[77TA]

I am seriusly considering a 10 to 1 455 for my next engine due to parts I have hand
(87cc HEADS). I know from reading Jim Hands wonderful write up on optimum compression it can be done but I was interesed to hear from those that have ran compression levels like this on the street regularly. I am thinking of things like driving on a vacation having to buy gas from gas stations your not familiar with and how about keeping the engine in tune and avoiding detonation. What about valve guide wear and things like that. I was just wondering is this something you can build and run several years and thousands of miles without major work after getting the cam,carb,& ignition tuned or is it a combo that may require new valve guides freqently and seals replaced to prevent oil seapage into the cylinders and how about carbon build up is it a problem. I am seeking to understand better what to expect if I do build this engine. It will not be a daily driver probly less than 4000 miles a year.
Thanks to all !!

[77TA]

I am seriusly considering a 10 to 1 455 for my next engine due to parts I have hand
(87cc HEADS). I know from reading Jim Hands wonderful write up on optimum compression it can be done but I was interesed to hear from those that have ran compression levels like this on the street regularly. I am thinking of things like driving on a vacation having to buy gas from gas stations your not familiar with and how about keeping the engine in tune and avoiding detonation. What about valve guide wear and things like that. I was just wondering is this something you can build and run several years and thousands of miles without major work after getting the cam,carb,& ignition tuned or is it a combo that may require new valve guides freqently and seals replaced to prevent oil seapage into the cylinders and how about carbon build up is it a problem. I am seeking to understand better what to expect if I do build this engine. It will not be a daily driver probly less than 4000 miles a year.
Thanks to all !!

[tempest455]

In a nutshell, the things to consider using high compression and pump gas are as follows.

Timing: Limit total timing to around 32-34 deg. Use adjustable vacuum
advance to eliminate part throttle ping.

Temperature: Engine temp 195 max. Between 180-195 is good. Colder air
intake (ram air) will help when car is properly jetted. Blocked heat
risers on intake will help.

Air/fuel ratio: Jet rich, this in effect lowers octane requirement.

Plug heat range: A colder plug (1 heat range AC 45, 44) will reduce
detonation but can foul more easily.

Use highest octane pump gas available: Stick with major manufacturers
and a station that has a lot of traffic (high product turnover in tank).
I like Amoco.

A looser converter will place less of a load on the engine and can
eliminate detonation.

A longer duration cam will reduce cylinder pressure. Example: A RA III
cam in a 10.0:1 motor will have more cylinder pressure than a RAIV cam
in the same engine.

Unless you plan on road racing or bracket racing every weekend, valves seats will not be a problem.

I hope this helps.
http://www.wauknet.com/douthitt/pumpgas.htm

Eric D.

[This message has been edited by Eric Douthitt (edited 12-26-1999).]

[Tom McQueen]

Eric pretty much nailed it. The only thing I can add is the way in which you arrive at the 10:1 figure. It is FAR better to get there with 87cc heads and a flat top/dished piston than to use a 107cc head and a piston with a 20cc dome. The domed piston is gonna rattle. A bigger rear end gear helps as well. Anything you can do to reduce the load the engine sees at the lower RPM's should be considered.

[PONTIAC DUDE]

Also, If you are using the E-heads the compression (theory) is 1 point lower w/ aluminum. So less of a problem. Later.

[77TA]

I am getting more comfortable with the idea of higher compression and pump gas after emailing some knowlegeable guys and reading articals by Jim hand and Eric. I am thinking about grinding the intake valve shroud bach flush with the chamber wall to add a few ccs to the chanmber as mentioned in Jim's artical. I will reread it before I do it to make sure I understood it right. I hope this will get me about 90-92cc and a little lower compression ratio. This is probably cheaper than redoing my 96 heads. since the stock valves in this one are in good condition.

[Lee]

I recently worked on a 6X-8 headed 455. The heads were milled, and the pistons were actually slightly out of the top, average CR was about 9.15. The cam is the Xtreme 224/230 installed on a 110ICL. Q-jet, Performer, R/A manifolds (2.5"), and a parts house HEI.

The HEI as delivered only had about 10 degrees mechanical advance, and the owner had resorted to setting the initial around 20 - and it pinged. We had it recurved for 20 mechanical, and had it come in around 2400 - dropped the initial to 12. I was shocked to find it still pinged! Slowed the curve to not finish until 3000, and everything worked well.

I drove another 6X/455 combo on a daily basis for nearly 3 years/25,000 miles. The cam was a single pattern (226, .465, 110lsa, 106 ICL). It ran fine on 93, but would occasionally ping a little if I got 92 from one of the cheaper stations. If I were to build a 455 and plan on taking it for long trips, I'd be a little on the conservative side on the CR.