HIGH FLOWING PORTED J HEADS

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tvt59

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Mr PRH and Mr Pittsburghracer, have y'all ever tried your best J heads on a large bore block? Like 4.185" to 4.220" ? What kind of HP do you think those heads could support on a properly prepared short block?
 
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tvt59 said:
Mr PRH and Mr Pittsburghracer, have y'all ever tried your best J heads on a large bore block? Like 4.185" to 4.220" ? What kind of HP do you think those heads could support on a properly prepared short block?
Click to expand...

Sorry I’m zero help to you. I haven’t played with a stock small block head since the 1970’s. My buddies Magnum heads stirred my curiosity some but there are the Mopar aftermarket head that came on the crate engines. BPE had a set of small valve heads on his 340 and ran I think 9.60’s
 
Shrouding shouldn't be a problem :) Depending on stroke and intended rpm feeding them might be.
 
That was always my dream for a f.a.s.t. build, big bore and a touch smaller stroke but that hasn't materialized yet. No doubt I'm sure it has been done dozens of times but 9's @ around 3200lbs is achievable with J's. Not sure what your end goal is.
 
As PBR mentioned above, Vic Bloomer has indeed been 9.60’s with a stock stroke 340. Think they were 596 heads he did. Want to say 1.88 valve, but might have been 1.92, would have to ask him.
Car weighed +- 2750

It’s back together now after he broke it a few years ago. He has been working on a thermoquad for it.
Hasn’t had it out yet.
 
That takes pure old school knowledge there...trickery.....f.a.s..t. does it on a 7" polyglass tire
 
Yeah I know and extrude honed manifolds...pure science
 
I'm just thinking about a iron headed 340. For a street car after I sell my AMX next year.
 
I have no experience with any large bore SB stuff…….so I can’t comment on that.

IMO, a good place to get higher flowing factory SB heads ported to “high” flow is KG engines in Ohio.

Edit-actually I do have a small block large bore SB story……

I use a 4.00” bore for testing most SB stuff.
I had a few heads come thru here that had been ported elsewhere, where my flow numbers were noticeably less than the ones supplied by the porting service.
I wondered if perhaps they had been tested using a larger bore……..so I tried it.
Basically zero difference.
 
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PRH said:
I have no experience with any large bore SB stuff…….so I can’t comment on that.

IMO, a good place to get higher flowing factory SB heads ported to “high” flow is KG engines in Ohio.

Edit-actually I do have a small block large bore SB story……

I use a 4.00” bore for testing most SB stuff.
I had a few heads come thru here that had been ported elsewhere, where my flow numbers were noticeably less than the ones supplied by the porting service.
I wondered if perhaps they had been tested using a larger bore……..so I tried it.
Basically zero difference.
Click to expand...


If the chamber works for a smaller valve it works. Give it a little shape and move on.
 
PRH said:
I have no experience with any large bore SB stuff…….so I can’t comment on that.

IMO, a good place to get higher flowing factory SB heads ported to “high” flow is KG engines in Ohio.

Edit-actually I do have a small block large bore SB story……

I use a 4.00” bore for testing most SB stuff.
I had a few heads come thru here that had been ported elsewhere, where my flow numbers were noticeably less than the ones supplied by the porting service.
I wondered if perhaps they had been tested using a larger bore……..so I tried it.
Basically zero difference.
Click to expand...
Thanks for that bit of information. I've always heard that a larger bore unshrouded the valve and allowed the head to flow more. That's why I asked the original question.
 
And Sometimes the stock bore is plenty big enough, and isn’t holding the head back.

I’ve tested several BB Indy heads on both 4.375 and 4.500 bore………and saw no gain from the bigger bore.

My experience has been that the bigger bore is often not a silver bullet.
 
tvt59 said:
Mr PRH and Mr Pittsburghracer, have y'all ever tried your best J heads on a large bore block? Like 4.185" to 4.220" ? What kind of HP do you think those heads could support on a properly prepared short block?
Click to expand...
A guy named Dan Smith, who was a big time regular bracket racer, got about the most performance I've seen from factory heads, block and flat tappet cam. Think he went 9.8s best at 3200lbs. I know he did his own head work so, he must know his way around. Albeit in a different way, I hope this answers your question.
 
I know the seat pressure on Dave’s old Roadrunner is more pressure the my over the nose pressure and the springs survive maybe a season….. They replaced them beginning of last season and broke one at MIR. At some point it has to be like pro stock, spin the tire and change springs. I’m sure CRUNCHING the ring and pinion didn’t help, but data showed no crazy rpm.
 
My car ran 10.60s with ported J heads with 3/8 stem valves on a 360, with a Mopar .508 cam, pump gas. not a all out race car, still have the AM radio.

Duster 3.jpg
 
ValiantS said:
A guy named Dan Smith, who was a big time regular bracket racer, got about the most performance I've seen from factory heads, block and flat tappet cam. Think he went 9.8s best at 3200lbs. I know he did his own head work so, he must know his way around. Albeit in a different way, I hope this answers your question.
Click to expand...
Dan Smith is a very sharp guy, also a very good racer.
 
Bigger valve, bigger bore helps.
I don't think we are talking 2.02 , more like 2.05 or 2.08.
280-290cfm
575hp
 
tvt59 said:
Thanks for that bit of information. I've always heard that a larger bore unshrouded the valve and allowed the head to flow more. That's why I asked the original question.
Click to expand...
Better don't always mean a lot better and or worth while, I remember a test where they compared Chevy heads on a 4 vs 3.75 bore and there wasn't a huge difference, like 5 cfm.

I'm sure idea those bore sizes are for valves a lot larger than 2.08"
 
273 said:
Better don't always mean a lot better and or worth while, I remember a test where they compared Chevy heads on a 4 vs 3.75 bore and there wasn't a huge difference, like 5 cfm.

I'm sure idea those bore sizes are for valves a lot larger than 2.08"
Click to expand...

That said, those 5 cfm could be 10-15 horsepower. Some guys would kill for that kind of gain.
I know Pro stock stuff is huge bore. Give me a bigger bore any day of the week
 
B3422w5 said:
That said, those 5 cfm could be 10-15 horsepower. Some guys would kill for that kind of gain.
Click to expand...
True depends on what your doing, In a highly competitive race class all those little things matter a lot, in a weekend burnout machine that may occasionally see the track not so much.
B3422w5 said:
I know Pro stock stuff is huge bore. Give me a bigger bore any day of the week
Click to expand...
There's definitely no advantage going smaller, but if we all cared that much everyone would be building 400/440 :)
 
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