70 LT1 new tuning results

[Larry M.]

Re: 70 LT1 new tuning results

Yes.........one or both heavier springs. It is trial and error unless you have access to a SUN distributor machine.

Larry

[Duke W.]

Re: 70 LT1 new tuning results

Rather than reduce total WOT advance to quell detonation I recommend slowing the centrifugal with heavier springs, but on a LT-1 don't slow it down to more than 3500 max centrifugal. If it still detonates with 3500 max centrifugal, reduce total WOT advance in two degree increments until the detonation stops.

What is the actual CR of your engine? You can get an idea by measuring head gasket thickness. The original was a .018" steel shim gasket. If you have access to a borescope to look inside the cylinders you can visually determine if the pistons are the OE domed type or something else.

In my tuning seminar I give recommended starting points for optimizing the spark advance map for any engine configuration, but it ALWAYS come down to each individual case because there are too many variables (some unknown) to completely rely on "modeling", as is the case for disease pandemics and climate change.

Ultimately it requires real data from road testing to get it dialed in.

Duke

[Richard G.]

Re: 70 LT1 new tuning results

Slightly off topic of original points style distributors.
However, I find it very interesting to be able to control you classic car distributor with a phone.

https://progressionignition.com/

Electronics have sure changed over the years! A few things you can do with it. No external boxes either.
REV LIMITER

Built-In and adjustable with your phone from 2000-10,000 rpm.


KILL SWITCH

Use your phone to disable the ignition for theft prevention. Every distributor is assigned a PIN number so only you can access.



Cheers.
Rick

[Dennis D.]

Re: 70 LT1 new tuning results

Changed out a black spring for a silver. WOT now 3300rpm. (sunoco 93/112 race mix )

Out and about for an hour or 2 in a variety of driving speeds. Around town stop and go cruising, Highway cruise at 60. acceleration to 80. No ping. Even got stuck in a highway shutdown for 40 minutes. Got some exhaust smoke with that though. No problem shutting down hot and restarting.

BTW tried the rubber band limiting. Went from 17 degrees to 14 degrees at idle. ( vacuum plugged). Not sure, band slipped.

Thanks for all the input.

[Duke W.]

Re: 70 LT1 new tuning results

Sounds like you've got it dialed in. You might want to try using just straight 93 PON pump gas to get rid of the hassle and expense of blending in race gas, but you might have to slow the centrifugal down a bit more.

Does the engine still have the OE pistons and thin .018" head gasket? You can measure it at the corners of the head block interface with feeler gages.

93 PON is equivalent to 97-98 RON so even with the OE compression ratio, which is probably closer to 10.5 than the advertised 11, it should run detonation free on 93 PON. Most premiums back in the day were in the range of 97-99 RON.

[Dennis D.]

Re: 70 LT1 new tuning results

Pistons are OE. Not sure about head gasket, but I will check.

[Dennis D.]

Re: 70 LT1 new tuning results

pic of pistons. Measured gasket thickness at corner of head and block below stamp pad. Get .040" approx.

1970 Corvette Misc Documents (4).jpg

[Lawrence M.]

Re: 70 LT1 new tuning results

Maybe the head gasket is the Fel-Pro 1004 wih .041 thickness or the 1043 with .039 thickness ? They were both recommended to me around 10 years ago to reduce compression on my L46 with original style TRW .030 pistons.

[Dennis D.]

Re: 70 LT1 new tuning results

Maybe the head gasket is the Fel-Pro 1004 wih .041 thickness or the 1043 with .039 thickness ? They were both recommended to me around 10 years ago to reduce compression on my L46 with original style TRW .030 pistons.

Yes. It was closer to .041. I did the same to the 70 l46 I had when I rebuilt. Thanks L

[Doug C.]

Re: 70 LT1 new tuning results

Has anyone tried one of the progressionignition distributors? https://progressionignition.com/ They advertise a mechanical tach drive version for corvettes which i'm considering for my 74 since i have striped gears (for the second time).

[Duke W.]

Re: 70 LT1 new tuning results

You should start a new thread with your inquiry with an appropriate title, which will aid any who search for the device you are asking about.

Duke

[Mark E.]

Re: 70 LT1 new tuning results

I've never seen this product before, but after looking at their website it looks intriguing: Using their smart phone app you can program the centrifugal and vacuum advance curves, set a rev limiter, and remotely disable the ignition. And it's compatible with Corvette's tach drive.

You can choose a male or female cap, but it doesn't look like the OEM cap.