Thread: Heads Port and Polish, Cam, etc

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I've got RHS Pro Action 64cc, 200cc heads on a forged 383 with a comp nitrous cam -CL08-301-8. Looking for a little more HP. Ideas on how much HP I'll gain from a port and polish and port match? Running a Perform RPM manifold. I know I've got room to move on the cam. Looking hard at the Comp XR294-HR. Any experience and comments on that cam would be appreciated. 700R4 with 2,800-3,200 stall.

Cam currenty installed- Part number CL08-301-8 NX276 HR 224/236 at .050, .502/.52, 113 separation

Cam I'm looking at- XR294HR, Part number 08-443-8, 242/248 at .050, .54/.562, 110 separation

Thanks all!

Welcome to the forum!
I'm not an engine builder but I'll toss in a couple of thoughts to give others something to yell at. If you're experienced with porting you might gain a few HP by smoothing the flow path, but if that was the only thing done you won't feel the difference in the seat of your pants. Repeated, consistent runs down the strip maybe a very slight change in your time slip, but not big changes. I've seen some articles showing that a little bit of mismatch on ports actually causes better mixing, especially at low to mid-range rpm's, and that at peak flow the pattern actually smooths over the small step - talking less than 3/32" step, not all the way around. Case in point, looking at the exhaust side the guys at Hot Rod did a series of dyno runs, starting with a new set of tube headers as a baseline, then started beating on the tubes with a hammer with dyno runs between rounds and found that they actually GAINED a HP or two on some runs. I'd say fix any big port mismatch, and you'll get more from the right cam selection than porting.

Now let the guys who really know the facts start telling you how everything I've told you is HogWash! And Woooooooooooo PIGS!!

I would sell the RHS heads and buy a set of Airflow Research heads.
Take a look at this tutorial that I wrote several years ago concerning cams, what to do and what not to do.
https://www.crankshaftcoalition.com/..._compatibility

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#1 to do: listen to Tech.

Yep, save yourself some time and trouble and listen to tech.

Definitely review the information that TechInspector provided. It's said that knowledge is power!

And know that speed costs money, how fast can you afford to go?
And lastly, do you really need to make a lot of power? And where will the power band be?
Now if this is for a full duty race car that never sees a street, by all means, invest all you can afford and have a ball doing it! 8-)

Originally Posted by DennyW

Sorry, not enough info on your total plans. What type of track ? Is it for street ? Show? or ???


By the way, please double check your typing. The number for the second one:
Refers to a Ford... Cam I'm looking at- XR294HR, Part number 08-443-9.

COMP Cams Xtreme Energy Camshafts 08-443-8

Just having a little fun...

Oh man! I fat fingered that 9! Yes.. Chevy part 08-443-8. Thanks for that! It's not a strip machine. It's most used for spirited off track driving. I cruise but want the power to be there when I want it there.

Welcome to CHR:

Can you tell us a bit more about what car you're running this engine in? Rear end ratio?

The cam your looking at needs a lot of compression and lives best at awfully high (for the street) RPMS.

I'm also curious why you're using a 700R4 - the 3.06 first allows you to really jump at take off but the huge (47%) jump to 1.63 second gear can be a big disappointment. It would be like first to third on a four speed manual. I would venture a guess that you rarely see the OD. Maybe a solid TH400 would help in the overall goal.

Regards,
Glenn

The car is an 82 Corvette. Compression is 10.5:1. The rear end is a 3.73. Why a 700R4? Well...it's what was in the car. Had it rebuild and built up a bit. I've never driven a TH400 but the OD is pretty nice with the 3.73 gears. Really want a Tremec 5 or 6 speed conversion but $$$. I am considering a 4l60E upgrade for the fine tuning of the shift points. Much less money than a 6 speed conversion.

Really searching for 500hp and with the nitrous cam and heads that's in it, I think I'm sitting about 450.

I sure do appreciate everyone's comments! A lot of knowledge and experience here.

Originally Posted by techinspector1

I would sell the RHS heads and buy a set of Airflow Research heads.
Take a look at this tutorial that I wrote several years ago concerning cams, what to do and what not to do.
https://www.crankshaftcoalition.com/..._compatibility

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Great info in that article! And thanks for the response. What's you're opinion on the cam I mentioned?

