Tailgate porting..

General engine tech -- Drag Racing to Circle Track

Moderator: Team

Old as Dirt
Pro
Pro
Posts: 290
Joined: Thu Oct 08, 2009 12:09 pm
Location: Monroe Washington

Tailgate porting..

Post by Old as Dirt » Sun May 10, 2015 12:17 am

Nice day in the PNW, low 70's..
working a set of 76cc "441X" SBC castings.. no shop, no mill.. so we do it "Oldschool" on the tailgate of my GMC.. LOL..

Mild 355 build for my Son's 72 SS El Camino(Turbo 350 with 4.88 geared 12 bolt and 3600 stall).. NOS forged 11cc TRW Dome pistons(should work out to 10.7 CR), Nodular Cast Crank and a set of resized "pink" rods w/GM rod bolts in a 4 bolt 1970 010 block.. Shortblock is complete and detailed w/ .0025 main/.002 rod and .006 piston clearance w/ Melling standard pressure pump and Moroso 7qt. pan.. ready to finish assembly.. but the heads suck.. doing the best with what we have.. :oops:

Comp XE 294H cam(came with the shortblock)w/ New Delphi "anti-pump" hydraulic lifters, and decked to .010" in the hole with .028 head gaskets.. Going with "Scorpion" 1.6 Rollers and 7.900" pushrods(best pattern was with 7.950 adjustable pushrods) w/checking springs.. but the pattern was too far from center by a bit towards the exhaust side.. at 90* mid lift.. so cheating a bit by going with .050 shorter pushrods.. and a stud girdle.. (3/8 pressed studs TIG welded to keep from pulling out) Using "Pipemax" as a reference for the build.. should be good from 4K to 6K with the 250/256 duration along with .553/.557 lift.. If I had some 1.5 rockers for the exhaust.. might be better.. hoping the "tailgate porting" will get close to 235/245 CFM flow.. as the piston demand looks to be about 243CFM @ 5600rpm.. we'll see..

Going with a modified(cut down divider and port matched to a Felpro 1205 gasket) RPM Performer "EPS" manifold and a fresh kitted 4777 650 Double pumper w/ a 1" spacer..
Bottom line.. Lots of timing(locked out 36* oldschool points ign w/Mallory Pro Coil and domed pistons) and the real question.. too much cam?

Seldom driven on the street, but maybe a fun SATURDAY NIGHT with his girlfriend... trailered to the track(Drag Radials)on Dads trailer.. what say you "Fast guys"?
You do not have the required permissions to view the files attached to this post.
Last edited by Old as Dirt on Sun May 10, 2015 1:10 am, edited 7 times in total.

Old as Dirt
Pro
Pro
Posts: 290
Joined: Thu Oct 08, 2009 12:09 pm
Location: Monroe Washington

Re: Tailgate porting..

Post by Old as Dirt » Sun May 10, 2015 12:25 am

[img]
A%20Sep%202%20resize2.jpg
[/img]
You do not have the required permissions to view the files attached to this post.

lada ok
Guru
Guru
Posts: 1089
Joined: Fri May 10, 2013 9:20 pm
Location: te puke, bay of plenty, new zealand

Re: Tailgate porting..

Post by lada ok » Sun May 10, 2015 2:03 am

Excellent :!: ... should be more of it :D

Things I would do that will make a difference, I have suggested these intake mods b4, but I don't get any +ve feed back :!:

:idea: I'd set or get a rev limiter for that crank / rod combo
Did you think about setting the p/rods to achieve max lift :?:

BigBlocksOnTop2
Pro
Pro
Posts: 430
Joined: Thu Mar 21, 2013 12:03 pm
Location: Chancellorsville Battle Field, Chancellorsville, Virginia

Re: Tailgate porting..

Post by BigBlocksOnTop2 » Sun May 10, 2015 8:09 am

Thats a lot of compression for the street with cast iron and pump gas.The issue is, lets say you have been filling up with 93 octane and the next fill up at the 93 pump is 91. Could be in trouble with the tune in question and 9.75 CR will give the extra ''fuse'' before disaster. I've done that old school thing....thats all part of hot rodding!

mag2555
Guru
Guru
Posts: 2530
Joined: Sun Sep 18, 2011 11:31 am

Re: Tailgate porting..

Post by mag2555 » Sun May 10, 2015 8:21 am

Get yourself David Visards soft cover book on reworking SB heads and digest it before you go off grinding and dropping off airflow!

Carnut1
Guru
Guru
Posts: 3991
Joined: Tue Jun 11, 2013 6:32 pm
Location: Melbourne fl.

Re: Tailgate porting..

Post by Carnut1 » Sun May 10, 2015 9:22 am

Old valves/new valves? Being so close to detonation limit on pump gas oil past the guides will put you over in a second. I would pay for a guide hone job sized to the valves used and a good 3 angle valve job. I broke the bank and bought a sunnen valve guide dial bore gauge and a sunnen honall. The difference is night and day and the valve job comes out first time with good concentricity. Super important if longevity of the valve job is wanted.
Servedio Cylinder Head Development
631-816-4911
9:00am - 9:00pm EST

wyrmrider
Guru
Guru
Posts: 6932
Joined: Thu Jan 10, 2013 10:52 pm

Re: Tailgate porting..

Post by wyrmrider » Sun May 10, 2015 10:38 am

"Did you think about setting the p/rods to achieve max lift"
Think of all the reasons not to set the rockers to tangent at max lift
where are they with the valve closed?

