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Compression-How much is too much?

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67Super Sport

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Discussion starter · #1 ·
Been a while since I have been on here. I have been in a transition of sorts. I believe I have decided to call it quits with bracket racing after 11 years. I am looking at putting my car back on the street. What I am trying to decide is what direction to go. My current 460 has Brodix RR-O heads, Eagle rotating assembly, 10.5:1 compression, Ede perf. RPM intake, 750HP carb, and a Comp solid roller 236/242 duration at .050. So my biggest question for you guys that have a lot of street tuning experience is how will this combo work on the steet as far as the compression goes? I know 10.5:1 isn't that much but is it too much with this little cam? It cranks at about 195 PSI. I don't want to be having to mix race fuels or buy expensive octane boosters. Just want to run 93 pump gas. Current trans is a full manual TH400 with a 5000 stall 8" ATI converter. That would be tightened up or I may even think about putting the M21 back in it, but am a little unsure if the M21 would hold up to the 460's power. I guess it would if it was with some sense:D.

Other consideration is selling this engine and putting the 396 back in the car along with the M21. When it comes to street cars I'm not all that in to having to have the biggest, fastest most powerful thing out there. A little ole 396 used to be just fine for me on the street. I've had enough of the keeping things together days.
 
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#2 ·
Sounds like a great street setup as it sits. 10.5 would be on the edge with iron heads, but with the aluminum heads you should be fine, as long as the quench is setup correctly. I agree, you'll probably want less converter in there for the street, probably something closer to a tight 3000.


Sent from my Autoguide iPhone app
 
Discussion starter · #3 ·
Deck has been set at .005 in hole, and I am using an .039 gasket. So, quench is right at .044.
 
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#4 ·
I'm running 10.5:1 with my afr 265's and have been running 91 octane with no problems in the Florida heat. I'm running the Keisler rs600 with 3:73 posi. I don't know how long the m21 will last, probably not long if you do any racing at all.
 
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Discussion starter · #6 ·
jvoiles said:
I'm running 10.5:1 with my afr 265's and have been running 91 octane with no problems in the Florida heat. I'm running the Keisler rs600 with 3:73 posi. I don't know how long the m21 will last, probably not long if you do any racing at all.
Click to expand...

What size cam are you running?

Won't be doing any racing at all. Just a weekend cruiser.
 
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#7 ·
As long as you get rid of your traction devices, slicks....The m-21 should hold up. Something is gonna give...best to be your tires instead of your running gear.

If it's the original numbers matching trans, I might save that one for later when you want to bring her back to original. Best not to take any chances.
 
Discussion starter · #8 ·
No traction devices will be on car and just regular street tires. No drag radials or anything.

It is the original numbers matching M-21 but bad thing is my dad lost the original numbers matching 396 block to a dropped valve back in the early 80's so the numbers matching part is gone. Really wish he had of kept the block. Probably could have been sleeved.
 
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#9 ·
On 93 I think you'll be fine. I am running my small block at 10.3 with aluminum heads and a 231/239 hydro roller. So give a couple for solid lash and I think your cam is about the same numbers in duration. For compression I would be ok going to 11-1. I don't want to give any other recommendations because like you my other stuff was years ago, and I am afraid to compare what I did on gasoline from back then compared to todays gas. I mean, I ran 10.5 up to 11 with steel heads on small and big blocks with 250/260 cams up to 7000 on 93 octane. I don't know if I would be so brave today. Today would definitely be aluminum heads at least.
 
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#10 ·
Chad,

No problems here with 10.5 scr and 92 octane pump gas. Quench is .041" and I have my timing locked out at 39 to 40 degrees. My cam is abit larger than yours and probably helps me out, but if you have a good cooling systems and don't get carried away with timing you will probably be ok. I can even lug mine in 6th gear at about 45mph and get no detonation.
 
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#12 ·
As said, you should be just fine with your 10.5 on pump gas. If you stick with the th400, I would drop to 3000-3500 stall. Beyond that, enjoy the cruising.
 
