1969 427 Disappointing Dyno Numbers
Thread Starter
Melting Slicks
Joined: Oct 2003
Posts: 2,077
Likes: 334
From: Dallas TX
St. Jude Donor '06-'09,'22,'25
1969 427 Disappointing Dyno Numbers
Had my recently rebuilt 427 dynoed last week and was a little disappointed at the HP numbers.
I think it's a little lean, but I was expecting a lot more HP.
Steve
I think it's a little lean, but I was expecting a lot more HP.
Steve
Team Owner
Joined: Jul 2001
Posts: 182,997
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From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
Stock 427? 427/390, 427/400, 427/435, 427/430?? Engine or chassis dyno?
If engine dyno, was the engine dynoed with the stock accessories attached?
Details on the engine please!
Don't forget that if you have a pre '72 engine or a crate engine that those engines are rated in gross HP. In addition to the drivetrain loss, you will have to consider accessory loss which can be 15+% depending on what accessories you are using.
If you are running stock exhaust with exhaust manifolds, you are dropping a large amount of HP right there.. Mech. fans cost you another 10+ HP etc. etc.. Typical accessory loss on C3's is about 12%, but often even more. So, if you have a TH400 and all mechanical accessories, you can expect 25% loss through the drivetrain + 12% from the accessories = 37% loss!! With a TH350, that would be about 32% loss. With manual transmission, it would be about 25 - 27% total loss..
Assuming that you have a 427/390.. If you dynoed on a engine dyno WITH the accessories attached, your dyno results should be 12 - 15% lower than the rating of the engine as the engines before 1972 have been rated gross and they were dynoed with open headers and no accessories.
390 HP - 15% = 331.5 HP
If engine dyno, was the engine dynoed with the stock accessories attached?
Details on the engine please!
Don't forget that if you have a pre '72 engine or a crate engine that those engines are rated in gross HP. In addition to the drivetrain loss, you will have to consider accessory loss which can be 15+% depending on what accessories you are using.
If you are running stock exhaust with exhaust manifolds, you are dropping a large amount of HP right there.. Mech. fans cost you another 10+ HP etc. etc.. Typical accessory loss on C3's is about 12%, but often even more. So, if you have a TH400 and all mechanical accessories, you can expect 25% loss through the drivetrain + 12% from the accessories = 37% loss!! With a TH350, that would be about 32% loss. With manual transmission, it would be about 25 - 27% total loss..
Assuming that you have a 427/390.. If you dynoed on a engine dyno WITH the accessories attached, your dyno results should be 12 - 15% lower than the rating of the engine as the engines before 1972 have been rated gross and they were dynoed with open headers and no accessories.
390 HP - 15% = 331.5 HP
Last edited by GrandSportC3; Mar 24, 2008 at 10:46 AM.
Le Mans Master
Joined: Jul 2006
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From: charlotte north carolina
is it a more or less stock engine? look at that wide torque curve! don't be disappointed when a high hp engine posts their curves. by the time their engine gets going, you're home allready. you can drive that thing around in 4th gear!
jeff
jeff
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From: Reno Nevada
2024 C3 of the Year Finalist- Modified
Hey it might be just me also....... I always thought the famed LT1 was also a dog. Mostly because it is just a little 350 ci.
Last edited by gkull; Mar 24, 2008 at 01:36 PM.
Race Director
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From: Forked River NJ
Team Owner
Joined: Jul 2001
Posts: 182,997
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From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
Just looked at your sig and noticed that it's a 4-speed.. Considering that the numbers are that low, it must've been a chassis dyno. Do you know if the compression ratio was changed on that car (i.e. with dish pistons)??
Lower CR would definetely cost you some HP.. Based on my calculation, you should be in the 285 RWHP range with the 4-speed..
However, you might lose some more HP if your CR is a lot lower than stock..
Lower CR would definetely cost you some HP.. Based on my calculation, you should be in the 285 RWHP range with the 4-speed..
However, you might lose some more HP if your CR is a lot lower than stock..
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
Carb and distributor tuning may help increase that quite a bit (if it hasn't already been done). Just looks like a "weak" motor. If there are no mechanical problems with heads or pistons, changes in timing/timing curve and carb performance may make some sizeable gains in HP/torque.
