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Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
I have a hydraulic roller 350 in good condition. It's 9.3:1 compression with stock bottom end. I don't want to mess with the bottom end since it is in great condition. I have a choice between a vic jr. or an rpm air gap intake. I'm going with Afr 195cc heads with 65cc chambers. I was wondering what cam to go with. I was thinking maybe comp 288hr or even a 294hr but I would like to hear what others have to say. Also the carb I'm deciding on is a Holley brawler 750 mechanical secondary race carb. I'm hoping for around 425 hp at the crank. This is mostly going to be a strip car very little street driving. I would appreciate your input. Thanks.
Agreed. If you can get the heads nearer 58CC you'd be better off. Get some HGs that put your deck height+HG thickness close to .040. If you have the headers etc. to go with it I bet you could hit 425 at the crank with a 276hr.
I'd use the RPM Air Gap and a Comp XR276HR. WIth that low (relatively) compression you need not to go too crazy on the cam. A 650 carb would probably be enough but a 750 is absolutely plenty. Esp if mechanical secondaries.
There's no such thing as "too much cam"; only, not enough motor. Which is the situation you'd be in if you got greedy.
That's an EEEEEEZY 400HP combo. More maybe even, with careful attention to detail like good TUNING, rocker arms, TUNING, the right rocker geometry (push rod length), TUNING, and … oh did I mention TUNING?
It'll want gears BIG TIME. Your 2.73s are going to CHOKE it.
276 is a good cam too. Get it down to 56-58 cc if you can would help tremendously. I still would like to see tighter lsa. But its been good on stock cam only Lt1’s
A faster lobe profile like an xfi lobe will help you build cylinder pressure at higher rpm with the low compression, without blowing off to much low end. 106-108 lsa would do well.
There are certain circle track and race series that have to spec low compression yet still make great power. You’d be doing something similar
Thanks for the reply. I was actually gonna mention the 282hr I like that cam a lot actually. If I left the heads at 65cc how much would it hurt my performance with the lower compression.
Thanks for the reply. I was actually gonna mention the 282hr I like that cam a lot actually. If I left the heads at 65cc how much would it hurt my performance with the lower compression.
with 65cc heads on the usual oem gm 350 short block you’d be around 9.3:1 compression. Which is fine on an iron headed engine with a stock cam.
with a bigger cam and aluminum heads you’ll bleed cylinder pressure at low rpm and lose more due to thermal conductivity. Effectively it will Lose torque at low engine speeds. Higher engine speeds will be less effected.
Victor reinz makes a gasket that is .026 compressed and should add about .5 compression over a normal gm .040 gasket thickness.
measure how much the piston is in the hole and you can start calculating the static and dynamic compression. Smaller cams usually have less overlap so their dynamic compression is higher. Regular pump gas likes dynamic in the 7-9:1 range.
I am running AFR 190 heads that I had milled to 60cc. With Comp Xr282Hr-12 cam, Holley 750 Street HP, and Edelbrock RPM airgap intake.
Gm makes a stock bore head gasket for a good price at .028. GM part number 10105117
Depends on which size runner and port finish you get.
I have the current AFR 195cc street ports on mine. I also opted to upgrade the valve train because this head on a 350 engine will breathe WELL beyond the valve/spring combo they come equipped with. My VT is good to 7200rpm and my car will easily bang off the rev limiter in 1st and 2nd gear before you can think 'shift'. AFR 195 Eliminator Street Port Flow Chart
Last edited by Thirdgen89GTA; 04-27-2020 at 11:36 AM.
Depends on which size runner and port finish you get.
That's why I'm asking.
With the Eliminator version (as you have GTA) a 350 with 280 CFM of breathing capacity, there's enough support there for well into the 7000+ range. Problem with the OP. and this has been mentioned, is that those heads won't realize their potential with a wheezy 9.3:1. You can't spec a suitable cam to make a good fit. Push the CR up to 11:1, and those heads will shine with the right cam. As it is though, they're not being utilized to the fullest.
This isn't to say you can't make it work with the earlier mentioned XR276HR or similar as the smaller cam will boost some of that compression pressure. It'd be a decent engine with the right parts. Just not a great engine. A Vortec headed version would be an even match given the CR and cam choices. A Vortecs arguably top out at less than 250 CFM.
Mill the heads (seeing as the shortblock is staying as it is).
The short block I used was a 91-92 L98. Mine got the 4-valve relief flat tops that was considered 9.8-1 compression vs the dish with 9.3-1.
So we estimated mine with milling the heads to 60cc / stock deck height / and a .028 gasket to be around 10.3-1.
