BJ8 Cast Iron Head Porting

[David_K]

What kind of horsepower increase will I be looking at with a mild porting job on a BJ8 engine? The compression, cam, and valves will NOT be changed. I'm also hoping to see a MPG increase at steady cruise on the interstate.

I calculated it out and a shop I'm looking into having the head sent to has quoted me $650 for porting, $175 for a valve job, and the guides, seats, and springs will be extra. I think this will end up costing me $1100 in the end.

 

[GregW]

Porting heads can be tricky. If you loose too much charge velocity, the horsepower can suffer. Does the guy you’re thinking of have experience with a Healey engine? It’s not like botching a job on a Chevy where you can pick up an extra head easily.

 

[David_K]

Hap Waldrop is the one who would be doing my head.

www.acmespeedshop.com

 

[David_K]

We haven't opened the engine up but I'm hoping it won't need much more than rings, bearings, seals, gaskets, and possibly an oil pump.

 

[Dave Russell]

Mild "porting" will likely result in a mild power DECREASE. It will almost certainly result in less gas mileage at cruising speeds. Strategic reshaping of valve seat entry & exit areas (multi angle valve job) could result in a little power increase at higher rpm, but the original BJ8 combination of carbs, cam, ports, & compression was pretty good. Any noticeable gains from changing things will come at above 5,000 rpm. Save the porting money for something that is more useful.
D

 

[David_K]

Whats the most cost effective way to get another 25 hp out of a BJ8 motor with a budget of $1000-1500? I thought some porting would sure get me close to that. I guess I was wrong that the Healey engine was less effecient than it really is.

I've read an article that Race Spec 3000s are producing north of 250 hp. Whats really involved in gaining that extra 100 hp?

Thanks!

 

[Dave Russell]

The problem of obtaining more horsepower is that you have to raise the rpm to get it. Having to run the engine at higher rpm to get the power isn't so much fun with a road/street driven car. You can run the rpm a lot higher & get a lot more power. However, it requires extensive & quite costly modifications to the engine to get it to run AND hold together at the higher rpm. Even then, engine life will be relatively short.

Pretty much, the only way to raise power without raising rpm a bunch is:
1- Increase engine displacement - not cheap to do
2- Increase compression ratio - it's already pretty high
3- Supercharging - expensive & a lot of possible problems
4- Use nitrous oxide - only good for short power boosts

One modification that would boost midrange & higher rpm power would be to install "good" headers. You would get a lot more go for your money than you would get from porting. Higher lift "roller rockers" might be a fairly simple way to get more power. Both of these modifications would increase power with only a moderate increase in required rpm.

Once the decision has been made to go for 200 plus horsepower, everything will have to be modified, cost a whole lot, the engine won't be much fun to drive on the street, & it's life will be shorter.

Greg showed a comparison of cams & headers here:
https://www.britishcarforum.com/ubbthread...true#Post158520
D

 

[Cutlass]

When I bought my 66 BJ8, it was stuck in 3rd gear. (Just a shifter problem.) It would still pull away from a standing start with no problem. The low end torque on these cars is amazing. Consider why you want horsepower. Racing? Fine, go for it. If you're like most, however, you will never use more horsepower. Those winding mountain roads in Tennessee are beautiful, and don't need to be viewed at 100 mph. Dave is correct in all respects. When I was hot-rodding forty years ago there was a saying, probably still around: "Horsepower costs money, how fast do you want to go."

 

[zblu]

Have had thoughts on going to fuel injection a la tr 4a etc as an alternative way to increase response etc, perhaps dave russell could enlighten all on merits, i'm thinking along the lines of the pre smog laws, makes the crossover much simpler

 

[Dave Russell]

[ QUOTE ]
Have had thoughts on going to fuel injection a la tr 4a etc as an alternative way to increase response etc,

[/ QUOTE ]
Strictly my opinion,
There could be numerous advantages to using fuel injection on a Big Healey:
1- More precise fuel metering under varying running conditions.
2- More equal fuel distribution to the cylinders by varying the metering to individual cylinders, not all cylinders require the exact same exact amounts of fuel.
3- Quicker throttle response.

