Team Chevelle banner

468 BB dynos at only 266 at wheel. what to do?

30K views 144 replies 47 participants last post by  Gtogeoff 
#1 ·
New 468 BBC. after upgrading rear end to a 9" ford, i had it dynoed and was a little disappointed.

its components:
Dart block
Quick Fuel Brawler 850cfm carb
Edelbrock performer 2.0 intake
Procomp PC3021 heads.
HEI distributor

Cam specs, heads specs, dyno in pics below

It runs and drives just fine, but I can't get over what it dynoed.
I'm looking for advice re: what to do to maximize it's potential. within reason. New intake?, new heads?
 

Attachments

See less See more
5
#6 · (Edited)
it did get tuned, that dyno was the second run. First pass was 257hp and 317 lb-ft, afr 12.2
second pass was 266hp and 326 lb-ft

I apologize for my ignorance on some of this. I'm not super-mechanically inclined and i need some guidance

AFR at peak HP was 13.9
 
#10 ·
If it's just a feel good thing then add another 20% for parasitic loss. Second - add another 50hp to that number because your running alternator, water pump, power steering and air cleaner that rob the engine of at least that much hp.
Keep in mind, just about all of the dyno numbers posted here are at the crank. They dyno the engines BARE with headers and a velocity stack sitting on top of the carb, and then they correct the outcome for DA. if needed - for a bigger number.

As an add on question.. What is your calculated static compression?
 
#7 ·
Never apologize for what your haven't yet learned. Team Chevelle is here to help other enthusiasts. I think you either accept what you have and try further tuning or you go back to the drawing board and select other parts, OR you do some reading here on available builders and go that route. You'd be stunned at what you may find here with butt loads of power. Have Fun...
 
#14 ·
1st thing I would do is what Mr. 4speed suggested - make sure your getting 100% throttle opening. Next, I'd do a compression test with all the plugs out and a fully charged battery, and and see what you have. Hopefully, the'll all be the same # on all cylinders. And hopefully, they'll be above 150 or so. Closer to 180 would be nice.

I would expect high 300's/low 400's on a dyno but yes, Mustang dyno's read low compared to some others. Hopefully those heads arent screwed up.
 
  • Like
Reactions: Kirk's67SS
#15 ·
Also, hard to see on the dyno sheet but was the pull to only 5300? Could be alot of HP missing between 5300 and say 6100.....
 
  • Like
Reactions: Kirk's67SS
#17 ·
With with Gary on this one, but dont want to offend Jim as he may have paid someone called "professional" to build this rat. If the attention to detail in parts choices is also reflective in care of assembly, it may be about right. I hope the fellas suggestions find a tuning issue tho. Assembling parts is NOT building an engine folks.

Anyway, yes WOT and timing. Heads too big and when the small intake runners hit the big head port - guess what velocity does? Drop like a stone. Stupid bad. MUST be changed. You can go from big to small ( velocity jumps) , but NOT the other way. You need to un-dickify that ASAP in my mind. Plus, on top of it all sits an 850. Its what a 500-600 hp rat needs to shine BUT in this context, it make the intake velocity drop off even worse!

BET it makes a crap load more power with a 600 cfm on it, which would prove my runner issue/ charge velocity problem. And means it NEEDS a new intake to get 20-30 hp more.

Good news Jim, I'm a numbers guy, not an automotive or fluid dynamics engineer, so hope I'm wrong. I'd STILL try a much smaller carb, I think it would surprise you. Good luck and keep the commo going; these fellas will root it out with you. As said before, no dumb questions here sir, only questions to be answered.
 
#18 ·
It seems someone had to work hard to find a combo of parts that would make that little power. Heads are too big, intake manifold needs to be at least a good dual plane (performer rpm or air gap as mentioned before). I can't see the stuff the OP posted well enough to read any of it, so no comment on cam. I suspect tuning issues too. A set of decent factory stock heads would probably make more power, and definitely more torque. Do a compression test as soon as you can, that'll give us an idea how good or bad the cam choice is for the current setup.
 
#19 ·
Go to a Dynojet and gain 40 hp and feel better haha.

Seriously, Mustang dyno's often are upwards of 10% lower than Dynojet dynos.

Lots of good advice, I would certainly be looking for problems. WOT, Timing, all cylinders firing, compression test, etc, etc.
 
#21 ·
I may have been a little too blunt in my last post. I tend to be that way sometimes, not on purpose. If you selected the parts and built the engine, don't feel bad. You've come to exactly the right place to learn what you need to fix this and get the power you should have. If you paid someone to build this, you're about to learn what they did wrong. If this is the case, again, don't feel bad. We've all gotten burned by someone who misrepresented their knowledge at some point or another.
 
