Hey guys! (Car in question 1975 L48 (350 .030 over.) TH400)

I measured all the removeable parts on my SB... Checked the size of the ports on the 882's, and the size of the intake ports on the intake. The intake is a bit smaller, 1.870in tall by 1.120 wide, compared to the head 2in tall by 1.2 wide. I've heard that matching the port sizes is something thats good for horsepwer. I've also heard, that as long as the flow goes from the small size to the large size, that its fine. (Headers.)

My question, what kind of power can be picked up by hogging the ports out to the size of the intake gasket? If I want to swap my heavy cast iron intake for an aluminum intake, what are a couple recomended dual planes?

As most of yall know (LSA thread...) my goal for this motor is to have a good bit of power from 1500-5500. I'd prefer more torque, sacrificing peak torque for a nice flat powerband. Quick reving, while maintaining low end efficiency. I'm leaning towards a dual plane, because all the reading I've done has suggested that a singleplane is in its element above 4k!

Currently, I have a set of TRW-L2256F30 on the stock rods, a 355 cube engine. 882's with 76cc (Havent CC'd em, but mortec says 76.) I'm thinking about using the steel shim .015 headgasket... given all that, I will have 8.62-8.85:1 compression.

Let me ask ya a dumb question. A 75's crank is 2.100? The mains on a normal Chevy are 2.450? The numbers all match up... but just for the sake of double checking!

Thanks guys!

 

not sure exactly the HP gain but it does help ,,if you do all the little things like that They really do add up
don't forget about piston to head clearence

 

I asked Edelbrock about port matching intakes & they told me that it really didn't show any noticable gains until you get over 500 HP- take it for what it's worth. As for aluminum intakes, the smallblock guys would know better than I would as to what would fit under your hood but I'm pretty sure the Edelbrock Performer is good to go & would match your RPM range pretty well.

 

Thanks guys... Going to call up some parts stores to see if any of them have some manifolds I can measure.

Going to try and find an aluminum one with ports a touch smaller than the heads, and go with a felpro gasket!

 

anti-reversion ( spelling ) i never match completely... i allways leave a small "edge" on the bottom ..... I'M shade tree....

 

This may end up being a tall order...

Gotta find a light weight manifold that fits under the stock hood! (C3) I'd like an Air gap... just because of the denser intake charge. I seriously dobut my un-ported 882's can fully use one though!

 

Something is fishy.
...
IMO, the intake manifold is a continuation
is the intake port of a cylinder head.
The ‘step’ in cross-section-area,
makes no sense. My feeling is
that ‘intake manifold companies’
did whatever they felt like,
whether it was good for ‘vette enthusiasts
or not, and now, will say anything to
sell product they already got made.

 

If you or anyone else is interested I have a brand new (in the box) GM/ LT-1 aluminum intake that I am not going to use!! e-mail DIRECT redvetracr@msn.com

 

DIY port job

 

Well...

Are valve seals re-useable? I had the heads done... but if they the seals are reuseable, I'll buy a spring compressor and touch up some casting flashing!

I just dont think it'd be the brightest thing for me to do... clean up some ports/gasket match em with the valves installed! Might make the rings seat out a little quicker than I'd like!

 

Small block Chevys are famous for the little white puff of smoke on start up that is the result of leaking valve seals. If you have new valve seals and can get them off without damage, it might be ok, but I wouldn't trust them. You are spending enough on engine work, replace the seals.

 

Well...

I spent 75 bucks getting the heads checked out... I guess I'll price some seals!

Part of me says run it like it is... the other part of me says, lets try it!

What kind of abrasives are you guys using?

 

I just finished mine.. Also pinned the rocker studs. Not going to port match the intake just in case there's an alignment problem, so I'd rather it be a bit smaller.

Before (gasket slipped down a bit in this pic):


After (later went back and removed more around the top centers):

 

Nice job done!!!
Must give some hp more!!!

 

did you do the pockets ??????

 

Good job! Total believer in port matching, even if the HP gains are minimal. Every little bit helps.

 

 

Not trying to bust ur bubble Mr Blue but hardly anything will change by portmatching a small cammed low rpm mtr - and sorry for such a late reply. And having the head ports a bit larger than the intakes helps reduce reversion and works without adding any restrictions to flow. But pocket porting (under/behind the vlvs) will help and its not much more effort than gasket matching. Chevy Hi Performance has and article posted in thier tech section on how to do this and showed how they pocket ported a set of World Products SR Torquers - less than 10 hrs. Bowl blended them too. Though I have never done this both Lingenfelter (may he rest in piece) and Vizard write "how to's" for pocket porting and saying its easy hp. And those stock heads are the best parts i can think of for learning - start slowly cutting small amounts at a time. Dremel tool really to small here but bigger flex shaft (1/4 hp) are selling in some hardware stores now (or maybe can rent 1) and u will need some carbide bits too as sand paper rolls are only for finishing really.
And be careful to keep ur vlvs and parts numbered to return them the cyl they were cut for. For vlv seals i like umbrella seals ($10) for stock heads though there are some Viton (PC) seals used on later corvette heads that may be better and install without machine work. Anyways i used the umbrella seals that ride on the vlv stem (not stuck onto guide) and installed the small stock O-ring seals too. I may have made a mistake (too late now) and installed the O-rings along with the umbrella seals before the slipping on the retainer. Should have been umbrella seal first then retainer then O-ring seal and then vlv locks. I just read Lindenfelter book saying to install O-ring after the retainer is slipped onto vlv stem and then the vlv locks - and i'm not sure why. Don't see the difference but I believe what J. Lingenfelter made a point of writing with a pix to show how.
For a alum intake i like that new Edelbrock EPS but only for square bore carb and don't know if you have a sqaurebore or spreadbore carb (Qjet). Now the Edelbrock Performer and Air Gap Perf fit both type carbs along with the GM lo-rise #10185063 (ZZ4 intake) and the hi-rise LT1 #24502592 GM says fits too BTW. So do Wieand 8000/8004 manifolds. For spreadbore carbs only GM alum intakes for late '70s sb are a dime a dozen at the swapmeets and should be cheap at the pick a part bone yards too. I just saw plenty alum intakes a few weeks ago and in several models that use the Chevy corporate sb. U could carve these expendables up as much as u need to test ur efforts. BTW David Vizard sells a book on how to modify intakes for hi-perf - "How to Build HP vol 2".
Happy hunting. cardo0

 

Thanks for the replys guys!

Even if the gain isnt all that great, I think I'm going to give it a shot for the heck of it...