Questions on tuning a 598 bbc

[GJ]

Thanx alot for the advices .
What some of other racers were telling me is that my scoop is realy bad . It is full open , so all the air exits to the lexan . And they said that at higher speeds it might wanna pull the fuel out . Can it realy do that . Several racers told me that its killing my mph alot . So they are trying to make a aluminum sheet that it covers the carb leaving only the carb opening open and close the back so all the air goes to the carb . Any more sugestions are welcomed .
Thanx
GJ

[GJ]

One other strange thing is that it isn't using almost any fuel . I have a 2 gallon fuel cell and it is only using about 1/4 of it for a whole run with burnout and driving back to the pit , when others with smaller engines like 540 and 565 are using half of the tank so about a gallon .
The fuel system is 12 from the cell to the pump ( filter removed for now and I know its dangerous but we can't get a filter on time for the races) and from the pump goes 10 to a BG 4 port regulator . They have 6 an outlets but I used 6 and to 8 an fitting from the regulator and from their to the bowls . I drilled the fitting cause the fitting hole was tiny . Now it has the same or close to the same orifice from the regulator all the way to the bowls . They said 6 an would be enough but i didn't want to risk it . The presure was set at 9 psi . So should I drop it ? Oh and I had a glide . The converter is a neil chance converter made for nitrous with anti ballooning etc . It stalls at 5000 . I tried at 4200 rpm and it spins alot , the 60 feet goes to 1.25 . I am gonna try running with less timing . I am gonna drop it to 34 to see how it goes .
Thanx
GJ

[GJ]

Yesterday we made plate around the carb and close the scoop in the back . From day 1 we had trouble with the exhaust popping loud when letting off the trottle when we rev from idle . We put a holley 1250 with 98-99 jets and the popping stopped , the trottle response is alot quicker . What can cause the popping with the demon and not the holley . Just by putting the holley the engine sounds alot better and more powerfull . Today i'm going to the track again to see how it does with the scoop in the back closed and the new carb .
GJ

[DOTracer]

...

[GJ]

We went to the track today for test and tune .
First run with the new carb (1250 holley) was 8.52@156 mph , 60 feet was 1.19 . Its getting better .Timing was 36 degrees .
The next run we put the timing to 35 degrees and it went 8.49@ 159 mph ,60 feet again was 1.19 . The engine is picking lots of power by dropping the timing . We couldn't do any more pass but we wanted to even try 34 degrees to see how it goes . We have 100 jets in the holley now and its asking for more fuel . Probably by just dropping the timing some it would richen out some . Tomorow is qualifying and race so we are going to try 34 degrees to see how it goes .I think i need to put other gears in there . Now it have 4.56 or whatever dana have in that range . I set the rev limiter to 8000 rpm and it hits the limiter at the finishline . With nitrous it would be worse . Shiftpoint is 7400 rpm .
GJ

[Doug Schriefer]

A couple of things:

1) Make sure that your air pan and scoop seal well, and that the air can't go past the back of the carburetor. Have it stop at the rear bowl on a single 4bl. If the air travels past there it can draw air and fuel out of the carburetor leaning it out.

2) Make sure you're maintaining proper fuel pressure going down track.

3) Try 33° or 34° of timing.

4) You need to go to a lower gear set or taller tire (or both) if you're still crossing at 8000, especially when you mention that you'll be putting nitrous on the engine.

5) You still may need to work with the air bleeds on the carburetor (which ever one you use) to get the proper amount of fuel at WOT.

[GJ]

Updates , with the same 35 degrees timing the car went 8.43@159 mph with a 60 feet of 1.16 . The car is going true the traps in limiter (8000rpm) . I Tought I had 4.56 gears in it , but we checked it and it was 4.88 gears . I have a set of 4.56 gears , should I use it or go all the way to 4.30 gears ? The car isn't running bad at all . The 345 darts are borrowed so I need some heads soon . I think i'm gonna get some victors from rfd . They look like the best for my combination . My plan was to run small nitrous to hit the 7s . But with some new victor heads from curtis I don't think I would need nitrous . My goal is just to run 7.90s . So I don't know if I would need the 2.400 valves or the 2.350 should be enough . I'm gonna call him in one of these days .
GJ

[CNC BLOCKS]

Geomar

On this build is this the block I sent you a few years ago??

[GJ]

Carl , this is a block I machined myself with parts I had laying around .
The block you did was for a 565 , 55mm cam ,grp rods , custome pistons , steve schmidt racing ported 12 degree profiler heads , profiler tunnel ram manifold with dual carburetor from Steve schmidt , lsm cam ,etc...
It should be a mean setup when done .

[Strange Magic]

P.S. Forget the bigger carb, set the timing at 33, jets at 100, a new set of plugs. Get yourself a real good baseline and then move 1 degree into it (34) and see if it responds with mph. A,B,A, test this timing to understand what it likes. I really can't see it wanting anything more than 33 degerees with a 4.5 stroke and fast piston speed from rod angle.

[GJ]

Strange magic , I wanted to try that but we were on race day so we didn't wanted to try other stuffs , we wanted to be constant . There is racing again in about 2 months . By then I should have some new heads already . Before I was thinking on getting some bmf 385 but for some more money I could get some better heads from rfd . Oh and I'm getting a custome carburator too.

[GJ]

I disassembled the engine and it had 10 broken innerspring . I checked the installed height and it was far from coil bind . The spring presure was 240-250 @ 2.000 installed height . Could going at the finishline in rev limiter at 8000 rpm cause these to break ? Well , they are not new springs . But it still ran strong and et was dropping on every pass . 3 exhaust valves kissed the piston . Light touch . I guess it is from valve floating cause it had more then .100 PTV clearance . I have a picture of the piston on how they burn . Its black mostly on the exhaust side and the rest of the piston looks clean . Is it the chamber design or what else could cause it to burn like this ?
http://good-times.webshots.com/photo/26 ... 0714JoaUSm
Thanx
GJ

[Strange Magic]

The cam is 288/298 dur , 825/7xx lift , 114 lobe sep .Heads were borowed dart 345 pro 1 heads .

I would first recommend that you make every attempt to somehow get 2.080-2.100 for installed height and then look for a spring which will yield you around 290-300 pds on the seat. At 240-250 you are playing with fire and I am shocked that you didn't lay some valves over because it was destin to crash from the get go.

Your best bet is a PSI spring for this application. You might want to seriously take a look at your roller lifters as well. Low spring pressures such as what you are running can seriously damage or take life expectancy away from the roller lifter.

Is it the chamber design or what else could cause it to burn like this ?

I wouldn't be soo concerned about how the piston looks at this time (you've been through many different tune up changes). Focus on the mechanical well being of the engine and the rest will take care of it's self.

[hsutton]

It may be from overreving or from sitting in a garage with a lot of moisture. I was told that springs will pit if allowed to sit in a damp garage for any length of time. They then break, at that pit, when run again.