KNIPPS

Engine is at the engine shop...a beefed up 427...engine guy was asking if I was going to run headers but I would really like to keep everything stock looking...porting of the manifolds was brought up to help the engine breath....I am not familiar with this process...has anyone done this??..is there a great benefit?..can it be done and is it recomended thanks..Jim

10caipirinhas

Port matching both manifolds (intake and exhaust) to the heads is worthwhile, also extrude honing the exhaust manifolds will help a lot with increasing exhaust airflow. You can also extrude hone your intake as well, depending on your specific application (RPM range and cam profile) if it is deemed worthwhile.

But I would definitely do the exhaust manifolds as it can improve airflow by 20% or more........

http://www.extrudehone.com/auto/auto-performance.php

KNIPPS

Is porting something that would be needed or would the stock manifold be fine? Is there any potential negatives for porting the exhaust manifold? The car has side exhaust if that info is needed

Ironcross

It`s a positive improvement...and only takes a little time to do....

Mossy66

I'm no expert, but I do know that the stock side pipes are very restrictive. If you are using stock side pipes, then I would think that porting the manifold would be a waste.

Gerry

robert miller

With the patrs matched ported will help more than you know, But if this car is only on the street and just hitting it for a short distance. Will not be able to tell that much at all. Now if you are in 1/4 mile and WOT on the top end of the track then yes. You would pull the shi% out of a stock set up car....

10caipirinhas

KNIPPS.....

Define what you mean by a "beefed up 427" for us..........

KNIPPS

well I am no engine expert but I will try...the engine is 427--.060 over it will have about 500-550 HP or so I am told...numbers will be determined once everything is put together...Dart heads, roller cam, forged pistons..basically everything will be new or rebuilt...to me its "beefed up"

Avispa

I'd call that "beefed up", too. All I have is a Crane solid cam with similar specs to the factory, 1.88 exhaust valves, 1.72 Comp roller tip rockers and stock rectangle port heads. Makes 454 on the engine dyno with only 10.25 compression. Mind you, the dyno uses headers and dyno mufflers. If you can't get 550 hp out of that setup on the dyno something is seriously wrong. You would almost have to port the exhaust manifolds to get all the benefit of the stuff you plan to run, though. Stock 2 1/2 inch exhaust pipes will supporet 225-250 RWHP per side so that should be ok. BTW, I think the Dart heads have the exaust ports raised .300 inches from the stock location. You may want to check about exhaust floor clearance and accessory(alternator/PS pump) mounting.

10caipirinhas

KNIPPS.......

OK.....it's all in the definition, that's a nice build........some folks think the THRUSH muffler sticker of the duck with the cigar adds 100 HP......that's why I asked. I just aged myself right there BTW...........

I'd port match and extrude hone everything then. Intake and exhaust manifolds.

I imagine you can run a freer flowing set of aftermarket side pipes with a less restrictive baffle under the OEM side pipe covers ? Your exhaust manifolds should give you equivalent power gains close to headers once the extrude honing and port matching is done. I am basing that statement on guys I know with OEM 426 HEMI exhaust manifolds who had the same thing done, and the power difference between an engine with headers was 5%.

IMHO 50% of power gains come from parts and 50% from machine work and attention to detail. If your engine builder hasn't stated he will port match everything at that power level I'd be concerned about his competence. The fact that he asked you if you'll be running headers already has me wondering to be honest.

As you asked about negatives, the only real one is that because the metal on both manifolds will have been contoured and machined to match the head openings (and vice versa) the process cannot easily be done again for a different engine should you need to swap parts. It can be built up and changed to suit, but it's not worth worrying about IMHO.

KNIPPS

Ok...what does that mean "raised exhaust ports" and what is it that I should be worried about things fitting properly ie alternator??..I dont have PS so I am not worried about that...like I said I am no engine expert!!!

10caipirinhas

You may need slightly longer manifold bolts.........and like Avispa said, will need to double check for the fitment of the PS pump and pulley/belt alignment. DART says on their website that most standard headers fit......and manufacturer's "tend" to make allowances for OEM accessories like pumps/alternators. Haven't read of many folks with problems on this or other websites, but it is something you always gotta check regardless, and your builder should know about. I'm no expert at all either, just read a lot and stay at Holiday Inn Express motels.

Basically to get better airflow the exhaust opening on the manifold side was raised .300 of an inch versus the stock head position. You will probably have lots of clearance between the manifolds and fender wells and other parts under there to accommodate this small difference. I don't now C2's at all and am here learning about them and C3's, since it has been 25 years since I last owned a C3.

If you had the two heads side by side you'd see that the opening was in a different spot. Imagine two windows in the side of a building, one placed slightly higher in the wall than the other...........and the higher window flowing more air a lot faster into the room and down the hallway, than the other window.

MiguelsC2

Extrude honing is really pricey. Intake and exhaust manifolds will cost $1500-1750. I wonder whats the dollar vs HP gain is?

10caipirinhas

That's true.......but a set of "Jet Hot" Hooker Super Comp headers for his car are $870 plus freight ($100 +/- ?)..........and then to gain the advantage of the nice engine build he'll need better side pipes and baffles hooked up to those headers.........so add $$ there as well........

I think one way or another the money will have to be spent...........or, the engine build scaled down a lot if he wants to keep it looking totally stock, with the benefit being he'll spend less $$ should he choose to do so.

Ahhhhhh, the slippery slope ride on a toboggan made of $100 bills.......weeeeeeeeeeeee........

robert miller

really not that much in the hp gain to be really able to tell the diff. But you could say it was done..

Vogie

Might do some research on extrude honing the intake. I bought one for a 454SS from a friend. He indicated that the smooth walls somewhat hindered the mixture of fuel and air at low RPM due to the lack of turbulence. I never used that manifold so I can't confirm this opinion. Good luck.

Kensmith

I did a very simple porting with my 383 stroker and stock exhaust 2 1/2" manifolds. I have the Dart Pro 1 Platinum Small Block Chevy Cylinder heads and I traced the exhaust side of the head and transfered it over to the exhaust ports of the exhaust manifold. I then took and colored in the areas that needed to be opened up. I used my die grinder with emery barrels to grind out the colored areas being careful not to get too close to any bolt holes. I also did the bottom opening to take some of the slag/rough areas out and smooth them. Everything from start to finish took maybe a day. And probably 2 dozed emery barrels.

DSR

This is what was done to mine. It was cheap and gets rid of any lip between the exhaust manifold and the head. We did the same on the intake.

Dave

Steve439

When I rebuilt my 439 I used a die grinder with carbide burrs to work on the exhaust manifolds.
The top of the manifold ports were about 1/8 inch lower than the top of the exhaust ports on the heads.
I also removed the AIR bosses and smoothed out what I could reach.

I'd at least check the match of the heads and manifolds.
It's practically free horsepower if the manifold sticks into the path of the heads.

KC John

An engine is just an air pump. If you are going to keep your side pipes, you will not gain a thing by doing anything to the ports. The side pipes are already too small to get all the power your engine will be able to make anyway.

If you decide to go with aftermarket side pipes that are at a minimum of 2.5", then you might see some improvement on the top end, if not use the money someplace else. JMO