RevTheory
Guru
Guru
Posts: 4999
Joined: Thu Sep 04, 2014 6:45 am

Re: Tailgate porting..

Post by RevTheory » Sun May 10, 2015 10:44 am

Interesting set of challenges. Not enough compression for the cam and at the same time, in the red zone for iron heads and pump gas.

wyrmrider
Guru
Guru
Posts: 6932
Joined: Thu Jan 10, 2013 10:52 pm

Re: Tailgate porting..

Post by wyrmrider » Sun May 10, 2015 10:47 am

but it ought to go rump de rump rump on date night
cam looses the low end, heads limit the top end
is that what you call a "win-win"?
We used to port jet skies at the river "while you wait" :)

Old as Dirt
Pro
Pro
Posts: 290
Joined: Thu Oct 08, 2009 12:09 pm
Location: Monroe Washington

Re: Tailgate porting..

Post by Old as Dirt » Sun May 10, 2015 11:26 am

Morning..
Appreciate the replies, and will respond..
Lada- Rev limiter has been discussed as the youngster probably has an uncontrolled path from his brain to his right foot.. :mrgreen: Sounds like a good idea, and the DP intake manifold will
most likely be about topped out after 6K anyways.. about the pushrods..I set them for best sweep using the "90* at mid lift method" I seen on YouTube.. believe Scott Foxwell made the video.. and the pattern ended up towards the exhaust side just shy of two thirds.. so I am going with a slightly shorter pushrod to bring the contact area closer to center.. as far as these old eyes could tell, sweep was about .030 wide..

BBOT2- ya.. CR is pushing it for premium pump, but the little it gets driven on the street, we'll mix up some race gas with the pump stuff if need be.. Didn't feel the need to buy a set of flat tops, as the shortblock already had the 11cc dome pistons when I purchased it from a friend.. only had about 10 min. runtime on it(cam break in and a couple of rips down the block) before they toasted the thrust bearing from a restricted cooler/Turbo 400/4500 stall.. sounded pretty crisp.. he ended up going with a new Big block and I scored the 355 shortblock for cheap.. had it tanked/line honed and put back together with new bearings..

Mag2555- been on the site here reading all I can for the past 6 years.. huge amount of info provided by some of the best in the business.. and I use that info in high regards..
Right now I am at the point of getting the intake ports sized to a 1205 gasket and getting a bit more volume(441's are about 160cc) along with cleaning up the bowls up to the bottom of the valve job, keeping the throat @ 89% for now(1.94 intake valve and a 1.72 throat).. blending the valve guide boss into the bowl.. baby steps for sure.. according to Larry's site the Average CSA is close to 1.74".. need to get these flowing around 235CFM as they are 200CFM stock.. small ports/high velocity and can stand to be opened up at the pushrod pinch by making the floor wider from what reading I've done.. can learn something every day here on the site..

here is a picture of one port in progress.. you can see the one next to it only has been gasket matched but not blended back into the port yet.. tough to do too much with a short bit.. ordering a few longer ones..
441 intake port.jpg
Carnut1- yes, new valves and guides from an old ex-410 sprint car builder who lives a couple of blocks from me.. 3 angle job looks good.. so I am being real careful to avoid having to touch up the seats if I accidently "touch" them..
You do not have the required permissions to view the files attached to this post.
Last edited by Old as Dirt on Sun May 10, 2015 11:40 am, edited 1 time in total.

Old as Dirt
Pro
Pro
Posts: 290
Joined: Thu Oct 08, 2009 12:09 pm
Location: Monroe Washington

Re: Tailgate porting..

Post by Old as Dirt » Sun May 10, 2015 11:38 am

wyrmrider wrote:but it ought to go rump de rump rump on date night
cam looses the low end, heads limit the top end
is that what you call a "win-win"?
We used to port jet skies at the river "while you wait" :)
Just trying to do the best we can on a very small budget.. I know the cam is bigger than needed, and the CR isn't ideal.. dome pistons suck and big chamber smog heads are about worthless.. but it's what we have, and will try to deal with it rather than $hitcan it because it doesn't fit the "Profile"

rfoll
Guru
Guru
Posts: 2278
Joined: Mon Jan 11, 2010 12:44 pm
Location: St. Helens, OR

Re: Tailgate porting..

Post by rfoll » Sun May 10, 2015 11:45 am

Yes it was also pretty nice here yesterday. I think the cam says you should have a bigger carb. A 3310 750 or 780 vacuum carb would work very well. Common carb and cheap to acquire. Just add lighter springs to the vacuum pot to quicken the secondary opening as needed.
So much to do, so little time...

wyrmrider
Guru
Guru
Posts: 6932
Joined: Thu Jan 10, 2013 10:52 pm

Re: Tailgate porting..

Post by wyrmrider » Sun May 10, 2015 11:54 am

We all ran motors exactly like that one
FUN

RevTheory
Guru
Guru
Posts: 4999
Joined: Thu Sep 04, 2014 6:45 am

Re: Tailgate porting..

Post by RevTheory » Sun May 10, 2015 12:30 pm

wyrmrider wrote:We all ran motors exactly like that one
FUN
That's a big no-shitter there :lol:

Old as Dirt
Pro
Pro
Posts: 290
Joined: Thu Oct 08, 2009 12:09 pm
Location: Monroe Washington

Re: Tailgate porting..

Post by Old as Dirt » Sun May 10, 2015 12:35 pm

Don't get me wrong here.. Dart little "M" along with a set of * 210 CNC'd Profiler heads and a Jones roller would be fantastic.. just not in the cards..

Post Reply