Looking for a few tips on porting 351c 4v heads

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thomas butt
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Looking for a few tips on porting 351c 4v heads

Post by thomas butt » Thu May 14, 2015 1:44 pm

About to start grinding on a set of 1970 351c 4v cc heads and would love to get some tips on porting the intake & exhaust port. I have read a lot of good information already and wanted to see if there was anything else I should know before I begin. This is for an NA application 550-650hp either 358 or 377 ci. And 7,000 rpm. I even uventually would like to see 650hp with these.

I will not be using port plates

Hopefully bronze guides. 2.19/1.71 valves.

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Re: Looking for a few tips on porting 351c 4v heads

Post by lada ok » Thu May 14, 2015 4:20 pm

First thing I'd do is check the port size as is, with pipe max or similar .... is this the Aussie designed head ? ...best thing to do would be take out any matial on the top of the port and maybe get the SSR to sort of match the back of the IN valve

Just remember that the V best formula A engines with a lot of good gear are around the 500 mark

I'd say you would also have to do massive amounts of work in the comb cham around the IN valve

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Re: Looking for a few tips on porting 351c 4v heads

Post by thomas butt » Thu May 14, 2015 6:09 pm

lada ok wrote:First thing I'd do is check the port size as is, with pipe max or similar .... is this the Aussie designed head ? ...best thing to do would be take out any matial on the top of the port and maybe get the SSR to sort of match the back of the IN valve

Just remember that the V best formula A engines with a lot of good gear are around the 500 mark

I'd say you would also have to do massive amounts of work in the comb cham around the IN valve
Take out material on the top of the port…your saying the guide boss? The top of the port is nicely shaped. i will try and post some pics in an hour or so. The SSR looks like it needs a little rounding as well as material taken out at the throat (a little not a lot) Again, i am a novice and have just picked up some tidbits here and there.

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Re: Looking for a few tips on porting 351c 4v heads

Post by BCjohnny » Thu May 14, 2015 6:20 pm

lada ok wrote:... is this the Aussie designed head ? ...
By the OP's description, no. He has the large port, closed chamber (cc) '4v' 351c head. All the 'Aussie' designed heads were essentially patterned after the US small port, open chamber '2v' 351c head, with the Aus 302c having closed chambers (similar to, but not the same as the early US 351c 'cc' heads), for obvious compression reasons.
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Re: Looking for a few tips on porting 351c 4v heads

Post by Abbottracingheads » Thu May 14, 2015 6:34 pm

Be careful digging by the valve guides in the exhaust ports. There is water there.
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Re: Looking for a few tips on porting 351c 4v heads

Post by thomas butt » Thu May 14, 2015 7:22 pm

image.jpg
Here is exhaust port cast form. Can I grind around the valve guide boss?
You do not have the required permissions to view the files attached to this post.

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Re: Looking for a few tips on porting 351c 4v heads

Post by lada ok » Thu May 14, 2015 7:45 pm

Sounds like ABBOT RACING HEADS has plenty of experience and good advise.,
You have to remove the guide boss and insert completely to do a good job . and then replace with a new guide which you can taper on a lathe b4 inserting.
You don't have to hog out heaps of material on the EX side only that it tapers gently to a bigger CSA at the flange face.

Your starting on the wrong side anyway :!: :!: it's the IN side you want to concentrate on

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Re: Looking for a few tips on porting 351c 4v heads

Post by roadrunner » Thu May 14, 2015 7:48 pm

I.I.R.C. the 4v heads had oversized ports for the engine combinations of the day, and I remember some folks actually shrinking them down to make them work, but that was using old tech cams/intakes so maybe things have changed since then. Have you c.c.'d the inlet port volume yet?
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Re: Looking for a few tips on porting 351c 4v heads

Post by thomas butt » Thu May 14, 2015 8:30 pm

roadrunner wrote:I.I.R.C. the 4v heads had oversized ports for the engine combinations of the day, and I remember some folks actually shrinking them down to make them work, but that was using old tech cams/intakes so maybe things have changed since then. Have you c.c.'d the inlet port volume yet?
Stock 4v Cleveland should be around 248c. I do not plan on shrinking the ports.

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Re: Looking for a few tips on porting 351c 4v heads

Post by thomas butt » Thu May 14, 2015 8:31 pm

lada ok wrote:Sounds like ABBOT RACING HEADS has plenty of experience and good advise.,
You have to remove the guide boss and insert completely to do a good job . and then replace with a new guide which you can taper on a lathe b4 inserting.
You don't have to hog out heaps of material on the EX side only that it tapers gently to a bigger CSA at the flange face.