We milled .030 off the heads.
Also we ported the heads and did a 3-angle valve job changing the angles on the valves for better flow on a bench.
I think an afr 195 head even with a low comp ratio will wipe the floor with a vortec head lol. 9:1 wont make as much power as it would closer to 11:1 with a good 230 deg cam to utilize the 195 head, but you can def make more power with 280 cfm vs a vortec 250 cfm with any moderate performance cam. Bottom end can get soft with low comp. a 9.5:1 stealth rammed afr 190 360” rebuilt motor i tuned with a 230/236 deg xfi cam had enough power to go high 11’s if it wasnt for valve float from wrong springs they put in it. Ran 12.2, dyno showed 330 before falling off due to float. 360 whp all day long with right springs. Would have pulled to 6500 easy. But it wanted alot of converter and gear to help the 60’. Compression would have helped
I think an afr 195 head even with a low comp ratio will wipe the floor with a vortec head lol. 9:1 wont make as much power as it would closer to 11:1 with a good 230 deg cam to utilize the 195 head, but you can def make more power with 280 cfm vs a vortec 250 cfm with any moderate performance cam. Bottom end can get soft with low comp. a 9.5:1 stealth rammed afr 190 360” rebuilt motor i tuned with a 230/236 deg xfi cam had enough power to go high 11’s if it wasnt for valve float from wrong springs they put in it. Ran 12.2, dyno showed 330 before falling off due to float. 360 whp all day long with right springs. Would have pulled to 6500 easy. But it wanted alot of converter and gear to help the 60’. Compression would have helped
Even with the low compression, the low and mid-lift flow#'s destroy vortecs, and the exhaust is a massive benefit. Overall, a way more efficient head. You could do some cam tricks to raise dynamic compression up. But even with a very mild cam, this head would probably want to be around 10.0 to 10.5:1 compression. If you were to say pair this head with a LT4 hot-cam or CC305 it would be a solid performer. Good idle, good mid-range, decent top end. It would feel like it had power almost everywhere.
That said, if you compare these #'s to stock LS3 heads, the stock LS3 heads win. Gen3+ head design is just so much better.
Thanks for all the replies guys. I appreciate it. So I'm guessing I need to mill the heads to about 58cc is the right way to go and .028 head gasket with 9.3:1 compression.
Thanks for all the replies guys. I appreciate it. So I'm guessing I need to mill the heads to about 58cc is the right way to go and .028 head gasket with 9.3:1 compression.
Be careful on how much you mill off. Too much can make the intake not seat properly also there is a difference between flat milling an angle milling. Plus if you rebuild the bottom end and add flat top pistons or have the block decked, It can push the compression to high for pump gas. You really need to know what your future plans are for the engine.
I think an afr 195 head even with a low comp ratio will wipe the floor with a vortec head lol. 9:1 wont make as much power as it would closer to 11:1 with a good 230 deg cam to utilize the 195 head, but you can def make more power with 280 cfm vs a vortec 250 cfm with any moderate performance cam. Bottom end can get soft with low comp. a 9.5:1 stealth rammed afr 190 360” rebuilt motor i tuned with a 230/236 deg xfi cam had enough power to go high 11’s if it wasnt for valve float from wrong springs they put in it. Ran 12.2, dyno showed 330 before falling off due to float. 360 whp all day long with right springs. Would have pulled to 6500 easy. But it wanted alot of converter and gear to help the 60’. Compression would have helped
What you've alluded to above is where I'm saying the strength of the Vortec is. With low compression and limited RPM (because of the smaller cam needed to work with the CR), the low lift capability of the Vortec will provide a VE boost in the low range and make up for some of that lost pressure. The big AFR port will be a little lazy velocity wise and torque production down as a result. Witness the need for converter and gear in the example above.
Keep in mind that I'm not saying the Vortec is superior, just saying that it will hold it's own in the right build circumstances.
Originally Posted by Thirdgen89GTA
Even with the low compression, the low and mid-lift flow#'s destroy vortecs,
Not really. AFR doesn't publish values less than .200" but that said Vortecs at .200"/.300" is 139/190 vs AFR .200"/.300" with 146/201. Hardly destruction and the smaller CSA in the Vortec will boost the VE at lower engine speeds due to the greater velocity. This will also cover up the lack of compression to some degree.
Just to be clear, the better engine will ultimately have the AFR heads but there are situations where the Vortec is competitive.
Thanks for all the replies guys. I appreciate it. So I'm guessing I need to mill the heads to about 58cc is the right way to go and .028 head gasket with 9.3:1 compression.