XR294HR, Part number 08-443-8, 242/248 at .050, .54/.562, 110 separation

My CR should be 10.5:1 with the PTS506A3 -5 Wiseco pistons and the 64cc/200cc heads. Felpro 1003 gasket with a .041 compressed thickness. Holley 770. Not a track car but I love a zero-60 and a 40 roll while on an evening cruise. Also a little worried about vacuum. It's a Vette and the whole car runs on vacuum. May need a vacuum pump.

Thanks again!

The 08-301-8 likes 9.5:1 to 10.75:1 static compression ratio. Currently, according to you, the motor is at 10.50, so it is just on the edge of almost having too much SCR for the cam that's in it now. You want to move to a 08-443-8 which wants 10.5:1 to 12.0:1, so it will be on the other leading edge of almost needing more SCR. You're closing the intake valve at "X" degrees after bottom dead center now and when you go with more cam, you will be closing the intake valve at "X+" degrees. You will be extending the intake valve closing point, which means that compression in the cylinder cannot begin until the piston is further up the bore than it is now at valve closing. There may be enough additional fuel and air pushed into the cylinder by atmospheric pressure with the new timing and valve lift to make up for the deficit of piston position in the cylinder with the later intake valve closing position........or there may not. I see you between a rock and a hard place. You need more SCR, but the available fuel quality will not allow it. And you darned sure don't want to enter the threshold of detonation. If there is E85 within 20 or 30 miles of you, I'd sure be looking at changing the whole mess over to alcohol, along with a new set of pistons delivering maybe 12.50 or 13.00 to 1 SCR and twisting a 08-444-8 cam. You may have heard the hot rodders axiom from back in the '50's......"If some is good, more is better and too much is just right."

Now, as far as the heads, I stand by my statement to change over to Airflow Research heads, 220 cc intake runners.
https://www.airflowresearch.com/220c...cylinder-head/

Scroll down and look at the flow of the Race Ready head at 0.550"......you could be over 0.550" lift by using 1.6 intake rockers and leaving the 1.5's on the exhaust......304 intake and 225 exhaust......ZOWIE. I tried to find the flow on those Fosdick RHS heads, but it eluded me. OK, that's all I've got.
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Originally Posted by techinspector1

The 08-301-8 likes 9.5:1 to 10.75:1 static compression ratio. Currently, according to you, the motor is at 10.50, so it is just on the edge of almost having too much SCR for the cam that's in it now. You want to move to a 08-443-8 which wants 10.5:1 to 12.0:1, so it will be on the other leading edge of almost needing more SCR. You're closing the intake valve at "X" degrees after bottom dead center now and when you go with more cam, you will be closing the intake valve at "X+" degrees. You will be extending the intake valve closing point, which means that compression in the cylinder cannot begin until the piston is further up the bore than it is now at valve closing. There may be enough additional fuel and air pushed into the cylinder by atmospheric pressure with the new timing and valve lift to make up for the deficit of piston position in the cylinder with the later intake valve closing position........or there may not. I see you between a rock and a hard place. You need more SCR, but the available fuel quality will not allow it. And you darned sure don't want to enter the threshold of detonation. If there is E85 within 20 or 30 miles of you, I'd sure be looking at changing the whole mess over to alcohol, along with a new set of pistons delivering maybe 12.50 or 13.00 to 1 SCR and twisting a 08-444-8 cam. You may have heard the hot rodders axiom from back in the '50's......"If some is good, more is better and too much is just right."

Now, as far as the heads, I stand by my statement to change over to Airflow Research heads, 220 cc intake runners.
https://www.airflowresearch.com/220c...cylinder-head/

Scroll down and look at the flow of the Race Ready head at 0.550"......you could be over 0.550" lift by using 1.6 intake rockers and leaving the 1.5's on the exhaust......304 intake and 225 exhaust......ZOWIE. I tried to find the flow on those Fosdick RHS heads, but it eluded me. OK, that's all I've got.
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You're awesome! Thank you for taking the time to look at my setup and provide this much detail. Much appreciated!