Your starting on the wrong side anyway :!: :!: it's the IN side you want to concentrate on
…Yes, will start with intake first

Sounds great. I didn't know if I needed to completely remove the guide boss. This is intake only correct?

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Re: Looking for a few tips on porting 351c 4v heads

Post by lada ok » Thu May 14, 2015 10:53 pm

NO... IN & EX

the straight part of the IN port only needs to be 95 = 150 cc + the guide to the valve head is say 30 cc = 120 - 180 cc, you'll have to figure out your CSA and work back to get a distance from the valve head to open face of the port, ( which may or maybe not within the head port itself )from which you can start expanding on a taper till you reach a CSA of about the val head.
That should get you close... perhaps someone with a good computer program can pitch in ?

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Re: Looking for a few tips on porting 351c 4v heads

Post by KnightEngines » Thu May 14, 2015 11:51 pm

Have a look at the intake port entry, you can see where the runner entry is huge, but then it chokes down through the pushrod pinch - fill the side of the port entry up to the pushrod lump, you're not shrinking the port, you're just filling inactive space & helping keep velocity more consistant.
You can fill the floor at the entry as well for the same reason. Use Z-spar epoxy. Yes, it most definitely is worth the trouble off filling those areas of the port, it's not hard & the TQ curve will thank you for it.
The short turn on these likes to be a near constant radius, if you move the peak of the turn in the floor of the port upstream a little you can get a nicer/larger radius in there.
You should be blending the bottom cuts of the valve job into that radius on the short turn side, but leave the sharp angles on the valve job on the long turn & sides of the bowl.
Guide boss can be thinned down a LOT.

On the exhaust side the guide boss needs to be thinned down a bunch, or even removed completely & replaced with a bullet nose press in guide.
Short turn needs to be laid back a lot, it's worth dropping the floor a little at the peak of the turn & laying the valve job right into the turn to straighten out the port as much as possible.
Raise the roof at the port exit to the limit of the casting - you may need to plug the header bolt holes & redrill them a little higher up.

Valve job:
Intake - 30 deg chamber cut, 38 deg top cut, 45 seat (.040" wide), 65 bottom cut & 75 throat. Sink the seats to get a good .060-.080" on the 38 deg top cut & allow decent cleanup with the 30 deg chamber cut. 88% throat.
Exhaust - 30 deg chamber, 35 deg top cut, 45 seat (.050"), radius into the throat & 86-88% throat, again sink the seats to get width on the top cut.

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Re: Looking for a few tips on porting 351c 4v heads

Post by mag2555 » Fri May 15, 2015 7:39 am

You had better build the 377 cid motor and plan on Caming and springing up the heads for a 8200 rpm power band, as that's where your headed, no pun intended!
Oh, and your compression needs to top 14 to 1!
The heads in stock form flow 280 CFM on the intake side and will make 550 HP with ease, you should be able to hit 650 HP with 320 cfm and you need to get that flow gain with a minimum increase in port area, something on the order of getting that 40 cfm gain with only a 20 CC gain or less in port volume!
Also the Exh ports suck in these heads as you may know?!

You should plan on using the biggest oversize exh valves you can fit ( even if custom ones are needed!)in while keeping the stock 2.19" intake and applying a 5 angle valve job shooting for very high low lift flow up to .250" lift so that the cylinder blows down very fast before the piston even thinks of starting up the bore on the exh stroke!

A 1.76" Exh valve will allow you to have a 1.58" throat and that should make for some good high lift flow numbers also.

Just a side note here, the 2bbl C heads ported up right will net you 600 HP and a much more street strip happy 7K power band if that's more where the motor will be used is!

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Re: Looking for a few tips on porting 351c 4v heads

Post by BigBlocksOnTop2 » Fri May 15, 2015 8:40 am

Its been many years but when laying back the short turn on the exhaust be careful there is water there too. Its best to find a similar head and cut it up to see what you are up against. The intake needs filling (believe it or not). Just look at it. See where its big and suddenly it gets smaller. Epoxy in the big area will pick up flow. That with a valve job gets the most bang for the buck.

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Re: Looking for a few tips on porting 351c 4v heads

Post by DaveMcLain » Fri May 15, 2015 10:19 am

Concentrate your efforts on the short sides, intake and exhaust but more importantly look at the intake manifold of choice I bet there's more to be found there than in the heads.

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