390 stroker build advice

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Stewie1977

Stewie1977

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Hi guys, Stewie from the great southern land of Australia here. Been reading FABO for a fair while now & have found some very interesting tech from some very knowledgable people. Time for me to get involved & ask a few questions. I have an Aussie A body valiant, basically a 4 door version of a 66 Plymouth val. I'm building a 390 stroker for it as our local authorities won't allow me to go any larger. They will however allow it to be stroked as all they seem to care about is the number cast into the block. I've already got a MP 4 in crank, a 73 standard 318 block & a set of 71 J heads machined for the 2.02/1.6 valves. It will mainly be for street work so I was thinking of going a comp cams mutha thumpr hydraulic, eddy air gap & 750 eddy carb. Looks like the only option for pistons are Icon so I'm going the flat tops to give me 10- 10.5 to 1 as 98 octane is everywhere here so fuel isn't an issue. I guess my question is has anyone run this cam in a stroker or a similar set up ? What sort of numbers was it putting out ? I'm hoping for around 450-500 flywheel. I really want an angry idle for car meets as the whole thing is going to look bog stock. That's going to be my wow factor. If there is a better option to give me what I'm after please let me know. I've found the advice from members on here to be the best of any site I've been to. Thanks
 
Mate, give Ashley a call form Brisbane, he built a 390 that did 11.2 on the quarter, 0403661575, where are you from?
 
Good cam^^^^… for 500 h.p. ,look at reworked heads/2:02-1:60 valves/ bowl- valve guide worked to 240-250 cfm at .550"-.600" lift.
 
mini said:
If you want any power out of this. DO NOT GO MUTHA THUMPER. These camshafts are for noise only. If you are going hydraulic, go this route for power.http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=629&sb=2
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That's complete BS! How many engines have you dyno tested with these cams? I've dyno'd around 10 engines of various brands using all three sizes of Thumpr cams and every time they made more power than expected and by no means did they underachieve.
Not only do they sound good, but most times there is a solid 2000rpm between peak TQ and peak HP. Very wide power band.
Brian
 
ou812 said:
That's complete BS! How many engines have you dyno tested with these cams? I've dyno'd around 10 engines of various brands using all three sizes of Thumpr cams and every time they made more power than expected and by no means did they underachieve.
Not only do they sound good, but most times there is a solid 2000rpm between peak TQ and peak HP. Very wide power band.
Brian
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A question, Brian: Do the Thumper lines run best installed as per cam card,or are you adding/retarding on the intake center line installation point? Was just curious,of course this is completely affected by intake/exhaust flow...(?)
 
vje55 said:
Mate, give Ashley a call form Brisbane, he built a 390 that did 11.2 on the quarter, 0403661575, where are you from?
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I'm from the Sunshine Coast. Was hoping to see Ashley at mopar Sunday last weekend so I could check his ute out. I've seen the build thread on queensland chryslers. Mine is going into a VC regal so it should move along alright
 
Abodybomber said:
Good cam^^^^… for 500 h.p. ,look at reworked heads/2:02-1:60 valves/ bowl- valve guide worked to 240-250 cfm at .550"-.600" lift.
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Is that the mutha thumpr or the 284 your referring to ? I'm match porting the heads to the manifold & bowl blending the chambers. I'm aiming for around 250cfm
 
Stewie1977 said:
Is that the mutha thumpr or the 284 your referring to ? I'm match porting the heads to the manifold & bowl blending the chambers. I'm aiming for around 250cfm
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Impressive,you have done your homework, mate. A well done 2:02 /1:60 ported head,should get there(expensive, it is). I always let the head porter choose the camshaft( just my opinion). Give the local machinist's some love,avoid the damn tariffs.
 
ou812 said:
That's complete BS! How many engines have you dyno tested with these cams? I've dyno'd around 10 engines of various brands using all three sizes of Thumpr cams and every time they made more power than expected and by no means did they underachieve.
Not only do they sound good, but most times there is a solid 2000rpm between peak TQ and peak HP. Very wide power band.
Brian
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Ah! You beat me to it. What are some people thinking?

