spot.

You can find the ignition timing in spec above.

gbak said:

You can find the ignition timing in spec above.

Click to expand...

Sorry, missed that. So, one more obvious question. Are you sure you retarded the cam, and not advanced it? (Sorry, gotta ask)

big2bird said:

Are you sure you retarded the cam, and not advanced it? (Sorry, gotta ask)

Click to expand...

I read a lot of articles and books before I did it, so yes I'm shure!

Even if I did advanced it, I wouldn't say it loud:
"I'm Bubba, and I did everything backwards!"


Acually I did the front sway bar backwards.
Ok, I did say it........

gbak said:

big2bird said:

Are you sure you retarded the cam, and not advanced it? (Sorry, gotta ask)

Click to expand...

I read a lot of articles and books before I did it, so yes I'm shure!

Even if I did advanced it, I wouldn't say it loud:
"I'm Bubba, and I did everything backwards!"


Acually I did the front sway bar backwards.
Ok, I did say it........

Click to expand...

:lol::lol::lol::lol::lol::lol:

Yeah that cam should want to spin a little past 6K, but those heads probably don't want to breathe that high. Those are good heads, but you have a little too much cam duration for them. Your 1 5/8" primaries are not ideal, but not a huge concern. Your 2 1/2" pipes are too small. And I'm willing to bet your manifold is choking you out, step up to a Victor Jr. don't risk it again with a chinese copy! You can buy a used one on E-Bay for about $135, and port match it.

And I'm still confused about whether you're running a 650 or a 750 carb. I would have gone with a 750. Not sure about retarding the cam, I would have left it alone. How is your timing set?

I'm not convinced that the manifold is all that big of a problem. I am running the Edelbrock Performer and although it is designed for lower rpm range it still has plenty of power above 4000rpm. That RPM copy should pull to 6000 without problems, unless of course it's a bad copy and very restrictive....

I did have a milled 650 dp last year, but swapped the mainbody in it to a HP 750 and used the old parts from the 650, instead of buying a new carb.

MYBAD79 said:

...unless of course it's a bad copy and very restrictive....

Click to expand...

:quote: :smash: