Disappointing day on the dyno

[Sweet5ltr]

Who the hell is AndyF

Just the guy who wrote the book on how to build high-performance B/RB engines.


https://www.amazon.com/How-Build-Ma...&keywords=how+to+build+high+performance+mopar

 

[1967coronet440]

Just the guy who wrote the book on how to build high-performance B/RB engines.


https://www.amazon.com/How-Build-Ma...&keywords=how+to+build+high+performance+mopar

I actually have that book and never looked at the author I guess

 

[Brewzer67]

I know that guy. He’s a crazy Canadian! Wait.... that’s me!
Glad my build is helping and inspiring others on the board. Remember my motor is 13.5-1. Not at all a pump gas friendly motor. That said the same combo with less compression should be very close to 800.

Thanks. Your build is definitely inspiring. I was very glad when the ported numbers on my 270's came out to what they did. When I had them ported there weren't any ported 270 numbers available so all I could do was hope. The near 800 mark is what I'm looking for. And for the record, some of my best friends are crazy Canadians!

 

[Bobo]

Hopefully someone can make me feel better. I took the Coronet to a dyno days event with the new combo and numbers were WAY below what I would have expected (see photo for dyno sheet). The motor in question is my 526" (4.375 x 4.375).
My combo is as follows:
10.78:1 cr
Custom ground 262/[email protected] .715 lift Solid roller bullet cam
TF 270's (ported by Larry Smith - see flow sheet)
Indy 4150 max wedge port single plane intake (also ported by Larry)
850 mighty demon carburetor (factory jetting with 35PV)
Ultimate 8.5" 3800 stall converter just built by Lenny for my combo.

I know I am handicapping the combo with the carb but I did not expect the numbers to be that low. No way would I ever have expected the max torque to be less than 500 ft. Lbs.

The dyno guys said the numbers are low due to the converter and the dyno can't accurately reflect the true numbers because of the high stall. I watched several other vehicles that I know weren't as built as mine laying down better numbers. Can someone educate me on where they think the problem is? I will run a compression check tomorrow to make sure everything is sealing but I don't think that is the issue. I am also surprised by how low the torque peak occurs.

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[68 HEMI GTS]

I would caution about putting a bigger carb on your engine...think it will be a waste of money.

I love it when people that know nothing about high hp engines feel the need to give advice.

 

[66Satellite47]

Very interesting thread. In 40 + years of racing, I've only had one motor, my current one, on a dyno. I always used the drag strip. I have no idea how much difference there is between a chassis dyno and an engine dyno. Those numbers are way low compared to what I would expect. My new 512 did above 690 HP with a fairly small cam, & bone stock 850 Holley at over 700 FT/lbs on an engine dyno. A deep investigation into the motor is likely needed. A bigger carb sure does seem required, but I'd look a little deeper.

 

[Cranky]

Years ago....1979? ...my brother's '69 GTX nylon timing gear failed. We had no money, trying to get through Texas Tech paying our own way...He paid a local rebuilder to rebuild the engine...think the builder bored it out .030. something like that. After everything was done, the engine would start and run, everything seemed fine, but nowhere near the power of the stock engine. On the dyno it showed 125 HP at the rear tires?! ...Before, it would set the tires on fire. After the rebuild, barely spin at all. And I have seen that many times when a rebuilt engine with bigger cam, cubes what ever and it just doesn't produce. Very disappointing. Also two engines built to same specs, one produces great power the other one nothing close.
I would caution about putting a bigger carb on your engine...think it will be a waste of money.

Unless you know exactly what the rebuilder used in it, this post isn't going to shed much light on the subject. Most 'local' rebuilders use low compression pistons along with thicker composition gaskets vs what the factory used in an X. Also, ALL stock big blocks came with thin steel shim head gaskets. In 69, the 440 was running just a hair over 10-1 compression with a decent cam. Your rebuilder engine most likely ended up with 8-1 or worse and a worse than stock cam. Sure, a bigger carb isn't going to do much on a worse than stock GTX engine that can barely turn 5000 rpm but we're not talking about a local rebuilder engine here. There are just so many things that a local rebuild isn't going to do to make sure the engine will run at it's full potential....

 

[66Satellite47]

Gee, sounds like the rebuilder may have the cam one tooth off.

 

[Cranky]

Gee, sounds like the rebuilder may have the cam one tooth off.

That's the problem with using the dot method of cam alignment. You just don't know where you are with it and it only has to be off several degrees for it to be off enough to affect performance. You never know if the cam has been ground off a couple of degrees or if the sprockets have been machined off a couple.....or the dots are not marked perfectly.....the tolerances can stack up. I degree ALL engines no matter if they are bone stock or not. That way I know exactly where the cam is and it gets rid of that question why it isn't running good. You can look elsewhere. I've seen it happen too many times where people chase their tails for weeks and finally look at the cam timing only to find it's off.

 

[66Satellite47]

I do too. I've a timing set that tricked me. Set things, looked good, but when I put the dial indicator on things, one tooth off.