These cams are very interesting. I wonder where the for the idea from. Considering, when I go back into memory lane some 20 years ago, people then (Myself included) used to run split cams (down around 108/106) with different ratio rockers and Rhodes lifters with as short as possible pushrods on the intake. They didn't exactly sound like a thumper, but we did what we could.

Stew, local authorities? LOL!

Search OU812's thread starting history. I do believe he has posted 1 or 2 Thumper builds here.
 
If my post came off harsh, I really didn't mean for it to sound like that...but I feel like I need to correct things when I know they are wrong. Sorry for that Mini!

What I should have said is don't discount the thumpr series of cams...they make power! Not always my first choice but everytime I dyno an engine with one, they make excellent power. So maybe I should use them more often...LOL!
Most of my customers don't want a super nasty idle so that's the real reason I don't use them often.
Brian
 
Thanks guys all makes sense to me. This is my first mopar stroker build so I want to make sure I get it right from the start. I think the mutha thumpr will give me what I want as far as sound goes, just hope it give the hp too. From reading a few other threads on here maybe I would be better going with a Weiand stealth ? Seems to have a much broader power range than the eddy air gap. It's all going to run through a 904 with a cheetah forward pattern manual valve body, 2800-3200 stall & LSD with 3.27 & 26 in tyres. Car weighs in around the 2800 mark. Any idea what it may run down the 1/4 ?
 
Just wanted him to be in right camshaft area to make the most available power. Holy
 
Just my opinion but I'd watch that static compression with the huge chambered heads on the 318 bore. Use a dished piston and keep it under 10:1 and run a cam that will maintain cylinder pressure. Your 98 octane fuel is no more than our 92 and the dish and 9.8-ish:1 will run on our pump 87.
I'd steer clear of the noise cams too. Yes - they make power. But - a good engine builder will always make good power. in my opinon, no - they are not the best cam in any scenario where the idle sound consideration is taken out of the equation. They are designed for sound and IMO that is made with a concession to maximum power for a given rpm range. Pick a cam designed for the power range you want and it will sound like whatever it needs to.
I would suggest something like the XE285HL, the Lunati 10200705, or the Crane H-302-2. That Crane is old but has made a track determined 480hp with a mildly ported set of 596s, runs 12.80s and gets 17mpg on the highway in a heavy E body with 3.23s. It would put an A body close to the 11s with those gears and the right traction.
 
I, & a lot of my friends have built other brands of engines over here with cast iron heads in the 10-10.5:1 & all have run quiet happily. I also have access to a ready supply of a gas if I ever need it. This car is going to be more a street/show car than strip monster so the appeal of the thumpr for me is that it will turn heads at the show n shine but still be reasonably streetable. The car is going to look stock, like grandad drives it to church on Sunday, then start it & people wonder what the hell is making all that noise ? Can't be pops car. As long as it will scare the missus when I open it up & I can possibly run a mid to high 12 on the rare trip down the strip I'll be pretty happy
 
Ok - I only mention the compression because it was a detonation issue even on th factory equipped cop cars withe the 318 lower end and 360 heads. There's a ton of dead space around that chamber and it has a high tendency to ping and detonate. If you have better fuel available then you're fine. If not you'll need a camshaft with another 10-15° @ .050 to bleed off pressure.
 
