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Old 08-27-2012, 10:22 AM
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head upgrade disappointment

Hi guys,
finally finished head swap on my 350 sbc

Originally had camelhumps un ported with 1.94 1.5 valves.
Upgraded to 210cc heads 64cc chambers aluminium. 2.02 1.6 valves.
I can say there is very little difference with the performance! Flat top pistons,
Cam,carb,headers all left as they are,cant see what Ive done wrong.

Engine specs
350 +60thou,holley 600v/s,edelbrock rpm intake,mallory unilite,magnum
480/480 lift and block hugger headers, any ideas??

3.09 rear gears T5 manual trans

Thanks in advance

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Old 08-27-2012, 11:22 AM
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what kind of aluminum heads?
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Old 08-27-2012, 11:28 AM
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Skip whites procomp heads, they are suppose to be around 400 horsepower,cant see my camelhumps anywhere near that!
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Old 08-27-2012, 11:38 AM
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You'd be surprised how much a good set of double humps will make.

Personally I think it's a case of the heads being a bit on the big side for a 350 unless you're looking to turn higher RPM's. Big ports and big valves combined with nearly stock gearing isn't going to give you a big change in seat of the pants feel. I would imagine once you get it above 5000rpms it starts to come one more so than the Dbbl humps.
What are the duration numbers on your cam?
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Old 08-27-2012, 11:54 AM
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Quote:
Originally Posted by dave350v8 View Post
Hi guys,
finally finished head swap on my 350 sbc

Originally had camelhumps un ported with 1.94 1.5 valves.
Upgraded to 210cc heads 64cc chambers aluminium. 2.02 1.6 valves.
I can say there is very little difference with the performance! Flat top pistons,
Cam,carb,headers all left as they are,cant see what Ive done wrong.

Engine specs
350 +60thou,holley 600v/s,edelbrock rpm intake,mallory unilite,magnum
480/480 lift and block hugger headers, any ideas??

3.09 rear gears T5 manual trans

Thanks in advance
These are really large port heads combined with big valves. All of this wants to move the power band way up the rev range. The carb, cam and type of exhaust header you're using will not support where these heads want to go in order to get the power.

To a very large extent the engine behaves in concert with the mixture velocity of the intake system. Physics tells us that for a given amount of flow, the flow velocity of a large pipe is slower than in a smaller pipe. In effect below some critical RPM the larger port head has lost so much flow velocity that it can no longer get the cylinder filled in the time allocated by the cam's duration and amount of lift. In fact the velocity may be so low that the piston rising on the compression stroke where the valve is still open will actually backward pump mixture into the intake and out of the carburetor, this is reversion. This is why using large port heads and big valves always reduce lower end performance.

A problem I have with Skip White's heads, which are ever so cost attractive, is that they come in big and bigger. They just are too much for a 350 unless you're going to take it over 6000 RPM. Back in my Ford Cleveland and Tunnel Port days I used a lot of marine grade epoxy to shrink those sewer pipe sized ports down to size; you may be in the same boat.

Bogie
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Old 08-27-2012, 12:25 PM
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Quote:
Originally Posted by dave350v8 View Post
Hi guys,
finally finished head swap on my 350 sbc

Originally had camelhumps un ported with 1.94 1.5 valves.
Upgraded to 210cc heads 64cc chambers aluminium. 2.02 1.6 valves.
I can say there is very little difference with the performance! Flat top pistons,
Cam,carb,headers all left as they are,cant see what Ive done wrong.

Engine specs
350 +60thou,holley 600v/s,edelbrock rpm intake,mallory unilite,magnum
480/480 lift and block hugger headers, any ideas??

3.09 rear gears T5 manual trans

Thanks in advance
There's a bunch of reasons you could have lost power, runner size really isn't one of them. Those 210's actually are about 200's, and believe it or not close to ideal for a street 350.

Now for the problems- are you certain your old heads were 64cc's? If the valves were changed, or those heads were ever milled you may have been closer to 60cc's or even less, which means you lost compression. Next, you have a pretty terrible exhaust, which on heads with larger runners can lead to reversion as already indicated- fixing your exhaust will fix that problem. Next you probably didn't retune your carb, which can have a BIG effect on power. Next, what head gaskets did you use, which kind did you replace? There's more compression loss there. Also, anytime you switch from iron to aluminum you need about a full point more compression to make the same power, you more than likely lost compression which means you went in the completely wrong direction there.

