Under performing 357 sbc

[dazimm531]

Hi I need some expert help.
I have a 357 sbc:
4.030 bore
3.5 stroke
6" rod
12.9:1
Rhs 235 heads unported
Cam:
Int .675 lift 263 @ .050
Ex .625 lift 271@ .050
106 lc in @ 104 icl
Hurricane intake 800 Holley on e85
The car it is in is a old square tube chassis car 2400 lbs powerglide 5700 stall 5.43 gears with 33" tire
Current et 6.35 106 1/8 mile 10.03 132 1/4 mile
The car seems to really fall off in the heat and just seems to me to be off somewhere in HP and torque compared to similar engines I have run.
Any info would be great. Thanks

[fdicrasto]

You need to give more detail on the heads. If I had to put on a blindfold and make a guess I would suspect the heads are way underperforming to what the camshaft needs. Maybe this will get the ball rolling for you.

[WeingartnerRacing]

The heads stock only move about 290s cfm on my bench and for that size runner it makes them a turd velocity wise. You port them and really wake them up but then they are larger than what you can use. As they are now with your combo the heads are already borderline. The older hurricane intakes are not as nice as the newer ones. However either way they are decent but not great. Porting helps them too.

[JoePorting]

When people talk about engine falling off, the first thing I think of is valve springs. I'd also check the ignition system and electrical system. I find using ground wires instead of chassis grounds also helps the electrical system.

Another area to check would be your fuel system. Make sure your fuel pressure stays up.

[Mummert]

10 degrees less exhaust duration and a smaller intake runner with similiar flow would help. Weve done a fair bit of bracket racing out here and smaller ports with more air speed seem to be more consistent et wise throughout the year, even throughout the day. Its pretty common to get a 1000ft DA change from 9:00 an to 2:00pm The powerglide is gonna need some wheaties down low. Where are you noticing your losses in the heat, 60' , 330'?
I don't know what other guys opinions are here but running more than a 2.02 valve on a 4.030 bore usually seem to make the swirl and wet flow characteristics go to crap, even though you might pick up a couple cfm. Not good for the kind of overlap your cam has.

[mag2555]

The port volume of those heads is too great for your cid motor and if you port them without running a bigger Cam and do what it takes to buzz to close to 8000 , maybe 8200 rpm then there's no point in porting them!

I would try a chase down a set of used heads that started life at 190 to 195 CCs and where then ported, and the freshen them up and install Behive springs or better yet conical types!

I would also want to confirm how much air flow that Intake can support?

[dazimm531]

Thanks for the feedback. I am hearing that these heads would be better suited for larger cubic inch and just are not a good performer for what I am doing. My 60 fits are down in my opinion, 1.35 in good air and drop to 1.37 when it gets hot. For the weight of the car seems slow to me. I originally put this engine together for a stick combo in this same car and it did run better. 9.83 133 and 1.27 60 ft once I got the clutch right. It appears to me I'm really lacking torque.

[mag2555]

Yes, your lack of Torque is due to lack of average port velocity which ties right in with the too large of a port volume .

[RevTheory]

Unless you've taken steps to really kill off any low-lift flow, aren't you 4 or 5 degrees too wide on your LSA? If so, that reversion can't be good for coming hard off the line.

This is in addition to the port volume already mentioned.

[dazimm531]

That is a very good thought. So I may be diluting the inlet charge at low speed causing it to run like crap in addition to low port velocity.
One more question, are the RHS 235 heads a good performer on a 421 CI engine, maybe worth saving for a larger build in the future ?

[steve316]

As far as the cam goes Lsa goes it is at least 2 degrees too close. Also a 1050 carb wood help.

[PRH]

More than likely all your current parts could be transferred into some other heads.
Something like the CNC heads Chad at SRH offers.

Maybe have the intake manifold done at the same time.

[Walter R. Malik]

Double Post ... this is slow this afternoon.

[Walter R. Malik]

Personally, I would put considerably more cam in it or a little less stall speed ... or some of both.

[steve316]

As far as the heads go epoxy the floor and the dead air space on the push rod wall to bring down the csa of the port. You don't need different heads you just need to make them work for your application.