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head upgrade disappointment

3K views 22 replies 8 participants last post by  dave350v8 
#1 ·
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
 
#4 ·
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?
 
#5 ·
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
 
#6 ·
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.
 
#8 ·
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
 
#9 ·
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
 
#11 ·
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
 
#12 ·
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
 
#13 ·
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
 
#16 ·
As it sits, HEADERS AND EXHAUST should be on the top of your priority list. I realize they may not make headers for your car, but custom ones can be made by you or a shop. You can get a kit with flanges and bends to get you started. Through in some good merge collectors and dual 3" exhaust and you'll see some serious power increase.

Just remember air can only come in as fast as it goes out. Also, a strong clean exhaust pulse can really draw in a lot of extra air through the intake.

There's a lot of things you can do to your car to get you some power but your engine is already being choked by the exhaust.
 
#20 ·
Along with the loss of compression from going from a 60ish cc chamber to 64ccs, you have also lost perhaps a point of effective compression because you went from a cast iron head to aluminum head. If you want to stick with flat-tops, you would be better served with a cast-iron head, perhaps an EngineQuest Vor-Tec head with the manifold mating surface that matches your existing intake manifold.

tom
 
#21 ·
Not to hijack the thread but I just used a set of those on an inboard boat engine. I have to say I was pretty impressed with them. The quality of the castings was up there and even the valve job could have been used right out of the box. For my customer it was a win win because he was able to retain his cast iron intake and get the benefit of a vortec style chamber. The price was also a steal at $280 each bare.
 
#22 ·
You may want to look at swapping to this cam:Lunati 60104 - Lunati Voodoo Camshafts - Overview - SummitRacing.com you have the springs to handle the additional lift,this cam is designed to bring back some of the low and mid-range you lost with the 210cc heads please read the description at the bottom of the specs,as mentioned earlier do advance the cam 4 degrees,some rear gears in the 3:70's will be a big help too.
 
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