I would shoot for 9.5:1 SCR and degree that cam at 100 installed, for a purely street car. Easier to stay away from detonation and will still make plenty of power.

Lou

_________________
Home of Slant6-powered fun machines since 1988

Wow! Lots of great info. Thanks, guys! I'll do some poking around on the forums and research over the weekend. I'm definitely curious on a 0.100" overbore, so I'll be scouring the forum for builds to see what other guys have done. I'm completely new to engine building (if that wasn't obvious enough), so I really appreciate all the advice. I'll keep you posted on what I decide.

_________________
Chuck and the Flying Valiant

This gives a pretty wide berth for fudge factor...I ran the numbers based on a 40 overbore just for fun....

If you 280/270 is ground per catalog standard at 111LSA and 4 degrees of advance:

-a 10.3SCR cam installed straight up will produce an 8.03 DCR (OK for regular, can run more timing on plus/super, but not needed) - recipe is .055 deck height, and a 53 cc combustion chamber...


Indexing the cam to 100 for more low end torque and limiting high end overall power puts the DCR at 8.5:1 (need Plus or Super every other tank as a standard)

Bumping SCR down to 9.73.1 but keeping the 100 degree centerline puts the DCR at 8:1.... (still a good number)

Bumping the SCR down to 9.55:1 (deck height .095)and same centerline
puts you at 7.89:1 DCR and will be fine on regular and a little more timing can be dialed in at higher octanes if desired.

You may need to recurve the distributor if heading in these directions.

Cheers!

Degreeing most 225 Slant cams at 99-102 will give best power overall and gives very little sacrifice (if any) in top end power. I tried 96 once and I could tell the top died off a bit.

111 LSA is way too wide for a Slant cam. I think I ordered my 280/270 with 108 LSA.

9.5:1 and degree at 100 still make most sense to me.

Lou

_________________
Home of Slant6-powered fun machines since 1988

Wow! Thanks, DI and Lou!

Thanks so much for running the numbers! I did forget to mention I have a recurved distributor tailored for this build by someone on the forums. I really wish I could remember who.

I've been playing with the idea of maybe just going big and doing a .60 or .100 overbore since I've got everything apart and maybe just going big. What do you guys think of that idea?

Thanks again for the number run. I've seen the dynamic compression ratio calculators before, but I'm really not sure how you get all the right numbers for a Slant. Mind showing how it's done?

Really, this is great stuff. I really appreciate it!

I'd be interested as well. Have tried to input the numbers into the Wallce calculators and must be doing something wrong or the numbers are backwards or something. Keep getting either negative compression ratios or extremely low numbers. Doing something wrong I am.

_________________
65 Dart station wagon slant 6 - now under construction
47 Dodge Custom 4 Door sedan
87 D100 Short Bed slant 6

Retired USAF 1966-1986
Retired US Postal Service 2004-2014

Okay, good. I'm glad it's not just me! I was about to check myself into the looney bin!

_________________
Chuck and the Flying Valiant

I have never used those. Just previous experience here. Maybe DI or someone else can chime in.

Lou

_________________
Home of Slant6-powered fun machines since 1988

I have used them numerous times on both slants and sbc. I use multiple calculaters to verify results. If the numbers are not repetable they are not valid.

I have used Wallace and Silvolite.

My last slant build (280/270 Erson 9.25CR) was based on a lot of calculator work. I find it important to know what you want to achieve and what fuel you wish to use. I chose regular fuel .....and got what I wanted.

My last sbc build led to the use of an oval track grind in a drag type application ......because of the converter and gear selections and the narrow rpm band . Without the calculators I doubt I would have ended up with the winning, dependable, cheapo small block setup that got me 2nd in a series dominated by huge block aluminum BBCs.

You MUST have all the numbers. If you dont know where the piston top/deck height is you are just guessing. You should do you compression ratio work and head work first.......and then figger your cam timing......and then your ignition timing.

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

Or just throw together whatever you have laying around and spray the snot out of it.

_________________
Official Cookie and Mater Tormentor.

I like your attitude!

I resemble that remark.

_________________
Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225