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Fang16 11-03-2012 10:13 AM

2x4 tuning - Flatlined chassis dyno
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Had my 355 sbc 41 Willys on a chassis dyno. Didn’t do any tuning at the dyno, just wanted to see how my ear n eye tune was doing. I was somewhat surprised to find the read out flat lined at around 4200 RPM. Max power is 319.4 and torque is 389.8. It runs good and turns back to back 12.4s @ 101. Specs are: 355 sbc, 11:1, comp cams xr292r kit, roller rockers etc, ported 2.02 double humps, 2x4 Holley 450 cfm, mechanical secondary’s on a Wieand tunnel ram. 1 5/8” gasser headers down to 2 ½” flow masters. Full advance 36 degrees @ 3000, 700r4, 390 gears, M/T et street radials at 30”, Race weight is 3257 lbs.
I’m thinking I need some tuning or even bigger carbs, maybe 650 double pumpers as I feel it wouldn’t have enough vacuum to run vacuum secondary’s at the track. I’ve included a pic of the dyno sheet and as you can see the a/f ratio looks pretty good which is what throws me off and leaves me at a loss as to what to do.
I ordered a LM-2 meter to help with tuning, which raises a question, with a true twin exhaust (no X pipe, etc) is there a need to take readings from both exhaust? Thinking about getting there clamp on exhaust pipe tool also, the one that slides into the tailpipe. Is it needed?

hcompton 11-03-2012 11:01 AM

Thats is a strange looking dyno graph but it looks like a flat power curve. It maybe carbs just choking out.

When you installed the cam did you degree it to make sure it was installed at zero. I am wondering if its not a few degrees off.

Carbs may need to be upgraded not sure about holley 450cfm are they race style carbs or small street setup for hotrods that dont need dual carbs. That may be an issue.

Greg T 11-03-2012 12:00 PM

Looks to me like it's running out of lungs.


Fang16 11-03-2012 12:57 PM

Yep, degreed cam at 4. The carbs are race 450's. Kind of thing I'm running out of carb.

E.Furgal 11-03-2012 01:47 PM

not so sure the carbs are the issue...
2 450's is more than enough...
I'd point finger at the camels

and maybe lack of signal to the carbs.. (ie the intakes to big for those heads..)

E.Furgal 11-03-2012 02:10 PM

900 cfm is a choke with heads that even ported by a pro will be hard pressed to use 900 cfm.. anywhere near the rpm that his power flat lines..
the heads ports are the choke, and the huge intake area isn't helping that fact
I'm willing to bet it'll make more power everywhere with a single plane and one 450 than whats on it now..
then put a 650 on that single plane and make even more..

tunnel ram 4500-8500 rpm..
way to big..

hcompton 11-03-2012 03:46 PM


Originally Posted by E.Furgal (Post 1606549)
900 cfm is a choke with heads that even ported by a pro will be hard pressed to use 900 cfm.. anywhere near the rpm that his power flat lines..
the heads ports are the choke, and the huge intake area isn't helping that fact
I'm willing to bet it'll make more power everywhere with a single plane and one 450 than whats on it now..
then put a 650 on that single plane and make even more..

tunnel ram 4500-8500 rpm..
way to big..

Well if you look at this a diferent way those haeds made more power in stock engines from the factory. So to say its the heads i would say they are not the issue. They are also really good heads. Most aftermarket heads start with the double hump design and add metal to allow for different port shape known to flow better. But you can make them flow pretty dam good as they are. But even with just simple clean up they wil flow enough for 450+ hp.

But two 450 cfm carbs dont flow 900 cfm. Closer to 700 and maybe not so good at that. Depending on choke plates and type of choke used. Cfm rating is just the hole not the carb measured.

Edelbrock 1405 are pretty cheap on ebay used or new. Manual choke can be removed for a little more cfm if need be. Easy to tune and little restrictions. Might be able to get some support on signal needed and low speed tuning. Even before purchase. You can run a sales rep around a little to find out what you need to buy to make it all work correctly.

hcompton 11-03-2012 03:51 PM

Victor manifold and a dominator is what will fix it for sure. Thats setup can be good for 500+ with msot dominator flavors. Even the victor jr is pretty well matched for the cam.

Fang16 11-03-2012 04:06 PM


Originally Posted by F-BIRD'88 (Post 1606534)
I would expect a lot higher MPH ( limited choked off horsepower) and the dyno shows that too.

Those tiny carbs that were never intended for a tunnel ram are killing it.
650-750 double pumpers or two 750 edelbrocks. There may be more,other issues killing off the top end too.
Peak engine HP should be in the 6500-6800rpm range.

