10.5 compression on pump gas

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berry-cuda

berry-cuda

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Hi everyone looking for some advice on the engine I'm building, it's a 360 J head 2.02 valves, I'm running kb190 pistons which are a domed piston, now going by the compression calculator with .055" head gaskets it will put me a 10.5-1 compression and if I go with .070" head gaskets it will bring it down to 10.2, I'm running a comp cam xe284h which is 507/510 lift and 240/246 duration at .050", with the size and duration of this cam do you think It will bleed off enough cylinder pressure to be able to run pump gas? Thanks
 
Yep. It'll be close.

I ran a 360 w/KB-107's+.030 @ zero deck, gaskets @ .039 thick & 72cc 2.02 J heads on 93 octane.
9.8-1.

Watch your timing. You may have to limit it.
 
Agree, make sure you knock all sharp edges down on the face of the pistons, valve notches, edges of dome etc. 600 sandpaper works great. Also check combustion chamber for same. I always deburr around spark plug holes and the chamber. Any sharp edge can create a hot spot. The weight of the car and gear ratio also come into play
 
All the above is good & true advice! Also the stall speed (if using an auto) helps a lot aswell! So your not "Lugging down low will help a lot too!
 
Use an online calculator and get your dynamic CR as well. You'll want to be somewhere in the vicinity of 8.0 or less DCR to run pump gas.

Oh and what is "pump gas" up there? That may make a difference too.
 
Yeah we are only 91 octane here, there is a couple places to get 93, it's a manual trans so stall isn't a issue, I have taken down all the sharp spots already, I will check my dynamic though
 
How do you find out intake closing poin abdc at .050" lift +15 deg for the dynamic compression
 
It will be on your cam card if you have it. If you don't have the card, I don't know how you'd figure it out.
 
68* is the number you use. You only add 15* if your IVC event is measured at .050". That 68* spec is advertised, not .050, so you use 68*.
 
What would be considered a "colder plug" I usually only run ngk's, is 8.12 dynamic to much for 91 octane? Also what would be a good starting point for the timing?
 
In general the colder the plug, the shorter the nose of the plug. The nose of the plug is the part of the insulator that is freestanding inside of the plug. To put it in NGK-speak, a BKR7E-11 is colder than a BKR5E-11. The underline is to emphasize the number that denotes heat range of the plug. It is not part of the part number.
 
berry-cuda said:
What would be considered a "colder plug" I usually only run ngk's, is 8.12 dynamic to much for 91 octane? Also what would be a good starting point for the timing?
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Nope, that's right in the ballpark. It might even run on less than 91. 8.5 is generally considered max, but there are always exceptions. You should be fine.
 
berry-cuda said:
https://www.uempistons.com/index.ph...=comp2&zenid=2675ee5e1ee62264f76ac16cd2743d69

So is the number 68 is that what I use in the calculator? Why does it say +15deg? If 68 is the number at 10.5 compression my dynamic is 8.12
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You should be fine with that. 8.0 for iron, 8.5 for aluminum is the general rule of thumb. But some combos may work better so they could accept higher DCR and vise versa. I'm at 8.0 with iron heads and run 91 with 28 degrees total timing. The engine might take more timing on 91 without issues, but I haven't tried it beyond that without race fuel. And for plugs, I've been running NGK-7 around town and track. That's about as hot of a plug as I want to run. NGK-8 or -9 would probably be better at the track in my situation.
 
I do 10.5 on PG all the time.

I'm in the process of 11.25 onPG with iron heads.

There are 2 things that matter. Cam timing and cooling system. If you try to run an off the shelf cam it will almost never work. If you call a COMPETENT cam company (preferably one who does NOT have a 6 digit advertising budget) and get a CUSTOM cam it will work.

FWIW I use (not in any particular order) Jim at Racer Brown, Cam Motion, and Mike Jones. I used to use UltraDyne when Brookshire owned it (now Bullet) but had issues with his constant idea of using lifts that were way too low and @.050 timing that way way too long.

But that is just me.
 
I have 9.8:1 compression with aluminum heads, smoothed chambers/edges/spark plug area, chamber fitted to bore so no overlap. Flat top pistons with quench around .030, IIRC. 63 ABDC on the cam. It's got a Dynamic ratio of 7.86

I run California pump 91 octane. In my 416 it will ping at 4000+ rpm going up hill accelerating at hard throttle. I've got the timing at 30 degrees total and run Autolite 3924's
 
autoxcuda said:
In my 416 it will ping at 4000+ rpm going up hill accelerating at hard throttle. I've got the timing at 30 degrees total and run Autolite 3924's
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Now that is very surprising that you get any sort of pinging considering your setup you've described. Any reason why it would do that with the DCR and SCR that low?
 
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