Low HP on Dyno
05-04-2009, 01:17 PM
#1
Thread Starter
Join Date: Jul 2006
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Posts: 25
Low HP on Dyno
Hello everyone,
This past Saturday was spent at the Dyno to get final numbers on the engine build on my 302. Not surprising, the results were lower than expected, but I need your input on some of the tech's comments.
Engine:
1969 302, bored .30 over
Stock crank, hyperutectic (spelling?) pistons, Edlebrock performer plus cam, performer rpm intake and 600cfm carb. Windage tray, petronix ignition. 1969 351w heads.
C4 tranny, mid shift kit with TCI 2400 stall converter (9 1/2" I believe)
So the result after tuning ended with 180rwhp @4800. The tech felt this was odd as we began losing hp after 4800rpm, which should have been still increasing through 5400rpm. He felt that the 351 heads are actually hurting the hp output by restricting the flow.
So what are some comments about these heads? Help or hurt?
This past Saturday was spent at the Dyno to get final numbers on the engine build on my 302. Not surprising, the results were lower than expected, but I need your input on some of the tech's comments.
Engine:
1969 302, bored .30 over
Stock crank, hyperutectic (spelling?) pistons, Edlebrock performer plus cam, performer rpm intake and 600cfm carb. Windage tray, petronix ignition. 1969 351w heads.
C4 tranny, mid shift kit with TCI 2400 stall converter (9 1/2" I believe)
So the result after tuning ended with 180rwhp @4800. The tech felt this was odd as we began losing hp after 4800rpm, which should have been still increasing through 5400rpm. He felt that the 351 heads are actually hurting the hp output by restricting the flow.
So what are some comments about these heads? Help or hurt?
05-04-2009, 02:20 PM
#3
6th Gear Member
Join Date: Apr 2007
Location: California
Posts: 10,468
The heads and cam aren't helping. But it's mostly the heads. A good set of heads(like the RPMs mentioned) will let it breathe much better through 5,500rpm, and help get the most out of that cam. But, that cam isn't very big, so when you combine it with a restrictive head they work together to suffocate the engine.
Were the heads cleaned up at all? Also, flat tappet cam? Was it broken in properly? Flat tappets hate modern oil, and can go flat rather easily if you're not careful.
Were the heads cleaned up at all? Also, flat tappet cam? Was it broken in properly? Flat tappets hate modern oil, and can go flat rather easily if you're not careful.
05-04-2009, 05:07 PM
#5
Thread Starter
Join Date: Jul 2006
Location:
Posts: 25
Thanks for the replies.
Yes, the the engine has flat tappits and we followed the posted break-in procedure to a T. There are really no other issues with the engine as it runs very strong and is at about 1000 miles now.
The heads were completely rebuilt, new valves, seats, springs, etc. We went with the 351W heads at the suggestion of our machine shop..........looks like I need some KY.....
So, it looks like a new cam/head combo is needed. I'm checking out the AFR vs Edelbrock heads.
Yes, the the engine has flat tappits and we followed the posted break-in procedure to a T. There are really no other issues with the engine as it runs very strong and is at about 1000 miles now.
The heads were completely rebuilt, new valves, seats, springs, etc. We went with the 351W heads at the suggestion of our machine shop..........looks like I need some KY.....
So, it looks like a new cam/head combo is needed. I'm checking out the AFR vs Edelbrock heads.
05-04-2009, 06:42 PM
#6
3rd Gear Member
Join Date: Dec 2006
Location:
Posts: 815
A side note on heads.
I have a S/c 347 with afr 185 heads they do what I expected they are a good head.....sorta
The complaints I have is the same you will see over and over for the cash theses cost why didnt they put inserts in the exhaust mounting holes. You breathe wrong instant cross thread and your tapiing a new head.
I will do a 408 or 393 next and planning on going with the Edelbrock just to compare.
I hope I dont have the issues others have had with the rocker stud pulling out. Not starting a flame AFR thread just a few things to note while your head shopping.
Now the other side this thing is a monster! The heads and cam work very well together.
I will be going back thru my heads installing inserts sooner or later in the exhaust mounting holes no doubt.
I have a S/c 347 with afr 185 heads they do what I expected they are a good head.....sorta
The complaints I have is the same you will see over and over for the cash theses cost why didnt they put inserts in the exhaust mounting holes. You breathe wrong instant cross thread and your tapiing a new head.
I will do a 408 or 393 next and planning on going with the Edelbrock just to compare.
I hope I dont have the issues others have had with the rocker stud pulling out. Not starting a flame AFR thread just a few things to note while your head shopping.
Now the other side this thing is a monster! The heads and cam work very well together.
I will be going back thru my heads installing inserts sooner or later in the exhaust mounting holes no doubt.
05-04-2009, 07:23 PM
#7
4th Gear Member
Join Date: Sep 2005
Location: Salisbury NC
Posts: 1,576
So, it looks like a new cam/head combo is needed. I'm checking out the AFR vs Edelbrock heads.
Unless you are building an all out race engine then I would go with the edelbrock performer RPM's they are very similar to the AFR 165's and cost several hundred less
Unless you are building an all out race engine then I would go with the edelbrock performer RPM's they are very similar to the AFR 165's and cost several hundred less
05-04-2009, 07:59 PM
#8
6th Gear Member
Join Date: Aug 2007
Location: Elk Grove, CA
Posts: 5,896
I'm going to blame the cam more than the heads. Those Performer Plus cams are pretty tame. The 351W heads run the same ports as GT40's, so performance should be decent. Not fantastic, and nowhere near aftermarket capabilities, but I think it's the cam more than the heads.
05-04-2009, 08:49 PM
#9
6th Gear Member
Join Date: Apr 2007
Location: California
Posts: 10,468
I think on the 302 I have now when I have more cash down the road, I'ma put Edelbrocks RPM XT heads on with a custom cam. Wring the snot out of it and see what it does. And still drive it on the street every day....though the mileage may not be quite as good.
05-04-2009, 08:59 PM
#10
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Posts: 572
69 351w heads have slighly larger int ports and same size ex ports as 289-302 heads, slightly bigger valves BUT lots of the time the CC is a bit bigger than 289-302 heads so you gain a bit of flow but loose a bit of compression so the gain is little to none. I agree, the performer plus cam is really small, it is best suited to heavy vehicles needing low end or for fuel economy.