I have a question that's been bothering me for some time now and I was hoping someone here might be able to help me figure out an answer.

I have a 1969 455/390hp original and unmodified engine that I am putting into my 1969 Cutlass S. That engine has a compression ratio of 10.5 to 1. Having owned a number of 60's-era "Ultra-High Performance" engines, I know that pre-ignition detonation is a serious problem, given the crap that passes for gasoline these days. I was thinking of running a 4-to-1 ratio mix of 93 octane and 100LL avgas. But perhaps there's a better solution to my problem.

My question is this:

Given the advances todays modern camshafts have over the original cams, would their improved design eliminate that detonation and perhaps even allow me to pick up a few horsepower at the same time?

I want to keep the engine as original as possible. I don't want to install adjustable rockers either. As my budget is already strained with other purchases, I can't go the roller cam route.

If it is of any help, here is my setup:

M41 HD Turbo Hydramatic 400 (original converter of unknown stall speed)
3.91 anti-spin, O-type, 12-bolt rear
Hooker Super Comp Headers
Torque Tech 2.5 Exhaust
Walker Super Turbo long-case mufflers

This is a street-driven car 99% of the time, with the exceptions being a couple trips a year to the drags at Musclepalooza.

Any suggestions are appreciated!

Thanks,
Uncle Hulka

 

I would think that upgrading to a mild modern cam would be a no brainier. It would give you a perfect opportunity to inspect/replace the timing chain, and the added power would be a huge bonus. I would think you could run premium fuel without any trouble, if the tune is good. Replacing the thin steel shim head gaskets with thicker aftermarket replacements would drop the compression just a bit also. However, once you remove the head, timing cover, intake, etc, its real easy to get into the MAWs!

 

Check with Cutlassefi, my thoughts are the stock valve train will allow about a 1/2" of lift, and a cam change on an unmolested motor should work, if a valve job has been done check valve stem ht's before proceeding..

 

Keep in mind that most replacement head gaskets are thicker and will drop your compression. I think a mild cam is a no brainer.

 

First of all you don't have 10.5:1, unless something has been changed. It's actually about 10.0:1 from the factory. With the right cam and setup you should be fine on 93 pump alone.


I sell an Erson TQ50 which would be perfect for your build. A little tone, easy on the valvetrain and will improve power for sure.
Specs are 228/235@.050 with .504 lift.

Let me know if I can help.

 

I don't want to lose any HP or torque, but if a mild cam will help eliminate detonation I'll look into it. Anyone here with personal experience that could suggest a specific cam?

Also, don't know how this will effect cam selection, but I am seriously considering going with a Muncie M21 instead of the M41 TH400. I have all the major parts on hand (trans, bellhousing, flywheel, pedals, etc.) from a parts car I bought a couple years ago. Of course, since I have to take out the crank and bring it to a machine shop to have it drilled for a pilot bearing, I'll have the heads off so I MIGHT AS WELL install thicker head gaskets......and since it's already torn down that far, I MIGHT AS WELL replace the timing chain....and since,,,,,,,

This is exactly how replacing a rusty battery tray in my '70 Chevelle, turned into a frame-off, nut & bolt restoration!!!!!

 

Sorry, Cutlassfi, I was mistaken. The Factory Service Manual says the L32 is 10.25 to 1. My Bad.

The cam you suggest has a .504 lift. Will that work with my stock, non-adjustable valve train?

 

Yes, given it worked ok before.

 

Email sent

 

Mild cam, you wont need to machine spring pockets, build for torque and go with an aftermarket, like Summit, HEI set up, reduce the amount of vacuum advance, raise timing until it starts to ping under load then retard slightly until it goes away. My 68 toro 455 runs great on mid grade gas with an agressive cam. Consider a vacuum 750 speed demon or holley carb, i get better throttle response over the q jet.

 

Thanks for the sound advice. Cutlassfi has given insight as well. As I told him earlier, after reviewing the time I have left before the Musclepalooza drags, and the large number of things left to do, I decided to install the engine and trans and run them as they are (for now). I also had to put the auto-to-manual conversion on hold until afterwards. I'll run leaded racing fuel at the drags, so detonation won't be an issue.

Really eager to see how she runs. The last time I had this car at 'Palooza (1 year ago this Spring) I was running the original 350/th350 with a 2.73 open rear. Hopefully it'll will be worth all the time and effort (not to mention money)

 

Uncle Hulka do you still have said 350 engine?