69red

I am doing a stock rebuild of my 1971 LT1 engine. I was considering having my stock heads pocket ported and port matched. My engine builder advised against it. He said that the minimal increase in performance wouldn't justify the cost.

I am looking for someone to tell me their experience with ported stock heads. Was there a noticeable performance increase

Thanks for the help.

Duntov

Are you going to rave it or run it in the upper RPM range a lot? If not leave it alone. Likely will lose some bottom end power and gainin the upper range as a result.

The13Bats

Im a modder but porting heads is when people are seeking a 10th here and a 10th there in the 1320 runs,
Its like said a higher rpm thing,
Your lt1 is super cool hipo factory engine even thought i dig mods i would keep that rebuild as close to stock lt1 specs as possible....

dugsgms74

I wouldn't bother with the port matching, but the pocket port is worth it in my opinion. Not alot of effort, easy DIY project and given the poor quality of the bowl shape of the pre-vortec heads, time well spent.

BTW, unlike port mods, bowl work will give gains in all rpm ranges.

jb78L-82

Not worth paying someone BUT if you could do it yourself, certainly worth a little time and effort with a grinder to clean up the heads. This really is a very easy DIY project!

I assuming that you are looking for a little more power from your 71 LT-1 (330 Gross HP, 9:1 compression) while retaining as much of the OEM LT-1 as possible? The 71 LT-1 is VERY similar to the later L-82's with the main difference being the solid lifter cam BUT almost identical Lift to the L-82 (.450 range) with higher duration (compared to 222 duration for the L-82). I would bet that raising the compression to 10:1 with that cam would certainly give you some boost in power since the stock 9:1 compression is pretty much on the low end for performance....just a thought....AND no one would know from the outside looking at the engine.

10:1 Forged pistons, slightly more performance solid cam, and the head work would really wake that LT-1 up and visually no one would be the wiser....

Last option would be to use the 70 LT-1 cam (370 Gross HP) along with the 70 LT-1 compression (11:1) if you have high quality Premium fuel near you. I don't think I would go this route if it was me....

Jason Staley

Also, you might consider replacing your valves with a decent set of aftermarket valves with improved flow profiles. The shape of the valve and valve seat make a big difference in flow while the valve is going thru the lower lift range (up to 0.3" lift). At these lower lifts, the valve is the chock point and not the port. I verified this on a home made flow bench, but that was ~15 years ago, and I don't have any numbers to show you regretfully.

With a little pocket porting, removing any casting imperfections/flash in the ports and smoothing them out, and replacing my valves with Manley Race Flow valves in my ZZ4 (alum L98) heads that only have 165cc intake runners I am pulling 328 rwhp, which equates to 385-400 net Hp at the engine. Not too bad for a head a lot of people considers junk.

jb78L-82

That is very interesting Jason...using the stock OEM cast iron heads with aftermarket valves for improved flow...could be the answer for many OEM stock enthusiasts that don't want to change to aftermarket heads...

BOOT77

Unless you have to use your heads I wouldn't bother. Porting iron can be costly, what the builder prob means is it would be more cost effective to buy aftermarket heads that would make more power than your ported stock ones. Port matching is not worth it unless you want every last ounce and it needs to be done right.

69red

I appreciate those who have taken time to answer my questions. I don't push my cars to the upper RPM range. I would like to get a little more performance out of this build. Switching to aftermarket heads is not an option. I want everything from the outside to appear and sound stock.

diehrd

Put a 383 rotating assembly in it to gain torque and it will still look OEM 100% and the engine will still match as far as correct heads and block ..

Revi

Because you want everything to remain stock appearing and don't push your car to the upper limits, it's your call on how much money you want to invest in a few HP gain.
Porting your 76cc heads or upping the compression can/will help with a performance gain, but it isn't going to be noticeable in your seat-of-your-pants driving.

I know the 1970 64cc heads benefit from porting, but I don't have any experience with the 71/72 76cc heads. The 76cc heads already flow better than the 64cc heads, not sure how much there is to gain with porting them?

If you need to order new pistons, just order a set of the 1970 LT-1 domed pistons. That'll up your compression a bit and won't cost anymore than ordering the stock pistons. A thinner head gasket will also up the compression a bit and will not cost you any more than a stock replacement.

jb78L-82

Upping the compression ratio by 1 point with different pistons (1.2 points with a thinner head gasket)and cleaning up the heads a bit should net you 20-25 more HP, which you will definitely notice. In addition to more power, throttle response should be better as well as slightly better gas mileage....all with the motor looking 100% stock. You win all around as long as you can run at least 91 octane (preferably 93).

69red

I already have the lowered end rebuilt. Otherwise, I would consider stroking the engine.

Taijutsu

I believe there have been a few articles on how much to rebuild stock steel heads vs Alm replacements.
By the time you have rebuilt the stk heads, it is almost as much as alm aftermarket heads.
I have also seen the same said about rods too, might as well upgrade w/aftermarket.

JMHO

R

Jason Staley

What I found really interesting was when comparing flow numbers to one of my friends that drag races is that my small Manley 1.940/1.500" valves actually flowed about the same as his heads with bargain 2.020/1.600" valves at the low lift values. His larger heads way out did mine once the valve passed .400" lift, but with a non-roller camshaft the valve spends quite a bit of its time at the low lift valves. If you backcut the intake valve and go to a multi-angle valve seat, there is even more room for improvement on a street oriented cam.





Just thought I would throw these options out there for the OP. Something to consider.

toddalin

If you've got the money, it is well worth the effort and doesn't show.

cardo0

If you want professional headwork on stock iron heads I would contact Brezinski: https://www.castheads.com

If those guys can't help you then you are asking for miracles.

Good luck.

tt 383

Best thing is to get a 5 angle vj done. You could blend the machine work done, and then just cleanup the ports, profile the guide boss. You aren't hurting anything as long as you don't change shape. A 6 inch double cut carbide burr is 30 dollars and in a good variable speed drill is pretty safe for a first timer. You can use stones to clean most of the ports and use the burr to knock down the guide boss to a teardrop shape. A burr finish is good just not pretty...

gkull

The best thing you can do is switch to 64cc heads. With flat top pistons with 4 valve reliefs 64cc gets you some place in the low tens compression

I had totally ported with screw in studs and guide plates 186 casting 64 CC. Manley race flow valves

I probably put 50,000 miles on my vet with those heads you can get a book on porting heads I think I had the Chevy how to make horsepower book. I bought a Makita 25,000 RPM Grinder. I went to a mid 500 lift cam using 1.6 roller rockers

Alex66

Brezinski: https://www.castheads.com