So to fix this mess of a poor installation you need to do a few things- pull the heads off and mill them down you'll likely need to mill a considerable amount to get your compression where it needs to be- depending on your cam and pistons. Get a decent set of headers (this part alone will give you more power than you had when you started). And get your carb properly tuned and/or replaced. Ignition timing also needs to be correct, but i assume you can figure that part out.

Fix those three major points and you'll start seeing some serious power. the next item would be having a valve job and bowl port work done on your new heads, but that can be a little costly.

Lastly, if those camel humps were really expertly ported they may flow more air through a smaller valve- which is always a good thing for a street engine.
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Old 08-27-2012, 12:31 PM
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Oh well bit disappointed now!
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Old 08-27-2012, 12:34 PM
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Hi
bogie and engineczar both of you are spot on! It does seem to at least match the camels at lower revs but then it wants to rev further than them!
The advertised duration is 280 and at .50 intake/exhaust is 230 degrees.
To be honest I dont fully understand these figures.

Skip whites website states with a cam around 480/510 lift it dynos at just over 400 horsepower on a 350.

Do you think changing rear gears and a bigger carb will help, I was considering a cam change as well if you have any suggestions?
Thanks again
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Old 08-27-2012, 01:01 PM
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Quote:
Originally Posted by dave350v8 View Post
Hi
bogie and engineczar both of you are spot on! It does seem to at least match the camels at lower revs but then it wants to rev further than them!
The advertised duration is 280 and at .50 intake/exhaust is 230 degrees.
To be honest I dont fully understand these figures.

Skip whites website states with a cam around 480/510 lift it dynos at just over 400 horsepower on a 350.

Do you think changing rear gears and a bigger carb will help, I was considering a cam change as well if you have any suggestions?
Thanks again
Could help, the T5 has ratios all over the place as well, do you know what these are? A 3.09 matched with a 700R4 or 4L60 comes out of the hole pretty hard but that is the combination of 3.53 low and the torque-multiplication of the converter, certainly the latter is something you don't get with a clutch.

Bogie
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Old 08-27-2012, 01:18 PM
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Originally Posted by oldbogie View Post
Could help, the T5 has ratios all over the place as well, do you know what these are? A 3.09 matched with a 700R4 or 4L60 comes out of the hole pretty hard but that is the combination of 3.53 low and the torque-multiplication of the converter, certainly the latter is something you don't get with a clutch.

Bogie
Hi, the trans gears are 1st 2.95:1 2nd 1.94:1 3rd 1.34:1 4th 1:1

My rear gears are 3.09 and tyre diameter is 23 inches if that helps

My car weighs 2600 lbs
Realistically what horsepower do you think I might have? What should I expect down the strip?
Sorry for all the questions!

Last edited by dave350v8; 08-27-2012 at 01:47 PM.
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Old 08-27-2012, 02:05 PM
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a 2600 pound car with 400 hp should run low 12s or better.the tires are only 23 inches? I think the heads are too big for a stock 350.If you are fast with a wrench the full the front off and advance the cam 4 degrees,couple hours and gaskets. If that perks it up then what bogie said about reversion,,,
NOTE:the top end increase in HP,you might not feel by seat of your pants driving even if you got 25 more horses.
If advancing the cam changes things a lot,then retuning is in order,probably cam and intake.

what you have done is put on entry level race heads on a very mild street engine. Think of it like putting an 850 double pumper on a stock 283
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Old 08-27-2012, 02:25 PM
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Yes I see what you mean! What does advancing the cam do as you have suggested?
Would a bigger carb help now,I have a 650dp on the shelf and a 750v/s

Yes my tyres are 23 inches in diameter! do you think that will be ok with the T5 ratios
and 3.9 rear?
I doubt I am anywhere near 400 horsepower now!

Thanks again
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Old 08-27-2012, 02:33 PM
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advancing your cam will make more cylinder pressure so more bottom end,generally,it robs from the top end though.This will tell old bogie what is happening and he will give 2 pages of ideas later. do 1 thing at a time.change the carb first and see what happens then cam or the other way around
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Old 08-27-2012, 02:42 PM
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Will try advancing cam then! Will do carb first as this is 30 minutes to do!
Would I gain more by putting in a bigger lift cam though?
thanks

Last edited by dave350v8; 08-27-2012 at 02:50 PM.
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Old 08-27-2012, 03:05 PM
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advance what you have to see the behavior then bogie will give ya the works
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