69 L36 427 swap to aluminum heads?

[Duke W.]

Re: 69 L36 427 swap to aluminum heads?

mine is a 390HP/427 with auto and 3.08 in the rear axle and dyno's at 260 Rear wheel HP and I'm trying to get it to something more peppy and fun to drive than my 2006 Honda Pilot

Have you optimized the spark advance map per my 2012 San Diego national convention tuning seminar? The OE map is set up for emission control, not performance and optimizing it will gain noticeable torque/power across the range. Peak power is a function of head flow, and massaging the original heads should add about ten percent to the top end and is likely less expensive than new heads. What's the head gasket thickness? Maybe the engine was rebuilt with "low compression" sometime in the past. A 427/390 even with a 3.08 axle should be a spirited performer is the "tune" is optimized.

[Joe L.]

Re: 69 L36 427 swap to aluminum heads?

Hi Joe...I will probably go all out and install a hydraulic roller cam with similar duration to the stock cam and more lift. Let me know if that narrows down the selection...Don

Don------

You could use any of the E-Street, Performer, or Performer RPM heads. If you purchase them bare, use the valve springs included with the roller cam kit or recommended for the roller cam you purchase. If you want to purchase them complete, then you'll need to go with the Performer RPM heads, Edelbrock #60455.

Please do keep in mind what Duke has mentioned, though. Your engine, as-is, properly tuned and with a modicum of modifications should run very well. The L-36/LS-5 cam is just about the best flat tappet street cam for a big block ever devised. So, while you'll be able to improve performance with the aluminum heads and roller cam, the performance increase might not be worth the cost of the heads and roller cam. The heads are going to cost in the neighborhood of $2,000 for the pair, complete, and the roller cam and lifters are going to add another $800-1000. If you can't do the installation yourself, that will add an additional significant cost.

[Don W.]

Re: 69 L36 427 swap to aluminum heads?

Hi Joe and Duke,
The engine was rebuilt by Steve at Automotive Expertise in Huntington Beach. The cast iron heads were reworked with larger valves, flow tested and cleaned up at shop specializing in head work. The pistons were replaced and compression was returned to about 10:1. The carb was totally restored. The distributor was run on a Sun machine and was adjusted and tuned. Exhaust was increased from 2" to 2 1/2". The car has been dyno tuned with adjustment to jetting and metering rods and timing. Max rear wheel output after those activities is 260 HP and 328 ft-lb torque and that is matched up with 3.08 gears in the rear and the THM-400 automatic transmission. I don't who specifically can tune it to Duke's recommendation and I don't have that skill myself.
Don

[Mark E.]

Re: 69 L36 427 swap to aluminum heads?

Do some google research on chassis dyno results for L36, even LS5. 260 rwhp sounds like a solid result for this engine. I was at a ZR-1 Gathering at the NCM in the early 2000s where they had a chassis dyno set up. Stock LT-5 engines were pulling about 300 rwhp. The LT-5 is rated 375 - 405 SAE net hp. The L36 is about 100 hp less.

With that said, some basic checks before spending $-

- Ignition advance curve as Duke and Joe suggested.

- Throttle linkage. Are all 4 throttle valves WOT when the gas pedal is floored? (Don't laugh; a common problem.)

- Secondary lock out. If the secondary linkage and choke are not properly adjusted, the secondary air door (or secondary throttles, depending on model of Q-Jet) can be prevented from opening.

- Vacuum diaphragm and secondary air door spring tension- An incorrect diaphragm or an improperly adjusted air door spring tension can prevent the secondaries from opening properly.

- Plugged fuel or air filter

- Inoperative transmission kick-down. A layman can mistakenly diagnose a lack of kick-down as a lack of engine power. As an enthusiast, you know the difference.

- Are the brakes dragging? Check the parking brake too.

- Good, even vacuum reading at idle? If not, find out why.

But since you're pulling 260 rwhp, all of the above may be fine. Maybe you expect more than a good running L36 automatic with 3.08 gears can deliver. If so, installing a more aggressive rear end gear may be less expensive than engine mods to achieve seat of the pants result.

[Duke W.]

Re: 69 L36 427 swap to aluminum heads?

Hi Joe and Duke, The engine was rebuilt by Steve at Automotive Expertise in Huntington Beach. The cast iron heads were reworked with larger valves, flow tested and cleaned up at shop specializing in head work. The pistons were replaced and compression was returned to about 10:1. The carb was totally restored. The distributor was run on a Sun machine and was adjusted and tuned. Exhaust was increased from 2" to 2 1/2". The car has been dyno tuned with adjustment to jetting and metering rods and timing. Max rear wheel output after those activities is 260 HP and 328 ft-lb torque and that is matched up with 3.08 gears in the rear and the THM-400 automatic transmission. I don't who specifically can tune it to Duke's recommendation and I don't have that skill myself. Don

Post all the data you have - head flow, spark advance map, dyno test graphs. Diagnosing problems requires test data, and it sounds like you have it. Is the camshaft OE equivalent? The emission oriented OE spark advance map provides 26 deg. crank advance at 3800, which is not bad, but initial timing is speced at on 4 deg. BTC, which yields total WOT advance of only 32 deg. versus the "ideal" of 38-40, so if the initial timing is at the OE spec, simply advancing it to 12-14 deg. should make the engine noticeably stronger as long as it doesn't detonate.

[Tom D.]

Re: 69 L36 427 swap to aluminum heads?

Please describe your pistons. And,in case I missed it in the discussion, please advise. Thanks.

[Don W.]

Re: 69 L36 427 swap to aluminum heads?

All, here is a copy of my dyno runs results. I have no other data to share. If anyone has a shop in the area of Huntington Beach that can check all of Duke's recommended parameters, pleasedyno results 001.jpg let me know. thank you..Don

[Duke W.]

Re: 69 L36 427 swap to aluminum heads?

I don't see anything fundamentally wrong in the test data. It shows a flat torque curve that is typical of most OE configurations. The test was terminated at only 4800, but the power probably won't roll off significantly until about 5500. You said the heads were flow tested and the distributor was tested on a machine, but you don't have the data. Is that correct? I take it you live in SoCal. Are you a member of the SoCal chapter? Maybe someone nearby or a buddy with a dial back timing light can record the spark advance map and set the initial timing to achieve 38-40 total WOT advance. If not and you're willing to drive up to Redondo Beach, I can check it out.

[Don W.]

Re: 69 L36 427 swap to aluminum heads?

Hi Duke,
Yes, I do not have any test data for the distributor nor the heads, and yes I'm a member of the So Cal Chapter. I would be honored to have you check it out and I'll send you a PM.
Don