bajardine
New member
Hey guys, I’m planning on doing the SRX head conversion on my ’03 Viper. The previous owner cut the head to have equal compression on all three cylinders. He then removed two layers of head gasket and even with that, I’m only reading 100 psi on all three cylinders. Yes, I’m checking it correctly with the 14 mm long threaded adapter. Operating temp, WOT, 5-6 hard pulls. I suspected the rings were bad so I built a leak down tester and read 96-98 psi on a two-gauge set up which = 2-4% loss so my rings are good. I checked the squish and got measurements at ¼ in from the edge of the cylinder from .07 to .095. This is way too high. I’m pretty sure whoever did the machining on the head messed it up pretty good and over cut the chambers. Instead of dealing with someone’s screw up I want to start fresh. I want higher compression and need better cooling to go with it so I bought a set of ’99 SRX heads but I have a few questions about the heads, compression, etc. I’ve been doing a lot of searching on the site and haven’t been able to answer my questions so here goes. This is what I have read in MANY other posts:
’98-’99 SRX Good compression is about 120 psi stock with good rings
26 cc domes
’00-’02 SRX Good compression ranges 125-135 psi
25 cc domes
Viper Stock compression 110 psi #1 cylinder, 130 psi #2-3 cylinders
24cc dome #1 cylinder, 21 cc #2-3 cylinders
Both the SRX and Viper have the same bore and stroke
Questions: I can understand the lower compression on the ’98-’99 SRX due to the larger domes – 26 cc’s. Why then would a Viper with 21 cc’s have the same compression? Why would the Viper with the #1 dome at 24 cc’s be lower compression than both SRX’s with larger dome sizes? I thought maybe a lower compression piston but according to the parts diagram, all three pistons are the same so I ruled that out. Is it all due to the head gasket used on the Viper vs. the o-rings used in the SRX? Does the SRX have a taller dome on the piston? I can’t think of anything else.
Next: If I bolt the ’99 heads on my Viper with one layer of head gasket can I expect 120+ psi of compression? If I have to cut the heads to get higher compression than that, in the 135-140 psi range, I imagine I would have to recut the squish band to set the heads up at .055 in. If I do, what is the stock squish angle and is there a better angle to cut it at? At 140-150 psi can you still run 92 octane with the stock squish angle without detonation? I’ll probably have to take the heads down a bit to get in the cc range I’m thinking of. I typically ride from 5,000-9,000 ft. The Peak Performance heads show 21 cc domes for 6,000-10,000 ft. Am I headed down the right road? I know what has to be done for the coolant rail so I don’t need any help there. Has anyone done this exactly and what altitudes did you ride at? I know someone out there has done this but I’m looking at more specifics than what I have come up with so far. Thanks guys!
Bruce
’98-’99 SRX Good compression is about 120 psi stock with good rings
26 cc domes
’00-’02 SRX Good compression ranges 125-135 psi
25 cc domes
Viper Stock compression 110 psi #1 cylinder, 130 psi #2-3 cylinders
24cc dome #1 cylinder, 21 cc #2-3 cylinders
Both the SRX and Viper have the same bore and stroke
Questions: I can understand the lower compression on the ’98-’99 SRX due to the larger domes – 26 cc’s. Why then would a Viper with 21 cc’s have the same compression? Why would the Viper with the #1 dome at 24 cc’s be lower compression than both SRX’s with larger dome sizes? I thought maybe a lower compression piston but according to the parts diagram, all three pistons are the same so I ruled that out. Is it all due to the head gasket used on the Viper vs. the o-rings used in the SRX? Does the SRX have a taller dome on the piston? I can’t think of anything else.
Next: If I bolt the ’99 heads on my Viper with one layer of head gasket can I expect 120+ psi of compression? If I have to cut the heads to get higher compression than that, in the 135-140 psi range, I imagine I would have to recut the squish band to set the heads up at .055 in. If I do, what is the stock squish angle and is there a better angle to cut it at? At 140-150 psi can you still run 92 octane with the stock squish angle without detonation? I’ll probably have to take the heads down a bit to get in the cc range I’m thinking of. I typically ride from 5,000-9,000 ft. The Peak Performance heads show 21 cc domes for 6,000-10,000 ft. Am I headed down the right road? I know what has to be done for the coolant rail so I don’t need any help there. Has anyone done this exactly and what altitudes did you ride at? I know someone out there has done this but I’m looking at more specifics than what I have come up with so far. Thanks guys!
Bruce
mopar1rules
Active member
i never knew the '98-'99 srx's had lower comp heads vs the '00-'02 srx's
800
New member
If you're bolting the srx head on and checking the compression, the difference is the head gasket, machine the thickness of the gasket off the srx head and try again. That usin on piece of a gasket doesn't always seal well, if you need water manifolds I have some.
At the altitude you said you ride at, I would have started with 600 srx heads. Get a set of 600 heads, cut them down to the step at the squish angle, recut the squish angle out to the correct bore size, bolt them on. Thats what we used to bring with us when we went out to the Big Horns, worked well.
At the altitude you said you ride at, I would have started with 600 srx heads. Get a set of 600 heads, cut them down to the step at the squish angle, recut the squish angle out to the correct bore size, bolt them on. Thats what we used to bring with us when we went out to the Big Horns, worked well.
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bajardine
New member
600 Heads
Are the SRX 600 heads that much smaller domes? Any ideas what cc's they are? I already have the set of 700 heads so I think I will start there.
Are the SRX 600 heads that much smaller domes? Any ideas what cc's they are? I already have the set of 700 heads so I think I will start there.
srx600 heads are 21cc, 98-99 srx700 heads are 26cc.
Bruce, your not taking into account the head gasket thickness, this is why the squish is so big and your compression low. You also can o-ring the viper cylinders and then you dont have any of the head gasket stuff, the heads will bolt right on like a srx and all the specs will apply. The srx and viper on average measure around .012" deck clearance.
Bruce, your not taking into account the head gasket thickness, this is why the squish is so big and your compression low. You also can o-ring the viper cylinders and then you dont have any of the head gasket stuff, the heads will bolt right on like a srx and all the specs will apply. The srx and viper on average measure around .012" deck clearance.
mopar1rules
Active member
mrviper, i sent you 2 pm's on viper porting. please reply. my buddy wants his viper ported.