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#13 ·
Hey Chad FWIW ......No detonation on track or street with 91 ( no ethanol content )
439ci with Brodix RR quench @ .040 ........ 37* total locked out ( retards to 35* at 4k ) cam is a Straub SR 252/268 !! my car is a stik car 4.30 rear so easier to not detonate while lugging




I too am thinking of putting my numbers 396 back in .......... right now doing stock rebuild with mild HR from Straub ..frankly more concerned about detonation on this motor compression is right at 10.1 with old school forged trw's and small 218* cam might be an issue ??

IMHO the Muncie will be fine even with 460 .....maybe some upgrades from AutoGear ...midplate etc but in reality youve done the racin thing I suspect you want to enjoy car in another way ........put in a nice soft clutch & have fun
 
Discussion starter · #14 ·
Yea Bill. You hit the nail on the head. I have done the racing thing and gotten that out of my system, so I won't be thrashing on this thing on the street.

You bring up a good point to about the 396. It has the old TRW slugs and the pistons in the hole .020 or more, which puts the compression on it around 9.5:1 but with a huge quench. If I use shim gaskets to tighten quench there we are at 10.25:1 but now with iron heads, instead of aluminum heads with a nice CNC machined chamber and SRP pistons. Good points.

As for the M21...that is all stuff I am not up on as far as upgrades. Will have to look into that stuff. The full manual auto isn't a bad option though either. Still makes you feel like you are rowing gears I guess:D.
 
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#15 ·
Chad, I personally wouldn't have a problem running that on the street. My 548 is 10.2 with iron heads and cranks 190ish. No problems with 93 at all. If you want to be cautious, you could pull a few degrees of timing and run a step or two cooler plug.
 
#16 ·
The one thing that might concern me for street use is the solid roller cam. If you're in an area where there's a lot of traffic and idle time I'd be worried about splash oiling with solid lifters. Might reach out to cstraub www.straubtechnologies.com and ask his opinion on whether or not your lobe profile would be too aggressive for a hydraulic lifter. There are a few guys on here that are running "hybrid" setups, maybe someone will chime in.
 
Discussion starter · #17 ·
The cam is a comp extreme energy solid roller. It is the XR274R cam ground on a billet core with 108 LSA. Comp 933 springs with 190 lbs. on the seat. Lifters are the crane standard lifters. They do have a pressure fed hole to the roller wheel but not to the needles like the crowers with HIPPO. I have thought about the solid roller thing as well.
 
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#18 ·
67Super Sport said:
Yea Bill. You hit the nail on the head. I have done the racing thing and gotten that out of my system, so I won't be thrashing on this thing on the street.

You bring up a good point to about the 396. It has the old TRW slugs and the pistons in the hole .020 or more, which puts the compression on it around 9.5:1 but with a huge quench. If I use shim gaskets to tighten quench there we are at 10.25:1 but now with iron heads, instead of aluminum heads with a nice CNC machined chamber and SRP pistons. Good points.




That is EXACTLY where I am at TRW .015 down in hole = approx 9.5 cr with huge quench ......or 10.1 with good quench ..........Experts telling me go with the best quench to avoid detonation even with higher static CR .& iron heads .so will be using shim gaskets .020


I am lucky enough to have my complete numbers 396 so hopefully will work out fine on pump gas ( when I actually put in car remains to be seen but will have motor ready to go when that day comes)

if I did not I might just paint my 439 all orange for stock look and recam with a HR to make it cruise nice with a manual ....... put the Muncie back if it was original :thumbsup:
Click to expand...
 
#19 ·
I have been running a solid roller 427, right at 11.5:1 comp on the street for around 7 years now. Iron heads and pump gas. However, i do pull some timing. Every now and then ill throw an octane booster in, but it still does fine on straight 91. I am curious now, as i did not record the quench last time the engine was out.

In regards to the m21, I ran an m20 behind the 625 horse 427 the whole time, with e.t streets. Leaving off the 3-step at the track and it survived, though only leaving at 4800. If you be careful with them, they will last, but your still taking a chance. Still nothing like a 4 speed :thumbsup:
 
#20 ·
What stands out to me is the 1.40 60' times. The gears in there now, likely 4.10's, you're probably not gonna like them on the street. Go 3.55, 3.42, 3.31, 3.08, etc... All of which are more practical. If you keep the th400, swap to a 10" converter.
 
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