Sorry, just went back and reread your posts, and seen you used a vacuum gauge to set the idle mixture. But after you set the mixture try to drop it in gear, set parking brake, then turn out an extra 1/8-1/4 turn to see if that helps idle stability. I know it won't change needing smaller heads, but may help current set-up.
I called AFR about a 350 I was building about four years ago with a slightly smaller cam than you have. 275/285 - 225/235 - 477/507 108
They recommended the stock 195's first. When I told them I was thinking about the 180's they said the Ported 180's would be good.
If you were to call AFR and tell them you have a 408 with that cam the first head they recommend isn't going to be the 180 heads unless you specifically tell them that's what you want. They'll recommend the 195 because the 408 can make use of them down fairly low. Sure the 180's will give you more off idle torque but on a 408 it isn't going to be long before the 195's are putting a world of hurt on them.
Give them a call, they don'e charge for that.
I appreciate everyone's input. I think my actual compression ratio is about 9.1:1 last time I figured it out. It has Keith Black #126 pistons I believe, 30cc dish.
I'm looking to run 91 octane. A friend of mine runs 91 in his 454 big block, it has Dart pro-1 aluminum heads and is just over 11.5:1 with 36-38 degrees total timing.
If I could get away without changing the cam that would be great, but if there is a better match with different heads I will change it. I was reading that the AFR's are better with single pattern cams because the exhaust side flows so well.
Looking for a good running package with strong bottom end. I would like to keep RPM's to 6000 max.
I failed to mention that an intake that's leaking around the ports internally will not show up with an external leak test like what you did.
The only way to tell that I know of is to pull the intake and look and see if there's oil in the runners.
CdnCutlass said:
I was reading that the AFR's are better with single pattern cams because the exhaust side flows so well.
Looking for a good running package with strong bottom end. I would like to keep RPM's to 6000 max.
With the 180 heads you'd have hella strong bottom end but I'm gunna guess you'd be giving up about 20HP at the peak. It's up to you to figure out what you would rather have more of.
That's probably correct about the single pattern cam but keep in mind the XE line doesn't have big exhaust figures compared to the intake side.
As for the compression ratio and that cam, with 9:1 I'd limit the cam to 230 intake that's for sure. If it was a 350 I wouldn't go there and would build it for at least 10:1 to gain better drivability (torque) down low. I don't think it'll be a problem with a 408. Combining a 180 head and a hyd cam with 222-226 intake duration it would be a torque monster but HIGHLY doubtful it would want to rev past 5500.
I run same cam, intake, carb, and 64 cc TFS G2's with Speed-Pro H615CP (which is 12 or 16 dish I can't remember). 89 octane 36* total @3000 rpm all day long no pinging runs cool. So 91 should be easy for you.
Should be REAL Easy to do with aluminum heads and that cam.
With only 9:1 that cam will already be low in the recommended compression range plus the aluminum heads will tolerate more compression from the start.
Should be REAL Easy to do with aluminum heads and that cam.
With only 9:1 that cam will already be low in the recommended compression range plus the aluminum heads will tolerate more compression from the start.
I am going to be raising the compression, just not sure by how much yet. I don't want to have high compression that needs a cam that is too big to bleed it off.
You could switch your pistons to Speed-Pro H615CP's to increase compression or if you like your KB's use Part# KB147. Both will bring you up to around 10:1, easily runable on pump gas with aluminum heads. Don't forget to get it re-balanced afterwards, unless you get a piston that is within a few grams of your current set.
I can't believe no one has mentioned checking where the rev limiter is set on the ignition box. Also verify the the timing is full in by 3 grand or so.
I can't believe no one has mentioned checking where the rev limiter is set on the ignition box. Also verify the the timing is full in by 3 grand or so.
Timing was all in by 3000rpm. The Hyfire 6A box I have does not have a rev limiter. It is a POS. I haven't heard back from Mallory yet on exactly what is defective. I had the same engine issues with the old HEI setup too.
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