A pair of HD8 carbs alone can supply all of the air flow that is needed. However the fuel distribution to the individual cylinders cannot be optimized. OTOH, use of Webers with one throat per cylinder or individual carbs per cylinder can be optimized to the engines individual cylinders requirements.

The down side to both Webers & fuel injection is greatly increased complexity & cost. Much of the gain will only be realized as increased power at the higher rpms & quicker throttle response at all rpms. Very helpful on a race engine, impressive on a street engine but showing little real gain in everyday street driving.

I know of a couple of folks who have tried very sophisticated electronic management fuel injection systems, complete with fully adjustable computer managed control systems. There are several of these systems available. They finally gave up & went back to carbs. Just too much tinkering time & not enough driving time.

IMO, fuel injection is for those who are very technically inclined, are well into computers, have a lot of money, & are very determined to prove a point.

Weber carbs, to a lesser extent, are in the same category. Lot of fun if you have the money & like to tinker.

For those who just wish to drive the cars, the HD8 carbs offer a good compromise. I'm sure there are others who will disagree.
D

 

[John Loftus]

Another question about "porting". When I had my BJ7 head in for a valve job I had them match the ports to the manifolds. That required some grinding on the head, some grinding on the ports to get them to line up. I have yet to run this motor but would like to get opinions. Do you think matching will decrease or increase power? Do you think ports were designed mis-matched to create turbulance with the flow?

Cheers,
John

 

[GregW]

I know I’m splitting hairs here. I consider port matching “cleaning up inconsistencies in the casting process”. I don’t think the port mismatching is intentional, just what happens when molten metal cools in a big block of sand.

 

[Dave Russell]

Hi John,
I doubt if any production port to manifold junctions are purposely mismatched. Any attempts to induce turbulence would be done in a more controlled manner inside the ports.

That being said, on some engines, a mismatch where the manifold port is smaller than the head port is sometimes used to create an anti reversion effect. This helps counteract the reverse intake port flow which occurs as the piston is rising after the intake stroke & the intake valve is still open. Nearly all cams are timed to keep the intake valve open as the piston is rising on the compression stroke. This is done to take advantage of the intake column inertia which keeps filling the cylinder in spite of the piston direction reversal. This inertia filling only takes place at the higher inertias, rpms, & so there is a tendency for the intake column of gasses to reverse directions at lower rpm.

The anti reversion step has to be very precisely located & matched to the rest of the engine to be effective.

Likewise, the exhaust manifold ports may be made larger than the head ports to accomplish a similar reverse flow blocking. Long fairly small diameter header primary tubes tend to keep the exhaust column inertia high & prevent some of the reverse flow. Sometimes called extractor effect. Some header designs even use a short collar at the port which is port size and a larger diameter tube over the collar for the main tube.

If in doubt, it would almost always be better to have the intake manifold ports a bit smaller than the head ports, & the exhaust manifold ports a bit larger than the exhaust ports. This generally applies to all engines.

This is a very brief summary. Much flow bench & dyno time is required to optimize these effects. This sort of "mismatching" is only seriously done where the last little bit of power is being sought.
D

 

[John Loftus]

Hi Dave,

Interesting info on the anti reversion effect (I think Lancome has some cream with the same name /ubbthreads/images/graemlins/grin.gif) The mismatch on the Healey motor appeared to be random .. some ports matched very closely and others were off 1/8" and figured it was from manufacturing tolerances as Greg points out (see I read your posts too!)

Cheers,
John

 

[GregW]

/ubbthreads/images/graemlins/lol.gif /ubbthreads/images/graemlins/lol.gif

 

[Brent P]

I think it was maybe Carroll Shelby that said, "Torque wins races, and Horsepower sells cars".

 

[MotorHead67]

Great picture Brent P.