AFR will have specs regarding cc per thou removed for both straight and angle milling.
EDIT: Flat Mill .006" per cc 60cc Maximum
Angle Mill .009" per cc 55cc Maximum
I just dont see it. 2.05 valve and a fast velocity design port profile of the afr ports is why they are one of the best out the box street heads. Vortecs are good but i dont think they will come close when each are cammed properly. Or even with same cam. To help the afr i would expect a faster more aggressive lobe shape and tighter lsa to build ve, if any is really lost at all. The afr’s arent a big port for what they are. I believe they are under 2” sq port area at min csa. 1.90’s i believe. That aint huge. There were guys on this forum who claim 40 hp with just afr head swap on stock cammed L98’s. I believe dyno don did it. Which i can believe since i picked up over 25-30 whp with just bolt ons.
I was trying to find the Engine Masters video where they compared the same head, but different runner sizes. Found it, but unfortunately they chose a 410ci ford and a tiny 218°/220° 110°LSA cam with .5" lift . So when you are comparing a 165, 195, and 210cc head, it really didn't make a difference since the big 410ci stroker is going to create way more velocity through the ports than a 350 would.
Wish they had done it on a regular OEM sized engine like a Ford 302, or a Chevy 350.
I was trying to find the Engine Masters video where they compared the same head, but different runner sizes. Found it, but unfortunately they chose a 410ci ford and a tiny 218°/220° 110°LSA cam with .5" lift . So when you are comparing a 165, 195, and 210cc head, it really didn't make a difference since the big 410ci stroker is going to create way more velocity through the ports than a 350 would.
Wish they had done it on a regular OEM sized engine like a Ford 302, or a Chevy 350.
I really like Engine Masters, but sometimes the engines they use in their tests are kind of "WTF ?". I get that in their world a stroked 410 ford or a 7,000 rpm big block might be "common", but I don't think it represents the average hot rod engine.
I really like Engine Masters, but sometimes the engines they use in their tests are kind of "WTF ?". I get that in their world a stroked 410 ford or a 7,000 rpm big block might be "common", but I don't think it represents the average hot rod engine.
Yeah, common is a 302, 305, 350. Aka OEM displacement engines that people are starting with is where that compare would best shine.
Its not the first time the runner size has come up on the forums, and unfortunately most of us do not have access to an engine dyno, and 3 sets of $2000 heads to test this out.
Hey guys I'm back with a different idea. I have been rethinking my build and have been deciding now between dart or brodix heads. I was just wondering if I should go with either 200cc or 180cc heads with 64cc chambers. I would still be using my low compression 350 bottom end but I could see myself upgrading to a 383 rotating assembly at some point in the coming years. I would think that the 180cc heads would be better for my 350 but if I go with a 383 in the future I could see the 200cc heads being the better option. I would still be using the same intake and carb and I'm still deciding between a 276 or 282 cam. I greatly appreciate your responses thanks so much.
Have you also re-thought the rest of the combination?
If you're inclined to, can you post back with the entire package and what you want to do with it? Without doing a lot of digging I've got "x" heads on an L98. Still TPI?
yea it's a 350 with 9.3:1 compression. I'm most likely going with rpm air gap intake, 750 mechanical secondary carb. Mostly going to be a track car. I just don't know if I should go 180cc or 200cc heads with 64cc chambers. Thanks.
Some member has said this better than me, but I will give it a try.
First you need to worry about rear gears, converter and exhaust.
Engine comes after those.
Are you more interested in getting the most out of your 9.3:1 350 or a flat top piston 383? All else being equal, the difference in SCR between the two CIDs is almost a full point given the same sized combustion chamber. The cams selected will (should) be considerably different.
Are you prepared to get the compression ratio a little higher? Going from 64 to 60 cc and using a .015" shim gasket (provided the deck surface of your block has a suitable finish to accept one), then you're looking at 10:1. Much better and that starts to get into the XR282HR territory.
If it's a track first car and you've got the gears and converter, go for a tighter LSA as Orr suggested way back. Something on a 108 with duration similar to the 282 or even a little less.
What the exhaust system like? Open headers? Dual dumps under the cabin? Single over the axle? This will change the spec some as well.
I think that you're overthinking it a bit. If you're building a 383 later, the afr 195's will still be very happy on them. I'd put them on the 350 out of the box, get a thinner head gasket, 22x/23x cam. It will run beautifully, I've done it. When the time comes for the 383, you'll have a virgin set of heads, and it will run even stronger then the 350, which I have done as well.
