Good stuff smitty. When does the exhaust system testing start ?

Did you try a carb spacer Smitty?

Sitting here drinking coffee and reviewing dyno data from other day, somethings seriously amiss in the comparisons of good 4150 carbed pulls vs the efi. Down 60 ft lbs at 4400, down 47 ft lbs at 4800 w afrs within 1/2 point of carbed pulls, no way, motor would either have to be seriously hurt and it makes about same hp so i doubt it or its in ign timing. Im thinking ign timing, going to verify base efi timing vs the tables and duplicat carbed timing. Ive tried timing between 30 and 34 in those areas, seemed to pick up tq at 30 BUT we had 38 at 4400 w carb and close afrs and made 593 ftlbs vs 534, i cant see 5 degrees whacking about 59 ft lbs, once weather clears up (raining w high humidity) going to see wtf

I should send you one of my Snith power ecm's to see how it does, very similar engines they were tuned for.

Something is certainly amiss. Haxby did a very similar experiment on the Facebook some months ago, although not as thorough or intensive, and his results were fairly identical with the carb making a touch more but negligible on top and the EFI making a smidge more midrange.

I just ran compression test and checked plugs, 142 to 145 which is what it previously tested st, keep in mind 8.48-1 with 252/259 cam, motors NOT hurt

Not too long ago I was reading an article where they did a similar test on a old Pontiac mill. Engine made about 525hp with the carb, and 500ish with the EFI system after tuning. I believe they concluded much of the gain with the carb, was due to the reduced intake temperature with the carb setup, vs the port efi setup. I gotta see if I can find that article.

EDIT.

Just found it. Actually, it was 520HP and 537FT lbs with the carb, and 502HP and 522FT lbs with the EFI setup.

Interesting, was they found lower BSFC numbers with the carb, and the engine liked 28* timing best, where as with the EFI , it liked 32 deg timing best.

http://www.hotrod.com/articles/hppp-...uel-injection/

I like that and supports what we discovered years ago but lost all documention when system crashed.

smitty,i would bet that timing is a big part of the difference .i was amazed at what 2 or 3 deg can do to power output.i am a believer of giving it as much lead as it wants.

That Pontiac EFI system set up was horrible. Spraying all the fuel from the injectors on a wall (floor in this instance) is brutal,,thus why more timing needed and bsfc's lower.


BTW: That dyno was pooched too. ,35 to .30 bsfc's ? Nope no way.