#22 ·
another question is what is the compression ratio? do you know what pistons were used. as said a cranking compression test would shed a little light on this. The reason I ask what numbers were on the intake is I'm not sure you can put an oval Port intake on Square Port heads. It seems like I remember the ports on the head being uncovered by the manifold. Maybe someone else on here can comment because I don't remember for sure
 
#24 ·
I think you have some good ideas here to check out. I would hope that the TQ and HP numbers would at least be equal instead of being down 60 points on the HP. If it has a Ford 9 inch the loss could be north of 25% depending on the stall converter. so a 25% total loss is actually a multiple of 133% (100/75). So 266 x 133% = 350 hp 326 x 133% = 437 tq. So you are definitely low on power somewhere. Like Mr. 4 speed said make sure throttle is opening all the way etc.
 
#25 ·
Depending what converter you have, a big amount of power is lost to a wheel dyno. And a Mustang is especially stingy.

Also, your intake choice is killing the engine. I bet a 50hp gain at the engine with a change to a performer rpm air gap for rect ports. You also MUST know what your total timing is. If the AFR starts at 13:1 range at full throttle at say 5000 rpm, but then leans out as the rpm increase, it could be the floats are too low, fuel delivery issue, or may just need a high speed air bleed change.

Also what exhaust do you have? Header size, and the rest of the system?

First thing I would do is change the intake, then have the timing curve tuned properly.
 
#26 ·
usually these dyno's are using a "sniffer" type AFR sensor which may read a little leaner than what it really is.
 
#27 ·
OP: Remember that your motor made those numbers....on that day.

But unless you quit now, your motor is not yet done. It's merely a work in process.

There is still a lot of room for improvement and some relatively inexpensive modifications you can make.

And don't think for a second that those of us whose cars are sorted out did so on the first try. Far from it.

I've had lots failure along the way....but that's how you learn.

Keep hacking at that big block........
 
#29 · (Edited)
Don’t let your results get you down, yes it has room for improvement, but it’s not the end of the world. What you discovered is far from unusual. More than a few people you will come across who are claiming 500-600 horsepower, would put up comparable numbers if their car ever saw a dyno. I’ve seen way too many cars with owners claiming those power levels run 15’s @ 90mph for it to be a fluke. Most are one and done, a few grind it out and make the changes to their combination to wake up their cars. There should be no “shame” associated with your results, you are among the minority that has put in the effort to try and support their talking points.

Steve R
 
#30 ·
Steve R is right on (as well as others in the same thought). Bravo for getting good data on the combo. You now have a place to start from.

I like to change one thing at a time and see the result...bit more in dyno time $, but absolutely confirms the improvement.

My first fun on my rebuilt 407 SBC with AFR heads was 273 WHP on a Mustang 250 dyno. Disappointment!

Then my fan belt popped off and gained 40 WHP! (found I was using a clutch fan without the clutch-direct drive)

Then pulled the cam and found my Comp Cams 282 Solid flat tappet was a rebox mixup (by Jegs) and actually was an emissions legal 305 hydraulic cam I was running solid lifters on! Wouldn't rev past 4700 RPM! With the 282...6700 no issues and now was up to 347 WHP.

Then switched to a CC 294 solid cam and gained nothing.

Then added AFR 220 heads, Straub hydro roller, etc....now at 450 WHP.

Again - glad you put it on the heartbreaker...could end up better than 90% of the combinations out there.

 
#34 ·
A totally stock LS6 Chevelle dynos 290 rwhp and like 320 tq at the tire (Super Chevy Feb 2011). The reason it is a little low (after factoring in driveline loss of say 25%) from the 450 hp advertised is GMs number is based on headers. You pop headers on it and you will see another 30-40 more. A Ford 9 inch you can take 20 off that number (less effecient). A chassis dyno or the drag strip will tell you if something is off. Like some of the people said could be not opening all the way on the carb miss-match of parts etc. This is just a starting point for you change some parts pick up 50 hp realize the carb was only 7/8 open another 30 hp etc.
 
#35 ·
I was thinking about this a little more, but just to show you cant put too much thought into these dyno's, my Mustang on a Mustang (how funny is that) made 490 rwhp. But at the track, the Wallace calculator based on mph shows 638 rwhp. Quite a difference. Just the #'s the dyno operator punches in can skew results, tire slippage, torque converter etc.
 
  • Like
Reactions: Dkar26
#42 ·
Had a similar thing happen with my mustang-dyno said 546 hp, wallace calculator said about 620. My 7100 lb dually trapped 98 mph, dyno said 450 hp, wallace says 514 hp. It's quite possible that the dyno your car was on reads really low, though it's still true that your engine needs some sorting out.
 
#36 ·
My only 2 cents is, with an 850, probably not a throttle not opening fully issue. If it is, it should have been severe enough to be obvious to whoever tuned it.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top