Ok experts, not the post to end all posts but….. I’m stumped.

Basically the jest is my new 12.5 to 1, 398ci combo with a mid 240 duration and .610 lift cam, 222cc intake volume, 300+ cfm flow Trick Flows hits the wall around 5400-5500 rpm and around 440 rwhp.

If anyone can host a dyno sheet, I’ll post it as it may help but I don’t have a clue right now as to what going on.

We hooked a vacuum gauge up on it and it is pulling 1-2 inches vacuum out on the top end indicating a restriction. We unhooked the intake running off the MAF and it made no difference. We then eliminated the MAF running the car in speed density mode and it also didn’t make any difference either, so it appears to be in the intake or 58mm TB.

The intake was just reported with the outside welded to eliminate any restrictions giving a straight shot into the heads port matched to off road LT4 gaskets. Doing the automotive math, the TB should be flowing 1050 cfm while @ 7000 rpm the engine should only need 900 cfm so we should be good to go with both.

Just for grins, we hooked up a fan and blew air directly into the MAF and it picked up 10 hp or so confirming it needs more air.

Am I just maxing out the 58 mm TB?? Or What??

 

I would guess the intake itself is the issue. My buddies old 396 lt1 with monoblade TB, ported/welded lt4 intake, afr 220s would only pull like 93-94 map up top.

 

Guess it could be, but you would need to see it to appreciate it. Really a nice job of welding and porting to open it up.

We are going to build a wooden spacer to see if it needs more volume, but right now we are just grabbing straws.

 

The motor might need more pleanum volume.... but with more pleanum volume comes lazy throttle response. You can see more power on the dyno with a huge pleanum but the car can actually slow down on the track... Then again look under Overtons hood at the carb spacers he was using...

I think Steve Quinn had a good idea opening up the intake from the top and making sure the effective flow area of the port entry was not going nuts and being a restriction. The problem then lies that if you are going to put that much effort into it... you are now spending mucho bucks to get something that doesn't help you make any TQ.

Also 1050cfm @ 7000 is at 1.5" which shows that would be a restriction.... you want to see 1.0" or lower for a zero restriction carb or TB setup.

With all of that said.... I think its the intake. I've done all the welding on the runners and making them have a constant cross section etc... and that solves that problem. The more cubes you put on a motor the more it restricts the motor, so that only leads me to think it's pleanum volume.

Bret

 

Thanks! Maybe that sheet metal intake is closer in my future than I thought.

The only fly in the ointment on the intake volume, is I was there when Jordon Musser dyno'd over 470 with a hot engine and a LT1 intake/monoblade. Besides, I've made more power than 440 with basically unported LT4 intakes.

Humm..... I'd still confused.

 

That cam is a might small for that combo, did you uncap the car on the dyno to see if that would help? What headers do you have? If it can't get out, it can't get in.


David

 

Cam or lack there of doesn't create vacuum...

Bret

 

I dont see where it would be possible to eliminate vacuum under wot, especially with modded stock parts. He has some other issues he hasnt found yet. If Mindgame can make the power that he does with one....with what his heads flow...I dont see the problem there.


David

 

Mindgame is also running an intake with spacing on it for the heads. That spacing may very well be enough added runner to help out alan's motor. I would be curious his map readings at high RPM.

I know bret has talked about "faux boost" from intake tuning. I would guess that would mean 1.01-1.02 map readings from an ideally tuned intake setup.

 

After MUCH thought, I agree there is another issue going on but still not sure what it is. Think the vacuum maybe showing up due to a venturi effect of air going past the the nipple we are using to check vacuum.

The cam for all practical purposes is the same that Jordon had when his car was making in the upper 400 range and with a 222cc intake port volume should peak somewhere between 6300 and 6500.

Thanks for the thoughts, but right now we are just scratching our heads. It did the same thing on me last build up and magically cleared itself.

 

Denny you measure the Intake Vacuum with something other than the MAP?

Bret

 

another tidbit- my car also pulled ~2" of vacuum at WOT as indicated by a vacuum gauge taped to the windshield.

Denny- I have 2 major LT1s in my shop, one has a vic jr(cause its actually going turbo soon) and the other that is staying NA has a Super Victor. Both converted to EFI.

IMO, this is the way to go for a serious NA setup, more drivability and more power. Course, this is obviously what I think is best cause the last 2 cars like this I built had them :-D

 

Nope.. Stuck a vacuum guage on it and it read just like Jordon's did. About 2" of vacuum starting at about the same spot it goes flat.

 

I may have to buzz by and check out what your doing.

We did a little more tuning today and got 456 rwhp and 432 torque so we're making a little headway, but it still goes flat. The good part is it still makes over 430 @ 7000 rpm so the powerband is pretty flat in the higher rpm range. Just doesn't peak like it shoud. We did figure out we are maxing out the 30 lb injectors so I just ordered some 36's.

Jordon..... You still in the same spot??

 

How you like that Super Vic? ;-)