So judging by the popularity of shaving .1 off to raise the comp ration to 10.5:1'ish, im considering this upgrade. Im assuming in order to achieve this i need a pre-1971 block/head combo, and should have adjustable valves instead of a hydralic lifter system. So with that said, i figure i need shorter pushrods, non hyrdralic roller lifters (smother = better?), and about .140 shaved off to compensate for a .4 thick aftermarket head gasket. I think i have the idea but some stuff is a bit cloudy, any advice would be greatly appriciated.

thanks,

aaron

you might just have to install a different ratio rocker arm assimbly.

check cliffordperformance.com

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1973 plymouth duster 225 slant six .30 over, erson 270 cam, 9.5 to 1 compression, big valves, headers, and a holley 4 bbl
http://cardomain.com/ride/3135091

hey that thing got a hemi? naw its just a slant six

If you want to use solid lifters, any year bock/head will work. Hydraulic was '81 and later, but you can change them over to solids easy enough.

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Official Cookie and Mater Tormentor.

carpdar,

If you plan it carefully when shaving the block and head, consider regrinding your cam to a taller profile and you will be able to use stock push rods. The cam regrind and head/block shaving can off set each other. That is what I did, which worked out very nicely. A regrind is a way to save some money as well as using stock push rods.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

To be honest, 10.5 is to much static compression for a street driven SL6 running a stock to near stock cam. Todays pump premium will ping with decent spark advance numbers and that much static compression.
As a general rule, when fuel quality is low, (pump gas) you will be better-off running a lower compression ratio and giving the engine more spark advance, then running a higher static compression ratio and having to turn the timing back to prevent spark knock.

Rule #2, camshaft profiles and static compression ratios are related, as one goes up, so does the other.

I can not stress enough to seriously think about the end use of the vehicle, set a realistic performance goal and then carefully plan the combination of parts needed to acheive the goal. The best running engines I have built are the ones that are carefully planned-out and then go together per the plan.
DD

Hi Doc and all

Tied together all the way - but try to get that into the average enginering works thick skull

What is the guide as far as the interlink between lift duration at 50 and seat to seat, to compresion ratio

EG

int/ex seat to seat 264
@50 220
lift .44 int/ex

lobe center 110
int center line 106

Application some racing /powercruiser

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Regards,
Fanie Gerber
It's never junk, it's just a part you're not currently using

http://www.valiant50.co.za
Just say I own a few Mopars

What is the total overlap and where does the intake valve close? (in degrees)
DD

If my figures are right he has 44 degree overlap. IVC @58 ( or 36 @.050).


That would put him at 186 cranking compression with a DCR of 9.8 to 1 if he had a true 10.5 to 1 static comp.


Thats probably pushing it a little, depending on the fuel.


If it was a true 10 to 1 the cranking comp would be 175 with a DCR of 9.3 to 1.


A true 9.5 to 1 the cranking comp would be 164 with a DCR of 8.8 to 1.



Jess

inlet open 24 btdc cloce 60 atdc

overlap 44

If you think about it all factors pertaining to how long the valves are open - together and seperate - by how much andwhen they are open in relation to the piston stroke will determine what the safe static cr is

I also surmise that the wilder - higher lift longer duration more overlap - the cam is the bigger the difference between the static and dynamic cr. - due to less volume being compressed with the valves CLOSED

Witch would need a higher cr

and so on

_________________
Regards,
Fanie Gerber
It's never junk, it's just a part you're not currently using

http://www.valiant50.co.za
Just say I own a few Mopars

Ok so maybe i would be looking at high 9:1's for compression after some re consideration.. But im not sure if i understand the relationship between the static compression ratio and the camshaft quite yet.
Right now i have a stock cam shaft, and i would defiantly like to get a meaner one or get it reground. Does anybody know a good combination of camshaft (re-ground or after-market) and head plaining to achieve just under 10:1?

If this helps the setup i plan to run with this is a super six intake w/ my rebuilt carter 2 barrel, 6 into 1 headers w/ 3 inch pipe, HEI ignition mod, and a mild ported head.

Thanks

I have very simialar questions, me too want to mill 0.1" and use same valves and cam for now. Will it ping or detonate for sure? Can I prevent it with advance adjustment?

Thanks

If you do not understand dynamic CR then you are not ready to mill.

I milled .160 (head and block) , Erson 280 cam and can run on 87octane on the street.

This took some planning......

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Yeah....Im the one who destroyed this rare, vintage automobile.....

First of all thank you very much "Sandy in BC" for replying my questions in both topics ... I knew what is DCR but I did not know it effected that much. I listened to you and searched DCR in the web and found very useful info. As I understand a Slant6 wont run good if I just mill the head. I need to change the cam with a suitable timing. I just thought this is a very low CR engine, which is in the safe side ( for long life) and will handle higher CR with the stock cam. I understand that it is impossible to avoid pinging and detonation with the stock cam. Than I again think that this project will be in my future plans since I have tight budget at the moment.

Ok, I understand that one should not only mill the head without replacing the cam with a high lift one. What if I change the cam with a high lift one? The DCR will decrease I guess so will there be no increase in HP?

No

With the new cam and head skim your dynamic CR will still be higher than your original - but your cam flows more or allows more air to flow into the cylinder ergo more HP - as a rule - overdoing things can be detrimental.

The whole shebang is so interlinked that you cannot just look at your lift - the duration is more a factor than lift alone - duration @ 50 that is - in other words how LONG was the valve open.

This is were RDP cams come into their own on our LONG stroke motors the exhaust valve does not need to be open as long as the inlet or have the same lift - the mixture is under presure at the bottom of the stroke so it will force itself out to some degree

Less duration and lift required on ex = higher DCR in effect needs less SCR, therefore, less stress on components etc

_________________
Regards,
Fanie Gerber
It's never junk, it's just a part you're not currently using

http://www.valiant50.co.za
Just say I own a few Mopars