Thanks Moper I will keep that in mind. The cam is 235@50 inlet & 249@50 exhaust with 107LSA. From memory lift is a smidge under 500 on both. We also have a ready supply of E85 at a lot of servos near where i am too which I believe is around 103 - 105 octane. Worst case I change the carb to suit the Ethanol blend, but from all the research I've done & advice from a few top engine builders I know over here the comp should be fine for the fuel we have. Unfortunately Chrysler engines are a bit of a black sheep over here. The good guys seem to admit they don't know them & you need to talk to someone who does as what works for them with a Cheb or Ford won't work with a Mopar. Those not so good will build it like anythig else & blame it on being a POS mopar when it doesn't work like their other garden variety small blocks. Hence my joining this forum, a lot of very knowledgable people with mopar experience, not chev or ford thinking that they're all the same.
 
lol... It's like anything else - builders get good building what they know best. if GM or Ford are more popular like they are here, you get more familiarity and aftermarket support for them making the job easier as time goes by. The physics is the same, but the parts availability and effect of changes and choices make Mopars a little tougher if you build the other makes often.
With that came (I consider that a little smaller then "medium sized") you may still have detonation potential. Not because the pressure is too high, but because of the dead space over the deck with the small bore, big chember, and big gasket. It lets fuel puddle and it's cooler so typically the fuel there is not part of any controlled ignition event. If you're building a close tolerance quench deal (like the 4" in a 340 or 360 and using modern closed chamber heads) then you'd definately be fine with it. I can't say for certain you're fine as you designed it with the early heads. But if the E85 switch is possible that might be a good backup plan.
 
sounds like your 390 will hit 500hp easily, and be very good on the street with a nice powerband.

the cam just complements the rest of the build.

what rear / trans do you have for the little beast?
 
I've got a 904 I'm building with a cheetah forward pattern manual valve body(the one with engine braking in 1st, picked that tip up here) 2800 - 3200 stall & disc brake LSD with 3.27:1. The diff is a BW78. Not sure if you have them over there. I think it's an 8 1/2", but there known to take some serious punishment. I'm also looking at putting a set of caltracs on it. Might make a good compromise for street & the odd trip down the strip. Wind them up for the drags, back them off for the street.
 
Stewie1977 said:
I've got a 904 I'm building with a cheetah forward pattern manual valve body(the one with engine braking in 1st, picked that tip up here) 2800 - 3200 stall & disc brake LSD with 3.27:1. The diff is a BW78. Not sure if you have them over there. I think it's an 8 1/2", but there known to take some serious punishment. I'm also looking at putting a set of caltracs on it. Might make a good compromise for street & the odd trip down the strip. Wind them up for the drags, back them off for the street.
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I am currently building a hemi 6 with 12:1, will run fine on the 98 fuel Stewie, had a 318 a couple of years ago with 10.5:1 Crane cam around 223/238@50 and was fine on the 98.
BJ
 
A 3.27 ratio huh? That is odd for around here. What is the deal with engine braking in first?
I don't know what a BW78 is.
 
rumblefish360 said:
A 3.27 ratio huh? That is odd for around here. What is the deal with engine braking in first?
I don't know what a BW78 is.
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Think you guys got a bw75 or 78 over there in a Pontiac or some other vehicle at some stage in the 80s referred to as an Aussie 10 bolt?
 
Yeah I think it was fitted to a few oddball cars over there. It came out of a XR8 falcon which is a pretty common car over here. The V8 is used for everything from cop cars to race cars & the 6 is pretty common for taxis. Same diff was fitted to a lot of cars here, I went with the ford for the stud pattern. 3.23 is a more common ratio but I guess I was just lucky. The lowest you seem to get stock is 3.45. Would have preferred that but you take what you can get. Short of a Dana or ford 9" it's probably one of the strongest doffs you can find around here, & a crap load cheaper than either. The engine breaking in 1st engages reverse as well so it doesn't over spin or load up the sprag if you get on & off the gas in 1st gear. Supposed to be a lot better for street use & seeing as most its time will be spent on the street I thought it might be a safer bet. Good to know that your 318 ran fine on 98 BJ. I've run 308's at 10.5 too so I was fairly certain it'd be fine, but it is a mopar. You just never know lol. Your teen would have moved along nicely ? Bet the hemi will too
 
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