She's built. Help with soggy bottom end...

Vinyl66 · Aug 25, 2004

I recently did a head and cam change on my '66 coupe. I will try to post a pic of the engine bay tonight.

The engine is a '71 model Mexican block 302. I went from stock cam and heads to a Comp. XE268H and twisted wedge heads. The cam is installed straight up (per Comp. directions) as all their cams have 4 degrees of advance built in. I set the initial timing to 17. The total timing is at 35 degrees per Trick Flow's website.

When I floor it from a dead stop it feels sluggish till about 2500 rpm then it really takes off and feels strong until I shift at around 5500. If I am cruising at around 2500 and floor it it pulls REALLY good and sounds great. It won't spin the little 205's from a start but it will chirp them going into 2nd gear at 5000 rpm.
I know a converter would help greatly, and that will be done soon, but with the power it is making it seems like it should have more down low.
Any ideas?

brianj5600 · Aug 25, 2004

Did you check deck clearance? What pistons are in it? Does it sputter below 2500?

allcarfan · Aug 25, 2004

you should probably have the car dyno tuned after mods like that

mustangracer · Aug 25, 2004

I had the same issues after a head, intake, cam, & carb swap.

Inital timing souds high, 12-14* should be closer to right.
I've heard 289-302s like 36-38* total advance. ( I'm at 36*)
I had to recurve/respring my distributor (mallory unilite) to increase the max timing, and bring the advance in the right time.

..the rest only helps if you have a holley 4bbl.

Accelerator pump, might need a longer/bigger shot, mine needs a longer, but I've crutched it by going to the bigger shot on the same squirters/cam.

That helped, but I found I needed a higher opening power valve, my cam runs around 16-17in idle vacuum (mild cam) and needed a 8.5 PV. Trick to find out is attach a vacuum gauge where you can see it and drive. Find a moderate hill and floor it around 35mph going up in third gear (second if its a C4) and see how low the reading gets. Install the next highest pv and you should be close. Or take an idle vacuum reading and divide by 2 and select the next lowest.

All this and I got a bit more oomph out of lower rpms, but the real fix is probably higher rear gears, they'll get the engine up in the powerband, even with the stock converter.

Vinyl66 · Aug 25, 2004

I did not check deck clearance. The block has been rebuilt by the previous owner and is bored .030 over and the pistons are slightly dished in the center (2" diameter).

I definitely need a dyno tune.

More information:
On the way home tonight I floored it from a stop light and it bogged so bad it went dead. It started back up instantly and I rolled on the throttle to 2000rpm then floored it and it pulls like crazy. I don't think it is all the carb's fault but I don't know what else it could be.

Does anyone with similar mods as I have run an Edelbog? And did you have to change anything in the carb. after the mods?

Vinyl66 · Aug 25, 2004

Speaking of torque converters, with my foot on the brakes I can bring my engine to just over 1000 rpm before the tires start spinning.

Ronstang · Aug 25, 2004

Got the check BTW, thanks. Anyway....if the pistons are slightly dished in the center your compression might be a little on the low side for the cam and those heads. Run a compression check and see what kind of numbers you are getting and also check with the Comp Cams about the CR requirements with that cam. A dished piston with those heads will have a CR somewhere in the 8:1s range....where I do not know but it will be sub 9:1.

brianj5600 · Aug 25, 2004

I think it is the carbconvertercompression.

TOM B · Aug 25, 2004

Good head selection. The rest looks good to. The cam you selected has a power band of 1600 to 5800 with a lobe separation of 110. good street machine cam, should have a mild lope to it. Comp cams also say you need a 2200 stall converter, I would go with a 2500. You should also have pistons of at least 9.5 to 1, but dont sweat it if you dont. I think if you install the 2500 converter you will be plenty happy of the power output because it will put the rmps in the cams power range. Then when you mash it to the floor at a red light you will need new tires!!

Vinyl66 · Aug 26, 2004

I appreciate the replys! Thanks again for the pushrods Ron. I had the car up and running this past weekend.
The cam does have a slight lope to it and made the engine sound great. It is much louder and racier than the stocker.

I have never performed a compression test but I would really like to know what mine is. I bet it is a bit on the low side because of the pistons.

The car desperately needs a converter though. If the converter does what it is supposed to do, get me from idle to the mid 2000rpm range fast, then I think I would be really happy because it pulls great everywhere else.
B&M recommended a 2400 Holeshot for my combination. TCI makes a 2400 Break-a-way. Do you guys have any experience with either of these? Or maybe another company?

TOM B · Aug 26, 2004

B&M recommends the hole shot 2400 because its the only one they make for the C4 24 spine, and just because there to lazy to make others for the 24 spline I would go with TCI. Im running a lot of HP so I went with a TCI 3000 stall converter. The 2400 is right for you though. You will love it. Then you will hate it-----when you need tires

Jonstantine · Aug 27, 2004

sounds like carburetor - but then again, i had the same problem with my edelbrock... soooo

PoliceInterceptor · Aug 27, 2004

You might lok at Hughes for the converter.

I had a TCI SNS behind a big block and liked it. It now has a breakaway, hasn't run yet but I'm not too impressed with the looks, not much attention to detail, at least on the outside. We will see, assuming I don't change it for something else.

Vinyl66 · Aug 27, 2004

I will be checking out the carb this weekend to see if I can get rid of the bog on takeoff.
That's good news that others like TCI. There is a Mustangs Unlimited just up the street and they sell the 2400-2600 Breakaway converter.
I will be going back to the strip next month and I really need to improve on my 15.2 I ran this summer. A friend of mine will be taking his '86 Porsche 911 and several guys think he will beat me.
That just can't happen

TOM B · Aug 27, 2004

When you go to the drags, get rid of that 600 carb and go bigger, the mods you have will handle alot more carb or you will loose. go with a 750 with mechanical secondary and you shoulf fly. thats with the new converter now.

D.Hearne · Aug 28, 2004

With the motor he has, going to a 750 mechanical sec carb will guarantee the Porshe to beat him. I also think his compression may be too low.

PoliceInterceptor · Aug 28, 2004

No bigger than a 650.

600 is more than enough.

I think it needs more compression

She's built. Help with soggy bottom end...

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