 

[Brewzer67]

Yeah, I had a Cloyes set once that was off by 5 degrees. I had degreed the cam with a single chain and then ran into a little extra cash so I was able to pick up a double roller before buttoning it up. I lined the new one up to the old one before removing it and you could see it was clearly off. The first chain was spot on. When I put the new chain on it was off by 5 degrees. I re-did them both dot to dot just to make sure I hadn't moved something accidentally. Nope, it was off. That was the first and last Cloyes set I ever bought. Now I only use ProGear and have never had an issue yet. The Bullet cam I have in now is a half degree off as near as I can tell with the smaller degree wheel I use so that is close enough for me.

 

[dvw]

A number is just a number. Watched a car this weekend that dynoed well over 900hp, 3600lbs yet the 1/8 mile ET/MPH indicate it would run maybe 10.0. That indicates about 700hp. So how happy is he with that dyno slip? Not very. Dyno numbers, flow numbers are just that, numbers. Plenty of big numbers thrown around. Even a few Engine Masters motors. The proof is in the pudding. How quick and fast is it? That's what matters.
Doug

 

[Fisher]

Dyno's can be made a little happy if the operator knows what he is doing. We have seen some motors come to Canada from the USA with a dyno sheet brand new, that made 150 HP less on our dyno here. That 150 hp must of been left at Customs. HAHAHAHAHA. I love cylinder head numbers and the debate which that starts too. Oh bigger is way better, lol well we dont race flow benches either.
Now having said that, a dyno number is just that a number. How will that motor work in the car with the converter trans and gear ratio. Its a complete package with lots to consider between parts, car chassis, fuel system, etc.

 

[bobtile]

A number is just a number. Watched a car this weekend that dynoed well over 900hp, 3600lbs yet the 1/8 mile ET/MPH indicate it would run maybe 10.0. That indicates about 700hp. So how happy is he with that dyno slip? Not very. Dyno numbers, flow numbers are just that, numbers. Plenty of big numbers thrown around. Even a few Engine Masters motors. The proof is in the pudding. How quick and fast is it? That's what matters.
Doug

I was on the opposite end of the spectrum with my GTX.
it was dynoed at 392@ wheels weighing 3690.
I was kind of disappointed with that number but ran 11.20 @ 121 on track.
I'll take the track performance over a dyno # any day.

 

[66Satellite47]

Over the years I've so many folks tell me about their dyno numbers. OK. My dyno number is on the time slip.

 

[Brewzer67]

I was on the opposite end of the spectrum with my GTX.
it was dynoed at 392@ wheels weighing 3690.
I was kind of disappointed with that number but ran 11.20 @ 121 on track.
I'll take the track performance over a dyno # any day.

Ditto. I am pretty sure this is how it will play out for me too. It will be fun to say I have a low 10 second car that only dynos at 400 hp. I should be able lull a few of those import boys into a false sense of security

 

[Cranky]

Never had an engine or a car on a dyno...

 

[68 HEMI GTS]

After watching your dyno pull that motor is smoking really hard out of the left tail pipe. I gotta wonder if it’s possibly got an internal issue going on.

 

[Brewzer67]

After watching your dyno pull that motor is smoking really hard out of the left tail pipe. I gotta wonder if it’s possibly got an internal issue going on.

I don't think so but wouldn't rule it out. I just redid the top end with new heads and the short block only has 1500-2000 miles on it. I did run a compression check and leakdown since the dyno runs and everything looked pretty good. I didn't write the numbers down unfortunately but the low on the compression check was something like 187 or 188 with a high of 194. Leakdown was less than 5% on the worst cylinder. There is still a lot of crap left in the exhaust from the prior heads. They were some Stage 6's that were allowing a bunch of oil past the valves. I also had a Wagner adjustable PCV on that day that I did not adjust yet so it could have been pulling some oil when it went to high vacuum when they let off the throttle. Plugs also didn't look bad (pictures of the two worst). I'll take a peek with my borescope to see if anything looks out of place. I also confirmed I'm not using any water from the radiator so there are no signs of head gasket leakage. I am still leaning towards having over powered and blown through the converter, and being under-carbed. The fact that it nose dives right at the expected stall is pretty suspicious.

 

[68 HEMI GTS]

I don't think so but wouldn't rule it out. I just redid the top end with new heads and the short block only has 1500-2000 miles on it. I did run a compression check and leakdown since the dyno runs and everything looked pretty good. I didn't write the numbers down unfortunately but the low on the compression check was something like 187 or 188 with a high of 194. Leakdown was less than 5% on the worst cylinder. There is still a lot of crap left in the exhaust from the prior heads. They were some Stage 6's that were allowing a bunch of oil past the valves. I also had a Wagner adjustable PCV on that day that I did not adjust yet so it could have been pulling some oil when it went to high vacuum when they let off the throttle. Plugs also didn't look bad (pictures of the two worst). I'll take a peek with my borescope to see if anything looks out of place. I also confirmed I'm not using any water from the radiator so there are no signs of head gasket leakage. I am still leaning towards having over powered and blown through the converter, and being under-carbed. The fact that it nose dives right at the expected stall is pretty suspicious.

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Ok, I agree. Sounds like your all over it!