Chassis dyno can show issues with trans converter, trans internal friction, trans High gear clutch/hyd fluid issues
common to th700r4's at high rpms. Tires can have a big effect on Chassis dyno HP. Exhaust system Flowmasters are one of the worst mufflers. Cars always run faster when these are uncapped. Again tunnel rams need to breath deep. Restricted carb and restrictive mufflers kill it.

correct valvesprings? fuel system flow volume @ WOT.

Start by ditching those carbs. A tunnel ram needs to breath deep.
Your car should be running 115MPH ++ I build junk krylon rebuild 355's with ported 305 heads that run faster.

Lock out the distributor mechanical advance . It will idle and run a lot better.
You are missing at least 10 MPH. what is the 1/8th mile ET and MPH? 60ft?

For sure ! I knew that 4200 wasn’t right. Lol The tranny is a maddog build with vette servo etc, 3500 stall from maddog also. I rarely get into third on the track. M/T says not to run their tires after being on a dyno so I put some 15’s on that I had laying around. They were a good 2” shorter in height
The flowmasters are the 10 series, still bad? What would you suggest? Comp roller springs, lifters, rocker arms. Running 6 lbs fuel pressure with ele pump and ½” lines. Doesn’t feel like it’s starving for fuel but may be right on the verge? Will uncap the headers at next track time.
MSD 6al and distributer, still lock out the advance? Mechanical - no vacuum advance. To be sure, ur talking bout locking it to full dist advance? What should total be, at what RPM? 2-3 degrees under kick-back?
1/8 mile: 7.8578 @ 88.83 mph 60ft. 1.8 then it took 4.5 seconds to ¼ mile ! LOL
Been away from it for a long time, read a lot of your responses and I’m impressed by your knowledge. Thanks for your help!

wwilliams181 11-03-2012 05:22 PM

I'd put a couple of nitrous plates on it and let it eat! :D

vinniekq2 11-03-2012 06:55 PM

what happens to your fuel pressure? 13.5 is lean but acceptable,just wondering if the fuel volume is adequate? low 12s at 101 is not very good horse power wise but very good et wise.Its acting like a very small engine for mph but et indicates it jumps off the line? whats your 60 foot time? cam specs? time on valve springs?

Fang16 11-04-2012 06:17 AM


Originally Posted by F-BIRD'88 (Post 1606687)
In a previous thread you said the car ran 107MPH.... Which is it 101 MPH or 107 MPH?

That was a one time thing. Never happened again. Turned a lot of 101's.

E.Furgal 11-04-2012 10:43 AM

not fer nothing.. but could you all be barking up the wrong tree..
the one lonely 107mph is telling me.. it might not be intake/fuel related, and yes I could be wrong.. as I'm here and his car is there..
but are the valves floating.. just a friendly guess..

Fang16 11-04-2012 11:11 AM

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Originally Posted by F-BIRD'88 (Post 1606812)
Some times you get a funky MPH on drag time slips.
I remember a long time ago my friend got a 130MPH on hs 12sec car once.
It does happen.

But from your numbers the car is wanting to go 113 Mph in the 1/4
but something is killing it.
What about the 1/8th mile data? what is the variance in the 1/8th MPH?
88.83MPH is a good 1/8th mile MPH (its at least in the program)
The car starts out well but flattens out at some point about 1/2 way down.

101 MPH sucks for that car. (there is a problem)

any 1000ft data? All this stuff can be analyzed. You definatly have a top end power robber, to find.
The air fuel ratio needs work. (those carbs suck on a T ram anyway)
(carbs-fuel system, (volume, limitiation))
could be spark scatter/crossfire. (ignition cap ionization, usually from too large plug gap and or too hot a coil, or poor cap/rotor phasing)
could be a fubared transmission or torque converter (no top end MPH)
could be a valvetrain issue.
The mufflers definatly suck- you will see from testing
once you find the other cork(s).

Your car should be running like a raped ape, but its got a problem.

Can you post the complete data from some time slips?

Per ur suggestion in another post I used irfanview to scan, resize etc trying to get this pic readable. Sure you can manage it. lol Seems I told a lie, or "misspoke" as the politicians say "lol" as u can see by the time slips. Hoping next year the track can afford some ink for their printer. hee hee Really apprecate your help.

Fang16 11-04-2012 12:30 PM


Originally Posted by F-BIRD'88 (Post 1606938)
A good suggestion...all these areas need to be looked at.

I've lost a few vavles in the past in cars and motorcycles. Doesn't seem to be any vavle float. Of course if they're not hiting anything. hee hee No really, don't seem to be.

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