Author Topic: 355 HP...really  (Read 4358 times)

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Offline Vcode

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Re: 355 HP...really
« Reply #15 on: September 24, 2018, 08:14:03 am »
The stroke call out must be a typo 3.394?
428's are 3.98
'69 Mach 1 SCJ

Offline RoyceP

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Re: 355 HP...really
« Reply #16 on: September 24, 2018, 08:45:36 am »
The dyno sheet ells the tale. Stock these engines have 10.5 to one compression. Yours has been lowered to 9:1 in order to be able to use the 91 octane fuel that was used for the dyno run. It says timing was 28 degrees, that alone would knock off 15 - 20 horsepower compared to the stock setting of 40 - ish degrees.

So you are probably losing 30 - 40 horsepower from the lowered compression / lousy gas.
Another 15 - 20 from the timing being way retarded.
Probably 10 horsepower loss due to rich jetting on the carb.

The cam might be another problem, it falls off in power really early compared to a stock cam. Maybe the cam timing is retarded for some reason? It looks to me that this engine could make better power if it were tuned and maybe a different cam installed. 
1910 Model T Ford Touring Red
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1968 Mercury Cougar XR-7 GT-E Green 427 W Code
1968 Mercury Cougar XR-7 428CJ R code 3.91 C6

Offline Jiffy

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Re: 355 HP...really
« Reply #17 on: September 24, 2018, 08:53:35 am »
If that’s a ‘racing cam’ then it seemed to fall over pretty early, everything was done by late 4,000’s and I’d have thought that there was more head room in a ‘racing cam’

Offline crossboss

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Re: 355 HP...really
« Reply #18 on: September 24, 2018, 09:31:44 am »
I also see some issues. As mentioned the cam/valve springs, AND Pertronix ignition (junk). During my 'tuning' days with my CJ, I had installed a bad camshaft grind that would not rev past 4200. Swapping in a 'good' cam, it picked up over a half a second and approx 4-5 mph the drag strip (that equates to about a 30HP difference). Btw, my engine also had 9.5 to 1 compression for street pump gas, with jetting @ 66/76, so in my opinion your good there. I believe some 'tuning' is in order to achieve better results.
<My old C.J. heap  aka  S-B Racing!
Current lifelong project: 1969 Mustang Fastback/FOX chassis, Powered by a modern Can-Am 494 (Boss 429), Kaase headed, Autolite 1425 cfm 'B' Inline carb, 6 speed, 4 wheel discs, ala Trans-Am style--Whew!

Offline 428 CJ hardtops

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Re: 355 HP...really
« Reply #19 on: September 24, 2018, 04:32:53 pm »
The dyno sheet ells the tale. Stock these engines have 10.5 to one compression. Yours has been lowered to 9:1 in order to be able to use the 91 octane fuel that was used for the dyno run. It says timing was 28 degrees, that alone would knock off 15 - 20 horsepower compared to the stock setting of 40 - ish degrees.

So you are probably losing 30 - 40 horsepower from the lowered compression / lousy gas.
Another 15 - 20 from the timing being way retarded.
Probably 10 horsepower loss due to rich jetting on the carb.

The cam might be another problem, it falls off in power really early compared to a stock cam. Maybe the cam timing is retarded for some reason? It looks to me that this engine could make better power if it were tuned and maybe a different cam installed.


If it only had 28 degrees the hp loss would be more like 75 hp maybe more .Have seen the difference at the track and its huge .
had many 428 CJ and SCJ cars over the last 30 years.I currently own a 68 1/2 coupe and a 69 R code SCJ Coupe and a 70 R code SCJ Cougar Eliminator .I am looking for a 70 428 coupe if anybody knows of one for sale.

Offline Richard Todd

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Re: 355 HP...really
« Reply #20 on: September 24, 2018, 08:54:07 pm »
When I first saw your dyno sheet the issue I feel that is most important is that your valve springs are too week to control the valves. Your valves appear to start bouncing on the seat at around 4200 RPM and by 4800 RPM the valves are in full float. I have seen this many times over the years on my dyno and you need to address this problem now before you damage your engine. This problem is very hard on your valve locks (keepers) and the end result is never good. My first suggestion would be to contact the company who made your cam and see what springs they recommend. You might also post your cam card to let us know what your running. The valve springs must be installed at the correct height and seat pressure to be effective. Changing valve springs although time consuming is not that difficult especially with the engine out of the car. If you have to pay to have it done it will be money well spent.

