Quick95Z

We finished a build of a 383 recently that I am a little disappointed in. The bottom end was done by a very reputable local builder. It is running 10.5 CR with ported stock heads (flow @ 280 at .600 Lift), Hooker Long Tubes, 52 mm TB, 30 LB. Injectors, CC 236/242 Cam (110 LSA), and SLP 2 OTL Exhaust.
We did about 2 hrs. of tuning with LT1 Edit and could only muster 370 HP and 375 TQ at the wheels. What Gives? I am expecting between 400 and 420 rwhp with this setup. It is an M6 with 10-bolt by the way. Where am I leaving power on the table? Would a better flowing exhaust help much? Any help would be much appreciated.

joeSS97

That exhaust shouldnt be holding you back.What is your a/f ratio.Where does the HP/TQ peak?

Quick95Z

HP Peaked right at about 5800 and stayed fairly level until 6200. Torque peaked about 3100 RPM and began falling off slightly at 3500. We maintained about 12.5 A/F.

joeSS97

I am no expert.You probably know. Shouldnt you have bigger injecters,maybe 36 lbs?What kind of dyno?

dust6928

i dont think it is the injectors because a 30lb inj should be able to support 450hp easily. if you use one of the calculators at a 85% duty rate of injectors with a brake specific fuel consumption of .45 the recommended injector size is 26.47lb/hr. injectors could be the problem but i would think it would be because one is not doing its job. i would maybe pm some guys who have your setup and ask them what they did in their tuning to get what they got out of theirs. there must be something you missed or the dyno was very strict.

zhevy-1

Who ported your heads? Even though the flow numbers are good, they may have killed your port velocity.

NightTrain66

The best I can remember the low lift #'s were not very good on the intake or exhaust ports due to some CRAZY valve job on the heads. That "might" be some of it.

I am not sure either about the incector but I would not think they are robbing the 30 HP that is missing.

I remember the heads were milled (.030??) so that being a 383 and I am sure that it was zero decked, you should have PLENTY of compression.

Are you tuning on the street with LT1 edit or on the dyno. I know you had dyno #'s but are you making pull after pull and making minor changes and checking A/F ratio, timing, KR, etc, or did you tune it and then make 1 pull?

There is a guy on here (CMillard) that can maybe shed some light on the tuning for ya.

I am really not sure but I would have guessed a 6 speed car with a 10 bolt and a STOCK BOTTOM END would put out those #'s with 280 cfm (looking past the low lift #'s) and that cam. I am sure that you are about fed up with the entire 383 and heads ordeal that you have gone through. If worse comes to worse and you can not get it worked and feel that THOSE heads are the problem and you are willing to tear back into we can rob the parts off of THOSE heads and start with some fresh cores that we can put a good valve job on and get the low #;'s much better. With all of the HELL that you have been through you might just want some AFR's and be done with it. Ya might check with Yelvi and show him the low/mid #'s and see if he thinks that is any of it. Or if you could post them here I am sure that you might get some feedback.

GOOD LUCK

NightTrain66

rskrause

A common culprit is knock retard. Are you seeing any? Disable it with LT1_Edit and test again.

Rich Krause

Beast96Z

Yea, NightTrain is right. My numbers are with a smaller cam and a stock bottom end. (sig.) I'm thinkin some crappy port work which made the big number, but killed low lift. Nothing will kill a motor like crappy heads. A buddy here made 451 RWHP with the same cam, 383, 24 lb injectors, and Stage 2 heads. There is deffinatly something up.

NightTrain66

The heads were a replacement set from Pro Performance that were brought to me and touched up a lil. They flowed well at .500 and .600 lift but that is the only spot the valve job worked at. The venturi size was like 95 % and had some strange angles. They flowed BAD below .300 lift. I do not remember specific #'s but they were BAD. After touching them up they flowed better mid and up top but there was nothing to do with the valve job since the metal was already gone and changing the seats is something that we really did not want to do.

We were aware at the time but we were just trying to make these heads work after all of the HELL that he had had. At that time he was expecting to bolt the heads on and be done but after installing these replacement heads he reaized the engine had a knock (bent rod) that was caused by the original set of Pro Performance heads leaking water in the motor. Several months (and lots of $$$$) this is the result. Low dyno #'s but at least they have not sprung any water leaks.......YET.


NightTrain66

Ai

This is your problem, as others have said. Search for old threads on that subject & just feel lucky they haven't ruined your new shortblock yet.

Of the two sets I've had, neither of them have been ANYWHERE near what they claimed it'd flow, and even worse, both were full of cracks and holes & would have required more welding to fix than they were worth in the first place. Here is a flowsheet from one poor guys "285cfm" heads. Standard deal, half inch clay radius etc. I felt bad for the guys.. I told them I would critique the machinework, if any had been done :0.

Its a safe bet that they're doorstops, sorry.

JSK333

If it isn't the heads, I wonder if it could be your ignition... because with that cam your HP should be peaking higher than 5800 RPM. Probably closer to 6500 or so, would be my guess.

What do you other guys think about that?

Beast96Z

hmm, I can't say you have good heads. I haven't taken anything of mine back out there since all these problems arose. Even though the numbers aren't what they are supposed to be, he is still doing good on the exaust. He really needs to work on the intake though. I've seen to many that fall off after .500".

JordonMusser

hm 255 @ .500 isnt too shabby, but the falling off is not good

CAJUN-Z

If you're not varying much on the 12.5 to 1 A/F ratio, you're fuel delivery should be ok. My guess would be intake and exhaust flow. Are you using stock rr's? If so, you may want to look into some 1.6:1 or 1.65:1 rr's...