2x4 tuning - Flatlined chassis dyno
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?
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.
Looks to me like it's running out of lungs.
Yep, degreed cam at 4. The carbs are race 450's. Kind of thing I'm running out of carb.
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?
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..)
You do not size carbs for a tunnel ram like grandma's grocery getter.
Those carbs are all wrong.
The quality of the Port job on the heads can be an issue.
Ported leaves a lot of room for interpretation.
A stock non ported camel back head should be running faster.
I see three strikes against this car right away. 450 holleys, flowmaster mufflers, th700r4 trans.
There may be more issues, including the heads.
The low MPH says it all. And the ET x MPH factor says the motor wants to go but is choked/limited or something is severly robbing power output above 3500rpm.
Did you leave a shop rag in the intake manifold and or is the transmission slipping/converter fubared?
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..
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.
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.
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!
I'd put a couple of nitrous plates on it and let it eat! :D
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?
Tranny::: That doesnt tell you anything. it still can be fubared.
and may be. These tranys have big issues.
My car picked up big time when I ditched the lame th700r4 for a th-350.
th700r4s are dogs. I don;t care who built it. Or how much it cost.
A power robbing internal trans issue is very common.
With only 3.90 gears why do you need overdrive?
This motor wants to rev ...OD is useless on this motor.
Flowmasters suck. get something else. anything else. Magnaflow, dynomax.
uncap it you'll see. Every other muffler on the market is BETTER.
Lock out the distributor 36deg locked fixed timing. Why are you asking at what rpm? The thing does not move with rpm when locked.
Its 36deg BTDC all the time. Get a ignition power interupt switch so it don;t "kickback" Be sure the GM starter motor brace/bracket is installed.
Lock out the emch advance and set the locked timing at 36deg BTDC
simple--- it will idle and drive much much better and launch harder.
Ditch the 450 carbs. thy are way too small and all wrong for a T ram. 650-750cfm
1.8 60ft is lame, that converter isn;t working. the car is leaving like a snale
the locked timing will help.
88.83MPH equals 113MpH in the 1/4 mile.
that 1/8th mph x 1.27 equals 1/4 mph.
That means something is sucking the hell out of the horsepower.
Typical of a th700r4 that hasa internal issue or fubared torque converter.
typical of a tunnel ram with those carbs on it.
typical of excessive exhaust restriction ( flowmasters)
you are missing 100hp and 10+++MPH the 1/8th to 1/4 mile MPH
possible fuel starvation. pressure means nothing without flow.
flow test your fuel system thru a test orrifice (after you ditch the carbs)
"I rarely get into third at the track" I guess not..... the motor is dying half way down the track. 101MPH should be 113++++++.
Are you sure there is not a rag or two in the intake manifold?????
this car should be going mid 11's at 115+++++MPH.
M/T says not to run their tires after being on a dyno
Don;t blame them at all. The dyno rollers are very hard on tires. Big point of friction and heat
(loss of energy)
But in this case the dyno test and drag test time slip agree. Something is eating all your horsepower.
These are areas I would look at. don;t overlook basic engine problems like ignition etc etc.
When you find the problem and fix it, and ditch those choking carbs and mufflers the car should run 115 to 117MPH in the 1/4 mile.
@117MPH with 30" M/T's and 3.90 gears, it will only be reving 5475RPM .
This motor wants to rev 6800+ rpm thru the traps @117MPH that means you need some
4.88 to 5.13 gears (30" tall tires) Put some gear in it.
This car must be about as much fun as watching paint dry.
With 5.13:1 gears..... NOW you got a reason to have a overdrive transmission.
Until you get some 4.88+++ gears there is no useful purpose for overdrive, in this car, with that high reving motor.
With 30" tires and only 3.90 gears YOU ARE ALREADY IN OverDrive as far as this motor is concerned.
with the right changes this car is a easy mid 11 sec @115-117MPH all street trim car.
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