Hi,
I have a sbc stock stroke bored out .060 and 9.5 compression and i have procomp 210 heads and im running Isky cam #20251. The last time at the track I ran a best of 12.20 @ 110mph I have a 3200 stall conveter and 3:73 gears with 29" slicks. I think Im running around 400hp right now with my set up. How much could my possible hp gain be going from 9.5 compressing press fit flat tops with cast std rings to 12:1 compresstion .275 dome hyper pistions with low tension rings and full floating pins? I know I will have to run 110 fuel but its just a drag car. what kind of gains could I get. Maby 25hp?

 

I think it's 10hp per compression point.

 

I have always heard rule of thumb is 2% per point. so both of you would be right on the money.

 

Don't bother going to 12:1. If you are going to bump to race gas go to at least 13.5:1.

Given your cam this may help more than people think. You are running a rather large cam with a narrow LSA, larger heads, and modest pump gas compression.

What is your actual displacement? You say "stock stroke" but don't tell us anything. EDIT: Saw you are running an overbored 350 in your profile. See comments below about shift points.

What are you using for an intake and carb?

What RPM do you shift at? If this is a 350 you should probably be shifting somewhere in the 7,000 to 7,500 RPM range. If you are running cast press-on pistons, and it sounds like you are, then 7,500 RPM will likely cause parts to evacuate from your engine after the first few nights.

This all screams mismatch, and would explain why you are only running low 12's in a full-race deal.

 

After a little searching I see you have been a few rounds already.

It seems you want to go into the 10's. After a quick look at the advertised flow figures for the heads and intake you have it is going to be hard without dropping these parts off for professional porting. These parts are going to need a crutch like nitrous. You should still be able to ride in the solid 11 second range with parts that maximize your heads, intake, and engine's power band.

Go to about a 4500 RPM torque converter. This will help you launch and get into the engine's power band quicker.

At least borrow a tach to confirm your tach is accurate. Then set your shift points by where your car goes fastest. Start at about 6,700 RPM and go up by 200 RPM increments until you find the point that the car runs the fastest. Honestly, with the cam you have now I expect the engine is losing power fast after it peaks so shifting way past the peak is throwing ET out of the window.

Your heads look like you need to be pushing the limit for the installed springs. If I were running those heads I would get the cam lift up to the low 0.600" area. This maximizes flow and gives some room for lash and deflection to drop my actual lift to about 0.600". This much lift will take good springs, pushrods, rockers, and plenty of measuring.

Going to a 13.5:1 compression ratio would be a good idea for your goals. With only 360ci to work with and marginal heads/intake you can't pass up the power bump from using high compression. Particularly if you intend on every spraying the engine something like the J&E 182023 pistons with a thin head gasket would be good. I have serious reservations about hypereutectic pistons, especially when involving high compression and nitrous.

You should seriously consider going to a solid roller cam. At high lifts it will be more stable, more reliable, and will produce more power. A Lunati 60134 would be a good starting point. The duration and lift on that model look good for your application. It might would be best ground with a slightly narrower LSA, but, if you intend to run nitrous you may not want it on a narrow LSA.

I am not sure if the Headman headers you list are the full length 1 3/4" ones, but if not, you need to be running full length 1 3/4" headers.

 

Im running a weiand stealth air strike intake. I did have a hurricane but It feels the like the weiand pulls way harder. I have just a plane jane 750 holley vs with light spring in and bigger poer valve. I do have a 750 dp Im going to try out. I have head man full length headers 1 5/8 headers. I have been shifting at around 6800 to 7200 some times the cam seems to not pull so hard after 7000. A 4500 stall would be way better Becase The car does dog of the line till it hits power band. I have speed pro hyper flat tops now and I have revved it up much past 7 and every thing has been fine. knock on wood Im bored .060 over so 360cid I do not want to stroke it beaces its stock block and cam clearenc issues. I also have a nitrus express hit man kit 75-200 hp but have not used it yet. Are speed pro forged pistions any good?

 

The 750DP would probably run faster with the proper converter. It is going to take some practice launching to not bog the engine worse on the launch.

Speed Pro forged pistons are not bad pistons. They aren't quite as nice as the Mahle or J&E pistons but they work fine as long as everything measures out properly.

The only listing I see for a Speed Pro forged piston that will give enough compression is a lightweight model that costs enough that you would probably be better off buying a better brand.

Keith Black lists a large domed piston for a good price. After their hypereutectic pistons I'll never buy another KB brand product again. Still, many people seem to like their forged pistons and I can't say I have heard of one being a problem.

Going with a large dome like this will mean careful checks for clearance issues before balancing the engine. You could very well have to grind parts of the dome for clearance or cut the valve pockets deeper. If that happens it needs to be done before the engine is balanced. It may be a good idea to run the part number by Procomp, if their customer service is worth a crap, and see if they are aware of any major clearance issues.

 

[quote=RebornFromAshes;4144290]The 750DP would probably run faster with the proper converter. It is going to take some practice launching to not bog the engine worse on the launch.

My problem isnt like just like a engine bog due to the carb not ajusted right its just that I get a dead hook off the line and my conveter stalls befour I hit power band. my 12.20 1/4 was flooring it off of 1500 rpm at the line and with 29" x 9" wide slicks.. Too big for the 3.73 gears.

I alredy have the speed pro .275 hyper coated pistions. I can get 13.2:1 compression out of them I think. Are they any good to rev over 7000rpm? I would like to buy forged pistions but I just dont have the budget right now.

Im also running 1.6 rockers so Im very closes to my .600 lift.

 

If I am not mistaken, you are not running the DP yet. Right now, off the line the secondaries should be closed. If you dump the full 750 CFM on the engine off the line, which is quite easy to do with a DP, it is going to bog a little unless the engine can easily pull to an RPM where it is making good power. You will have to spend a little bit of time practicing your launch so that you open the throttle as fast as the engine can take the flow.

If your tune is good, clearances right, and you don't rev harder than necessary then those pistons will probably hold. Hypereutectic pistons are descent for outright strength, they just don't hold together well with abuse. Make sure your mixture doesn't go lean and that you have no detonation.

If you are finding shifting right around 7000 RPM works best now I don't see why you would need to shift higher after bumping the compression. I would play with the shift point a little to make sure you are still shifting at the best point, which could possibly be lower with more compression.

 

OK I see what you are saying about the mech sd on the dp carb.

Heres my plan.
Im going to pull the engine and pull out the 9.6 pistions and the i beam rods. I baught some eagle esp hbeam rods off ebay for a deal so Im going to put one .275 dome pistion on the rod and check my pistion to head clearence. If every thing works out there Im planning on having the heads shaved down to where the chambers are 58ccs. Run mls head gaskets. So my compression should be a tad over 13:1 Then do some light porting and polishing to the heads. Then get my rotatating assemboly ballenced.
Im planning on putting in low tesion rings for less friction and have them gapped for a 150 shot of nitrous. Then run a summit evac system for the low tension rings. Im also thinking of adding a windage tray and a lifter valley oil deflector. so my set up will be

750 carb
air strike dual plane intake
the same Isky cam #201549 cam with 1.6 rr
13:1 compression
slight port and polish to the 210 heads
probly keeping the 1 5/8 headers for now.
going to keep the same stall for now till more money comes in.
going to run 110 gas.

Thats about it.
any Suggestions? I can't thank you guys enough for the help!

 

I would definitely look into 1 3/4 headers and maybe a single plane intake. With those heads they will need to breath on the intake side and the exhaust side.