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Thread Starter
Melting Slicks
Joined: Oct 2003
Posts: 2,077
Likes: 334
From: Dallas TX
St. Jude Donor '06-'09,'22,'25
Yes, it's a 4-speed car, on a chassis dyno (LG Motorsports). The only accessory it has is the alternator. No power brakes, or power steering. It was converted to electronic ignition (no points).
In late 2005, it had a full $9,000+ rebuild...
Comp Cams CB XE 2744-10, with the following specs...
Gross Valve Lift: 0.552 Intake, .555 Exhaust
Duration at .006: 274 Intake, 286 Exhaust
Valve timing at .006: 31 Intake Open, 63 Intake Close
77 Exhauist Open, 29 exhaust Close
Duration at 0.05: 230 Intake, 236 Exhaust
Lobe Lift: .325 Intake, .327 Exhaust
It has Pro Mag rockers, forged pistons, and is .030 over. I don't know what the compression ratio is - I'll have to pull the paperwork and see if it's listed there.
The cast iron exhaust manifolds were put on because it made more torque with them, apparently.
In late 2005, it had a full $9,000+ rebuild...
Comp Cams CB XE 2744-10, with the following specs...
Gross Valve Lift: 0.552 Intake, .555 Exhaust
Duration at .006: 274 Intake, 286 Exhaust
Valve timing at .006: 31 Intake Open, 63 Intake Close
77 Exhauist Open, 29 exhaust Close
Duration at 0.05: 230 Intake, 236 Exhaust
Lobe Lift: .325 Intake, .327 Exhaust
It has Pro Mag rockers, forged pistons, and is .030 over. I don't know what the compression ratio is - I'll have to pull the paperwork and see if it's listed there.
The cast iron exhaust manifolds were put on because it made more torque with them, apparently.
Race Director
Joined: Sep 2002
Posts: 10,362
Likes: 5
From: San Diego - Deep Within The State of CONFUSION!
Yes, it's a 4-speed car, on a chassis dyno (LG Motorsports). The only accessory it has is the alternator. No power brakes, or power steering. It was converted to electronic ignition (no points).
In late 2005, it had a full $9,000+ rebuild...
Comp Cams CB XE 2744-10, with the following specs...
Gross Valve Lift: 0.552 Intake, .555 Exhaust
Duration at .006: 274 Intake, 286 Exhaust
Valve timing at .006: 31 Intake Open, 63 Intake Close
77 Exhauist Open, 29 exhaust Close
Duration at 0.05: 230 Intake, 236 Exhaust
Lobe Lift: .325 Intake, .327 Exhaust
It has Pro Mag rockers, forged pistons, and is .030 over. I don't know what the compression ratio is - I'll have to pull the paperwork and see if it's listed there.
The cast iron exhaust manifolds were put on because it made more torque with them, apparently.
In late 2005, it had a full $9,000+ rebuild...
Comp Cams CB XE 2744-10, with the following specs...
Gross Valve Lift: 0.552 Intake, .555 Exhaust
Duration at .006: 274 Intake, 286 Exhaust
Valve timing at .006: 31 Intake Open, 63 Intake Close
77 Exhauist Open, 29 exhaust Close
Duration at 0.05: 230 Intake, 236 Exhaust
Lobe Lift: .325 Intake, .327 Exhaust
It has Pro Mag rockers, forged pistons, and is .030 over. I don't know what the compression ratio is - I'll have to pull the paperwork and see if it's listed there.
The cast iron exhaust manifolds were put on because it made more torque with them, apparently.
Drifting
Joined: May 2001
Posts: 1,651
Likes: 13
From: Holly MI
I am looking at my dyno plot right now from when my 427/390 was rebuilt. The guy running the dyno didn't start recording until 3000 RPM, so he missed the torque peak. However, the numbers were 326 ft-lbs @ 3000 RPM and 214 HP at 4750 RPM. The curve looks almost identical to yours. This was on a Mustang chassis dyno.
My build was all stock except a slightly larger cam (smaller than yours); roller rockers; and an HEI. My carb was rebuilt by Lars just before this, but the timing curve was whatever the HEI gave me at the time. This was all breathing through the stock intake and exhaust; including the tiny 2" pipes.