I can't say I disagree with you Matt and it's been done a million times but the OP stated that it's the 350 he wants to optimize so I went with that. And if it's a track car (also stated) then to me it's all out.
Otherwise we're building a street orientated 350 that will run "beautifully" but is leaving something on the table.
yea it honestly a strip car. maybe a quick trip down the road for fuel thats about it. GTA Matt metions the afr 195's, however I've decided against them as I feel I could get decent performance from brodix or dart heads for a lower price. Obviously if I spent more money I could get better performance from the afr's but the price tag is just too high at this point. Again I just don't know if I should go with 180's or 200cc heads. The exhaust is going to be LT headers with dual straight pipes dumped behind the rear wheels I already have that sorted out.
Which Dart and which Brodix are you considering? Depending specifically on the port cross section with respect to the port flow, I've seen where 180cc is capable of supporting north of 450 HP at 6000 on a 383. So, more than enough for a 350. Keeping the port volume smaller (for a given CFM) puts a little more energy into the intake charge. This can help with low engine speed cylinder filling and make up for some of the torque lost with the lower CR.
Or so the theories go.
So, if I were to choose between heads with comparable flow, I'd go for the smaller port volume.
Maybe you can scare up some flow numbers for your choices.
im almost sold on brodix IK 180's. I've heard people being very happy with them and the 180 port size will help with my low compression 350 compared to the 200's. I'm thinking a comp 276hr cam with a Holley 750 double pumper and an rpm air gap intake should be a pretty strong runner. I'm hopping for somewhere between 400-425hp at the crank.
FWIW: 350 with 10:1, Vortecs (170cc), XR276HR went upper 12's @ 106. Heavy @ 3700 lbs. 10" converter (maybe 3000 stall), 3.27 gears on bias street slicks. Guesstimate HP at 350? Maybe more. Generous online calculators say 400+.
Conventional thinking says that if you have to choose between two cams, pick the smaller one.
AFAIK, those Brodix heads flow more than the Vortecs so your power potential is up. It's the wheezy CR that's cramping things otherwise I'd say step up.
I found the 276 to be a solid all around performer but I didn't have a single purpose vehicle. To me, building a drag car engine is about compression and what you can do with it. The 276 will help some with cylinder pressure and you're less likely to get that sinking over-cammed feeling. Keep in mind that you're going to run out of steam before 6000. It'll carry past that but tailing off for sure.
That's my thinking anyway.
Remember this from the beginning?
Originally Posted by sofakingdom
I'd use the RPM Air Gap and a Comp XR276HR. WIth that low (relatively) compression you need not to go too crazy on the cam. A 650 carb would probably be enough but a 750 is absolutely plenty. Esp if mechanical secondaries.
That's an EEEEEEZY 400HP combo. More maybe even, with careful attention to detail like good TUNING, rocker arms, TUNING, the right rocker geometry (push rod length), TUNING, and … oh did I mention TUNING?
.
I'd say yes to the 282 but only if the CR gets bumped like Orr suggested.
The idea of building a strip only car does have a certain appeal. I might be heading that direction myself.
Good luck with your build.
Just note the fastest stock head type motors, including 90’s Lt1 type cars that are in the 10:1 comp range and even late model ls1 cars which are in the 10.5:1 range all use giant cams lol
compression is nice but not totally needed with gear and converter. Depends how fast you wanna go and how much money you wanna dump into the valvetrain to make it work
a fellow member here ran a L31 vortec headed motor into the 11’s with a 288hr cam. Its not even 10:1 compression. He revs the crap out of it tho
Sure. A shitty compression ratio with a big cam and great heads....RPM makes HP. But not touching the stock L98 bottom end and nothing mentioned of the valvetrain, how high will you go?
I'm just keeping it in the OP's field of view. I do appreciate the discussion nonetheless.
Personally, the lump I have now is a 10:1 with a "sort of" ported Vortec (255 CFM @ .550"). Even with the anemic compression (the 288 fits an 11:1 CR nicely) the 288 wants to pull to the stratosphere. I was shifting at 6500 and was looking forward to racing (new trans and converter too) but something in my build process went sideways. Now it's just a pile of parts waiting for a post-mortem. (I'm guessing I lost the cam thrust button)
So I get it.
But in all reality, the standard recipe is to match compression with duration and overlap. It's not the only way to go but it is the traditional path.
As for Super Stock, that's way outside the topic. There's so much going in one of those engines I don't know where to begin. Talk to Speier about his heads or Jones about the cam. It's crazy.
04-26-2020, 03:27 PM