Offline geraldt52

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Re: 355 HP...really
« Reply #21 on: September 24, 2018, 10:45:27 pm »
When I first saw your dyno sheet the issue I feel that is most important is that your valve springs are too week to control the valves. Your valves appear to start bouncing on the seat at around 4200 RPM and by 4800 RPM the valves are in full float...

It begs the question if the engine builder may have intentionally used weak springs for the purpose of breaking in the cam, with the expectation that they'd be changed out before a full rpm test was run.  It's hard to imagine those are the springs recommended by the cam manufacturer.

Offline markharvey9077@gmail.com

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Re: 355 HP...really
« Reply #22 on: September 25, 2018, 01:07:24 am »
thanks for all the comments...I will get the information and post it...I am a novice engine builder so I outsourced it...

Offline Richard Todd

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Re: 355 HP...really
« Reply #23 on: September 25, 2018, 07:18:04 am »
After my post I flipped thru my old dyno files and I found a test session I did on a 390 which had a similar problem. When I tested the spring pressure they were all good with the seat and open pressure within 10 lbs. of spec. The HP numbers seemed low and it was done by 4500. I replaced the rocker arms with a set of stock Ford adjustable rockers and push rods an adjusted the valves to 0 lash plus 1/8 turn of preload and it cured the problem. The engine ran to 6000 RPM an picked up 55 HP. With the stock non adjustable rockers the pushrods had to much preload in the lifters and as the RPM and oil pressure increased the lifters pumped up and held the valves open. 99 times out of 100 its a valve spring problem but this time it was not. My point here is you need to test the springs before you do anything else. What rocker arms are you running on you engine?

Offline lr68cj

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Re: 355 HP...really
« Reply #24 on: September 25, 2018, 10:36:34 am »
Losing 100 hp from 4700 to 5200 sound like valve springs to me. Hydraulic cam should rev to 6200 with no issues. Torque should fall off after 5252, but hp should still be going up or at least leveling off. Had a 351c of mine on the Dyno and wouldn't rev past 5500. Springs we're bouncing all over the place. Not enough spring pressure closed or open. First place I'd look. My 2¢.

Offline geraldt52

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Re: 355 HP...really
« Reply #25 on: September 25, 2018, 12:01:33 pm »
... With the stock non adjustable rockers the pushrods had to much preload in the lifters and as the RPM and oil pressure increased the lifters pumped up and held the valves open...

I've never heard of that, but I don't doubt it and it's really interesting.  You probably don't remember, but had the deck and heads on the engine been heavily milled?  Was there a high pressure oil pump involved?  Were the valve stem heights within specs?

Offline Richard Todd

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Re: 355 HP...really
« Reply #26 on: September 25, 2018, 02:13:33 pm »
Don't know how much the heads and deck were cut on the 390. I was not involved in the build, just the dyno test. The oil pressure did run in the 80-90 psi range which I considered too high but the engine is still running strong. I did not check the valve stem heights as the owner had asked me to try to make what was there work if at all possible. Since shimming the rocker stands on a street/strip engine did not seem to be a sound option I went with the rockers. I agree that 99 out of 100 times it will be the springs but my point of this post is that the springs need to be checked before replacing them just to be sure.

Offline geraldt52

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Re: 355 HP...really
« Reply #27 on: September 25, 2018, 03:29:59 pm »
... the owner had asked me to try to make what was there work if at all possible. Since shimming the rocker stands on a street/strip engine did not seem to be a sound option I went with the rockers...

I'm not questioning that choice at all.  Shorter pushrods could have been used, but the adjustable rockers would have allowed you to play with/diagnose it, while pushrods have to be ordered to a specific length.

Offline Richard Todd

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Re: 355 HP...really
« Reply #28 on: September 25, 2018, 04:56:19 pm »
So true about the push rods but I did not have the luxury of time. I had 3 sets of bushed adjustable rockers left over from my FE stock class drag car and a large number of good used push rods so it was a no wait option. When I had to halt a session to order parts I would have to remove the engine from the dyno for the next job then put it back on when the parts arrived. Lots of extra work which some time you have no choice but if I could find a way around it without compromising the quality I would take it. He got a great deal on the parts.

Offline markharvey9077@gmail.com

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Re: 355 HP...really
« Reply #29 on: September 26, 2018, 11:49:59 pm »
the cam is 214/224 duration 50 thou lift...520/546 valv lift...lod110....I asked for a modest cam that will have the sound but not a vacuum stall issue...I do not race...just pickup Chevy guy's wives...I iwll have the exhaust info in a day...I have the 735 holley with 68/72 jets..