I love driving the car, because I can cruise around in 4th all the time. It's not fast, but it's great for weekend cruiser. It has even seen about 5-6 track days without issue. When I rebuild the engine the next time, I will go for more power. Until then, I am very happy with my engine.
Ken
My build was all stock except a slightly larger cam (smaller than yours); roller rockers; and an HEI. My carb was rebuilt by Lars just before this, but the timing curve was whatever the HEI gave me at the time. This was all breathing through the stock intake and exhaust; including the tiny 2" pipes.
I love driving the car, because I can cruise around in 4th all the time. It's not fast, but it's great for weekend cruiser. It has even seen about 5-6 track days without issue. When I rebuild the engine the next time, I will go for more power. Until then, I am very happy with my engine.
Ken
Burning Brakes
Joined: Jul 2006
Posts: 830
Likes: 1
Totally... btw...HP/dyno numbers are waaaayyy out of reality in my OPINION. Only in the last 5-7 years have people really begun to "value" HP ratings.
FACT...My wifes VW or Saturn. They both "advertise" HP ratings of 225 to 245. "WOW...it's a race car" a general idiot on a car lot thinks. But, put it on a Mustang dyno & the car punched out 139hp... Parasitic loss & a bunch of bench-racing BS is what todays HP ratings are (mostly).
Last edited by OregonVette80; Mar 24, 2008 at 01:14 PM.
Thread Starter
Melting Slicks
Joined: Oct 2003
Posts: 2,077
Likes: 334
From: Dallas TX
St. Jude Donor '06-'09,'22,'25
But an advertised 390hp that actually dynoes 233 at the rear wheels?
It seems like 41% is a BIG parasitic loss. I will have it dyno-tuned and see how much of a difference it makes.
It seems like 41% is a BIG parasitic loss. I will have it dyno-tuned and see how much of a difference it makes.
Race Director
Joined: Sep 2002
Posts: 10,362
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From: San Diego - Deep Within The State of CONFUSION!
Le Mans Master
Joined: Apr 2007
Posts: 7,353
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From: Graceland in a Not Correctly Restored Stingray
Knowing your CR is going to tell us a lot. Regardless, if performance is a higher priority than correctness, IMHO the stock exhaust manifolds were a mistake. Also, I can understand an auto soaking up a lot of power, inefficient as they are, but just how much do you guys think a Muncie eats up, M20/21 and/or M22?? I've always thought a Rock-crusher only lost ~5%, but maybe I'm way off.
Melting Slicks
Joined: Dec 1999
Posts: 2,116
Likes: 156
From: Mid West
Cruise-In III Veteran
Is your carb. opening up all the way at WOT?? I had mine mis-adjusted once and I lost ~100 HP at the rear wheels. Man that was disappointing
.
Le Mans Master
Joined: Dec 2003
Posts: 5,727
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From: Fremont CA
Not really true, I've driven them. The 427/390 was a real dog. Big heavy boat anchor. Then add all these years in to the equation is why it only puts out 230 RWHP. Sub 300 hp at the crank. The TQ figures are also uneventful.
Hey it might be just me also....... I always thought the famed LT1 was also a dog. Mostly because it is just a little 350 ci.
Hey it might be just me also....... I always thought the famed LT1 was also a dog. Mostly because it is just a little 350 ci.
Race Director
Joined: Feb 2005
Posts: 16,100
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Most are disapointed first time around...Dyno tunning is key....then go from there...this takes some tweaking....
http://www.motorgen.com/vid/showphot...to/207/cat/510
http://www.motorgen.com/vid/showphot...to/207/cat/510
Burning Brakes
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Race Director
Joined: Sep 1999
Posts: 11,361
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From: Plano TX
Something is amiss.
Here's a rear-wheel (dynojet) dyno of my '71 454/365. At that time the car was bone stock except for a mild hydraulic flat tappet cam (219/229 dgr). It had stock exhaust manifolds and pipes.
Red curve: As purchased
Blue curve: Tweaked timing advance and installed K&N filter.
Here's a rear-wheel (dynojet) dyno of my '71 454/365. At that time the car was bone stock except for a mild hydraulic flat tappet cam (219/229 dgr). It had stock exhaust manifolds and pipes.
Red curve: As purchased
Blue curve: Tweaked timing advance and installed K&N filter.